Scielo RSS <![CDATA[Chilean journal of agricultural research]]> vol. 78 num. 3 lang. <![CDATA[SciELO Logo]]> <![CDATA[Inbreeding depression and performance of partially self-fertilized maize progenies in a top cross]]> ABSTRACT Information on the effect of endogamy and combining ability of inbred families is essential in hybrid maize (Zea mays L.) breeding programs. The objective of this study was to evaluate the effect of inbreeding in a maize population and the performance of top-cross hybrids from this population, with a broad genetic base tester. First, 110 S1 families were generated and established in the field along with families from the original population. The experiment was arranged in a randomized block design with three replicates, in 3.0 m plots with 15 plants. Traits of agronomic importance, inbreeding depression, and the general effect of dominance deviations were estimated the first stage. In the second stage, 69 inbred families (S2) with low inbreeding depression were evaluated by top-cross tests using the F2 generation of the commercial hybrid AG 6040 as tester. The same traits from the first stage were evaluated. Inbreeding depression in the first stage was higher for traits related to production, which indicates that the heterozygous loci contribute more to these traits, with the additive effects being less important. In the second stage, the best estimates of the general combining ability (GCA) for grain weight were found in progenies 51, 33, 17, 9, 3, and 67, showing good performance and good potential for use in breeding programs. <![CDATA[Application of artificial neural networks to frost detection in central Chile using the next day minimum air temperature forecast]]> ABSTRACT Predicting future climatic events is one of the key issues in many fields, whether in scientific or industrial areas. An artificial neural network (ANN) model, based on a backpropagation type, was developed in this study to predict the minimum air temperature of the following day from meteorological data using air temperature, relative humidity, radiation, precipitation, and wind direction and speed to detect the occurrence of radiative frost events. The configuration of the next day ANN prediction system allows operating with low-power computing machines; it is able to generate early warnings that can lead to the development of effective strategies to reduce crop damage, lower quality, and losses in agricultural production. This paper presents a procedural approach to an ANN, which was trained, validated, and tested in 10 meteorological stations in central Chile for approximately 8 yr (2010-2017). The overall mean results were classified by a confusion matrix and showed good performance in predicting minimum temperature with a mean square error (MSE) of 2.99 °C for the network, 1.71 °C for training, 1.77 °C for validation, and 1.74 °C for the testing processes. Frost detection results had an appropriate 98% overall mean accuracy (ACC), 86% sensitivity (TPR), and 2% error rate (ER). Differences and errors in frost detection can be attributed to several factors that are mainly associated with the accuracy of the sensors meteorological stations, local climatic and geographic conditions, and the number of parameters that enter in the ANN training processes. <![CDATA[Analysis of rhamnogalacturonan I fragments as elicitors of the defense mechanism in tomato fruit]]> ABSTRACT The rhamnogalacturonan I (RGI) is part of pectin plant cell wall, and currently there is scarce information about the elicitor effect of its fragments in the fruit defense mechanism. In this work, the effect of the fragments of RGI on the defense mechanism in tomato (Solanum lycopersicum L.) fruits was evaluated. Three fragments of RGI released from enzymatic degradation by RG lyase were characterized according to their physical-chemical and structural characteristics. Two of RGI fragments (F-1 and F-2) were selected and applied on tomato fruits during 48 h. At different exposure times (0, 0.5, 1, 6, 24, and 48 h) tomato samples were taken, and the enzymatic activity of chitinase was assessed by fluorometry, and β-1,3-glucanase and peroxidase by spectrophotometry (UV-visible). The absorption bands determined by Fourier transform infra-red (FT-IR) spectroscopy in the RGI fragments, was different concerning RGI no fragmented. The RGI had a molecular weight of 64 kDa and an intrinsic viscosity of 40.9 mL g-1; while the molecular weight of F-1 and F-2 fragments were 20 and 16 kDa, and an average intrinsic viscosity of 27 and 26 mL g-1, respectively. The content of galacturonic acid decreased, and the neutral sugars increased concerning the time of enzymatic degradation. F-1 and