Submitted to: Journal of Cotton Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/23/2004
Publication Date: 11/1/2004
Citation: McPherson, M.G., Jenkins, J.N., Watson, C.E., McCarty Jr., J.C. 2004. Inheritance of root-knot nematode resistance in M-315 RNR and M78-RNR cotton. Journal of Cotton Science. 8:154-161. Interpretive Summary: Root-knot nematode is a serious pest of cotton primarily in sandy soils. A high level of plant resistance has been developed in experimental lines of cotton; however, no commercial varieties of cotton have been developed with this high level of resistance. This study investigated the genetic inheritance of the high level of resistance in M-315 RNR and of a moderate level of resistance in M-78-RNR. Each was crossed with M-8, a very susceptible line of cotton, and the parents, F1, F2, and backcross generations were grown and evaluated for plant resistance to root-knot nematode in the greenhouse. Evaluations were based upon reproduction at 40 days following inoculation with nematode eggs. Analysis of data indicated that one dominant gene, Mi1, and one recessive or additive gene, Mi2 controlled resistance in M-315 RNR and one dominant gene Mi1 controlled resistance in M-78 RNR. This indicated that the high level of resistance should be easily transferable to commercial cultivars.
Technical Abstract: The southern root-knot nematode (RKN) (Meloidogyne incognita (Kofoid & White)) is a serious pest of cotton (Gossypium hirsutum L.) with detrimental effects being most pronounced on sandy soils that are also infested with Fusarium. Varietal resistance to RKN is an effective means of managing the root-knot/Fusarium wilt complex. In 1970, a high level of RKN resistance was developed in the germplasm line 'Auburn 623' (Auburn 623 RNR), but no commercially available cultivar has been developed with this near-immunity level of resistance. The objective of this study was to evaluate the mode of inheritance of RKN resistance in 'M-315' (M-315 RNR), a germplasm line with the Auburn 623 source of resistance and in 'M-78' (M78-RNR), a day-neutral version of the race stock line 'T78'. These lines were crossed with 'M-8', and RKN-susceptible cotton line and with each other. The parental, F1, F2 and backcross generations of these crosses were evaluated in the greenhouse for RKN reproduction 40 d after planting in a Wickham sandy loam (fine loamy, mixed thermic Typic Hapudult) that had been infested with 5,000 or 10,000 RKN eggs pot-1. The number of genes conditioning resistance to M-315 and M-78 was estimated to be two and one, respectively. Mendelian analyses indicated that a two gene, one dominant (Mi1) and one additive (Mi2), model fit the data for M-315. The crosses with M-78 suggested that it had the dominant Mi1 gene. These data indicate that the Auburn 623 source of RKN resistance should be easily transferable to commercial cultivars.