Resumo em Inglês:

ABSTRACT The objective of this study was to create a single mathematical equation able to estimate the leaf area of different cassava cultivars from one lineal dimension without destroying any plant tissue. Two hundred leaves per cultivar from ten cultivars were used to calibrate the model and more than one hundred leaves per cultivar were used to test its predictive capacity as independent data. All equations were the result of the nonlinear correlation between the leaf area and the length of its central lobe. To validate it as a “general” equation, another set of five cultivars were used. A “specific” equation for each cultivar was also calibrated to compare with the “general” equation’s performance. Cultivar Vassourinha has remarkably different leaf morphology from the other nine cultivars, making the “general” equation’s tendency line deviate and lowering its coefficient of determination. Therefore, one more equation was generated excluding that cultivar and, as a result, it was not possible to estimate the leaf area from all the cultivars using only the “general” equation. The “general without Vassourinha” equation has a high accuracy level when estimating leaf area of the other nine cultivars, plus the extra five cultivars that were included to validate the general equation; all of them present similar leaf morphology. Due to its importance, Vassourinha cultivar’s “specific” equation should be used when estimating leaf area for this cultivar or other cultivars with similar leaf morphology.

Resumo em Inglês:

ABSTRACT An accurate, efficient and informative statistical method for analyses of genotype × environment (G × E) interactions is a key requirement for progress in any breeding program. Thus, the objective of this study was to quantify individual variation in reaction norms using random regression models fitted through Legendre polynomials in eucalyptus (Eucalyptus spp.) breeding. To this end, a data set with 215 eucalyptus clones of different species and hybrids evaluated in four environments for diameter at breast height (DBH) and Pilodyn penetration (PP) was used. Variance components were estimated by restricted maximum likelihood, and genetic values were predicted by best linear unbiased prediction. The best-fitted model for DBH and PP was indicated by the Akaike information criterion, and the significance of the genotype effects was tested using the likelihood ratio test. Genetic variability between eucalyptus clones and very high accuracies (rg^g ≥ 0.90) were detected for both traits. Reaction norms and eigenfunctions generated genetic insights into G × E interactions. This is the first study that quantified individual variation in reaction norms using random regression models fitted through Legendre polynomials in eucalyptus breeding and demonstrated the great potential of this technique.

Resumo em Inglês:

ABSTRACT Spinach seeds are sensitive to high temperatures during germination and plant growth. It is known that seed priming with water or with seaweed extract (SWE) may enhance germination and seedling growth. The objective of this study was to evaluate the effects of seed priming with SWE (Ascophyllum nodosum) on the germination, seedling growth and antioxidant capacity of spinach seedlings under conditions of heat stress. Five concentrations of SWE (0.0, 0.15, 0.30, 0.60 and 1.2%) were used for priming the seeds under two temperatures (15 and 30 °C). Seeds primed with 0.3% SWE had the greatest activity of antioxidant metabolism and showed improved germination percentage, germination speed and seedling vigor under conditions of heat stress (30 °C) compared to nonprimed controls. Hydropriming and priming with 0.3% SWE resulted in lower contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA) under heat stress than control (nonprimed spinach seeds). This study showed that seed priming with SWE was effective to mitigate stress due to high temperatures and to improve spinach seed germination and seedling vigor.

Resumo em Inglês:

ABSTRACT This study, consisting of two independent experiments, was conducted to optimize presowing guava seed treatments and evaluate the optimized treatments in improving germination and seedling growth of guava under heat and osmotic stresses. In the first experiment, seeds of guava cultivar White Flesh Local I were soaked in water, gibberellic acid (GA3) (0.05 and 0.1%), hydrochloric acid (HCl) (5 and 10%) and sulfuric acid (H2SO4) (5 and 10%) for 24 and 48 h (for water and GA3), and 2 and 5 min (for HCl and H2SO4). Seed soaking (priming) with GA3 (0.1%, at 48 h) and HCl (10%, 2 min) were the most effective treatments to improve seed germination and early seed growth of guava and were used in the second experiment. In the second experiment, treated and untreated seeds were sown in plastic boxes between two layers of filter papers maintained at osmotic potentials of 0, -1.5 and -3 MPa. The germination boxes were incubated at optimal (25 °C) and higher (32 °C) temperatures. Germination was significantly suppressed at a higher temperature and with an increase in the osmotic potential. However, seed treatments with GA3 and HCl were effective to improve the germination and seedling growth of guava under both temperature and osmotic stresses. In conclusion, chemical and hormonal seed treatments may help improve the seed germination and seedling growth of guava under heat and osmotic stresses by modulation of antioxidant enzymes and leaf proline. Seed treatment with GA3 (0.1%, 48 h) was the most effective in this regard.

