An Approach to Screening for Resistance to Water and Heat Stress in Sorghum (Sorghum bicolor (L.) Moench)

Sorghum (Sorglttrm bicolor (L.) hlocnchl is an important food crop of thc arid and scmiarrd tropics but average yields are s t i l l bclow 1.000 kilograms per hcctare. and under drought conditions these may fall below 100 kilogranls per hectare or there may evcn be total crop failure. Breeding for drought ,resistance in sorghum is a complex problem. Th e ohjec~ivco f thi s paper is to drscribc the developnicnt of a screening technique. based on a "physiological approach." Itiitially. a sample of gcnotypes ucrc selected from the sorghum genetic rcsources acccs5ions at the lntcrnational Crops Research I nsti tute for the Semi - Arid Tropics (ICKISAT) Ccntcr 10 rr'prc=,cnt material collected from many countries over a range of altitudes (0 to 2.000 rnetcrs) and nwan annual rainfall (250 to 2 .SO0 niillimcters). covering most of the taxonomic groups. Some advanced hrccding materials were also included in this sample of over 700 lines. They were scrccncd undcr suvcre drought conditions at ICRISAT in thc relatively rain-free summers from 1983 to 19S5. Considerable genetic variation was shown in the response of these genotypes to ~.atcarn d heat stress. Visually observcd dillercnces in "resistant" and "susceptible" genotypes in tcrnis of desiccation tolerance or avoidance. recovery resistance and ability to produce grain after the onwt of rains was thcn shown to be associatcd with spccilic physiological traits. Sc'lcctcd physiological data from a fc\v contrasting genotypes wcrc shown on relati\'e leaf-watcr content (RL\VC). leafwater potential and lcaf stoniatal conductance (gl). Thcse results vcrify that the visual "resi~- tance" traits identificd earlier were bascd on measurable physiological responses. In conclusion. i t is argued that thc approach described has proved to be succcsslul in idcntifying drought-mistant germplasni. With more basic research on the same contrasting genotyps. the problcm of idcntifying drought-rc%istant sorghums could be largely ovcrcome