Improvement of the host contribution to nitrogen fixation has been proposed as a method of increasing nitrogen fmtion. Significant variability and generally high broad-sense heritability estimates (.60 k .27 to .82 f .26 for nitrogenase activity and .53 2 .29 to .85 f .26 for shoot dry weight) have been reported for F,-derived families from a cross between the virginia (Arachis hypogaea L. ssp. hypogaea var. hypogaea) cultivar NC 6 and the Spanish (ssp. fastigiata Waldron vulgaris Harz.) breeding line 922, indicating selection for increased nigtogen fixation should be effective in this population. Lines from this population were chosen randomly from F,-derived families selected for high and low nitrogenase activity and high and low shoot dry weight after evaluation at three dates and two locations in each of 2 years (FS and F, generations). This study's objectives were to evaluate the N,-fixing ability of the selected lines and to evaluate the association between plant growth habit and N, fixation. Twenty-four lines in each of the four selection groups and the parents, NC 6 and 922, were evaluated at two sampling Results from selection for increased N, furation are generally consistent with the notion that this symbiotic process can be enhanced by improvement of the host via traditional breeding methods. Duhigg et al. (4) reported progeny of genotypes selected from Mesilla alfalfa (Medicago sativa L.) for high acetylene reduction and intermated had acetylene reduction values 82% greater
Genotype (G) x environment (E) interactions were measured in sweet potatoes (Ipomoea batatas L.) for yield (seven genotypes, six locations, 3 years) and selected quality factors (nine genotypes, six locations, 2 years). Yield of all grades of roots and all quality factors tested were affected significantly by genotype, environment, and G × E interactions. Quality factors were less affected by G × E interactions than yield factors. Broad-sense heritability estimates ranged from 75% to 92% for yield factors and 94% to 99% for quality factors. Estimates of variances of clonal means with varying years, locations, and replications suggest that 2 years, four locations, and four replications would provide reliable test data for yield and quality factors.
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 ...
The response of 501 open-pollinated seedlings of 9 parental clones of sweet potato [Ipomoea batatas (L.) Lam.] to the severe russet crack strain of sweet potato feathery mottle virus (SRC-FMV) was evaluated under greenhouse conditions. Sixty-four percent of the seedlings showed foliar, root, or foliar/root symptoms, indicating that SRC-FMV can be sap-transmitted to seedlings. Fifty-nine percent showed foliar symptoms only. Seedlings from the parental clone with the highest percentage of symptom expression (88%) in the greenhouse were used to study the effect of selected environmental factors on foliar symptom expression. The predominant symptom was veinbanding. The percentage of plants showing symptoms varied from 0% to 46% and was influenced significantly by the interaction of light intensity × daylength × temperature.
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