Scielo RSS <![CDATA[Chilean journal of agricultural research]]> http://www.scielo.cl/rss.php?pid=0718-583920210003&lang=en vol. 81 num. 3 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.cl/img/en/fbpelogp.gif http://www.scielo.cl <![CDATA[Hormetic effect of gamma irradiation under salt stress condition in <em>Phaseolus vulgaris</em>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300256&lng=en&nrm=iso&tlng=en ABSTRACT Common bean (Phaseolus vulgaris L.) is widely grown around the world and sensitive to stress conditions. Accumulation and degradation of amino acids are informative indicators of plant tolerance. In this study, the vegetative growth and amino acid profiles of two common bean cultivars (Öz Ayşe and F16) under salt stress (50, 100, 150, 200 mM NaCl) were investigated to determine the hormetic effect of low-dose gamma rays (10, 20, 30, 40 Gy 60Co). The irradiated mature embryos of seeds were regenerated in vitro using embryo cultures. The effects of gamma rays on vegetative growth and amino acid profile under stress and non-stress conditions differed. In terms of vegetative growth, 10 Gy for ‘Öz Ayşe’ and 20 Gy for ‘F16’ had hormetic effects and stimulated plant growth under non-stress conditions. Under salt stress conditions, the effect of gamma rays varied according to the severity of the stress. 30 Gy for ‘Öz Ayşe’ and ‘F16’ at 100 mM salt stress had hormetic effects on vegetative growth. The combined effects of salt stress and gamma rays on the amino acid profile are supported by the vegetative growth results of the plants. Amino acid accumulation occurred at 100 mM at 30 Gy for ‘Öz Ayşe’ and ‘F16’. The most accumulated amino acids were glutamic acid (127.63 mg kg-1), alanine (173.07 mg kg-1), glutamine (188.96 mg kg-1), proline (124.50 mg kg-1), tyrosine (29.23 mg kg-1) in ‘Öz Ayşe’ and tyrosine (29.88 mg kg-1) in ‘F16’ under stress. This study shows that low-dose gamma application under moderate stress conditions has a hormetic effect, not under severe salt stress. <![CDATA[<em>Trichoderma harzianum</em> mutants enhance antagonism against phytopathogenic fungi, phosphorus assimilation and drought tolerance in Jalapeño pepper plants]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300270&lng=en&nrm=iso&tlng=en ABSTRACT The Trichoderma harzianum fungus is one of the most widely used biological control agents in agriculture. A new T. harzianum THITR01 strain was isolated and their spores were mutagenized with ethyl methane sulfonate obtaining 174 mutants. M7, M14, M21 and M24 are mutant strains that showed 97.4%-100% antagonist effect against Sclerotium rolfsii, Rhizoctonia solani and Sclerotinia sclerotiorum compared to the wild strain. Under potato dextrose agar (PDA) medium with either NaCl, sorbitol or NaHCO3 there were nonsignificant growth rate differences between the mutants and the wild strain. M14 and M21 mutant strains were inoculated on ‘Jalapeño’ pepper plants (Capsicum annuum L. var. annuum) with unavailable P promoted a significant increase in root fresh weight (54% and 40%, respectively) and dry weight (28% in both strains), compared to plant inoculation with the wild strain. The M14 strain presented the highest P solubilization ability (13.4 μg g-1) in the substrate and promoted a change on root architecture. There was a higher relative water content (82.9%) in drought stressed plants inoculated with the M24 mutant than in plants that were inoculated with the wild type strain (76.3%), and also higher levels of proline in chili pepper plants inoculated with the M24 mutant (939.5 μg g-1 dry weight) than in plants inoculated with the wild type strain (419.8 μg g-1 dry weight). Therefore, M14, M21 and M24 mutant strains could potentially be used as biocontrol agents and plant protector from abiotic stress. <![CDATA[Different strategies for estimating genetic parameters for collar rot resistance characteristics in <em>Passiflora</em> spp.]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300281&lng=en&nrm=iso&tlng=en ABSTRACT The use of several strategies for estimating genetic parameters in passion fruit (Passiflora spp.) segregating populations has important implications for understanding the nature of variances, especially the traits of resistance to collar rot. The objective of this study was to estimate genetic parameters and predict gains with the selection of genotypes resistant to collar rot in a population of interspecific passion fruit hybrids. For the analysis of restricted maximum likelihood/ best linear unbiased prediction (REML/BLUP), 40 interspecific hybrids obtained by crossing resistant wild species with Passiflora edulis Sims genotypes were analyzed. The Comstock and Robinson Design II methodology used two male parents (P. nitida Kunth and