Genotypic Correlation and Path Analysis of Some Traits related to Oil Yield and Grain Yield in Canola (Brassica napus L.) under Non-stress and Water Deficit Stress Conditions
دوره14 شماره4 سال1394
اصلاح و دستیابی به ارقامی از گیاه کلزا که دارای عملکرد قابلقبول بوده و بتوانند شرایط آبوهوایی خشک و نیمهخشک کشور را تحمل نمایند، حائز اهمیت است. انتخاب بر اساس یک یا چند صفت زراعی بدون توجه به نحوه ارتباط و همبستگی بین صفات گمراهکننده بوده و اطمینان از نتایج مورد انتظار را بهشدت تحت تأثیر قرار میدهد؛ لذا شناخت ارتباطات ویژگیهای ژنتیکی ارقام بهویژه در شرایط تنشهای محیطی بسیار حائز اهمیت میباشد. از این رو بهمنظور بررسی ارتباطات و همبستگی ژنتیکی صفات و تعیین صفات مؤثر بر عملکرد دانه و روغن در ارقام مختلف کلزا، آزمایشی در قالب طرح بلوکهای کامل تصادفی با سه تکرار در شرایط تنش کمآبیاری انتهای فصل رشد و شرایط بدون تنش اجرا گردید. نتایج نشان داد که ژنوتیپها از نظر تمامی صفات اختلاف معنیداری دارند و همچنین تنش خشکی باعث کاهش تظاهر در تمامی صفات گردید. ضرایب همبستگی ژنوتیپی و فنوتیپی بین تمامی صفات محاسبه شد و با استفاده از رگرسیون گامبهگام مناسبترین مدل در هر دو محیط ارائه شد. تجزیه مسیر روی همبستگی ژنتیکی بین عملکرد دانه و سایر صفات مرتبط نشان داد که در شرایط بدون تنش، صفات تعداد خورجین در هر بوته و طول خورجین اثر مستقیم و بالایی روی عملکرد دانه داشته در حالیکه در شرایط تنش خشکی، طول خورجین و ارتفاع بوته بیشترین اثر مستقیم را نشان دادند. همچنین نتایج نشان داد که عملکرد دانه بیشترین اثر مستقیم را در هر دو شرایط محیطی بر روی عملکرد روغن دارد؛ بنابراین مهمترین صفات بهعنوان شاخص گزینش برای افزایش عملکرد دانه و عملکرد روغن در شرایط تنش خشکی بهترتیب شامل طول خورجین و عملکرد دانه بود.Introduction
Obtaining varieties with acceptable yield and tolerant to different arid and semi-arid climate condition of Iran is an important goal in canola breeding programs. Selection of genotypes base on one or more traits without regarding to correlation between them, could biases the expected results. Therefore, identifying of genetic correlation among traits especially in environmental stress condition is very important. The use of genotypic correlation helps evaluating the magnitude and direction of associations between characters facilitating the application of indirect selection, because genetic changes in a given trait may change other traits, leading to faster and larger genetic gains in plant breeding programs. Therefore, the selection for another trait may result in indirect response in the low heritable trait, provided the following conditions are satisfied: the genetic correlation between them is substantial, and the heritability of the secondary trait is greater than that of the primary trait. The purpose of this study was estimating the total genotypic variability, genotypic correlations, and path analysis among some important traits for selection criteria for improving seed and oil yield in canola under water deficit stress condition.
Materials and Methods
For evaluation of genetic correlation among traits and identifying important affecting traits on grain yield and oil yield in canola genotypes, an experiment was conducted based on a randomized complete blocks design with three replications in two different conditions of water deficit (stress and non-stress). Different traits were measured including seed yield, 1000-seed weight, number of seeds per pod, number of pods per plant, silique length, oil content, days to maturity, protein content, plant height and water use efficiency. Genotypic and phenotypic correlation coefficients were calculated for ten characters during growing seasons. The genotypic correlation coefficients between seed yield and different characters were subjected to path coefficient analysis separately for partitioning these values into direct and indirect effects. Step-wise regression technique was used to determine the best model, which accounted for variation exist in plant seed and oil yield as dependent variables in separate analysis. Direct and indirect effects of traits entered to regression model were determined by using path coefficient analysis.
Results and Discussion
Results of this study showed significant differences among all genotypes performances, and also stress condition caused a significant decrease in performance of all studied traits. The highest seed yield obtained from Geronimo and Dante (with 3668 and 3505 kg.ha-1, respectively) under non stress condition, and the highest seed yield obtained from Zarfam and Dante (with 2948 and 2860 kg ha-1, respectively) under drought stress condition. Genotype Licord produced the highest oil content, which was significantly higher than that produced by other genotypes in either regime. Genotypic and phenotypic correlation coefficients were estimated between all traits and using stepwise regression, best model was introduced for two conditions. Under Non-stress condition, the average of genetic correlations between grain yield and silique length was high and positive (0.92**), suggesting that the selection of prolific plants resulted in a gain of selection for yield. Under water deficit stress condition, a negative average of genetic correlations (-0.28) was observed for grain yield and days to maturity. Path analysis based on the genotypic correlation under non-stress conditions between grain yield and other traits showed that number of pods per plant and pod length had direct effects on grain yield, while under drought conditions, pod length and plant height had important direct effects. Results of path analysis for oil yield under non-stress and stress conditions showed that grain yield had the most direct effect on oil yield.
Conclusions
Finally, the most important traits in order to select index for grain yield and oil yield improvement under stress condition were pod length and grain yield, respectively. Therefore, selection based on these traits would be more effective to improving seed yield of canola in well-watered and water-deficit stress conditions. So, the method of path coefficients proved useful in analyzing correlation coefficients in this system of interrelated variables