F-2 fragments induced an increase in the level of β -1,3-glucanase activity in tomato fruits; however, an increase in the enzymatic activity of chitinase and peroxidase was observed after 0.5 h of exposure to F-2 fragment. It was concluded that the RGI fragments were structurally different from the RGI no fragmented and induced the natural defense mechanism of the tomato fruit. <![CDATA[Long-term maize stalk retention reduces seedtime soil respiration]]> ABSTRACT Cropland soil respiration (Rs) is a major part of CO2 transportation between the atmosphere and terrestrial ecosystems. Stalk retention is an effective method to conduct sustainable agricultural development. However, the relationship between long-term maize (Zea mays L.) stalk retention and seedtime Rs is not yet fully understood; two experimental zones with the same management history were therefore chosen to conduct the comparative study. Rainfed maize monoculture was the only crop cultivated in the study site. One zone (CZ) was covered by 5639 kg ha-1 maize stalk residue (MSR) after harvesting, and the other zone (BZ) has been left bare since autumn 2000. Annual measurements with 10 replicates were conducted at seedtime in 2015, 2016, and 2017. Results showed that mean Rs was 4.11 and 4.99 (g CO2 g-1 soil h-1 for CZ and BZ, respectively. Compared with BZ, CZ soil moisture was higher, but its soil temperature was lower. Although soil microbial abundances in CZ and BZ had decreasing trends between two adjacent seedtimes, there was a nonsignificant decrease of actinomycetes (p &gt; 0.1) and fungi (p &gt; 0.1) in BZ. The mean percentages of alkyl-carbon (Alkyl-C) were 25.6% and 35.0% for CZ and BZ, respectively. Redundancy analyses (RDA) showed that decreasing soil temperature, soil fungi, Alkyl-C as well as increasing soil moisture could explain reduced Rs in CZ. Maize stalk retention reduces seedtime Rs, thus maize stalk retention might contribute to soil C sequestration. <![CDATA[Plant growth promoting rhizobacteria with ACC deaminase activity isolated from Mediterranean dryland areas in Chile: Effects on early nodulation in alfalfa]]> ABSTRACT Alfalfa (Medicago sativa L. subsp. sativa) has emerged as an alternative crop for Mediterranean dryland areas in Chile. These soils show deficient nutritional levels affecting legume nodulation and N fixation through symbiosis with Ensifer meliloti. The objective of this work was to select plant growth promoting rhizobacteria (PGPR) associated with alfalfa and to evaluate their effects in plant growth and nodulation. Bacterial strains were isolated from the rhizosphere of alfalfa cultivated in dryland soil in Mediterranean areas of Chile. The 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, production of indole acetic acid (IAA), phosphate solubilization and the compatibility with E. meliloti was assessed for each strain. The selected bacterial strains were identified by the amplification of the 16S rRNA gene. Twelve of the 32 isolated strains were compatible with E. meliloti as they did not show signs of antagonism. Eight strains solubilized phosphate, 12 produced IAA ranging from 13.71 to 26.22 mg L-1 and only the GN-8 isolate reported ACC deaminase activity. In the plants, the nodulation was greater when the strain with ACC deaminase and E. meliloti were co-inoculated both in laboratory and greenhouse conditions (P &lt; 0.05). The selected bacteria GN-2 and GN-8 belonged to the genus Bacillus, while GN-4 to Pseudomonas. In conclusion, PGPR collected in marginal soils of Mediterranean areas of Chile showed ACC deaminase activity, IAA production and phosphate solubilization. The co-inoculation with E. meliloti and Bacillus sp. GN-8 allowed earlier nodulation in alfalfa. <![CDATA[Environmental factors on seed germination and seedling emergence of <em><em>Phleum paniculatum</em> Huds.</em>]]> ABSTRACT Phleum paniculatum Huds., commonly known as British timothy, is an increasingly serious weed in wheat field of China. However, the biology of its seed germination and seedling emergence remain unclear. In the present study, the effects of environmental factors on seed germination and seedling emergence of P. paniculatum were explored. Phleum paniculatum seeds had a shallow dormancy (20-30 d) when stored at room temperature (25 ± 5 °C). Seeds could germinate at constant temperatures between 10 and 25 °C, except for 5 or 30 °C. Light was not essential for seed germination, and pH values from 4 to 10 did not inhibit germination. Seeds were moderately adaptable to water potential and NaCl concentration, and germination rates would be decreased 50% when water potential was -0.4 MPa or NaCl concentration was 130 mM. Increased soil burial