Estimation of combining ability for seed yield and oil content in sunflower under normal and disease stress environments

The present study was conducted in the field by using 84 sunflower crosses (derived from fourteen lines and six testers through line x tester analysis) along with their parents. These genotypes were evaluated under normal and disease stress conditions for different plant traits to estimate their combining ability, gene action, proportional contribution and heritability. Pooled analysis of variance revealed significant differences among sunflower genotypes (line, tester and their crosses) for all plant traits. However, environment differences were non- significant for days to flower initiation. Significant differences of genotype x environment interaction for most of the plant trait suggested separate analysis of data under each experiment. Significant differences existed among sunflower genotypes for all the plant traits recorded under normal and disease stress condition. Significant differences for parents vs. crosses for all the plant traits under normal and disease stress conditions revealed presence of heterosis. Crosses exhibited significant differences for all the plant traits evaluated except oil content under normal condition. Whereas under disease stress condition, crosses exhibited significant differences for all plant traits except seed yield and oil yield. Both lines and testers showed significant differences among themselves for all the traits evaluated under normal and disease stress conditions except the testers for disease reaction. Lines x testers interaction was significant for days to flower initiation and days to flower completion under both normal and disease stress conditions. While under disease stress environment, lines x testers interaction was significant for days to maturity, 100-achene weight, and seed yield and disease reaction. The sunflower parental line ORI-4 performed best for earlier flower initiation, flower completion, plant maturity, seed yield per head, number of seeds per Be a d, oil content, seed yield and oil yield under both normal and disease stress environments. However, ORI-37 followed by ORI-4 was best suited for plant height under both the environments. The lines ORI-41 and ORI-4 performed better under both environments for larger head diameter, respectively. The sunflower lines ORI-1 and ORI-41 performed consistently better for heavier 100-achene weight under both the environments. The lines ORI-4 and ORI-27 were the most resistant to the charcoal rot disease. Restorer line RL-77 followed by RL-27 was best suited for earliness in flower initiation, flower completion and maturity under both the environments. Sunflower restorer lines RL-46 and RL-27 performed consistently better under both the environments accordingly for plant height, head diameter, seed yield per head, seed yield per ha and oil yield. Restorer line RL-55 followed by RL-27 performed best for greater oil content under both the environments. Restorer lines RL-77 and RL-46 ga v e better performance against sunflower charcoal rot. The sunflower hybrid "ORI-10 x RL-55" is earliest in flower initiation and flower completion, hybrid "ORI-4 x RL-27 followed by ORI-1 x RL-27" is earliest in maturity; cross "ORI-1 x RL-55" is the best for 100-achene weight, cross combination ORI-49 x RL-46" is promising for maximum number of seeds per head, hybrid "ORI-1 x RL- 46" is highest in oil content and the cross "ORI-1 x RL-84" is the best for higher oil yield under both the environments. The hybrid "ORI-29 x RL-46, and ORI-20 x RL- 77" depicted the best performance for plant height and head diameter, seed yield per head and seed yield per ha under normal conditions. Whereas the hybrid "ORI-20 x RL-69, ORI-29 x RL-77 and ORI-6 x RL-77" performed better for plant height, head diameter and seed yield per ha, respectively under disease stress conditions. However, the hybrids "ORI-6 x RL-77, ORI-6 x RL-84, ORI-6 x RL-69 and ORI-48 x RL-77 were resistant to Macrophomin a phaseolina infection. Sunflower parental lines revealed that ORI-1 is the best general combiner for earlier flower initiation and flower completion, heavier one hundred achene weight and increased oil content under both the environments. The lines ORI-29 and ORI-49 expressed the best general combining ability effects for larger head diameter, more number of seeds per head and oil yield, respectively under normal condition whereas the lines ORI-37, ORI-22 and ORI-1 proved to be the best general combiners for these traits under disease stress