An in vitro screening technique for the identification of grain mould resistance in sorghum

Grain mould (GM) is the most important biotic constraint of sorghum (Sorghum bicolor) in India and other parts of the world and host plant resistance is the most convenient method of control of this disease. Breeding for disease resistance has been slow due to the total reliance on field screening which is used once a year during rainy season. To conduct screening independent of season and to detect possible escapes from field screening, an in vitro screening technique has been developed. The technique involves dip inoculation of mature seed in a mixed spore suspension (1 x 106 spores ml-1) of major GM fungi (Fusarium moniliforme [Gibberella fujikuroi], F. pallidoroseum and Curvularia lunata [Cochliobolus lunatus]), transfer of inoculated seeds to the pre-sterilized Petri dish humid chamber at 25 seeds plate-1, and their incubation at 28±1°C with or without light for 5 days. Visual evaluation of mould infection was done on a 1-9 scale (where 1=no colonization and 9= > 75% seed surface colonization by the mould fungi) using an illuminated magnifier. The efficiency of the technique was measured by comparing the mean grain mould scores (MGMS) of 43 accessions evaluated at Bhavanisagar, Mysore and Patancheru in India.There was a significant correlation (P < 0.01) between in vitro MGMS and field scores at or across three locations. Of the 66 photoperiod-sensitive accessions that were screened using the in vitro screening, 14 showed high level of resistance even under field disease nursery situation. The usefulness of the technique in GM resistance programme is discusse