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Chilean journal of agricultural research

versión On-line ISSN 0718-5839

Chilean J. Agric. Res. vol.72 no.3 Chillán set. 2012

http://dx.doi.org/10.4067/S0718-58392012000300003 

Agricultural Research 72(3) July - September 2012

RESEARCH

 

Heterosis for Yield and Yield Components in Okra (Abelmoschus esculentus (L.) Moench)

Heterosis para Producción y Componentes del Rendimiento en Gombo (Abelmoschus esculentus (L.)Moench)

 

Thirupathi Reddy Medagam1*, Haribabu Kadiyala2, Ganesh Mutyala3, and Begum Hameedunnisa1

1Vegetable Research Station, Agricultural Research Institute, Rajendranagar, Hyderabad-500030, Andhra Pradesh, India. *Corresponding author (medagamtr@yahoo.co.in).
2Andhra Pradesh Horticultural University (APHU), Venkataramannagudem, West Godavari (Dist.), Andhra Pradesh, India.
3Acharya N.G. Ranga Agricultural University (ANGRAU), Rajendranagar, Hyderabad-500030, Andhra Pradesh, India.


The study of heterosis would help in selection of heterotic crosses for commercial exploitation of F1 hybrids in okra (Abelmoschus esculentus (L.) Moench). Forty five F1S were developed by crossing 10 elite lines of okra: P1(IC282248), P2(IC27826-A), P3(IC29119-B), P4(IC31398-A), P5(IC45732), P6(IC89819), Py(IC89976), P8(IC90107), P9(IC99716), and P10(IC111443), in half diallel fashion during summer 2009. All 45 F1s along with their 10 parents and one standard control (Mahyco Hybrid N° 10) were evaluated in a randomized complete block design with three replicates during early kharif (June to September) 2009 at the Vegetable Research Station, Rajendranagar, Andhra Pradesh, India, for heterosis of yield and its components of okra. Significance of mean squares due to genotypes revealed the presence of considerable genetic variability among the material studied for almost all yield and yield attributes except plant height. The overall mean heterosis over mid parent and standard control for total yield per plant was 6.92 and -15.44%, respectively, while for marketable yield per plant were 6.64 and -22.18%, respectively. Negatively heterotic crosses like C19 (P3XP5) for days to 50% flowering (-4.35%) and C4(P1XP5) for first flowering and fruiting nodes (-15.22%), respectively, are important to exploit heterosis for earliness in okra. The crosses with non-significant standard heterosis in any given direction for total yield per plant C42, C31, C35, C25, and C36 (8.63, -0.08, -2.61, -3.26, and -4.57%, respectively) and marketable yield per plant C42, C31, and C36 (-5.87, -6.56, and -10.54%, respectively), were statistically on par with the standard control in their mean performance and are found to be as promising as that of the standard control. The F1 hybrid C42(P7XP10) with high yield potential has the potential for commercial cultivation after further evaluation for early kharif season.

Key words: Abelmoschus esculentus, F1 hybrids, half diallel crosses, heterotic pattern, hybrid vigour, mean performance, parental lines.


El estudio de heterosis podría ayudar en la selección de cruzas heteróticas para la explotación comercial de híbridos F1 de gombo (Abelmoschus esculentus (L.) Moench). Cuarenta y cinco F1s fueron desarrolladas cruzando 10 líneas elite de gombo: P1(IC282248), P2(IC27826-A), P3(IC29119-B), P4(IC31398-A), P5(IC45732), P6(IC89819), P7(IC89976), P8(IC90107), P9(IC99716) y P10(IC111443), en forma de medio dialelo durante el verano 2009. Todas las 45 F1s junto con sus 10 padres y un control estándar (Híbrido de Mahyco N° 10) fueron evaluadas en un diseno de bloques completos al azar con tres repeticiones durante kharif temprano (junio a septiembre) 2009 en la Estación de Investigación de Vegetales, Rajendranagar, Andhra Pradesh, India, para heterosis de la producción de gombo y sus componentes. La significancia de cuadrados medios debida a genotipos reveló la presencia de variabilidad genética considerable entre el material estudiado para casi toda la producción y atributos de producción excepto la altura de planta. La heterosis media total entre los padres y control estándar para la producción total por planta fue 6,92 y -15,44%, respectivamente, mientras para la producción comerciable por planta fue 6,64 y el -22,18%, respectivamente. Cruzas negativamente heteróticas como C19(P3XP5) para días a 50% floración (-4.35%) y C4(P1XP5) para primera floración y nudos fructíferos (-15,22%), respectivamente, son importantes para explotar heterosis de precocidad en quingombó. Las cruzas con heterosis estándar no significativa en cualquier dirección dada para producción total por planta C42, C31, C35, C25, y C36 (8,6; -0,08; -2,61; -3,26; y -4,57%, respectivamente) y producción comerciable por planta C42, C31, y C36 (-5,87; -6,56, y -10,54%, respectivamente), fueron estadísticamente iguales con el control estándar para rendimiento medio y fueron tan prometedoras como aquellas del control estándar. El híbrido F1 C42(P7XP10) con alto potencial de rendimiento tiene potencial para cultivo comercial después de evaluación adicional para la temporada kharif temprana.

