Genetic loci responding to two cycles of divergent selection for grain yield under drought stress in a rice breeding population

Four sets of selected strawberry (Fragaria ×ananassa Duch.) genotypes were generated from within a single breeding population to evaluate the correspondence between predicted and realized selection response for fresh fruit color traits. Genotypes were selected for extreme phenotypes, dark or light, of either internal or external color value (CIELAB L*). Genotypic selection response was evaluated empirically by scoring fruit from the clonal derivatives of these selected genotypes, and response for breeding value was estimated by scoring the offspring of crosses performed among a subset of the genotypes within each selected set. Realized selection response was slightly larger than predicted for internal and external L* when calculated for selected genotypes. Also, more than half of the selected genotypes had genotypic values for L* outside the range of the original parents, providing evidence for transgressive segregation. Realized selection response for breeding value in exterior and interior color was slightly less than predicted. Compared in a different way, genotypic selection response for external color was significantly greater than selection response for breeding value, whereas genotypic and breeding value responses did not differ for internal color. These observations suggest the presence of some nonadditive genetic variance for external color but support the conclusion that the heritabilities predicted previously were reasonably accurate. Estimates of variance components within each of the offspring populations demonstrated that genetic variances were modified substantially by one generation of selection. Selection for dark fruit color reduced genetic variance to nonsignificant levels, with internal color more affected than external color. The total genetic variances within both of the offspring populations from parents selected for light color were changed little by one generation of selection, but substantial dominance variance was detected that had not been found in the original population. The rapid response to selection and large changes in the distribution of genetic variances may indicate the presence of a few genes with comparatively large effect in strawberry color expression. Additional divergent selection response can be expected, but primarily in the direction of light fruit color.

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Correlation and Path Analysis of Yield Components in Rice (Oryza sativa L.) under Irrigated and Reproductive Stage Drought Stress Condition

Current Journal of Applied Science and Technology ◽

10.9734/cjast/2020/v39i830593 ◽

2020 ◽

pp. 60-68

Author(s):

Sadia Perween ◽

Anand Kumar ◽

Fariha Adan ◽

Jitesh Kumar ◽

Prince Raj ◽

...

Keyword(s):

Drought Stress ◽

Grain Yield ◽

Path Analysis ◽

Stress Condition ◽

Reproductive Stage ◽

Yield Attributes ◽

Drought Stress Condition ◽

Biological Yield ◽

Selection For ◽

Correlation And Path Analysis

Aim: The current experiment was conducted to study correlation and path analysis among morphological traits and their contribution towards yield under irrigated and drought stress condition using forty eight diverse rice genotypes. Study Design: The experiment was studied in three replications using Randomized Block Design. Place and Duration of Study: The research was carried out during Kharif 2018 at Rice Research Farm, Bihar Agricultural University, Sabour (Bhagalpur), India. Methodology: The experiment was conducted in two different sets; irrigated and drought stress condition. The yield and yield attributes were recorded under both the conditions to conduct the correlation and path analysis. Results: The analysis of variance revealed that genotypes significantly varied in yield and yield related traits. In addition, growth and yield attributes such as effective tillers per hill, biological yield, harvest index (%) and number of fertile grains per panicle were significantly and positively correlated with grain yield per plant under irrigated as well as reproductive stage drought stress condition. It was observed that total number of grains per panicle, number of fertile grains per panicle and biological yield had high positive direct effect on grain yield per plant in both irrigated (control) as well stress condition, indicating true relationship of these characters with grain yield and direct selection for these characters will be rewarding. In rest of the characters studied, correlation was mainly due to indirect effects through component characters and hence indirect selection will lead to yield improvement in rice. Conclusion: The potential for direct and indirect selection for reproductive stage drought stress tolerance using the associated characters may be useful to the breeder to formulate appropriate breeding plans for the selection of the genotype which tolerate high temperature condition.

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Additive Genetic Effects for Resistance to Foliar Powdery Mildew in Strawberry Revealed through Divergent Selection

Journal of the American Society for Horticultural Science ◽

10.21273/jashs.139.3.310 ◽

2014 ◽

Vol 139 (3) ◽

pp. 310-316

Author(s):

Colleen Kennedy ◽

Luis F. Osorio ◽

Natalia A. Peres ◽

Vance M. Whitaker

Keyword(s):

Powdery Mildew ◽

Genetic Correlations ◽

Breeding Population ◽

Field Trials ◽

Divergent Selection ◽

Response To Selection ◽

Additive Variance ◽

Susceptible Population ◽

High Heritability ◽

Selection For

Powdery mildew (PM) of strawberry (Fragaria sp.) is a ubiquitous, wind-spread disease caused by the obligate parasite Podosphaera aphanis. To control PM, multiple fungicide applications are necessary each season, and none of the major cultivars in Florida have high levels of resistance. Therefore, the objectives of this study were to observe the response to selection and to estimate genetic parameters for PM and related traits in the University of Florida breeding population. In 2010, clonally replicated individuals from seven biparental crosses arising from 11 parents were included in a field trial in which clonally replicated seedlings were evaluated visually for percent coverage of PM mycelium using a modified Horsfall-Barratt scale of 0 to 6. Broad- (H2) and narrow-sense (h2) heritabilities for PM score were (mean ± se) 0.50 ± 0.08 and 0.40 ± 0.39, respectively, for the base population. After the second round of selection in the resistant population, no additive variance was detected, indicating that alleles for PM resistance had become fixed. In contrast, after two rounds of divergent selection in the susceptible population, there remained considerable additive variance (h2 = 0.42 ± 0.65). Moderate to high heritability estimates and a clear response to selection indicate that resistance to PM is genetically controlled through mostly additive effects. Selection of parents based on field trials with natural inoculum should result in good progress toward more resistant cultivars. The consistently moderate to strong genotypic and genetic correlations among PM and canopy density (CD) indicate that selection for PM resistance will result in reduced CD. Therefore, CD must be monitored over successive rounds of selection for low levels of PM to prevent CD falling below the commercially acceptable range.

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