Date of Award

1988

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Plant, Enviromental and Soil Sciences

First Advisor

Jack E. Jones

Abstract

Four Gossypium hirsutum L. lines (La. RN 910, Auburn 612 RNR, M 019-RNR, and 'Deltapine 41' (Dp 41)) were selected for a genetic study of their reaction to reniform nematode, Rotylenchulus reniformis Linford and Oliveira, based on observed differences. Dp 41 (susceptible) was crossed to each of the three moderately resistant lines. F$\sb1$ generations were selfed and each was backcrossed to each of its parents. Estimates of mean gene effects and the three types of digenic epistatic effects affecting genetic variation of resistance to reniform were calculated using the generation means of P$\sb1$, P$\sb2$, F$\sb1$, F$\sb2$, P$\sb1$F$\sb1$, and P$\sb2$F$\sb1$. Six generations of the three crosses were evaluated for reniform resistance as seedlings grown in the greenhouse in plastic pots holding 500 grams of a sterilized mixture of Olivier silt loam soil and river sand. Each experiment (cross) consisted of two planting dates of two replications arranged in a randomized complete block design. Blocks of ten plants per replication for non-segregating generations (P$\sb1$, P$\sb2$, and F$\sb1$), blocks of 20 plants for P$\sb1$F$\sb1$ and P$\sb2$F$\sb1$ generations, and a block of 40 plants for the F$\sb2$ generation were grown. At the first true leaf stage, each plant was inoculated with 2,000 reniform juveniles. An average growth period of 43 days was allowed in the winter and 32 days in the summer. Entire root systems of plants were harvested to determine egg numbers. Significant differences among generation means and generally higher coefficients of variation for F$\sb2$ and backcross populations than for parental and F$\sb1$ populations indicated that differences between parents for reniform resistance in 2 of 3 crosses were under genetic control. Wide and non-discrete frequency distributions in segregating populations and high coefficients of variation indicated that resistance was quantitative in nature and greatly influenced by environment. No pattern was observed for the significance of additive and dominant gene effects. Significant epistatic gene effects occurred in most cases and transgressive segregation for susceptibility suggested that resistance to reniform nematode in these cotton lines was controlled by at least two pairs of genes. Estimates of broad-sense heritability ranged from 0 to 86% with a mean of 53% for eggs per root system. (Abstract shortened with permission of author.).

Pages

108

Share

COinS