Palabras clave: Abelmoschus esculentus, F1 híbridos, cruzas medio dialelo, patrón heterótico, vigor híbrido, rendimiento medio, líneas parentales.


Cultivated okra (Abelmoschus esculentus (L.) Moench) is originated in tropical Africa. It is an introduced vegetable crop in India. Although, it is a multipurpose and multifarious crop, it is extensively grown for its tender pods, which are used as a very popular, tasty and gelatinous vegetable. It is a powerhouse of valuable nutrients. It has huge socio-economic potential for enhancing livelihoods in both rural and urban areas. It offers a possible route to prosperity for small, medium, and large-scale producers alike. Okra is the most important vegetable crop in India accounting for 5.5% of the total vegetable cropped area and 3.6% total vegetable production of the country (NHB, 2010). India is one of the largest producers and consumers of okra in the world. Despite its recognized potential and significant area and consumption in the country, it is being neglected because of non-availability of high yielding open-pollinated varieties. Yield plateau seems to have been reached in open-pollinated varieties of okra.

To break the yield barriers in existing open-pollinated varieties of okra, a hybridization-based breeding strategy would be desirable. Heterosis breeding has been the most successful approach in increasing the productivity in cross-pollinated vegetable crops. Okra is one often-cross pollinated vegetable crop where the presence of heterosis was demonstrated for the first time by Vijayaraghavan and Warrier (1946). Since then, heterosis for yield and its components were extensively studied. Several research workers have reported occurrence of heterosis in considerable quantities for fruit yield and its various components (Venkataramani, 1952; Joshi et al., 1958; Partap and Dhankar, 1980; Elangovan et al., 1981; Partap et al., 1981; Mehta et al., 2007; Weerasekara et al., 2007; Jindal et al., 2009). The ease in emasculation and very high percentage of fruit setting indicates the possibilities of exploitation of hybrid vigour in okra. The presence of sufficient hybrid vigour is an important prerequisite for successful production of hybrid varieties. Therefore, the heterotic studies can provide the basis for the exploitation of valuable hybrid combinations in the future breeding programmes and their commercial utilization.

Variation in most of the agronomical and horticultural traits is available in the germplasm of cultivated okra (Dhall et al., 2003; Singh et al., 2006; Dakahe et al., 2007; Mohapatra et al., 2007; Reddy, 2010). The initial selection of parents to be involved in any effective hybridization programme depends upon the nature and magnitude of relative heterosis (heterosis over mid parent), heterobeltiosis (heterosis over better parent), and economic heterosis (heterosis over check) present in genetic stocks. Exploitation of heterosis is primarily dependent on the screening and selection of available germplasm that could be produced by better combinations of important agronomical and horticultural traits. Heterosis breeding based on the identification of the parents and their cross combinations is capable of producing the highest level of transgressive segregates (Falconer, 1960). The choice of the best parental matings is crucial for the development of superior hybrids and because combinations of hybrids grow exponentially with the potential number of parents to be used, this is one of the most expensive and time-consuming steps in hybrid development programmes (Agrawal, 1998). The magnitude of heterosis provides a guide for the choice of desirable parents for developing superior F1 hybrids, so as to exploit hybrid vigour. It also helps in choosing suitable crosses to be used for commercial exploitation as well as in component breeding programme.

The present investigation aims primarily to study the direction and extent of relative heterosis, heterobeltiosis and economic heterosis for yield and its associated traits in 10 x 10 half diallel crosses for utilization of existing genetic diversity to develop heterotic F1 hybrids in okra.

MATERIALS AND METHODS

Ten elite and nearly homozygous lines of okra namely P1(IC282248), P2(IC27826-A), P3(IC29119-B), P4(IC31398-A), P5(IC45732), P6(IC89819), P7(IC89976), P8(IC90107), P9(IC99716), and P10(IC111443) selected from the germplasm were crossed in n(n - 1)/2 possible combinations during summer 2009 to generate the breeding material. The resulting 45 one way crosses along with their 10 counterpart parental lines and one standard control (Mahyco Hybrid N° 10) were evaluated in a randomized complete block design with three replicates. The experiment was conducted at the Experimental Farm, Vegetable Research Station, Rajendranagar, Hyderabad, Andhra Pradesh, India. The experiment was conducted during early kharif (June-September) 2009. The Experimental Farm is situated at 17.19° N, 79.23° E, 542.6 m a.s.l. The soils are sandy loams. Each entry was raised in a double row plot. The individual plot was of 3 m length and 1.2 m width. A row-to-row spacing of 60 cm and plant-to-plant spacing of 30 cm was adopted. Ten plants per row and 20 plants per plot and entry were maintained. Standard agronomic practices were followed from sowing till harvest. Since lines were grown on ridges, furrow irrigation was given at weekly interval. Recommended doses of manure (farm yard manure 25 t ha-1) and fertilizers (150 kg N ha-1, 150 kg P ha-1 and 150 kg K ha-1) were applied in the experimental field. Regular plant protection measures were carried out to safeguard the crop from major insect pests and diseases. Biometric data were recorded for 17 quantitative characters. Observations on the characters like plant height (cm), number of branches per plant, internodal length (cm), first flowering node, first fruiting node, fruit length (cm), fruit width (cm), and fruit weight (g) were recorded on five randomly selected competitive plants, while the observations on the characters like days to 50% flowering, total number of fruits per plant, number of marketable fruits per plant, total yield per plant (g) and marketable yield per plant (g), fruit and shoot borer (FSB) infestation on fruits and shoots (%), and Yellow vein mosaic virus (YVMV) infestation on fruits and plants (%) were recorded on whole plot basis in each entry in each replicate. The replicate mean values of FSB infestation on fruits and shoots (%) and YVMV infestation on fruits (%) were subjected to square root transformation, while YVMV infestation on plants (%) were subjected to arc sin transformation to restore distribution to normality. Relative heterosis, heterobeltiosis and standard heterosis were determined as percent increase (+) or decrease (-) of F1 over mid parent (MP), better parent (BP) and standard control (SC) using the formulae (F1-MP/MP x 100), (F1-BP/BP x 100) and (F1-SC/SC x 100), respectively (Singh, 1973). The statistical significance of heterosis, heterobeltiosis and standard heterosis was assessed by t-test (Wynne et al., 1970).

