Immature zygotic embryos of sunflower fertility restorer line 147 R were treated with ultrasound before plating to embryo culture medium. Some mutant plants were isolated and self-pollinated for several generations. New sunflower forms with inherited morphological and biochemical changes were obtained through selection and self-pollination. Genetic changes that occurred during the regeneration procedure included fifteen morphological and biochemical characters. In this study, negative genetic changes were registered for most of the indices. Positive changes were registered for leaf petiole length and number of leaves. Plant height was the least stable of all characters under study. Mutation for resistance to the local population of Orobanche cumana (race A-E) was obtained from the susceptible Bulgarian control line 147 R. All five investigated mutant restorer lines possessed 100% resistance to Orobanche and stable inheritance in subsequent generations. Our results showed that mutagenesis in sunflower can be successfully used to develop new lines useful for heterosis breeding.
Broomrape presents serious problems to sunflower production in Bulgaria. This leads to considerable losses expressed, on the one hand, in yield decrease, and on the other in lower quality of the obtained produce. Furthermore, the parasite forms new, more virulent races which overcome the resistance of the varieties and hybrids commonly used in production. With a view of limiting the parasite's distribution and decreasing the losses it causes, it would be preferable to know the distribution area of the individual races, and the rate and percent of broomrape attack. The results from this investigation showed that at the present moment there are three races of the parasite in Bulgariaraces D, E and F. Race E had the widest area of distribution among them. It was widespread in all sunflower production regions of the country. Three Orobanche sources, Morava, Tsarevets and Byala-2, overcame the resistance of the line P-1380 (Or-5), i.e., this is a new race for Bulgaria-race F (Bulgaria). It was registered during the growing seasons of 2003 and 2004 and it had limited distribution in individual fields of central-northern Bulgaria. An insignificant portion in the Orobanche population belonged to race D which was isolated from two samples only.
Orobanche cumana Wallr., an obligate root parasite of sunflower can cause severe damage to this crop. The genetic diversity obtained with random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) on two Orobanche populations were compared. Nei and Li distance matrices obtained with both methods among the two populations were correlated significantly according to Mantel's test and could partition the populations. The sampling variance of genetic distances within and among populations estimated using bootstrap procedure were not significantly different between the two techniques. The principal difference between the two techniques is that AFLP markers gave a higher degree of resolution for discriminating closely related germplasm than RAPD.
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