Resumo em Inglês:

ABSTRACT It was evaluated how straw management modifies the development, growth, nutrient cycling and crop water productivity of sugarcane in the semiarid region of Brazil. The experiment was carried out using two plots with 5 ha each, being one without straw on the soil surface and one with 26 Mg·ha-1 covering the soil. Sugarcane growth and development and straw decomposition coefficient were evaluated, whereas the industrial yield, juice quality, dry matter partitioning, and crop water productivity were determined at harvesting. The straw decomposition coefficient was 0.0049 Mg·ha-1·day-1, and the remaining dry mass was equal to 24%. The straw affected the sugarcane growth and development until the first 100 days. The individual internode volume can be adopted as an indicator of the effect of straw on sugarcane growth because the internode volumes up to the sixth position in the with-straw treatment crop were lower than in the no-straw treatment, which was not observed in other variables of the stalks. Keeping straw on the soil surface reduced the crop lodging. Yield and juice quality were not affected, but crop water productivity was increased by keeping sugarcane straw in the field.

Resumo em Inglês:

ABSTRACT The genotype + genotype × environment (GGE) biplot methodology has the potential to determine combining ability effects, identify efficient testers, and distinct heterotic groups in a line × tester study. However, it has not been adequately applied for such analysis. Therefore, this study was done to assess the combining ability of some maize inbred lines and testers for grain yield, identify most efficient testers and classify inbred lines into heterotic groups using GGE biplot. Fifteen experimental single cross hybrids, generated from a 5 x 3 line by line × tester crosses procedure, were evaluated across seven sites in Iran in 2018 using a randomized complete block design with three replicates per entry at each site. According to the pooled analysis of variance, crosses showed significant differences for grain yield. Also, the differences observed among the testers, inbred lines, and interactions for the line × tester, crosses × environments, line x tester x environment was significant. The inbred line L4 was recognized as outstanding for its general combining ability (GCA) effect and the tester K18 was highly efficient based on its discriminating power. It can be concluded that the crosses of L4 x K47/3 and L4 x B73 are suggested to release high grain yield hybrids. Results of the GGE biplot analyses were close to the conventional line × tester method in combining ability and heterotic patterns of the yield of lines, grouping, and identification of testers.

Resumo em Inglês:

ABSTRACT Plants of local cacao variety from Southern Bahia were evaluated in order to verify if there are different levels of resistance to witches’ broom disease in the study population and if the evaluation of adult plants in the field is a good predictor of these resistance levels. The seedlings were maintained under greenhouse conditions and inoculated with the fungus Moniliophthora perniciosa. Evaluations of symptoms occurred 60 days after inoculation. In the field, the same genotypes were evaluated by counting the number of dry brooms per plant, per year, and assessing trunk diameter size. The data were subjected to analysis of variance and averages grouped by the Scott–Knott test, differentiated by Tukey’s test and compared by Student’s T test. The Scavina-6 and CCN51 clones as well as the Catongo variety were used as resistance, moderate resistance and susceptibility patterns, respectively. Twenty-eight percent of the genotypes were among the most resistant and the genotypes 4119 and 4033 were considered the most susceptible to the disease in both field and greenhouse evaluations. Field evaluation was promising as a predictor of resistance level. The selected materials presented good characteristics for witches’ broom resistance, with different levels deserving special attention in the context of reducing the vulnerability of Brazilian cacao cultivation to the effects of the disease, especially in the cacao region of Bahia.

Resumo em Inglês:

ABSTRACT The evaluation of genetic diversity among the accessions of a germplasm collection results in information about promising materials suitable for breeding programs. Thus, the goal of this work was to characterize Capsicum baccatum accessions from different Brazilian regions, based on morphological, biochemical and molecular traits, aiming to support chili pepper breeding programs. The fruits were morphologically characterized based on fruit length, diameter, fresh mass and pericarp thickness, and biochemically analyzed for their content in ascorbic and phenolic acids, flavonoid and antioxidant activity by 2,2-diphenyl-1-picrylhydrazyl radical (DPPH•) and ferric reducing antioxidant power (FRAP) assays. All phenotypic traits showed significant differences among the chili pepper accessions, indicating a wide variability. The fruits were also characterized using amplified fragment length polymorphism (AFLP) molecular markers. The combination of six AFLP primers resulted in 1117 bands, 1033 of which were polymorphic. Divergence between accessions was estimated by the Ward’s hierarchical agglomerative clustering method, resulting in three and two clusters for fruit phenotypic traits and molecular data, respectively. In Bayesian analysis, molecular data also clustered the accessions in two groups. There was no association between the phenotypic descriptors and AFLP markers, indicating that both characterizations are important to better understand the genetic variability. Furthermore, it was not possible to group the accessions solely based on their origin for neither phenotypic descriptors and AFLP markers. The accessions G1, G5, G6, and G20 showed interesting characteristics and can be used in breeding programs, aiming the development of Capsicum spp. cultivars with desirable morphological and biochemical traits.