RESULTS AND DISCUSSION

The attainment of maximum crop yield is an important objective in most breeding programmes and the major emphasis in vegetable breeding is on the development of improved varieties. The utilization of the effect of heterosis is very rightly considered to be as one of the most outstanding achievements of the vegetable breeders in the 20th century. Vegetable breeders have widely exploited and used heterosis in boosting up yield of many crops. The goal of okra hybrid breeding is to identify and then reliably reproduce superior hybrid genotypes. Virtually all commercial okra hybrids are made from crosses of inbred lines. Knowledge of heterotic groups from which to draw parental germplasm for hybrid combinations is limited. Improvement of complex characters such as pod yield may be accomplished through the component approach of breeding. This method, in general, assumes strong associations of yield with a number of characters making up yield and simpler inheritance for these component characters.

Analysis of variance
ANOVA (Table 1) indicated significance of mean squares due to genotypes for almost all characters under study except plant height. This can be attributed to the fact that there were clear cut genotypic differences among the parents and their hybrids, which were phenotypically expressed. The mean squares due to parents were highly significant for almost all characters except plant height under study. The mean squares due to crosses were highly significant for almost all characters under study except plant height. The mean squares due to parents versus crosses, which are a measure of the importance of average heterosis, were highly significant for majority of the characters except plant height, number of branches per plant and internodal length, FSB infestation on fruits and shoots and YVMV infestation on fruits and plants.

Table 1. Analysis of variance for heterosis in okra.

>
*, **Significant at P < 0.05 and P < 0.01 levels, respectively. Values in parentheses denote degrees of freedom.
FSB: fruit and shoot borer; YVMV: Yellow vein mosaic viirus.

 

Mean performance
From the mean performance of the genotypes, it is evident that, in general, the mean values of crosses were desirably higher than those of the parents (Table 2) for number of branches per plant, fruit length, fruit weight, total number of fruits per plant and number of marketable fruits per plant, total yield per plant and marketable yield per plant. On other hand, the mean values of crosses were desirably lower than those of the parents for internodal length, fruit width and FSB infestation on fruits and plants. In general, the range of mean values of parents as a whole was highest for total yield per plant (248.84 to 359.06 g) followed by marketable yield per plant (203.26 to 300.50 g) and plant height (155.13 to 187.40 cm). Similarly, the range of mean values of crosses as a group was highest for total yield per plant (240.53 to 409.65 g) followed by marketable yield per plant (204.32 to 325.25 g) and plant height (149.60 to 195.67 cm).

Table 2. Range and average performance of parents, crosses and control and average and standard heterosis in okra.



AH: Average heterosis; SH: standard heterosis; FSB: fruit and shoot borer; YVMV: Yellow vein mosaic virus.

The range of mean performance of 10 parental lines and their 45 cross combinations are presented in Table 2. Plant height among the parents and crosses varied from 155.13 to 187.40 and 149.60 to 195.67 cm, respectively. Number of branches per plant varied from 1.47 to 3.07 and 1.20 to 3.60 among the parents and crosses, respectively. Internodal length among the parents and crosses varied from 5.52 to 7.89 and 5.55 to 7.95 cm, respectively. The number of days taken to 50% flowering among the parents and crosses varied from 36.33 to 38.67 and 36.67 to 39.33, respectively. The first flowering and fruiting node varied from 4.00 to 5.10 among parents and 3.90 to 5.30 among hybrids. Fruit length among the parents and crosses varied from 11.47 to 15.72 and 12.20 to16.33, respectively. Fruit width varied from 1.70 to 2.07 among parents and 1.70 to 2.03 among hybrids. Fruit weight varied from 12.75 to 17.35 among parents and 13.78 to 17.80 among hybrids. Total number of fruits per plant among the parents and crosses varied from 18.13 to 22.07 and 15.60-24.87, respectively. Number of marketable fruits per plant varied from 14.94 to18.82 and 13.29 to 21.36 among the parents and crosses, respectively. Total yield per plant among the parents and crosses varied from 248.84 to 359.06 and 240.53 to 409.65 g, respectively. Marketable yield per plant varied from 203.26 to 300.50 and 204.32 to 325.25 g among the parents and crosses, respectively. FSB infestation on fruits among the parents and crosses varied from 2.42 to 3.08 and 2.29 to 3.08%, respectively. Similarly, FSB infestation on shoots among the parents and crosses varied from 1.95 to 2.63 and 1.94 to 2.62%, respectively. YVMV infestation on fruits among the parents and crosses varied from 2.31 to 3.15 and 2.11 to 3.41%, respectively. Similarly, YVMV infestation on plants among the parents and crosses varied from 34.15 to 49.80 and 30.78 to 60.07%, respectively.

