Combining Ability Analysis of Root-Knot Nematode Resistance in Cotton
1995
McPherson, G Randall | Jenkins, Johnie N. | McCarty, Jack C. | Watson, Clarence E.
The southern root-knot nematode (RKN), Meloidogyne incognita (Kofoid and White) Chitwood, is a serious pest of cotton (Gossypium hirsutum L.). This study determined the combining abilities of eight cotton lines for RKN resistance. The 28 possible single crosses among the susceptible M8, the adapted resistant M-315 RNR, and the day-neutral converted primitive resistant lines M19-RNR, M25-RNR, M75-RNR, M78-RNR, M188-RNR, and M487-RNR were evaluated for resistance in two greenhouse environments. Number of eggs per plant was determined on the basis of a five-pot row 40 d after planting one seed per 250-cm⁻³ pot 7 d after each pot was inoculated with 10 000 Race 3 RKN eggs. Since the relative plant resistance to RKN is inversely proportional to RKN reproduction, negative combining ability effects indicated resistance. The general combining ability (GCA) effects were highest for M-315 RNR. Specific combining ability (SCA) effects of six hybrids were significant in both environments. The SCA effects for M8 crossed with M-315 RNR or M75-RNR were negative, while the SCA effect of M-315 RNR with M75-RNR was positive. Although M-315 RNR and M75-RNR had the highest GCA, the two lines combined poorly together suggesting that they may have the same resistance genes. The SCA effects for MS crossed with M78-RNR and M188-RNR were positive, while the SCA effect of M78-RNR with M188-RNR was negative. This suggests that M78-RNR and M188-RNR may have different resistance genes that combined to produce progeny more resistant than predicted from the GCA effects. Part of a Ph.D. dissertation. Contribution of the USDA-ARS in cooperation with the Mississippi Agric. and Forestry Exp. Stn
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