P. quadrangularis L.) and two female parents of P. edulis. The evaluations took place for 33 d and 10 variables of resistance to collar rot were characterized. The expression of most variables was due to the genetic effect. Dominance effects predominated. High estimates of heritability based on clone average and selective accuracy were observed, which provides favorable gains in reducing the severity of collar rot by selecting the genotypes 115-5, 115-4, 115-7, 115-6, 115-3, 115-1, 128, 115-9, 115-4. <![CDATA[Foliar application of 5-aminolevulinic acid alleviated high temperature and drought stresses on wheat plants at seedling stage]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300291&lng=en&nrm=iso&tlng=en ABSTRACT Wheat (Triticum aestivum L.) seedling establishment is very sensitive to temperature and drought stresses. The present study was conducted to investigate the effects of foliar exogenous 5-aminolevulinic acid (5-ALA) application on wheat seedling under different temperature (25, 30, and 35 ℃) and water regimes (normal and 65% watering). Five different levels of 5-ALA (0, 25, 50, 100 and 150 mg L-1) were applied as foliar application. Leaf area, stem diameter, shoot and root lengths, fresh and dry weights of shoot and root, and physiological parameters were measured. Drought stress (W2) decreased leaf area by 14.9% compared with normal watering (W1). High temperature (35 ℃) increased malondialdehyde (MDA) content by 72.1% compared with control (25 ℃). 35 ℃ with W2 reduced root and shoot dry weights by 71.8% and 51.9% relative to 25 ℃ and W1. At 35 ℃, 25 mg L-1 5-ALA increased root length by 17.1% and 3.4% at W1 and W2, respectively. 150 mg L-1 5-ALA increased root fresh weight by 101.0% compared with 0 mg L-1 5-ALA at W1 and 35 ℃. The highest protein content (8.35 mg g-1 FW) was achieved at the interaction between W2, 35 ℃ and 50 mg L-1 5-ALA. At W2 and 35 ℃, 150 mg L-1 5-ALA increased proline content by 66.5% relative to 0 mg L-1. The results of the present study suggest that foliar application of 5-ALA could be useful to alleviate the temperature and/or drought stresses of wheat seedling. <![CDATA[Shading stress after heading enhances the remobilization of nonstructural carbohydrates in rice under different ecological conditions]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300300&lng=en&nrm=iso&tlng=en ABSTRACT Low light levels during rice (Oryza sativa L.) growing seasons may lead to significant reductions in grain yield and quality. The effect of shading stress on remobilization of nonstructural carbohydrates (NSC) from the stem plus sheath (SPS) to the grain, a process crucial to rice grain formation, was investigated. Field shading experiments were conducted in Hanyuan and Wenjiang, China, using two rice varieties (Huanghuazhan and Guichao II) subjected to shading stress after heading. Stored NSC of 60.00-159.15 g m-2 were remobilized from SPS after heading, contributing 9.63%-23.63% to grain dry weight at maturity. Shading stress resulted in the 23.99%-50.30% and 31.65%-61.33% reduction in NSC content of SPS at 20 d after heading (DAH20) and maturity stages, respectively. This contributed to the 13.80%-89.00% increase in the remobilization of stored NSC from SPS to the grain (RASN) and 15.86%-73.30% increase in remobilization percentage of removed NSC from SPS to the grain (RPRN). The effect of shading stress on remobilization differed between sites and varieties. Owing to a greater sink capacity, shading stress led to a higher RASN and RPRN from heading to DAH20 for ‘Huanghuazhan’ in Hanyuan. To compensate for photosynthate deficiency under shading stress, rice is adapted to remobilize stored NSC during early grain filling stages. Consequently, grain yield loss caused by shading could be reduced by increasing the SPS remobilization ability (especially in low light areas). Increasing NSC accumulation in SPS before heading for later remobilization may be a feasible way to alleviate rice yield loss under adverse light conditions. <![CDATA[Response of green manure species and millet cultivars to different populations of <em>Meloidogyne javanica</em>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300310&lng=en&nrm=iso&tlng=en ABSTRACT The use of non-host cover crops is a key strategy for controlling root-knot nematodes in infested fields. However, pathogenicity of nematodes to cover crops may vary between populations and localities. This study assessed the response of green manure species and millet (Pennisetum glaucum (L.) R.Br.) cultivars to four populations of Meloidogyne javanica (denominated Mj-2, Mj-3, Mj-6 and Mj-7). Seedlings of radish (Raphanus sativus L.), pigeon pea (Cajanus cajan (L.) Huth) ‘IAPAR 43’, buckwheat (Fagopyrum esculentum Moench) ‘IPR 92-Altar’ and millet ‘BRS 1501’, ‘ADR 300’ and ‘ADR 500’ were inoculated with 1000 eggs and second-stage juveniles of M. javanica. Soybean (Glycine max (L.) Merr.) ‘M6210 IPRO’ was used as control. At 60 d after inoculation, plants were evaluated for root fresh weight, gall index (GI), number of nematodes per gram of root and reproduction factor (RF). For GI, Mj-3 and Mj-6 were the most aggressive to soybean (GI = 5.0). In pigeon pea, Mj-7 resulted in the highest GI (3.5). Radish had the lowest GI (0.67) with Mj-2. For buckwheat, Mj-3 was the most aggressive population, with a GI of 4.50. Mj-3 and Mj-7 resulted in the highest GI in ‘ADR 300’, and Mj-6 and Mj-7 in ‘ADR 500’. The reproductive ability of nematode populations differed between hosts. Mj-2 was the most pathogenic to ‘ADR 300’ (RF = 10.88), Mj-3 to buckwheat (RF = 53.46) and radish (RF = 4.81), Mj-6 to ‘ADR 500’ (RF = 19.58) and Mj-7 to pigeon pea (RF = 2.99) and ‘BRS 1501’ (RF = 15.05). Soybean was susceptible to all M. javanica populations (RF = 33.69 to 257.22). Green manure species and millet cultivars varied in their responses to M. javanica populations of different origins. <![CDATA[Induction of salt stress tolerance in chives by priming with H<sub>2</sub>O<sub>2</sub> in hydroponic cultivation]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300317&lng=en&nrm=iso&tlng=en ABSTRACT The use of salt stress attenuators is considered an important tool to minimize the deleterious effects of salts. However, its application to chives (Allium schoenoprasum L.) has not been studied. This study aimed to evaluate the induction of salt stress tolerance in chives plants in relation to growth and enzymatic reactions, when subjected to different salinity levels of the nutrient solution, after acclimation of seeds with hydrogen peroxide (H2O2) for 24 h. The experiment was conducted in a greenhouse, where chives seeds were acclimated by H2O2 at concentrations of 0.0, 0.15, 0.30, 0.45 and 0.60 mmol. After germination, the plants were cultivated in hydroponic system with electrical conductivities of 1.0, 2.0, 3.0, 4.0 and 5.0 dS m-1. Plant height, length and number of leaves, H2O2 content, malondialdehyde and catalase (CAT) activity were evaluated in chives plants. The increase in the salinity of the nutrient solution up to 5 dS m-1 reduced by 5.88%, 17% and 9.63% plant height, leaf length and number of leaves, respectively. It was observed that the acclimation of chives seeds with H2O2 at 0.45 mmol g-1 fresh mass in plants that were cultivated in nutrient solution of 3.73 dS m-1 led to maximum CAT activity, minimizing the deleterious effects of nutrient solution salinity on plant growth. <![CDATA[Molecular profiling of sweet cherry cultivars present in Chile using polymorphic microsatellite markers]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300326&lng=en&nrm=iso&tlng=en ABSTRACT Sweet cherry (Prunus avium (L.) L.) is one of the most important fruit crops of temperate climates. In Chile, the actual planted area is over 42 000 ha that produce over 260 000 t yearly. The accurate identification of sweet cherry cultivars is key for processes involved both in breeding new cultivars and along the production chain. In this study, we performed the molecular characterization of 87 sweet cherry genotypes cultivated in Chile, using nine microsatellite markers originally described for both peaches and sweet cherries. The analysis showed that 69 of these genotypes corresponded to unique cultivars, each harboring a unique allelic pattern. They could be differentiated using only five markers (BPPCT-037, BPPCT-039, BPPCT-040, PMS-30 and UCD-CH18). The remaining 19 genotypes could correspond to misidentified, mutated or even synonyms of the studied genotypes, since they have allelic patterns identical to one or more of the 69 individualized genotypes. Between 3 and 8 alleles per marker were identified, with a mean of 6, while the expected heterozygosity over the nine polymorphic loci averaged 0.72, ranging from 0.59 in UDP96-001 to 0.78 in BPPCT-040. Phylogenetic and population structure analyses showed that most cultivars were grouped according to their country of origin or the breeding program from where they were released, being also coincident with their presumed pedigrees. These results are the basis for a fingerprinting protocol, based on microsatellite markers, for sweet cherry cultivars. <![CDATA[Characterization of <em>Brachiaria decumbens</em> ‘Basilisk’ pasture subjected to flexible grazing by sheep]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300338&lng=en&nrm=iso&tlng=en ABSTRACT The sustainability of animal production on pasture is based on improving the management of forage species used, which ensures increase in animal productivity, pasture perenniality and