conditions. However, ORI-29 and ORI-49 are the best general combiners for plant height and seed yield per ha under both the environments. Female lines ORI-4 followed by ORI-27, ORI-29 and ORI-22 are better general combiners for resistance reaction against disease (Macrophomina phaseolina). Among testers, RL-27 for days to maturity; RL-84 for plant height; RL-46 for number of seeds per head; and RL-77 for increased seed yield per plant an d seed yield per ha were the best general combiners under both the environments. Under normal conditions tester RL- 27 for earlier flower initiation and flower completion RL-46 for larger head diameter RL-84 for heavier 100-achene weight and oil yield and RL-69 for increased oil content were the best general combiners. Whereas under disease stress condition RL-77 for days to flower initiation, head diameter and oil yield; and RL-55 for days to flower completion, 100-achene weight and increased oil content were the best general combiners. Restorer lines RL-77 and RL-27 are the best general combiners for resistance reaction against charcoal rot. The estimates of specific combining ability effects revealed that the hybrids ORI-49 x RL-46, ORI-4 x RL-55, ORI-6 x RL-27 and ORI-29 x RL- 46 under normal and hybrids ORI-3 x RL-77, ORI-6 x RL-84, ORI-20 x RL-69 and ORI-49 x RL-46 under disease stress condition were the best specific combiners for earlier flower initiation, maturity, p l ant height and number of seeds per head, respectively. The cross ORI-27 x RL-46 was the best in terms of specific combining ability for earlier flower completion under both the environments. The hybrid ORI-22 x RL-27 is the best specific combiner for larger head diameter, higher seed yield per head, I00-achene weight, seed yield per ha and oil yield under normal conditions whereas the hybrids "ORI-6 x RL- 46" for head diameter; "ORI-6 x RL-77" for seed yield per head, 100-achene weight and seed yield per ha; and ORI-4 x RL-27" for oil yield were the best specific combiners under disease stress environment. The hybrid "ORI-49 x RL- 46" under normal and hybrid "ORI-1 x RL-46" under disease stress conditions were the best specific combiners for oil content. Ten crosses viz, "ORI-49 x RL- 46, ORI-37 x RL-46, ORI-10 x RL-69, ORI-10 x RL-84, ORI-3 x RL-55, ORI-1 x RL-77, ORI-48 x RL-77, ORI-29 x RL-55, ORI-49 x RL-69 and ORI-22 x RL-27 displayed better resistance reaction in terms of specific combining ability effects against sunflower charcoal rot (Macrophomina phaseolina). Dominance effects were predominant for days to flower initiation, days to flower completion and 100-achene weight under both the environments. Additive gene action was predominant for plant height; oil content and oil yield under both the environments. Under normal conditions, dominance gene action was predominant for head diameter, number of seeds per head and seed yield per ha but under disease stress conditions these traits came under the predominant additive genetic control. However, additive effects under normal and dominance effects under disease stress conditions were predominant for days to maturity. Resistance to charcoal rot was under the influence of dominance effects. Proportional contribution of lines was more important for days to flower initiation, days to flower completion, plant height and oil content percentage while line x tester interaction was more important f o r seed yield and oil yield under both the environments. Lines for 100-achene weight, testers for head diameter and number of seeds per head, and lines x tester interaction per days to maturity under normal conditions contributed more proportionally. While under disease stress conditions the contribution of lines for days to maturity and 100-achene weight testers for 100-achene weight and lines x tester interaction for head diameter was more important. Lines x testers interaction contributed more for disease reaction. The estimates of broad sense heritability were significant for all the plant traits evaluated under both the environments. It is therefore concluded that the only cross combination ORI-22 x RL-27 has positive and significant SCA effects for oil yield under normal conditions. The estimates of SCA effects in crosses ORI-20 x RL-70, ORI-47 x RL-69, ORI-29 x RL-46, ORI-49 x RL-69, ORI-10 x RL-55, ORI- 48 x RL-77 and ORI-37 x RL-77 are also impressive for oil yield u n der normal conditions. Whereas hybrids viz. ORI-4 x RL-27, ORI-48 x RL-55, ORI-10 x RL- 27, ORI-6 x RL-77 and ORI-6 x RL-46 have higher SCA effects for oil yield under Macrophomina phaseolina stress conditions.