Selection for resistance to pythium ultimum trow within four cultivars of cotton (Gossypium hirsutum L.)

Four commercial cotton (Gossypium hirsutum L.) cultivars were chosen for an experiment involving selection for resistance to Pythium ultimum Trow. Two cultivars, Auburn M and Delcot 277J, previously had been found to be slightly more susceptible than Coker 310 and Dixie King 3. The potential for inheritance of resistance was based on the large variation that occurred among plants within the cultivars. The relative susceptibility or resistance found previously was confirmed in a field test with the four cultivars. Pathogens were isolated with frequencies similar to that recorded in the literature. Parent seeds of the four cultivars were planted in sterilized sand and grown at 27 C for eight days before being inoculated with P. ultimum. Inoculated seedlings were incubated at 18 C and rated for dis-ease severity after seven days. Surviving seedlings of different ratings were transplanted to sterilized soil and grown to maturity. Plants were self-pollinated and progeny seeds obtained were planted in sterilized sand. Seedlings obtained were inoculated as before and rated for dis-ease severity after seven days. Heritability of each cultivar was calculated by three methods. Values obtained by the regression method were not different from zero at the 5% level of probability. Heritability values for Delcot 277J and Coker 310 were significantly different from zero at the 107. level. The partition of variance method was thought to contain too much error due to environmental effect and was included for comparison only. The realized heritability method was used to determine the response to one generation of selection. From values obtained by this method. Auburn M could have the most potential of the four cultivars in a future breeding program. Values for realized heritability can be employed to predict future response to selection. Coker 310 met the criteria necessary for accurate predictions.