cost reduction. The objective was to characterize productive, structural, physiological and normalized difference vegetation index (NDVI) responses of Brachiaria decumbens Stapf ‘Basilisk’ over the flexibilization of the grazing management adopted. Four defoliation combinations were evaluated, which consisted of the arrangement of two (85% and 95%) light interceptions (LI) and two (1.3 and 1.8) residual leaf area indexes (RLAI), as parameters of entry and exit of the animals from the pasture, respectively. Higher total forage biomass was observed (TFB, kg DM ha-1) 18.82%, when the canopy was managed at the lowest defoliation frequencies (95% LI), but with a higher morphological composition of the stem component and dead material. The 95% LI produced an extra layer of leaves than the canopy managed at 85% LI. The physiological variables were affected by the higher frequency of defoliation (85% LI), with lower photosynthetic rates. NDVI was higher in the canopy managed in the pre-grazing condition at 95% LI (0.88) and residual condition at 1.8 RLAI (0.49), when compared to 85% LI (0.86) and 1.3 RLAI (0.44). For greater production per animal, managing at 85% LI × 1.8 RLAI with pre-grazing and residual NDVI of 0.85 and 0.49, respectively, is the most suitable while for greater animal production per area, managing at 95% LI × 1.3 RLAI with pre-grazing and residual NDVI of 0.88 and 0.44, respectively, becomes more efficient. <![CDATA[Effect of effective microorganisms on wheat growth under salt stress condition]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300351&lng=en&nrm=iso&tlng=en ABSTRACT Effective microorganisms (EM) are important beneficial fungi and bacteria mixed culture that is used as an inoculant to improve soil quality and health, enhance plant growth, yield, and quality. This study was conducted to evaluate the effect of inoculating various concentration of EM (50, 100 and 200 mL L-1) on growth of wheat (Triticum aestivum L.) seedlings, grown under NaCl regime (6 dS m-1), including fresh and dry weight, chlorophyll content, maximum fluorescence yield (Fm), variable fluorescence yield (Fv), optimum photosystem II (PSII) quantum yield (QY) and ratio of fluorescence decline in steady state (RFD). Seedlings subjected to salt treatment exhibited significantly 60% and 30% reduction in both fresh in dry weight; respectively, however, when seedlings under saline condition were treated with EM at both 50 and 100 mL-1, fresh weight was increased two folds. However, for both dry weight and plant length, EM at 100 mL-1 showed the highest significant values compared to salt treated seedlings (40% and 18%, respectively). Salinity treatment reduced significantly chlorophyll content, Fv/Fm and QY, however, the addition of EM at 200 mL L-1 alleviated the effect of salt stress on photosynthetic parameters. The application of both 100 and 200 mL L-1 alleviated the salt effect resulted in a similar chlorophylls content as the control (36.23 and 34.12 SPAD units) respectively. EM application at 200 mL L-1 significantly lowered electrical conductivity from 14.35 to 10.29 dS m-1 of the media. In conclusion, EM can be used to counter act salt effect in soil and improve growth behavior of wheat plants under salinity conditions. <![CDATA[Experimental and numerical analysis of triaxial compression test for a clay soil]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300357&lng=en&nrm=iso&tlng=en ABSTRACT Soil compaction causes negative effects on crop yield and its mechanical response analysis has recently gained relevance for research through numerical methods. In this work, Finite Element Method (FEM) using the Mohr-Coulomb (MC) and Hardening Soil (HS) constitutive models were employed to simulate the mechanical response of a Vertisol agricultural soil. First, an experimental study of the unconsolidated-undrained (UU) triaxial compression test with different moisture contents (w = 10%, 20% and 34%) and confining pressures (σ3 = σc = 0.05 MPa, 0.10 MPa and 0.15 MPa) was carried out, to obtain the shear strength parameters cohesion (c) and friction angle (φ), as well as the Young’s modulus (E) of the soil. The experimental study was conducted through a 32 factorial design with three replicates that it was used to evaluate the influence of the w and σc on E of the studied soil. Also, an analysis of the behavior of the φ and c parameters at each w was performed. Numerical simulations were done with similar conditions as the experimental tests with respect to loading and boundary conditions. A comparison of the mechanical response between numerical results and physical experiments was carried out. As a result, the MC model allowed to estimate satisfactorily the stress-strain relationship of the soil for w of 10% and 