Evaluation and heritability of resistance to sugarcane red rot

Heritability of resistance to red rot, caused by Colletotrichum falcatum, 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 severity. Significant differences in susceptibility were detected, although high levels of resistance were rare in the breeding and selection populations of the Louisiana sugarcane cultivar development program. Narrow-sense heritability estimates determined by mid-parent-offspring regression for the different disease traits ranged from 0.19 +/- 0.04 to 0.31 +/- 0.05. Potential genetic gain by selection for resistance, using 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 heritabilities among years for the disease traits in the parent population. The range was from 0 to 0.42 +/- 1.07 on an entry basis. The results indicated that the population level of red rot resistance can be increased by careful choice of parent clones and cross-based selection. Genotype by 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.