ABSTRACT The objective of this study was to evaluate the effect of different irrigation depths applied by drip system and nitrogen fertilization levels that promote higher yield and water use efficiency in onion (Allium cepa L.). The treatments consisted of five irrigation depths (50; 75; 100; 125; 150% of crop evapotranspiration), applied by drip system, combined with five nitrogen fertilization rates (0, 40, 80, 120 and 160 kg ha−1), in a 5 x 5 factorial scheme, in a randomized block experimental design, with four replicates. Irrigation depths estimated at 120.2% and 77.81% of crop evapotranspiration promoted higher yield and water use efficiency for total yield of onion bulbs, respectively. Nitrogen dose of 160 kg ha−1 promoted maximum total yield and water use efficiency.

ABSTRACT Triploid watermelon is highly appreciated by the most demanding markets, and due to its small size, it is ideal for consumption by small families. With the growth in areas cultivated with seedless watermelon worldwide, there is a demand for the development of tetraploid germplasm to obtain triploid hybrids with better agronomic performance. This study performed two tests to induce polyploidy in the powdery mildew–resistant line developed by Embrapa Semi-Arid, LDRO, under different colchicine concentrations and application methods. In Experiment 1, the seeds were treated with colchicine (0.0%, 0.1%, and 0.2%) for 24 h and 48 h. In Experiment 2, 0.2% colchicine was applied by different methods: (a) directly on the seed (MDS) with and without scarification, (b) on seeds with radicle emission (MER), (c) at the insertion point between the hypocotyl and the root (MIHR), (d) at the seedling apex (MAP), and (e) in the inverted hypocotyl (MHI). Chromosome count (cytogenetic analysis), number of chloroplasts per pair of guard cells, number of stomata, seedling height, and hypocotyl diameter were measured. In the LDRO line, chromosomal duplication occurred in some plant cells, but it was not possible to obtain 100% tetraploid plants. Colchicine (0.2%) for 48 h without mechanical scarification induced chromosomal duplication in watermelon. The analysis of the number of chloroplasts identified the level of ploidy early, reducing the number of plants needed to be evaluated by cytogenetics, which allowed us to more accurately identify the different levels of ploidy of the plant.

ABSTRACT Mango (Mangifera indica L.) is a tropical fruit of great importance in the world. However, fruit postharvest losses are caused by anthracnose, a disease caused mainly by phytopathogenic fungi from the Colletotrichum genus. Thus, this work aimed to study morphology, genetic similarity, and pathogenicity of Colletotrichum spp. isolates from mango in Rio Grande do Norte state, Brazil. Morphological evaluation of 28 isolates, based on colony color, size of conidia and appressoria, and growth rate, showed that the isolates belong to the C. gloeosporioides species. It was later confirmed with species-specific oligonucleotides. Also, combined evaluation with RAPD (Random Amplified Polymorphic DNA) and ISSR (Inter Simple Sequence Repeats) showed a genetic similarity of 0.23 between Isolates 12 and 21, and 0.71 between Isolates 2 and 4, an indication of high variability among isolates, with dissimilarity over 75%. Moreover, the dendrogram generated by the UPGMA method indicated that the isolates were arranged in eight groups, which did not correlate with the collection site. Based on pathogenicity, although most isolates showed low virulence for Tommy Atkins cultivar, some of them proved to be highly aggressive (Isolates 9, 15, 20, 21, 24, 26, and 27). Also, pathogenicity did not correlate with clusters. In conclusion, the results revealed high genetic and pathogenic variability in C. gloeosporioides isolated from mango cultivars in one of the main exporting regions in Brazil.