20%, while HS model exhibited a better approximation for w of 34% in comparison with the MC model. Finally, the methodology and the adjusted parameters of the agricultural soil obtained in this work, can be used in the study of soil compaction produced by the agricultural machinery. <![CDATA[Interaction of rice salinity screening in germination and seedling phase through selection index based on principal components]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300368&lng=en&nrm=iso&tlng=en ABSTRACT Salinity stress can reduce rice (Oryza sativa L.) productivity and cause crop failure. This problem needs a solution by development of tolerant varieties, and this development closely relates to the effectiveness of its screening. Screening at the phase of germination and seedling are the most common ones. However, the interactions between screenings based on the growth character selection index have not been widely reported, particularly with the principal component analysis (PCA). Therefore, the aim of this study was to determine the interaction between phases of rice salinity screening through a selection index based on PCA. This study consisted of two phases of salinity screening, namely growth phase of germination and seedlings. Both screenings were designed with a nested randomized complete block design, where replicates were nested in a selection environment. The selection environment consisted of two levels, normal (0 mM NaCl) and saline (120 mM NaCl). The genotypes consisted of eight varieties and was repeated three times. Observations were based on morphological and physiological characters, especially in seedling phase screening. Results showed that morphological character approach of the seedlings had a large distribution of salinity tolerances. The use of stress tolerance index and PCA were considered effective in the formation of the selection index on salinity screening. As for, the morphology index was formulated as 0.32 shoot height + 0.33 root fresh weight + 0.33 shoot fresh weight + 0.26 root length + 0.01 number of tillers, length + 0.34 total biomass fresh weight. Therefore, the use of this analytical concept is recommended in screening the tolerance of rice lines to salinity stress. <![CDATA[Bacterial community associated with canker disease from sweet cherry orchards of central valley of Chile presents high resistance to copper]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300378&lng=en&nrm=iso&tlng=en ABSTRACT The Chilean sweet cherry (Prunus avium (L.) L.) industry became the leading exporter worldwide. The bacterial canker is the most significant disease causing major economic losses. Pseudomonas syringae pv. syringae (Pss) is the only related pathovar recognized in Chile and it is mainly controlled with Cu-based antimicrobial compounds (CBAC). Soil contamination and the decreasing efficacy of CBACs by the emergence of Cu-resistant bacterial strains threaten the long- term sustainability of sweet cherry production. This study aimed at characterizing the bacterial community associated with canker infection injuries by assessing Cu resistance in sweet cherry orchards in the O’Higgins Region of Chile. Eighty bacteria isolates were obtained from tissue that presented bacterial canker symptoms from cherry trees. We assessed the production of fluorescent pigments in Fe-deficient media, presence of the housekeeping genes rpoD and cts, and presence of syringomycin-producing genes syrb and syrD. Their pathogenic ability was evaluated on immature sweet cherry fruits and Cu resistance was determined as the minimum inhibitory concentration (MIC) using CuSO4. Only five isolates were Cu-susceptible (MIC &lt; 0.8 mM), while 75 isolates exhibited different levels of Cu resistance (MIC &gt; 0.8 mM). At least one gene of the copABCD operon/or and its regulatory genes were detected in 17 isolates, suggesting that most isolates likely have different mechanisms of Cu tolerance. Six isolates were identified as Pss, presenting different degrees of Cu resistance, but all presented at least one feature of the copABCD operon. A bacterial community that presents high Cu-resistance, probably under control of diverse genetic mechanisms, decreases the efficacy of CBAC. <![CDATA[Essential oil of <em>Peumus boldus</em> Molina against the nematode <em>Haemonchus contortus</em> (L3) and three stored cereal insect pests]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300390&lng=en&nrm=iso&tlng=en ABSTRACT Alternative methods of control against different parasites affecting livestock and agriculture are currently being sought. The essential oil of Peumus boldus Molina has anthelmintic and insecticidal activity against the nematode Haemonchus contortus and stored cereal insect pests. The present study