Stability of Sorghum Midge Resistance1

Abstract

Eight sorghum (Sorghum bicolor (L.) Moench) entries which are claimed to be resistant to sorghum midge (Contarinia sorghicola Coq.), were studied at different levels of midge populations on 16 planting dates. The midge population was maintained all year on sorghum and wild sorghum (verticilliflorum) (Stendel) stapf.) at Serra Talhada Research Station, Pernumbuco, Brazil. Adult emergence data were analyzed using the stability technique that will be described in Materials and Methods. Stability was described by the average number of insects from a random sample of exposed heads and by the regression of the average number of adults on an environmental index (in this case environments being different seasons). A stable line should have: a low average adult emergence; a regression coefficient equal to or near zero; the deviations from regression as small as possible. Sorghum line ‘AF‐28’ was shown to be most stable source of resistance tested. Two selections (IS 2757C and IS 2508C) from the Cooperative Texas Sorghum conversion program showed moderate stability. Other sources of midge resistance were less stable over planting dates. The linear regression technique adequately describes the stability of entries over a range of midge populations and environments. This technique facilitates the breeder in his search for adequate sources of resistance to different pests.