ABSTRACT Cowpea [Vigna unguiculata (L.) Walp.] is an important socioeconomic crop in Brazil, mainly in the Northeast and more recently in the Midwest of Brazil. Charcoal rot caused by Macrophomina phaseolina (Tassi) Goid, is an important disease in semiarid regions, where edaphoclimatic conditions are favorable to the development of disease. The aim of this study was to evaluate the response of 100 cowpea lines to two isolates of M. phaseolina. The experiments were conducted in a completely randomized design, with five replications (two plants per pot). The main variables evaluated were lesion length and relative growth compared to control (RGCC). Among the evaluated accessions, 15% of the lines were resistant to isolate 59 and 11% of the lines were resistant to isolate CMM 2106 of M. phaseolina. Therefore, these accessions can be used as a source of resistance to M. phaseolina by farmers directly as new cultivars or in future hybridizations of cowpea genetic breeding programs.

ABSTRACT Soybeans are among the world’s main crops because they are excellent sources of proteins, micronutrients, and oil. Considering that abiotic stress affects agribusiness, resulting in losses, the grain yield of the crop must be maintained even at high temperatures. In this context, the objective of this study was to select markers related to soybean yield assessed under high temperatures, using associative mapping. The mapping population included 80 soybean PIs and 15 controls. For phenotyping, genotypes were evaluated at high temperatures in an experiment conducted in Teresina (in the state of Piauí) and four characters of interest for agronomy were evaluated: height of the plant when mature, agronomic value, 100-seed weight, and grain yield. Genotyping was carried out using the Affymetrix Platform (180 K Axiom® Soybean Genotyping Array), and the imbalance in the connection between pairs of markers was calculated through the coefficient of determination using the fast permutation test. The analysis of the association between markers and the phenotype of interest was carried out using a generalized linear model approach, including phenotyping data, SNP markers, and information on population structure. The results revealed that 34.06% of loci showed a significant linkage disequilibrium (p < 0.001), and 16 significant associations were found for the four characters related to heat tolerance. These associations can aid breeders that aim to incorporate high temperature tolerance in programs of soybean genetic improvement via selection assisted by markers.

ABSTRACT Fusarium wilt, caused by the fungus Fusarium oxysporum f. sp. passiflorae (Fop) is the main fungal disease in passion fruit crops. Chlamydospores, which are structures of resistance produced by Fop, allow the fungus survival in the soil for several years and have saprophytic activity. Biofumigation with incorporation of cabbage and bitter cassava has been a viable alternative, among management methods, for the control of soil pathogens. The objective of this work was to evaluate the effect of different plant debris (plant residues) on survival of Fop under laboratory conditions. In vitro tests were carried out with incorporation of leaves of yellow passion fruit, cabbage, bitter cassava, and sweet cassava plants into substrates infested with different Fop isolates. Mycelial growth and chlamydospore production and germination were evaluated. The incorporation of cabbage and bitter cassava debris had a fungistatic effect on Fop, with decreases in mycelial growth and chlamydospore production. The incorporation of cabbage into the substrate totally inhibited the chlamydospore germination in 78% of the evaluated isolates and decreased the germination percentage in the others.

ABSTRACT Green manuring with spontaneous species from the Caatinga has emerged as a viable alternative to supply vegetables with nutrients and thus increase their productivity. This study aimed to evaluate and estimate the maximum physical and economic efficiencies of coriander productive characteristics as a function of equitable biomass amounts of hairy woodrose [Merremia aegyptia (L.) Urban] and roostertree [Calotropis procera (Aiton) W. T.] in different cropping seasons. The experimental design was a randomized complete block with five treatments and five replicates. The treatments consisted of green manure amounts (16, 29, 42, 55, and 68 t ha-1 on a dry basis). A treatment without fertilization (control) was used in each experiment. The maximum agronomic efficiency (coriander green mass yield) was possible with the incorporation of equitable amounts of 49.56 t ha-1 of M. aegyptia and C. procera biomass, respectively. The maximum economic efficiency of production (evaluated in terms of net income and rate of return) of this leafy vegetable was achieved with the addition to the soil of 42.68 and 41.64 t ha-1 of biomass of these green manures, respectively. The net income and the rate of return optimized for these amounts of green manures were 30,243.92 R$ ha-1 and 2.79 reais for each real invested in the production of this leafy vegetable. The use of biomass from Merremia aegyptia and Calotropis procera from the Caatinga biome proved to be a viable technology for producers who practice the cultivation of coriander when monocropping in a semiarid environment.