Heterosis
Overall average heterosis and standard heterosis of hybrids as a group were estimated and presented in Table 2. The hybrids, in general, manifested highest average heterosis in desirable positive direction for total yield per plant (6.92%), followed by marketable yield per plant (6.64%), total number of fruits per plant (3.68%) and number of marketable fruits per plant (3.66%). Similarly, the hybrids, in general, exhibited highest standard heterosis in desirable negative direction for internodal length (-4.75%) followed by days to 50% flowering (-0.70%).

The range of heterosis and the number of crosses displaying significantly positive and negative heterosis over the mid parent, better parent and standard control (Mahyco Hybrid N°10) are presented in Table 3. There was huge amount of variation in heterotic effects as they varied differently for different characters. For plant height, heterosis over mid parent, better parent and standard control ranged from -18.56 to 13.94, -20.17 to 8.70 and -23.65 to -0.14%, respectively. For this trait, only one cross over mid parent manifested significantly positive heterosis. For number of branches per plant, average heterosis, heterobeltiosis and standard heterosis ranged from -25.00 to 37.85, -41.46 to 25.00 and -45.45 to 63.64%, respectively. For this trait, nine crosses over better parent and five crosses over standard control manifested significantly positive heterosis. Heterosis over mid parent, better parent and standard control varied from -27.80 to 28.09, -29.63 to 28.09 and -22.49 to 11.03%, respectively for internodal length. For internodal length, four crosses over mid parent, six crosses over better parent and four crosses over standard control manifested significantly negative heterosis.

Table 3. Ranges of heterosis over three bases and number of crosses with significantly positive and negative heterosis for seventeen traits in okra.


*, **Significant at P < 0.05 and P < 0.01 levels, respectively
RH: Relative heterosis; HB: heterobeltiosis; SH: standard heterosis; FSB: fruit and shoot borer; YVMV: Yellow vein mosaic viirus.

For days to 50% flowering, relative heterosis, heterobeltiosis, and standard heterosis ranged from -1.79 to 5.83, -2.65 to 5.36 and -4.35 to 2.61%, respectively (Table 3). Only one cross over standard control manifested significantly negative standard heterosis. Heterosis over mid parent, better parent and standard control ranged from -12.36 to 20.93, -13.73 to 16.67 and -15.22 to 15.22%, respectively for first flowering and fruiting nodes. For these traits, five crosses over mid parent, fifteen crosses over better parent and 13 crosses over commercial control manifested significant heterosis in desirable direction (negative).

For fruit length, relative heterosis, heterobeltiosis, and standard heterosis ranged from -14.22 to 19.22, -15.04 to 9.81and -12.44 to 17.22%, respectively (Table 3). Twenty six crosses over mid parent, 11 crosses over better parent and 25 crosses over standard control manifested significantly positive heterosis for this trait. For fruit width, heterosis over mid parent, better parent and standard control ranged from -5.81 to 10.27, -14.15 to 4.38 and -8.09 to 9.35%, respectively. For this traits, 11 crosses over mid parent, three crosses over better parent and 30 crosses over commercial control manifested positively significant heterosis. For fruit weight, heterosis over mid parent, better parent and standard control ranged from -13.38 to 12.30, -16.37 to 9.88 and -15.98 to 8.54%, respectively. For this traits, 21 crosses over mid parent, six crosses over better parent and five crosses over commercial control manifested positively significant heterosis.

For total number of fruits per plant, heterosis over mid parent, better parent and standard control ranged from -19.59 to 36.88, -24.52 to 36.63, and -32.95 to 6.88%, respectively (Table 3). For this trait, ten crosses over mid parent and three crosses over better parent manifested positively significant heterosis. For number of marketable fruits per plant, average heterosis, heterobeltiosis, and standard heterosis ranged from -21.27 to 38.80, -25.83 to 34.81, and -37.68 to 0.16%, respectively. For this trait, nine crosses over mid parent and three crosses over better parent manifested positively significant heterosis.

For total yield per plant, heterosis over mid parent, better parent and standard control ranged from -16.40 to 38.83, -23.77 to 35.87, and -36.22 to 8.63%, respectively (Table 3). Nineteen crosses over mid parent and six crosses over better parent manifested significantly positive heterosis for this trait. For marketable yield per plant, average heterosis, heterobeltiosis, and standard heterosis ranged from -18.17 to 40.90, -25.12 to 33.67, and -40.83 to 5.81%, respectively. Seventeen crosses over mid parent and five crosses over better parent manifested significantly positive heterosis for this trait.

