ESTIMATION OF THE GENETIC ACTION AND COMBINING ABILITY OF SUNFLOWER USING CYTOPLASMIC MALE STERILITY

The research was conducted in the fields of a farmer in Ramadi city, Iraq, on the left bank side of the Euphrates River. The study aimed to know sunflowers' ability and genetic action using cytoplasmic male sterility. Five cytoplasmically male-sterile sunflower lines (A6, A10, A12, A13, and A16) were crossed with three testers carrying fertility restoration genes and the multi-head trait (R1, R2, and R3). A (line × tester) system was applied to 15 hybrids. The lines were planted during the spring of 2023 to produce 15 hybrids. In the autumn season of 2023, seeds of the genetic combinations (8 parents + 15 hybrids) were planted using a randomized complete block design (RCBD) with three replications. The experiment aimed to evaluate the lines and hybrids, estimate the general and specific combining abilities of the parents and hybrids, and study other genetic traits. The results of the genetic combining ability showed significant differences in all the studied traits. A10 line exhibited the highest value in disk area, measuring 194.31 cm², with 934.40 seeds per disk and a yield of 67.73 g.  A13 line excelled in 1000-seed weight, yielding 74.2 g. Meanwhile, the A6 line showed the highest oil content in seeds, reaching 49.12%. Among the testers, R1 was the best for most traits. The hybrid A10×R3 recorded the highest values in disk area of 249.13 cm², number of seeds per disk of 1356.04 seeds, and yield of 94.71 g. On the other hand, the hybrid A12 × R1 recorded the highest oil content in seeds, with 47.21%. The specific combining ability variance components were more significant than the general combining ability variance components. Moreover, the dominance genetic variance was more significant than the additive genetic variance. The narrow-sense heritability ranged between 3.95% for oil content and 55.09% for plant height. This led to a dominance degree higher than one for most of the studied traits. It can be concluded from this study that confident superior parents can be utilized in crosses to develop individual hybrids with specific combining abilities, leading to high seed yield. This is because most traits were influenced by dominance and over-dominance