IDENTIFICATION OF 2 RAPD MARKERS TIGHTLY LINKED WITH THE NICOTIANA-DEBNEYI GENE FOR RESISTANCE TO BLACK ROOT-ROT OF TOBACCO

Linkage of randomly amplified polymorphic DNA (RAPD) markers with a si ngle dominant gene for resistance to black root rot (Chalara elegans N ag Raj and Kendrick; Syn. Thielaviopsis basicola [Berk. and Broome] Fe rraris) of tobacco (Nicotiana tabacum L.), which was transferred from N. debneyi Domin, was investigated in this study. There were 2594 repe atable RAPD fragments generated by 441 primers on DNAs of 'Delgold' to bacco, a BC5F8 near isogenic line (NIL) carrying the resistance gene i n a 'Delgold' background, and 'PB19', the donor parent of the resistan ce gene. Only 7 of these primers produced eight RAPD markers polymorph ic between 'Delgold' and 'PB19', indicating there are few RAPD polymor phisms between them despite relatively dissimilar pedigrees. Five of t he eight RAPD markers were not polymorphic between 'Delgold' and the N IL. All of these markers proved to be unlinked with the resistance gen e in F-2 linkage tests. Of the remaining three RAPD markers polymorphi c between 'Delgold' and the NIL, two were shown to be strongly linked with the resistance gene; one in coupling and the other in repulsion. Application of the two RAPDs in the elimination of linkage drag associ ated with the N. debneyi resistance gene and marker-assisted selection for the breeding of new tobacco cultivars with the resistance gene is discussed.