aimed to assess the in vitro activity of P. boldus essential oil against H. contortus (L3) unsheathed and Sitophilus zeamais, Tribolium castaneum, and Plodia interpunctella. The essential oil was obtained from leaves of P. boldus and its principal compounds identified by phytochemical analysis. Essential oil was tested at concentrations of 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75 and 2.0 mg mL-1 on unsheathed L3 H. contortus larvae and in concentrations of 0, 35, 70, 100, 125, 150, 175 and 200 μL L-1 air on adult insects. The main constituents detected in the essential oil were 1,8-cineole, terpineol, terpinene-4-ol, γ-terpinene, p-cimene, methyl eugenol, safrole, (E)-germacrene D, β-tujene, and ascaridol. The nematode H. contortus and insects were exposed to the essential oil for 72 h. In a bioassay with H. contortus larvae, treatment with 2.0 mg mL-1 showed the highest toxicity with 99.2% mortality. Regarding insecticidal activity, S. zeamais was the most susceptible species with a mortality of 90% at 200 μL L-1 air. The present study suggests that the essential oil of P. boldus has potential anthelmintic and insecticidal activity. <![CDATA[Acute toxicity of lethal and sublethal concentrations of neonicotinoid, insect growth regulator and diamide insecticides on natural enemies of the woolly apple aphid and the obscure mealybug]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300398&lng=en&nrm=iso&tlng=en ABSTRACT Based on the importance of using low-risk compounds to protect beneficial agents, the present study evaluated the acute toxicity of lethal and sublethal concentrations of the insecticides thiacloprid, pyriproxyfen, and chlorantraniliprole on adults of Aphelinus mali (Haldeman), the main parasitoid of the woolly apple aphid, Eriosoma lanigerum (Hausmann). Similarly, acetamiprid, buprofezin, pyriproxyfen, chlorantraniliprole and cyantraniliprole were evaluated on adults of the parasitoid Acerophagus flavidulus (Brethés) and also on larvae and adults of the predator Cryptolaemus montrouzieri Mulsant, both species important natural enemies of the obscure mealybug, Pseudococcus viburni (Signoret). Natural enemies were exposed to insecticide residues of minimum recommended rate (1x) and between one to four concentrations (0.5x, 0.25x, 0.1x and 0.05x) of the minimum recommended rate on apple leaves. Our results indicate that thiacloprid was moderately harmful to A. mali at 1x, and acetamiprid was harmful to A. flavidulus causing 100% mortality from 0.1x to 1x concentrations. Buprofezin, pyriproxyfen and chlorantraniliprole were harmless or slightly harmful for both parasitoids. Cyantraniliprole was slightly harmful from 0.25x to 1x for A. flavidulus. For C. montrouzieri, acetamiprid was harmless or slightly harmful for larvae and adults on the concentrations evaluated. Buprofezin, pyriproxyfen and chlorantraniliprole were harmless for larvae and adults of C. montrouzieri. Cyantraniliprole was slightly harmful on larvae and moderately harmful on adults of C. montrouzieri at 1x. Our data suggest that buprofezin, pyriproxyfen and chlorantraniliprole could be compatible with the natural enemies evaluated, while thiacloprid and acetamiprid were less compatible with parasitoids than with the predator. Finally, cyantraniliprole seems to be less compatible than chlorantraniliprole at 1x with the natural enemies evaluated. <![CDATA[Evaluation of nitrogen status in a wheat crop using unmanned aerial vehicle images]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300408&lng=en&nrm=iso&tlng=en ABSTRACT The excessive use of N in agriculture has created various environmental and economic problems. Remote sensing and unmanned aerial vehicles (UAV) are feasible solutions to infer the status of a crop and enable a better management during the growing season. The objective of this study was to correlate experimental N content and wheat (Triticum aestivum L.) crop aboveground biomass data with vegetation indices estimated using UAV images. In this study, the N nutrition index and N dilution curve were used as indicators of the state of plant N; input variables to estimate these indicators were the N content and aboveground biomass. Four flight campaigns were conducted at different phenological stages of a wheat crop and seven N doses were evaluated. A linear relationship of blue normalized difference vegetation index (BNDVI) and green normalized difference vegetation index (GNDVI) with aboveground biomass and N content was identified. BNDVI and biomass demonstrated high R2 during boots swollen and end of anthesis growth stages (0.62 and 0.68, respectively), while GNDVI showed the highest R2 during the ear half emerged and beginning of anthesis growth stages (0.84 and 0.79, respectively). For N content