For FSB infestation on fruits, heterosis over mid parent, better parent and standard control ranged from -10.18 to 4.47, -14.79 to 1.33, and -4.82 to 28.77%, respectively (Table 3). Two crosses over mid parent and 12 crosses over better parent manifested significantly negative heterosis for this trait. For FSB infestation on shoots, heterosis over mid parent, better parent and standard control ranged from -9.90 to 5.90, -19.94 to 3.37, and -1.70 to 32.59%, respectively. Fifteen crosses over better parent manifested significantly negative heterosis for this trait. For YVMV infestation on fruits, heterosis over mid parent, better parent and standard control ranged from -26.19 to 32.79, -28.54 to 25.74, and 37.95 to 133.86%, respectively. For this trait, two crosses over mid parent and four crosses over better parent manifested significantly negative heterosis. For YVMV infestation on plants, heterosis over mid parent, better parent and standard control ranged from -30.11 to 46.11, -33.06 to 32.10, and 11.86 to 118.28%, respectively. For this trait, two crosses over mid parent and five crosses over better parent manifested significantly negative heterosis.

From the results of the heterosis studies, it is evident that none of the 45 F1 hybrids of okra showed consistency in direction and degree of heterosis over three bases for all the characters studied. Some of them manifested positive heterosis while others exhibited negative heterosis (data not shown), mainly due to varying extent of genetic diversity between parents of different cross combinations for the component characters. Significant heterosis was observed for all the growth, earliness and yield attributes. It is inferred that the magnitude of economic heterosis was higher for most of the growth and earliness characters under study. In the present study, the estimates of relative heterosis, heterobeltiosis, and standard heterosis were found to be highly variable in direction and magnitude among crosses for all the characters under study. Weerasekara et al. (2007) and Jindal et al. (2009) also reported such a variation in heterosis for different characters. The manifestation of negative heterosis observed in some of the crosses for different traits may be due to the combination of the unfavorable genes of the parents.

Of the 17 characters under study, plant height, number of branches per plant, and internodal length largely determine the fruit bearing surface and thus considered as growth attributes. Okra bears pods at almost all nodes on main stem and primary branches. Higher the plant height with more number of branches on the main stem, higher is the number of fruits per plant because of accommodation of more number of nodes for a given internodal length. Shorter distance between nodes accommodates more number of nodes on main stem, which will ultimately lead to higher fruit number and higher fruit production. Hence, positive heterosis is desirable for plant height and number of branches, while negative heterosis is desirable for internodal length to accommodate more number of nodes and to get higher fruit yield in okra. Most of the crosses displayed negative standard heterosis for plant height, which is in the undesirable direction. However, appreciable amount of standard heterosis in desirable direction was observed for number of branches per plant (up to 63.64%) and internodal length (up to -22.49%). Ahmed et al. (1999), Dhankar and Dhankar (2001) and Rewale et al. (2003), Singh et al. (2004), Weerasekara et al. (2007) and Jindal et al. (2009) also reported the similar projections for number of branches in okra. For internodal length, similar projections were also made by Rewale et al. (2003), Singh et al. (2004), and Jindal et al. (2009).

Days to 50% flowering, first flowering node, and first fruiting node are the indicators of earliness in okra. Early flowering not only gives early pickings and better returns but also widens fruiting period of the plant. Flowering and fruiting at lower nodes are helpful in increasing the number of fruits per plant as well as getting early yields. Negative heterosis is highly desirable for all these three attributes of earliness. In the present study, cross C19 exhibiting high negative heterosis over standard control for days to 50% flowering (-4.35%) and the cross C4 displaying high negative heterosis over standard control for first flowering and fruiting node (-15.22%) are, therefore, important to exploit heterosis for earliness in okra. Weerasekara et al. (2007) and Jaiprakashnarayan et al. (2008) also noticed heterosis in desirable direction for days to 50% flowering in okra. The negative estimates of heterobeltiosis and economic heterosis for earliness revealed the presence of genes for the development of earliness in okra. The estimates of heterosis over mid parent, better parent and standard control for both first flowering node and first fruiting node were of equal magnitude in all the crosses, indicating 100% fruit set in the early stages of flowering. Tippeswamy et al. (2005) and Jindal et al. (2009) also noticed desirable heterosis for first flowering node in okra. Mandal and Das (1991) noticed desirable heterosis for first flowering and fruiting nodes in okra.

Total number of fruits per plant and fruit length, width, and weight are considered to be associated directly with total yield per plant, for which positive heterosis is desirable. The cross C35 displayed highest positively significant relative heterosis (19.22%) and standard heterosis (17.22%), while the cross C22 exhibited highest positively significant heterobeltiosis (9.81%) for fruit length. The cross C22 exhibited highest positively significant relative heterosis (10.27%) and heterobeltiosis (4.38%), while the cross C25 exhibited highest positively significant standard heterosis (9.35%) for fruit width. For average fruit weight, highest positively significant relative heterosis (12.30%) and heterobeltiosis (9.88%) and standard heterosis (8.54%) was displayed by the cross C35. Similar results were also reported by Ahmed et al. (1999) and Jaiprakashnarayan et al. (2008) in okra. Cross combinations C23 (36.88%), C24 (23.50%), C36 (21.31%), C19 (18.84%) and C43 (16.23%) were the top five crosses on the basis of average heterosis, while cross C23 (36.63%), C24 (16.13%), and C36 (13.85%) were the top three on the basis of heterobeltiosis for total number of fruits per plant. Similar results have been reported by Weerasekara et al. (2007) and Jaiprakashnarayan et al. (2008).