Resumo em Inglês:

ABSTRACT Biological control using entomopathogenic nematodes (EPNs) is known as an ecofriendly strategy in integrated pest management. The terrestrial slug Parmacella ibera is a major pest of vegetables and citrus trees in north of Iran. The heavy costs and environmental concerns of synthetic molluscicides led the study to use EPNs, against the slug P. ibera. The present study was arranged to evaluate and compare the performance of EPNs, Steinernema feltiae, S. carpocapsae and Heterorhabditis bacteriophora on P. ibera population (mortality rate) and the feeding rate in vitro, and also its damage (seedlings establishment rate) in vitro. Phasmarhabditis hermaphrodita, as a slug parasite nematode, and also the metaldehyde, as a molluscicide, were used as positive controls. The results of the study showed that the highest mortality rate (%) and the seedlings establishment rate (%) of the slug population were observed in S. carpocapsae, S. feltiae and H. bacteriophora treatments, respectively. The feeding rate (%) of the slug declined in the treatments with H. bacteriophora, S. feltiae and S. carpocapsae, respectively. The mortality rate of the pest was enhanced by extending the exposure time and increasing levels of the nematodes. Therefore, it can be concluded that the EPNs S. carpocapsae, S. feltiae and H. bacteriophora are able to control the slug P. ibera population.

Resumo em Inglês:

ABSTRACT Biotic and abiotic stresses, either individually or in combination, may affect soybean growth and development negatively, besides competitiveness with weeds. This study aimed at evaluating the effect of heat stress and plant recovery on crop–weed interaction by analyzing growth variables. Experiments were set up as replacement series of soybean with slender amaranth. Treatments followed a factorial scheme, which was composed of heat stress [high temperature (38/22 ± 2 °C) against the control (28/22 ± 2 ºC)] and of proportions of soybean and slender amaranth, i.e., 100:0 (pure stand of soybean), 50:50 and 0:100 (pure stand of slender amaranth). After being submitted to high temperatures, plants were analyzed in terms of their recovery from heat stress. Variables under evaluation were height, leaf area and shoot dry weight. Results led to the conclusion that the weed shows more competitiveness than soybean, regardless of the heat stress. Interspecific competition for soybean and intraspecific competition for slender amaranth influence their height, leaf area and shoot dry weight negatively, while high temperature affects slender amaranth positively.

Resumo em Inglês:

ABSTRACT In March 2016, wilt and shoot blight were observed on five-year-old apple trees (Malus domestica) cultivar Maxi Gala in a commercial orchard in São Joaquim city, state of Santa Catarina, Brazil. Isolation on culture media, biolog, biochemical, LOPAT tests, and whole genome sequencing were performed. Koch’s postulates were fulfilled on apple stems, leaves and fruits. The taxonomic position of a representative strain was determined by in silicoDNA-DNA hybridization using the Genome-to-Genome Distance Calculator which showed 93.9% similarity with Pseudomonas syringae. Results of biolog and biochemical tests did not match those expected for pv. papulans, morsprunorum or syringae. To our knowledge this is the first report of P. syringae causing bacterial canker in commercial apple orchards in Brazil.

Resumo em Inglês:

ABSTRACT The conservation tillage systems is based on the surface protection by crop residue and reduced soil disturbance. These two principles can favor the soil quality and promote sustainable agricultural systems. The study was developed with the objective of measure soil microbial biomass, soil basal respiration, enzymatic activity and soybean yield in conservation systems cultivated with cover crops species in the Northeastern Cerrado. The experiment was carried out in 2016/2017 and 2017/2018 cropping seasons, performed in a randomized blocks design. The treatments were soil tillage systems allocated in the main plots: no-tillage (NT) and minimum tillage (MT) and the cover crops were allocated in the subplots: Pennisetum glaucum (millet), Urochloa ruziziensis (brachiaria), Crotalaria spectabilis (C. spectabilis), Crotalaria ochroleuca (C. ochroleuca), Pennisetum glaucum + Crotalaria spectabilis (millet + C. spectabilis) and spontaneous plants with three replicates. The evaluated variables were dry mass (DM) production and nutrient accumulation in cover crops; soil biological properties, namely microbial biomass carbon and nitrogen (MBC and MBN, respectively), respiration, metabolic quotient (qCO2), dehydrogenase enzymatic activity (DH), fluorescein diacetate (FDA); and soybean yield. The higher production of dry mass and nutrient cycling occurs with the intercropping millet + C. spectabilis and single millet. The highest soybean yield occurs in succession to C. ochroleuca and intercropping of the millet + C. spectabilis. Cover crops in conservation systems improve soil microbial quality and increase soybean yield.