estimation, GNDVI showed a higher correlation than BNDVI, and the adjustment curve showed an R2 up to 0.81 only for the last flight (end of anthesis), BNDVI showed an R2 of 0.78. Remote sensing and vegetation indices estimated from UAV images can be reliably used to estimate N content and wheat biomass, contributing to knowing the crop N status. <![CDATA[Site-specific management zones based on geostatistical and fuzzy clustering approach in a coastal reclaimed area of abandoned salt pan]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300420&lng=en&nrm=iso&tlng=en ABSTRACT Agricultural measures for cotton (Gossypium spp.) cultivation generally adopt a traditional and uniform management method in the reclamation area of the abandoned salt pan on the southern coast of Laizhou Bay, without considering spatial variability of the soil’s physical environment. This method might lead to overfertilization in some high-nutrient plots and poor fertilization in other low-nutrient plots, which will cause high heterogeneity of crop yields and low profits. The objectives of this study were to delineate and to assess the suitability of the resulting site-specific management zones by describing spatial variability in soil attributes and crop yields. A 4.8 ha field of reclamation area in the coast was selected as the research object. A total of 12 soil attributes representing the physio-chemical attributes of soil (0-20 cm) and aboveground biomass (AGB) of cotton on 48 sampling locations were chosen from the study area. Principal component analysis and the fuzzy k-means clustering method were used to determine optimal clustering number of the study area and identify management zones. Results showed that the number of reasonable management zones were two, and confidence levels of soil organic matter (SOM) and AGB were significantly different at a probability level p &lt; 0.01, while total N, available N, available K, cation exchange capacity, and soil salinity showed significant differences at p &lt; 0.05. Management zones determined based on the selected soil attributes and crop AGB provide farmers with the opportunity to perform specific site management in cotton fields to achieve precision agriculture and provide a reference for formulation of a reclamation strategy for the salt pan. <![CDATA[Changes in elastic modulus, leaf tensity and leaf density during dehydration of detached leaves in two plant species of <em>Moraceae</em>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300434&lng=en&nrm=iso&tlng=en ABSTRACT The quick adjustments of leaf traits are critical for keeping the survival of plants under dehydration. In this study, we examined the hypotheses that plants would adapt to dehydration by shrinking its mesophyll cells to offset the water loss, or triggering water regulation mechanism caused by enzymes. Leaf structure, elastic modulus (Em), leaf tensity (LT) and leaf density (LD) were determined with detached leaves of Broussonetia papyrifera (L.) Vent. and Morus alba L. at each water loss moment (0, 1, 2, 3, 4 and 5 h). The coupling model between gripping force and LT was established using the Gibbs free energy equation, and the initial LT was determined. The intracellular water availability of M. alba decreased at 4 h, which was earlier than that of B. papyrifera. The intracellular water availability of M. alba was more sensitive than B. papyrifera. Broussonetia papyrifera adapted to dehydration by shrinking its mesophyll cells to offset the water loss, or triggering water regulation mechanism caused by enzymes, i.e., carbonic anhydrase. The sponge parenchyma of B. papyrifera at 3 h decreased by 25.73% of that at control. Morus alba maintained intracellular water availability just by changing the leaf structure. The offset effects through shrinking cells differed between B. papyrifera and M. alba, because the elastic-plastic behavior of their leaves and cells were different. The Em of M. alba was over five-fold higher than that of B. papyrifera. The investigations of water status were more accurate in terms of leaf physical traits instead of water content. <![CDATA[Rice straw biochar and different urea rates on rice yield and CH<sub>4</sub> and CO<sub>2</sub> gases emissions]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300448&lng=en&nrm=iso&tlng=en ABSTRACT The application of biochar using inorganic fertilizer has been reported as being more efficient for the effective growth of soil microbes. However, there is no evidence that rice straw biochar (9 t ha-1) and different urea rates have had any effect on greenhouse gas (GHG) emissions of rice (Oryza sativa L.) production in tropical soils. Therefore, this study was conducted to investigate the effects of urea and the application of rice straw