depth decreased the seedling emergence, and no seeds emerged when the burial depth was more than 4 cm. Taken together, our results provide useful information of the germination and emergence of P. paniculatum seed, and strategies such as proper drainage systems managed and deep plowing are recommended to limit its detrimental effects on agricultural production. <![CDATA[Effect of saponins of <em>Quillaja saponaria</em> extracts in combination with <em>Pseudomonas protegens</em> to control <em>Gaeumannomyces graminis</em> var. <em>tritici</em> in wheat]]> ABSTRACT Extracts rich in saponins from Quillaja saponaria Mol. and populations of rhizobacteria from the genus Pseudomonas, which produce antimicrobial compounds, have been associated with reduction of the fungus Gaeumannomyces graminis var. tritici, the causal agent of take-all disease, which is responsible for severe loss of wheat (Triticum aestivum L.) crops worldwide. However, there is a limited background on the interaction between these bacteria and natural triterpenoids. The aim of this research was to assess the effect of saponin rich extract on Pseudomonas protegens strains 2,4-diacetylphloroglucinol-producers under in vitro and in plant conditions and determining the synergistic effect to be used together to control G. graminis var. tritici in wheat plants. We determined that 8% and 90% of saponins rich Q. saponaria extracts have a differential effect on P. protegens according to their purity (P ( 0.05). On wheat seedlings, quillaja extract with 90% of saponins did not affect the three antagonistic bacterial strain populations assessed, but affected biofilm formation at saponins concentration of 7360 mg L-1. Pseudomonas protegens strains had a variable antagonist activity in wheat plants, and controlled the fungus when were combined with different concentrations of pure Q. saponaria extract, with the concentration of 1840 ppm reducing the take-all disease in 32.5% with respect to the control inoculated with G. graminis var. tritici (P ( 0.05). However, no synergistic effects when the plant extract was combined with the bacterial strains were observed. These results showed the promising and complexity of combining bacterial and plant extract to develop a biopesticide, which could control this fungal disease. <![CDATA[Antagonistic activity of <em>Trichoderma asperellum</em> and <em>Trichoderma harzianum</em> against genetically diverse <em>Botrytis cinerea</em> isolates]]> ABSTRACT Trichoderma species have been identified as potential biocontrol agents of many plant pathogenic fungi, including Botrytis cinerea Pers., one of the major pathogens in tomato (Solanum lycopersicum L.) production in the Republic of Macedonia. The aim of this study was to evaluate the in vitro antagonistic activity of Trichoderma asperellum and T. harzianum against 18 genetically diverse B. cinerea isolates. The results showed considerable antagonistic abilities of both Trichoderma species against all tested B. cinerea isolates. Both antagonists significantly (p &lt; 0.01) inhibited the mycelial growth (T. asperellum from 74.246% to 96.915% and T. harzianum from 71.072% to 95.889%) and conidial germination (T. asperellum from 76.932% to 95.107% and T. harzianum from 76.933% to 93.658%) of B. cinerea isolates. The antagonistic abilities were not related to the genetic group, but apparent association with the region of origin of the pathogen isolates was observed. Trichoderma asperellum and T. harzianum are promising biocontrol agents for control of gray mold disease in tomato. <![CDATA[Relationship between the number of partial resistance genes and the response to leaf rust in wheat genotypes]]> ABSTRACT The adult plant resistance conferred by genes with an additive effect is an alternative to achieve durable resistance to leaf rust caused by the fungus Puccinia triticina in wheat (Triticum spp.) The objective of this study was to know the response to this disease in bread wheat genotypes that possess the partial resistance genes Lr34, Lr46, Lr67 and Lr68. The severity level of the disease was measured in 280 wheat genotypes in three locations. The presence or absence of partial resistance genes was determined by molecular markers for each gene in 245 wheat genotypes. The different combinations of adult plant genes resulted in the genotypes were classified into nine groups. In 77 of these genotypes, the markers were negative for these genes. The Lr34, Lr46, Lr67 and Lr68 genes were identified individually in 48, 48, 5, and 14 genotypes, respectively. The combination of two genes, Lr34+Lr46, Lr34+Lr68 and Lr46+Lr68, was determined in 18, 17, and 12 genotypes, respectively. Only in six genotypes the