For number of marketable fruits per plant, the crosses C23, C36, C24, C19, and C31 displaying an average heterosis of 38.80, 24.28, 23.88, 15.70, and 13.88%, respectively were the top five crosses, while the crosses C23, C36, and C24 manifesting a heterobeltiosis of 34.89, 17.25, and 13.56% were the top three crosses for this trait. The cross C23 displayed highest positively significant heterosis over mid parent (38.83%) and better parent (35.87%) for number of marketable fruits per plant. Maximum significantly negative heterosis over better parent was displayed by the cross C12 (-14.79%) and C7 (-19.94%) for FSB infestation on fruits and shoots, respectively. The cross C14 not only displayed highest negatively significant heterosis over mid parent (-26.15%) and better parent (-28.54%) for YVMV infestation on fruits, but also displayed highest negatively significant heterosis over mid parent (-30.11%) and better parent (-27.32%) for YVMV infestation on plants.

Griffing (1956) has suggested the possibility of working with yield components which are likely to be more simply inherited than is by itself. Grafius (1959) suggested that there is no separate gene system for yield per se and that the yield is an end product of the multiplication interaction between the yield components.

The contribution of components of yield is through component compensation mechanism (Adams, 1967). Since then component breeding rather than direct selection on yield has commonly been practiced. It is obvious that high heterosis for yield was built up by the yield components. Hybrid vigour of even small magnitude for individual components may result in significant hybrid vigour for yield per se. This was confirmed by the present investigation where none showed hybrid vigor for yield alone. The high heterosis for fruit yield observed in these crosses could probably be due to combined heterosis of their component characters, as these hybrids were not only heterotic in respect of fruit yield but were also found superior for one or the other yield components. Thus, the observed high heterosis for total yield seems to be due to increase in the total number of fruits per plant rather than increase in the size and weight of fruits, which is a desirable requirement in okra improvement. The results obtained in the present investigation were encouraging and tremendous increase in yield was obtained in most of the hybrids. Based on the overall performance of the hybrids and parental lines, some of the lines could be used as parents of hybrids of okra with high to moderate yield potential.

The major components of marketable yield are not only the total number of pods per plant, pod size, and weight but also the percent infestation of fruits and shoots by FSB and fruits and plants by YVMV. In the present investigation, in general, positively high heterosis for marketable yield per plant was associated with positively high heterosis for total number of fruits per plant, size (length and width) and weight of fruits and negatively high heterosis for FSB infestation on fruits and shoots and YVMV infestation on fruits and plants. Thus, the observed high heterosis for marketable yield seems to be due to decrease in the incidence of FSB on fruits and shoots and YVMV on fruits and shoots. Most of the hybrids showing positive heterosis for marketable yield also showed significantly negative heterosis for FSB on fruits and shoots and YVMV on fruits and plants.

Significantly positive heterosis has been observed mainly in terms of total yield in crosses over their mid and better parents. The crosses C23, C43, C24, C42, and C34 were the top five heterotic crosses, manifesting an average heterosis of 38.83, 26.44, 24.93, 21.45, and 20.59%, respectively, while the crosses C23, C43, C22, C42, and C31 were the top five crosses, displaying a heterobeltiosis of 35.87, 24.20, 21.06, 14.09, and 13.99%, respectively for total yield per plant (Table 4). These results are in agreement with the findings of Weerasekara et al. (2007) and Jaiprakashnarayan et al. (2008). None of the hybrids showed positively significant heterosis over standard control for this trait. However, crosses C42, C31, C35, C25, and C36, displaying 8.63, -0.08, -2.61, -3.26, and -4.57% non-significant standard heterosis in any given direction are as promising as that of standard control (Table 5). It is apparent that the high heterosis for total fruit yield may probably be due to dominance nature of genes. The significantly positive heterobeltiosis for total yield per plant could be apparently due to preponderance of fixable gene effects, which is also reported by Elangovan et al. (1981) and Singh et al. (1996).

Table 4. Top five crosses with significant heterosis in desirable direction for 17 traits in okra.


*, ** Significant at P < 0.05 and P < 0.01 levels, respectively.
RH: Relative heterosis; HB: heterobeltiosis; SH: standard heterosis.


Table 5. Top five crosses on the basis of per se performance and heterotic effects for total and marketable yield per plant in okra.


*, **Significant at P < 0.05 and P < 0.01 levels, respectively.
LSD: Least significant difference.

Significantly positive heterosis has been observed mainly in terms of marketable yield in crosses over their respective mid and better parents. The crosses C23, C24, C43, C21, and C34 were the top five heterotic hybrids, manifesting an average heterosis of 40.90, 25.28, 21.82, 19.08, and 18.95%, respectively, while the crosses C23, C43, C28, C31, and C22 were the top five heterotic hybrids, displaying a heterobeltiosis of 33.67, 20.20, 17.20, 16.42, and 16.41%, respectively for this trait. Similar results were also found by Tippeswamy et al. (2005) and Jindal et al. (2009). None of the hybrids showed positively significant heterosis over standard control for this trait. However, crosses C42, C31, and C31 displaying -5.81, -6.56, and -10.14% non-significant standard heterosis in negative direction are as promising as that of standard control for this trait.