Resumo em Inglês:

ABSTRACT High rates of agricultural gypsum, above the recommended levels, have been used on a regular basis to deepen plant roots and to alleviate recurrent water stress in Cerrado areas. However, very little is known about the consequences of this practice to arbuscular mycorrhizal fungi (AMF). Therefore, the objective of this study was to evaluate whether or not applying high rates of agricultural gypsum affects the mycorrhizal fungi community, glomalin content and coffee yield. The study rates were: 0; 3.5; 7.0; 14 and 56 t·ha-1 of agricultural gypsum applied in the planting row of the coffee plantation on top of the previous recommended gypsum application. Samples were collected for analysis at the depths of 0-20, 20-40 and 40-60 cm at the end of dry and rainy seasons of the year. In the coffee plantation, 16 AMF species were identified. Gigaspora sp. and Glomus macrocarpum were dominant in all situations. The rate of 7 t·ha-1 favored greater diversity of AMF species and the rate of 56 t·ha-1 reduced AMF diversity and mycorrhizal colonization in deeper layers. In the rainy season, there was a linear decrease of easily extractable glomalin-related soil protein (EE-GRSP) levels as the agricultural gypsum rate was increased. Coffee yield was reduced with the highest gypsum rate (56 t·ha-1), even though the coffee plantation had higher phosphorus contents in beans and leaves. This may have resulted from a number of reasons, including a negative effect on the AMF community.

Resumo em Inglês:

ABSTRACT Oxisols are important soils that have been converted from native vegetation to croplands, and can affect soil biological properties such as microbial biomass and enzyme activity. Thus, the aim of this study was to evaluate the changes on soil microbial biomass and enzyme activity when native vegetation (NV) was converted to cropland (CL), such as maize or sugarcane in six oxisols from São Paulo state, Brazil. Soil microbial biomass C (MBC) and N (MBN), and the activity of arylsulphatase, dehydrogenase and fluorescein diacetate hydrolysis (FDA) were assessed in samples collected at 0-0.20 m. In general, MBC was higher under NV than CL (about + 40%), while MBN and FDA did not show a consistent pattern between NV and CL. All soils showed higher values of arylsulfatase (increased from 101 to 717%) and dehydrogenase (increased 15 to 220%) under NV than CL. In conclusion, soil microbial biomass C is usually higher under native vegetation than cropland. Arylsulphatase and dehydrogenase were the attributes that presented better differentiation between native and cropped soils.

Resumo em Inglês:

ABSTRACT Legume green manure is a popular practice for sustainable agriculture in tropical environments. The use of grain, forage and purely green manure legumes in a subhumid tropical area in Northeast Brazil was investigated to determine the total C and N contents and estimate C-microbial biomass, soil basal respiration, microbial and metabolic quotients, before and after green manures and after the following corn. It was hypothesized that, although all legumes would increase microbial biomass and activity, there would be different effects in function of the main economic usage of the legume. The experimental design evaluated the soil before and after harvest of seven legumes: (i) purely green manures – sunn hemp (Crotalaria juncea L.) and velvet bean (Stizolobium aterrimum Piper & Tracy); (ii) forage – Campo Grande stylo (a physical mixture of 80% of Stylosanthes captata Vog. and 20% of Stylosanthes macrocephala) and calopo (Calopogonium mucunoides Dev.) and (iii) grain – common bean (Phaseolus vulgaris L.), cowpea (Vigna unguiculata L.) and peanut (Arachis hypogaea L.), followed by corn crop. After corn harvest, soils had the same total C and N contents before legume seeding, but C-microbial biomass was significantly higher in soils with grain and purely green manures, which produced higher shoot and root dry mass. Soil basal respiration decreased after corn harvest for all legumes comparing to control treatments, but metabolic stress increased in soils with forage species. Despite this, microbial quotient indicated an efficiency of the microorganisms in degrading the residual organic matter of all green manures used in corn.