RESPONSE OF SOME COMMERCIAL MAIZE HYBRIDS AND THEIR PARENTS TO DOWNY MILDEW DISEASE AND YIELD LOSSES

Abstract

Thirty four white and yellow maize (Zea mays L.) inbred lines and hybrids were evaluated to downy mildew disease caused by Peronosclerospora sorghi (Weston and Uppal) C.G. Shaw. This study was performed in 2006 -20007 growing seasons at Gemmeiza Agricultural Research Station, El-Gharbea Governorate, Egypt. Out of the white maize genotypes, only the inbred lines Gm.22 and Gm.21were highly resistance( 0 and 0.48% disease infection, respectively) . The other inbred lines showed infection types ranged from resistance (Gm.4 and Gm.30), moderate resistance (Gm.14, Gm.27 and Sd.7). Both of Gm.2 and Sd.63 showed moderate to susceptible infection types. The white hybrids (S.c.11, S.c.12, S.c.13, S.c.14 and S.c.26 ) were moderately resistant, while, hybrids S.c.21, S.c.22, S.c.27, T.w.c.321, T.w.c.325 and T.w.c326were moderately susceptible then hybrids S.c.10, S.c.15, S.c.25, T.w.c.322 and T.w.c.327were susceptible. It can be concluded that inbred lines Gm.4, Gm.21, Gm.30 and Sd.7 play a role in conferring resistance in their hybrids and could be considered as sources of resistance to downy mildew. All the tested yellow maize inbred lines and hybrids showed moderately susceptible, and susceptible infection types. Losses in grain yield were in a parallel line with disease infection. The yellow maize genotypes scored the highest percentage of yield reduction compared with the white genotypes . All of the white inbreds and hybrids showed losses in grain yield except the inbred line Gm.22. The highest % of grain yield losses were detected in the inbred lines Sd.63 and Gm.2 (31.19 and 21.22%, respectively) as well as the hybrids S.c.10 (34.48%), S.c.21 (31.61%) and S.c.26 (31.26%). Concerning with yellow maize genotypes, the highest losses % were noticed in the inbred lines 1021 and 1002 (66.11 and 64.85%, respectively) as well as the hybrids T.w.c. 352 (87.47%), S.c.52 (63.79%), S.c.155 (73.77%) then T.w.c351 (51.93%).