combination Lr34+Lr46+Lr68 was identified. The genotypes with the Lr34, Lr46, Lr67 and Lr68 genes in a unique form showed 21%, 24.8%, 21.9% and 21.8% of rust severity on average, respectively. An additive effect was observed in the combinations of two genes, and higher effect in the combinations that included the Lr34 gene since genotypes with this gene combination showed on average 11.4% of rust severity. The combination of three genes Lr34+Lr46+Lr68 provide greater protection in the genotypes with 9.7% of rust severity on average. <![CDATA[Changes in herbage mass and time of herbage allocation modify nutritional and metabolic status of dairy cows]]> ABSTRACT In temperate milk production systems, it is important to study the effect of grazing strategies in both the quantity and quality of the diet, resulting in potential impacts on animal metabolism. The aim was to evaluate the effect of timing of herbage allocation and herbage mass on blood indicators. Forty Holstein-Friesian cows were grouped according to milk production (24.7 ± 2.8 kg cow-1), body weight (580.6 ± 51.7 kg) and days in milk (74 ± 17.1 d). The groups were randomly allocated to one of four treatments: 1) L-AM, access to new herbage allocation after morning milking with herbage mass of 2000 kg DM ha-1; 2) L-PM; access to new herbage allocation after afternoon milking with herbage mass of 2000 kg DM ha-1; 3) H-AM; access to new herbage allocation after morning milking with herbage mass of 3000 kg DM ha-1; 4) H-PM; access to new herbage allocation after afternoon milking with herbage mass of 3000 kg DM ha-1. Milk production was only different for H-PM in 1.1 kg higher than L-PM. Urea in milk was affected by treatments, being 22% higher for L-AM than other treatments. ß-Hydroxybutyrate and blood urea concentrations were 47% and 30% higher, respectively, for AM compared to PM treatments. Plasma albumin concentration was lower for H-PM compared to other treatments at week 3 of blood sampling. PM treatments modify the herbage composition and animal metabolism, while combining it with a high herbage mass impacts positively in production and milk composition. <![CDATA[Xylem structure and function in three grapevine varieties]]> ABSTRACT Xylem vessels are responsible for conducting water, in a metastable state, to the transpiring leaves. As tension increases, hydraulic failure may occur. At any given tension, the resistance of the xylem vessels to cavitation depends on their morphology, of which vessels diameter has been pointed out as relevant. Grapevines (Vitis vinifera L.) are often cultivated in Mediterranean climates and mostly under controlled water déficit conditions. Besides, a high variability in the stomatal sensitivity exists in different varieties. 'Cabernet Sauvignon' (CS) is recognized as isohydric, 'Syrah' (S) as anisohydric, and no clear information exist for 'Carménère' (C), an important grapevine variety for the Chilean wine industry. In the present study, xylem morpho-anatomical traits from stems in CS, S, and C, growing in a single vineyard, were analyzed, inferring their specific theoretical hydraulic conductivity. Also, the maximal hydraulic conductivity and vulnerability to cavitation, the latter expressed as the xylem water potential reducing a 50% loss in hydraulic conductivity (PLC50) were assessed in stems collected from the field. Higher vessels diameter was found in S and C, followed by CS, in general ranging from 21 to 120 Lim, resulting in an expected proportional theoretical hydraulic conductivity of nearly 40 to 43 kg s-1 m-1 MPa-1 in C and S, and merely 23 kg s-1 m-1 MPa-1 in C. This values were similar -but not proportionally- to maximal actual hydraulic conductivity measured in stems with median values, in average, of 28, 17, and 13 kg s-1 m-1 MPa-1 in S, C, and CS, respectively. Even though wider xylem vessels have been correlated with higher xylem vulnerability to cavitation, PLC50 was significantly higher in S (-2.3 MPa) compared to C (-1.1 MPa), and even though xylem vessels diameter were similar between S and C, C was as vulnerable as CS. We found no such tradeoff between hydraulic efficiency and vulnerability. <![CDATA[Effects of dietary concéntrate supplementation on enteric methane emissions and performance of late lactation dairy cows]]> ABSTRACT Dietary supplementation with concentrates is regarded as an effective strategy to decrease the intensity of methane (CH4) emissions, although it has rarely been evaluated in late lactation dairy cows. The aim of the present study was to investigate the effects of two levels of dietary concentrate supplementation on CH4 emissions and milk production and composition of dairy cows in late lactation. The