Selection Among Early Generation Peanut Progeny for Enhanced Nitrogen Fixation1

Abstract

Recurrent selection provides an established methodology for host improvement which should be applicable to increasing N, fixation. This study was conducted to evaluate response to three cycles of phenotypic selection for fresh plant weight, nodule number and dry weight, and acetylene reduction when individual peanut (Arachis hypogaea L.) plants were evaluated in the greenhouse using a mixture of four Bradyrhizobium strains as inoculum. The F, generation derived from a single cross, Florigiant x CES 101, constituted the base population. In each of three cycles the 20 superior individuals were selected and randomly intermated to generate the subsequent cycle for selection. The 20 selections from each cycle were bulked and evaluated with the original parents in two greenhouse trials to evaluate response to selection. No variability for fresh plant weight, nodule number or dry weight, or acetylene reduction was detected among cycles. Realized heritability estimates were 0.0120.02, 0.05+0.03, -0.06-+0.06, and 0.3120.32 for fresh plant weight, nodule number, nodule dry weight, and acetylene reduction, respectively. Agronomic traits of the same entries were evaluated in one field study. No variability for these traits was detected among cycles. Insufficient control of environmental variation was suggested as a possible cause of lack of response to selection.Key Words: Arachis hypogaea L., Bradyrhizobium, recurrent selection, realized heritability, acetylene reduction, groundnut.Recurrent selection encompasses such a variety of breeding procedures that the only common aspect is the cyclical process of selecting and recombining superior individuals. Population improvement per se or population improvement prior to extraction of inbred lines may be the goal. In either case, improvement via increased frequency of favorable alleles is sought while maintaining genetic variability in the population.Recurrent selection methods may be divided into two types: phenotypic and genotypic (35). Phenotypic recurrent selection includes all recurrent selection methods in which the phenotype of the selection unit is the basis of selection. Control of microclimatic variation is essential to the success of a phenotypic recurrent selection procedure (16).Although first proposed for use in cross-pollinated crops, recurrent selection has been extended to use in self-pollinators. The number of pollinations required during the recombination phase and the length of time between cycles were inititally seen as obstacles to its use in self-pollinators. Compton (14) 23,28,37,38,42), tobacco (Nicotiana tabacum L.) (19,26), and wheat (Triticum aestivum L.) (5,12,13,25,27). This paper reports the results of phenotypic recurrent selection for enhanced nitrogen fixation in peanut. The objectives of this study were to a) measure response to three cycles of phenotypic recurrent selection when selection for increased fresh plant weight, nodule number and dry weight, and acetylene reduction was practiced; b) estimate realized heritability for each of ...

Heritability of N2 Fixation Traits, and Phenotypic and Genotypic Correlations between N2 Fixation Traits with Drought Resistance Traits and Yield in Peanut

“…Similar results of relatively low h 2 b estimates for NN have been observed in other studies (Pimratch et al, 2004b;Phudenpa et al, 2005). Arrendell et al (1988) also reported very low realized heritability estimates for NN (0.05) and NDW (0.06). Cruickshank et al (2004) reported that the heritability estimates varied signifi cantly between crosses and traits depending on levels of genetic variation in parents.…”