ABSTRACT Pochonia chlamydosporia (Pc) is a nematophagous fungus with saprotrophic activity. However, little is known about the interaction between Pc and green manure. This study aimed to investigate the interaction effects of different green manures and Pc on the control of Meloidogyne javanica in soybean. Two greenhouse experiments were conducted in different periods using a 6 × 2 factorial design, with six replicates. The first factor was green manure application (oat, brachiaria, crotalaria, millet, buckwheat, and untreated control) and the second factor was treatment with Pc (in-furrow application and untreated control). Cover crops were grown separately and applied to pots as green manure 15 days before soybean sowing. At 5 days after sowing, soybean was inoculated with 2 000 eggs and juveniles of M. javanica. At 60 days after inoculation, nematode and vegetative variables were determined. All green manures reduced nematode population levels, especially oat, crotalaria, and buckwheat. Pc treatment did not influence nematode population levels. Soybean plants treated with oat or crotalaria green manure had greater height than untreated plants in both experiments. The effects of factors on shoot fresh and dry weights differed between experiments, and green manure application did not affect root development. The findings confirmed the potential of plant residues to control M. javanica.

ABSTRACT Several tropical woody species are highly responsive to arbuscular mycorrhizal fungi (AMF) and depend on their symbiosis for nutrition and successful establishment in the field. The objective of this study was to evaluate the response of Schinus terebinthifolius, a native species of the Brazilian Atlantic Forest and Caatinga, to inoculation with three AMF species (Dentiscutata heterogama, Gigaspora margarita, and Rhizophagus clarus), either individually or mixed, at different levels of phosphorus fertilization (0, 71, 213, and 650 mg kg−1 of P). We conducted the experiment in 1 kg pots, following a completely randomized design with six replicates per treatment, to evaluate morphological and nutritional traits after 116 days, including stem diameter, plant height, plant biomass, and shoot P content. Our results showed that S. terebinthifolius was highly dependent on mycorrhizae and presented different responses depending on the AMF species. The greatest total biomass accumulation occurred when a mixture of the three AMF species was used, which indicated synergism between the fungi. The highest overall positive response to inoculation were observed at an intermediate P level (213 mg kg−1), and although shoot biomass was reduced at the intermediate P doses, an increase in root biomass compensated for this. These results indicate complementarity as opposed to functional redundancy of the AMF species and highlight the importance of using a mixed inoculum in seedling production of S. terebinthifolius for revegetation programs.

ABSTRACT Watermelon has great economic relevance, but edaphoclimatic factors and inadequate management have favored the salinization of the water used for irrigation, which is a limiting factor for the growth and production of the crop. However, it is considered that the use of growth regulators belonging to the group of cytokinins and auxins may contribute to the development and yield of crops, even under adverse conditions such as salinity. Thus, the objective was to evaluate the influence of cytokinin and auxin proportions on the growth and quality of watermelon irrigated with saline water. The experimental design was completely randomized, with four replicates and 5 x 2 factorial, referring to five proportions of growth regulators (0/100; 25/75; 50/50; 75/25 and 100/0%) corresponding to concentrations of 1.0 and 10.0 mg L−1 of forchlorfenuron (CPPU)/ indoleacetic acid (IAA), and two salinity levels, one composed of water without adding salt (0.3 dS m-1) and the other with 2.0 dS m−1 electrical conductivity. The proportions of cytokinin and auxin influenced the growth and quality of watermelon subjected to salinity in irrigation water. The 25/75% (CPPU/IAA) proportion favored smaller decreases in leaf area and total dry mass under a saline condition of 2.0 dS m−1. For fresh and dry fruit mass, the 75/25% (CPPU/IAA) proportion favored smaller reductions. Fruit firmness and soluble solids were favored by the proportions 25/75 and 50/50% (CPPU/IAA) at EC of 2.0 dS m−1. Acidity was only influenced by the proportion of 50/50% (CPPU/IAA) between the electrical conductivity levels.