In the present study, it is apparent that high heterosis for yield may probably be due to dominance nature of genes. For yield attributes, some crosses were non-heterotic which may be ascribed to cancellation of positive and negative effects exhibited by the parents involved in a cross combination and can also happen when the dominance is not unidirectional as also pointed out by Gardner and Eberhart (1966) and Mather and Jinks (1982) . Heterosis is thought to result from the combined action and interaction of allelic and non allelic factors and is usually closely and positively correlated with heterozygosity (Falconer and Mackay, 1986).

According to Swaminathan et al. (1972) heterobeltiosis of more than 20% over better parent could offset the cost of hybrid seed. Thus, the crosses showing more than 20% of heterobeltiosis viz. may be exploited for hybrid okra production. Although the range of average heterosis and heterobeltiosis manifested by the crosses for different characters was comparatively wide, but it might not be of much significance unless it shows sufficient gain over the standard control. In the present study, the moderate extent of relative heterosis and heterobeltiosis as observed for yield and yield components could be attributed to its often-cross pollinated nature. The extent of heterosis over standard control for total yield per plant (8.63%) and marketable yield per plant (-5.81%) appears to be sufficient for exploitation of heterosis commercially (Table 5). F1 hybrids C42, C31, C35, C25, and C36 with nonsignificant standard heterosis in any given direction for total yield per plant (8.63, -0.08, -2.61, -3.26, and -4.57%, respectively) and F1 hybrids C42, C31, and C36 with nonsignificant standard heterosis in any given direction for marketable yield per plant (-5.87, -6.56, and -10.54%, respectively), were statistically on par with the standard control in their mean performance and are found to be as promising as that of the standard control (Mahyco Hybrid N° 10) under comparison (Table 5). For both total yield and marketable yield per plant, the crosses C42(P7XP10), C31(P5XP6) and C36(P6XP7) were found to be as promising as that of the standard control (Mahyco Hybrid N° 10), which can be exploited for commercial cultivation after further testing during early kharif in Andhra Pradesh.

CONCLUSIONS

On an average, okra displays heterosis for yield and its component traits studied. However, for each trait important differences exist among hybrids for the individual values of heterosis. Yield components should be considered to increase the yield through selections. In the present study, cross C19 exhibiting high negative heterosis over standard control for days to 50% flowering (-4.35%) and the cross C4 displaying high negative heterosis over standard control for first flowering and fruiting nodes (-15.22%) are, therefore, important to exploit heterosis for earliness in okra. For both total yield and marketable yield per plant, the crosses C42(P7XP10), C31(P5XP6), and C36(P6XP7) were found to be as promising as that of the standard control (Mahyco Hybrid N° 10), which can be exploited for commercial cultivation after further testing during early kharif in Andhra Pradesh.

ACKNOWLEDGEMENTS

The authors are highly grateful to the NBPGR Regional Station, Thrissur, for providing the germplasm of okra from which the parents for the present study were selected.


LITERATURE CITED

Adams, M.W. 1967. Plant architecture and yield breeding. Iowa State Journal of Research 56:225-254.         [ Links ]

Agrawal, R.L. 1998. Fundamentals of plant breeding and hybrid seedproduction. Science Publishers, Enfield, New Hampshire, USA.         [ Links ]

Ahmed, N., M.A. Hakim, and M.Y. Gandroo. 1999. Exploitation of hybrid vigour in okra (Abelmoschus esculentus (L.) Moench). Indian Journal of Horticulture 56:247-251.         [ Links ]

Dakahe, K., H.E. Patil, and S.D. Patil. 2007. Genetic variability and correlation studies in okra (Abelmoschus esculentus (L.) Moench). The Asian Journal of Horticulture 2:201-203.         [ Links ]

Dhall, R.K., S.K. Arora, T.S. Dhillon, and R. Bansal. 2003. Evaluation of advance generations in okra (Abelmoschus esculentus (L.) Moench) for yield and yield contributing characters. Environment and Ecology 21:95-98.         [ Links ]

Dhankar, B.S., and S.K. Dhankar. 2001. Heterosis and combining ability studies for some economic characters in okra. Haryana Journal of Horticultural Science 30:230-233.         [ Links ]

Elangovan, M., C.R. Muthurkrishnan, and I. Irulappan. 1981. Combining ability in bhendi (Abelmoschus esculentus (L.) Moench). South Indian Horticulture 29(1-4):15-22.         [ Links ]

Falconer, D.C. 1960. Introduction to quantitative genetics. p. 254. Oliver and Boyd, Edinburgh, Scotland.         [ Links ]

Falconer, D.S., and T.F.C. Mackay. 1986. Introduction to quantitative genetics. Longman Group Ltd., Harlow, England.         [ Links ]

Gardner, C.O., and S.S. Eberhart. 1966. Analysis and interpretation of the variety cross diallel and related population. Biometrics 22:439-452.         [ Links ]