study was conducted using 24 multiparous Holstein Friesian cows in late lactation (253 ± 18 d in milk), and had a duration of 3 wk, including 2 wk of adaptation to the diet and 1 wk of measurements. Treatments consisted of two levels of concentrate supplementation (4 vs. 8 kg d-1 cow-1; as-fed) offered daily in two equal rations during milking. In addition, diets included 2 kg DM grazed grass and 8 kg as-fed of grass hay. In week 3 of the study, CH4 emissions were measured for 7 consecutive days using the sulfur hexafluoride tracer technique. Average total DM intakes for the cows fed the 4 and 8 kg concentrate treatments were 12.3 and 15.6 kg DM, respectively. Treatments had no effect on milk yield, milk fat, or milk lactose concentrations. Milk protein concentration tended to increase in cows offered 8 kg of concentrate. Higher concentrate intake tended to increase cow body mass gain, but not condition score change. The 8 kg treatment increased total CH4 emissions (g d-1) by 10.7%, whereas CH4 yield (g kg-1 DM intake) was decreased by 12.7%. Methane intensity (g kg-1 milk yield) was unaffected by treatments. Dietary concentrate supplementation for late lactation cows is ineffective in mitigating CH4 emission intensity, because animals do not respond with an increase in milk production. <![CDATA[Effect of abscisic acid and methyl jasmonate preharvest applications on fruit quality and cracking tolerance of sweet cherry]]> ABSTRACT Rain-induced cherry fruit cracking is one of the most important problems in the cherry industry, and its occurrence causes significant economic losses. Sweet cherry (Prunus avium [L.] L.) is a non-climacteric fruit affected by both abscisic acid (ABA) and methyl jasmonate (MeJA) during development. The objective of this study was to evaluate the effect of these phytohormones on cracking susceptibility and quality parameters of sweet cherry fruit ('Bing'), located in the central region of Chile. During two seasons, independent pre-harvest applications of ABA (0.1 mM) and MeJA (0.4 mM) or both combined, at fruit developmental stages of fruit set or fruit color change, significantly reduced the number of mature cracked fruit after 6 h of immersion in water (p &lt; 0.05). In both seasons the combinations of ABA and MeJA applied at fruit set reducing cracking index in an 87% compared to the control without compromising the weight or the diameter of the fruits. Moreover, in the second season ABA and MeJA applications at fruit set increased fruit firmness (11% and 6% respectively) and fruit color parameters regardless of the fruit stage at application, although slight decreases in soluble solids content were observed in most of the treatments. <![CDATA[Herbivore-induced plant volátiles emitted from avocado shoots infested by <em>Oligonychus yothersi</em> (Acari: Tetranychidae) increases the attraction of micro-coleopterans]]> ABSTRACT The avocado red mite, Oligonychus yothersi (McGregor) (Acari: Tetranychidae), is a polyphagous pest that causes damage to a wide range of plants. In Chile, is commonly found in avocado (Persea americana Mill.) orchards, and the plant damage is expressed as a reduction of photosynthetic activity in leaves, causing defoliation of trees under severe attack conditions. Oligotapygmaea (Solier) (Staphylinidae) and Parastethorus histrio (Chazeau) (Coccinellidae) micro-coleopteran predators are found on 'Hass' avocado orchards, infested by O. yothersi. This study investigated the role of volatile compounds released by avocado in response to O. yothersi infestation in the tritrophic interaction avocado-O. yothersi-O.pygmaea-P. histrio. Plant volatiles were collected from live plants by headspace technique on Porapak Q traps and analyzed by gas chromatography coupled to mass spectrometry (GC-MS). In the chemical analysis, several chemical groups were identified including terpenes, aromatic compounds, and green leaf volatiles. Eight chemical compounds were detected only in the infested plants volatile profile, and differences were observed in the emission of 10 compounds between infested and uninfested plants (P &lt; 0.05). The behavioral responses of the insects to plant volatiles were evaluated in a choice-test using a Y-tube as olfactometer. Uninfested plant volatiles were significantly attractive to O. yothersi, while infested plants volatile extract repelled the mites. Two compounds, i?-limonene and (-pinene, elicit an attractant behavioral response from O. yothersi. Oligota pygmaea and P. histrio females registered a strong attraction to volatiles from infested plants, and the compounds (Z)-(-ocimene and methyl salicylate detected only in infested plant also were attractive to predators.