DEVELOPMENT OF SCREENING METHODS AND IDENTIFICATION OF STABLE RESISTANCE TO ANTHRACNOSE IN SORGHUM

Effective greenhouse- and field-screening techniques were developed to identify resistance to anthracnose (Colletotrichum graminicola) in gr ain sorghum (Sorghum bicolor). In greenhouse screening, sorghum plants were spray-inoculated at the 6-8 leaf stage with a conidial suspensio n (4 x 10(5) conidia ml-1) of C. graminicola. Inoculated plants were i ncubated in a high humidity chamber (greater-than-or-equal-to 90% RH) for 24 h at 25-28-degrees-C and relocated to a greenhouse at 25 +/- 2- degrees-C. Anthracnose development was scored 7-8 days after inoculati on. In the field-screening technique, in every fifth row, a highly ant hracnose-susceptible sorghum line was sown as an infector row. Ten day s later, test lines were sown between infector rows, and infector row plants were inoculated at the 6-8 leaf stage with either spore suspens ion or by dropping infected sorghum grains into the leaf whorl. High h umidity was provided by frequent overhead sprinkler or furrow irrigati on. Test lines were scored for anthracnose development at the hard-dou gh stage. Significant positive correlation (r = 0.88, P < 0.001) was f ound for anthracnose severity between seedling screening in greenhouse and adult plant screening in the field. The field-screening technique was successfully transferred to several locations in Africa and India . Thirty lines were selected from more than 13 000 sorghum germplasm a ccessions and advanced breeding lines screened for anthracnose resista nce, using the field-screening technique at Pantnagar (North India) be tween 1982 and 1991. They were evaluated in multilocational tests at h ot spots in Burkina Faso, India, Nigeria, Zambia, and Zimbabwe for 1-1 0 years. Eleven lines (A 2267-2, IS 3547, IS 8283, IS 9146, IS 9249, I S 18758, SPV 386, PB 8892-2, PS 18601-3, PM 20873-1-3, and M 35610) sh owed stable resistance across these locations over the years. Some of the resistant lines are being converted into male-sterile lines throug h backcrossing with different sources of cytoplasmic male sterility.