Fixação biológica de nitrogênio em genótipos ancestrais de feijão-caupi

Abstract

The variability found in legumes on the efficiency of biological nitrogen fixation (BNF) has emphasized the importance of plant breeding. The objective of this study was to identify ancestor’s genotypes of cowpea cowpea (Vigna unguiculata (L.) Walp) with potential for biological nitrogen fixation. This study was conducted in a greenhouse and in the field, respectively at Embrapa Agrobiologia, Seropédica, RJ and Embrapa Meio-Norte, Teresina, PI. Two experiments were conducted in greenhouse, arranged in a randomized blocks with three replications. In the first experiment 15 cultivars were evaluated and in the second, 16 ancestors genotypes of cowpea. In both experiments were used two strains of Bradyrhizobium (BR 3267 and 3299) evaluated in isolation and in consortium. The samples were taken at the vegetative growth stage and in early flowering stage to determine nodulation traits. Analysis of variance showed significance (p <0.05) for cultivars and cultivars x strains interaction in the first experiment. In the second experiment, there was statistical difference for ancestors and for ancestors x strains interaction in relation to nodulation. In field experiments the experimental design was randomized block with three replications. In the first experiment, 16 ancestral genotypes with strain BR 3267 were evaluated. In the second, a fatorial 6 x 5 was used, consisting of six treatments (four strains, one treatment with N and other without inoculation and without N) and five cowpea genotypes (four ancestors and one cultivar). In the first field experiment, the variance analysis indicated a significant effect for ancestors, harvest and ancestors x harvest. In the second experiment, were observed significant effects to ancestors and ancestors x strains. The results of experiments in the greenhouse indicated that the cultivar Mauá was superior in number of nodules; nodules dry weight; shoot dry matter; nitrogen accumulated in shoots; and efficiency of nodulation in early flowering. The ancestral genotype Alagoano was higher than the others, associated with the strain BR 3267, in nodule number; nodules dry weight and shoot dry matter, during the vegetative growth, under aseptic conditions. In field conditions, the ancestors genotypes TVu 1190, TVu 59, TVx 3777-04E e TVx 4659-03E in interaction with strain BR 3267 were higher in nodules dry weight, shoot dry matter and nitrogen accumulated in shoots. The ancestral genotype Alagoano was higher than others in weight of 100 seeds, weight and length of pod, seed weight per pod and number of grains per pod, under field conditions. The FBN was measured using the 15N natural abundance technique. The largest percentage of BNF was obtained with the ancestors TVu 1190 and Alagoano and the highest amount of N derived from BNF was shown by genotype Alagoano.