EVALUATION AND HERITABILITY OF RESISTANCE TO SUGARCANE RED ROT

Heritability of resistance to red rot, caused by Colletotrichum falcat um, was studied with progeny from 40 crosses among 24 parental clones of sugarcane. Resistance was assessed by comparing disease development in detached, inoculated stalks. Disease severity was assessed as the number of nodes beyond which fungal infection symptoms were observed, the number of nodes rotted, the extent of internode rotting, and a rot index (Ri) combining the number of nodes passed and internode rot sev erity. Significant differences in susceptibility were detected, althou gh high levels of resistance were rare in the breeding and selection p opulations of the Louisiana sugarcane cultivar development program. Na rrow-sense heritability estimates determined by mid-parent-offspring r egression for the different disease traits ranged from 0.19 +/- 0.04 t o 0.31 +/- 0.05. Potential genetic gain by selection for resistance, u sing a 10% selection intensity, ranged from 14 to 37% of the mean. The RI provided the highest heritability estimate and the most potential genetic gain from selection. We estimated low broad-sense heritabiliti es among years for the disease traits in the parent population. The ra nge was from 0 to 0.42 +/- 1.07 on an entry basis. The results indicat ed that the population level of red rot resistance can be increased by careful choice of parent clones and cross-based selection. Genotype b y year interaction, however, greatly affects evaluation, hence single- year evaluations for red rot resistance are not reliable. The scarcity of resistance in the current breeding population indicates a need to identify new sources of resistance.