biochar (9 t ha-1) on yield and GHG emissions. Treatments were 150 kg N ha-1 (T1 control) and rice straw biochar (9 t ha-1) combined with 30, 60, 90, 120, and 150 kg N ha-1 (T2, T3, T4, T5, and T6, respectively). The experiment had a randomized complete block design with four replicates. Grain yield increased 20.7% in plants grown in T3, T4, and T5 compared with the control. Although all biochar treatments had increased cumulative CO2-C emissions compared with the control (5.0% to 7.6%), the cumulative CH4 emissions significantly decreased compared with the control (20% to 27%). Therefore, it could be suggested that T3 and T4 (9 t ha-1 rice straw biochar with 60 and 90 kg N ha-1) increase yield and reduce CH4 emissions relative to the control. Although this study was limited to a pot experiment with no nutrient leaching, the synergetic effect of rice straw biochar (9 t ha-1) and reduced urea rate is worth mentioning for acidic paddy soil; a field experiment is suggested to determine the long-term effect of biochar. <![CDATA[Nitrogen, phosphorus, and potassium use efficiency for perennial ryegrass and white clover cultivar mixtures]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300456&lng=en&nrm=iso&tlng=en ABSTRACT The nutrient use efficiency of perennial ryegrass (Lolium perenne L.) (PR) and white clover (Trifolium repens L.) (WC) cultivars can affect the grass-legume compatibility of different cultivar combinations, thus impacting the sustainability of animal production systems, especially on marginal soils. The objective of this work was to evaluate N, P, and K absorption efficiency (NAE, PAE, and KAE) and use efficiency (NUE, PUE, and KUE). This study included two experiments with the same full factorial treatment structure (4 PR cultivars × 3 WC cultivars) in a randomized complete block design under field conditions and a completely randomized pot design. The field cutting experiment was carried out on sites with two contrasting soil depths and the pot experiment was conducted under shade conditions. Results showed nonsignificant (P &gt; 0.05) factor interactions for DM yield and both nutrient absorption and use efficiency. The NAE and PAE of PR ‘Extreme’ and ‘Bealey’ were higher under field conditions than pot conditions. In the field experiment, NAE of WC ‘Will’ (2.33 kg DM ha-1/mg N kg-1) tended to be similar (P &lt; 0.05) to other cultivars in deep soil, but was significantly higher (P &lt; 0.001) than ‘Ladino’ and ‘Bounty’ in shallow soil (0.70 kg DM ha-1/mg kg-1). The evaluation of NUE and PUE under field conditions and KUE under pot conditions showed that PR ‘Bealey’ and WC ‘Ladino’ reached higher values. In conclusion, results showed a cultivar effect on nutrient use efficiency in PR/WC mixtures, which had an impact on PR- WC compatibility, mainly due to the higher absorption efficiency of PR ‘Bealey’ and WC ‘Will’, both of which exhibited the highest degree of compatibility for total DM yield. <![CDATA[Prediction of <em>Brachiaria decumbens</em> forage biomass using structural characteristics]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392021000300467&lng=en&nrm=iso&tlng=en ABSTRACT Tools that generate models with good biomass predictive capacity are essential to maintain the sustainability of production systems. The objective was to analyze the relationship between forage biomass and structural variables and generate models to predict total forage biomass (TFB) and green leaf blade biomass (GLB). Irrigated pastures of Brachiaria decumbens Stapf ‘Basilisk’ were kept under rotational stocking with sheep (Ovis aries L.) The TFB, GLB, leaf area index (LAI), height (cm), and normalized difference vegetation index (NDVI) were evaluated. The experimental design was completely randomized with four replicates: ten and five cycles of defoliation management, respectively, were used to generate and validate the stages of the models. The best goodness of fit was obtained by nonlinear models for both TFB and GLB, which can be confirmed by high Spearman’s correlations and significance (P &lt; 0.0001). The path analysis showed low collinearity (42.60) between NDVI, LAI, and height; the high determination coefficient (R²) with values of 0.8421 and 0.7767 demonstrated their associations with TFB and GLB, respectively. Among the studied models to predict TFB and GLB, only exponentials using NDVI and power using LAI and height showed the best fit. In the validation stage, the models related to height exhibited the highest performance with 0.9531 (TFB) and 0.9638 (GLB) d-index, -2.3 (TFB) and -7.20 (GLB) bias, and 0.8532 (TFB) and 0.8932 (GLB) R². Only nonlinear models using height (cm) to predict TFB and GLB had the best practical application potential, thus ensuring efficiency in data collection.