Grafius, J. 1959. Heterosis in barley. Agronomy Journal 51:551-554.         [ Links ]

Griffing, B. 1956. Concept of general and specific combining ability in relation to diallel crossing system. Australian Journal ofBiological Sciences 9:463-493.         [ Links ]

Jaiprakashnarayan, R.P, S.J. Prashanth, R. Mulge, and M.B. Madalageri. 2008. Study on heterosis and combining ability for earliness and yield parameters in okra (Abelmoschus esculentus (L.) Moench). The Asian Journal of Horticulture 3:136-141.         [ Links ]

Jindal, S.K., D. Arora, and T.R. Ghai. 2009. Heterobeltiosis and combining ability for earliness in okra (Abelmoschus esculentus (L.) Moench). Crop Improvement 36(2):59-66.         [ Links ]

Joshi, A.B., H.B. Singh, and P.S. Gupta. 1958. Studies in hybrid vigour III Bhendi. Indian Journal of Genetics and Plant Breeding18:57-68.         [ Links ]

Mandal, N., and N.D. Das. 1991. Heritability and heterosis stud in okra (Abelmoschus esculentus (L.) Moench). Experimental Genetics 7(1):22-25.         [ Links ]

Mather, K., and J.L. Jinks. 1982. Biometrical genetics. 3rd ed. Chapman and Hall Ltd., London, UK.         [ Links ]

Mehta, N., B.S. Asati, and S.R. Mamidwar. 2007. Heterosis and gene action in okra. Bangladesh Journal of Agricultural Research 32:421-432.         [ Links ]

Mohapatra, M.R., P. Acharya, and S. Sengupta. 2007. Variability and association analysis in okra. Indian Agriculturist 51(1/2):17-26.         [ Links ]

NHB. 2010. Indian Horticulture Database 2001. 197 p. National Horticulture Board (NHB), Gurgaon, India.         [ Links ]

Partap, P.S., and B.S. Dhankar. 1980. Heterosis studies in okra (Abelmoschus esculentus (L.) Moench). Haryana Agricultural University Journal of Research 18:336-340.         [ Links ]

Partap, P.S., B.S. Dhankar, and M.L. Pandita. 1981. Heterosis and combining ability in okra (Abelmoschus esculentus (L.) Moench). Haryana Journal of Horticultural Science 10:122-127.         [ Links ]

Reddy, M.T. 2010. Genetic diversity, heterosis, combining ability and stability in okra (Abelmoschus esculentus (L.) Moench). PhD. thesis. Acharya N.G. Ranga Agricultural University, Rajendranagar, Hyderabad.         [ Links ]

Rewale, V.S., V.W. Bendale, S.G. Bhave, R.R. Madav, and B.B. Jadhav. 2003. Heterosis for yield and yield components in okra. Journal of Maharashtra Agricultural Universities 28:247-249.         [ Links ]

Singh, D. 1973. Diallel analysis over environments-I. Indian Journal of Genetics and Plant Breeding 33:127-136.         [ Links ]

Singh, N., S.K. Arora, T.R. Ghai, and T.S. Dhillon. 1996. Heterobeltiosis studies in okra (Abelmoschus esculentus (L.) Moench). Punjab Vegetable Grower 31:18-24.         [ Links ]

Singh, B., A.K. Pal, and S. Singh. 2006. Genetic variability and correlation analysis in okra (Abelmoschus esculentus (L.) Moench). Indian Journal Horticulture 63(3):63-66.         [ Links ]

Singh, B., S. Singh, A.K. Pal, and M. Rai. 2004. Heterosis for yield and yield components in okra (Abelmoschus esculentus (L.) Moench). Vegetable Science 31:168-171.         [ Links ]

Swaminathan, M.S., E.A. Siddique, and S.D. Sharma. 1972. Outlook for hybrid rice in India. p. 609-613. In Rice breeding. Internationa Rice Research Institute (IRRI), Los Banos, Philipinnes.

Tippeswamy, S., M. Pitchaimuthu, O.P. Dutta, J.S.A. Kumar, and M.C. Ashwini. 2005. Heterosis studies in okra (Abelmoschus esculentus (L.) Moench) using male sterile lines. Journal of Asian Horticulture 2(1):9-15.         [ Links ]

Venkataramani, K.S. 1952. A preliminary studies of some intervarietal crosses and hybrid vigour in Hibiscus esculentus (L). Journal of Madras Agricultural University 22:183-200.         [ Links ]

Vijayaraghavan, C., and V.A. Warrier. 1946. Evolution of high yielding hybrid bhindi (Hibiscus esculentus L). 163 p. Proceeding of the 33rd Indian Science Congress, Bangalore, India.         [ Links ]

Weerasekara, D., R.C. Jagadeesha, M.C. Wali, P.M. Salimath, R.M. Hosamani, and I.K. Kalappanawar. 2007. Heterosis for yield and yield components in okra. Vegetable Science 34:106-107.         [ Links ]

Wynne, J.C., D.A. Emery, and P.M. Rice. 1970. Combining ability estimates in Arachis hypogeae L. II. Field performance of F1 hybrids. Crop Science 10:713-715.         [ Links ]


Received: 21 November 2011.
Accepted: 17 April 2012
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