The selection of southern rust-resistant genotypes caused by Puccinia polysora (Pucciniaceae) is considered an efficient way to control this disease, which causes high crop losses in popcorn. To help ...choose adequate cultivars, we examined the combining ability of lines and the agronomic performance of popcorn hybrids for rust resistance. Eight S7 popcorn lines were used, which were crossed in a complete diallel mating scheme, resulting in 56 hybrids. The disease incidence on the whole plant (INC), severity on a leaf of the main ear (SEV), grain yield (GY), popping expansion (PE) and volume of expanded popcorn per hectare (PV) were evaluated. Analysis of variance was performed and the means were grouped by the Scott-Knott algorithm. The analysis diallel was performed by the method of Griffing, using the Diallel I method. The hybrids L76xP8, P8xL70, L77xP8, P8xP1 and L55xL76 stood out with a GY of >3000 kg.ha-1 and PE of >30 mL.g-1. For the traits GY and VP, the non-additive effects were predominant, and the heterosis effects high. For the trait expression of INC, SEV and PE, the additive effects were more relevant. The estimates of general combining ability of lines L70, L61, P1 and L76 were negative for INC and SEV. For commercial cultivation, L77xL76, L76xP1, L77xL70, L76xL70, L70xL76 and L77xP1 are recommended, in view of their excellent agronomic performance and superior resistance to rust.
Brazil nut is a native Amazon species of high commercial value classified as vulnerable in terms of extinction risk due to marked illegal-burning activity and agricultural-frontier expansion ...processes occurring in the region. This study was undertaken to analyze the genetic diversity within and between two natural Brazil-nut populations occurring spontaneously in the Southern Amazon region spaced 50 km apart, both of which were located in the municipality of Alta Floresta, northern Mato Grosso state, Brazil. These are rural areas and samples were from native forest patches. Leaf samples were collected from 86 plants from distinct areas; 36 were from population AGRO (Agrocondor II Farm, geographic coordinates 55º30' W and 9º00' S) and 50 from population CAR (Carolina Farm, geographic coordinates 57º00' W and 11º00' S). A molecular-diversity study was conducted using 11 microsatellite loci developed for the species. To determine the level of genetic diversity between and within subpopulations, we applied principal coordinate analysis, analysis of molecular variance, observed and expected heterozygosity, polymorphic information content (PIC), UPGMA-based clustering, and Bayesian inference structuring. Seventy alleles were found with the SSR markers, with an average PIC of 0.72. Average Ho and He were 0.43 and 0.82, respectively. AMOVA revealed that 81% of the variability is within populations, as found in other studies of Brazil-nut in the states of Pará, Acre and Amazonas. The dendrogram obtained by the UPGMA method and the clustering provided by Bayesian inference resulted in two and four groups formed, respectively. All 36 individuals of the AGRO population were allocated in Group I, and the 50 individuals of population CAR were allocated in Groups II, III, and IV. The two subpopulations have sufficient genetic variability for the composition of an in situ germplasm bank that can be used in breeding programs and in programs for the conservation of the species.
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