Estudos biométricos e de QTL associados à fixação biológica de nitrogênio em feijão-caupi

Abstract

The studies were carried out to obtain information on the genetic control of traits related to the biological fixation of nitrogen (FBN) in cowpea, to guide the development of cultivars more efficient to N2 fixation. Three parental lines of cowpea, with different levels in symbiotic performance, IC-1 (inefficient), BRS Pujante and BRS Marataoã (efficient), were crossed (IC-1 x BRS Marataoã and IC-1 x BRS Pujante) to obtain F2 populations. Segregation was evaluated by FBN-related parameters, such as dry matter (MSPA), fresh nodule matter (MFN), number of nodules (NN) and accumulated nitrogen (NA). Segregation for efficient and non-efficient plants indicated that N2 fixation is controlled by two genes, with epistatic dominant recessive effect (13: 3). Narrow-sense heritability values were 78% and 90% for MSPA, 58% and 78% for NN, 58% and 86% for MFN and 71% and 85% for NA in the IC-1 x BRS Pujante and IC-1 x BRS Marataoã crosses, respectively. Significant and positive correlations were estimated between MSPA x MFN and MFN x N, while NN showed significant negative correlation with NA and MSPA. The parents, IC-1 and BRS Marataoã, and 90 plants of the F2 population were genotyped with 46,300 single-base polymorphism (SNP) markers, of which 910 polymorphic markers were used for map construction. The results revealed 11 linkage groups, with a mean of 82 markers per chromosome and a mean distance of 1.26 cM between markers. The recombination analysis of the SNP markers indicated 2_12850 and 2_24723 SNPs, located in the linkage group 11, flanking the gene of FBN (cpi) with 6.7 cM and 5.64 cM distance, respectively. The inclusive composite interval mapping method (ICIM) identified a single QTL for MSPA, NN, and NA, that accounted for 43.4%, 48.2%% and 51.24% of the total variation, respectively. Five SNPs markers in one side of the QTL were validated in the F2 population, IC-1 x BRS Pujante, with tera-primer ARMS-PCR technology, with 96% of certainty. This result indicates a potential use of these markers for assisted selection for improvement FBN in cowpea. The over all results indicated that FBN in cowpea can be improved by single breeding methods.