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Genetics of Resistance to Reniform Nematode in Upland Cotton

Dep. of Agriculture Punjab (Research Wing), Cotton Res. Stn., Multan, Pakistan
Dep. of Agronomy, Louisaina Agric. Exp. Stn., LSU Agric. Ctr., Baton Rouge, LA 70803

^* Corresponding author.

Reniform nematode (RN), (Rotylenchulus reniformis Linford and Oliveira) is an economically important pest of upland cotton (Gossypium hirsutum L.). Sources of resistance to RN have been identified, but inheritance of resistance has not been studied previously. Four cotton lines [La RN-910, Auburn (Aub) 612-RNR, M 019- RNR, and ‘Deltapine 41’ (Dp 41)] were selected as parents for genetic study of resistance to RN reproduction. Deitapine 41 (susceptible) was crossed to each of the three lines previously reported as resistant. Means of P₁, P₂, F₁, F₂, BC₁P₁, and BC₁P₂ generations in the three crosses were analyzed by the generation mean analysis procedure to estimate gene effects. Seedlings grown in the greenhouse were individually inoculated at the first true leaf stage with 2000 RN juveniles. After an average growth period of 43 d in the winter and 32 d in the summer, the entire root system of each plant was harvested, and RN eggs were extracted and counted. Significant (p < 0.05) differences among generations and nondiscrete frequency distributions in segregating populations indicated that RN resistance in two of three crosses (La RN-910 x Dp 41 and Aub 612- RNR x Dp 41) was under genetic control and inherited in a quantitative manner. No pattern was observed for the significance of additive and dominance gene effects, but significant (P < 0.05) epistatic gene effects occurred in most cases. The occurrence of transgressive segregation for susceptibility and epistatic gene effects suggest that resistance to RN in these cotton lines was controlled by two or more pairs of genes. Advancing generations to F₄ or F₅, while maintaining genetic variability prior to selection, may improve selection efficiency by reducing nonadditive gene effects for RN resistance. High coefficients of variation and general lack of additive gene effects suggest that future genetic and breeding studies for RN resistance may be enhanced by reducing environmental effects and exploring other sources of resistance.

Received for publication October 3, 1988.