Maize in subtropics is grown in 17 million hectares around the world; 60% is planted to hybrid seed mainly in Mexico, China, India, Egypt, Zimbabwe and South Africa. Studies on heterosis and the combining ability of subtropical maize populations and pools were published by Vasal et al. (1987) and Beck et al. (1991); that information helped breeders identify superior germplasm sources to exploit heterosis for developing new superior inbred lines. CIMMYT strategies in hybrid breeding for the subtropics include five components: 1) Identification of heterotic patterns, 2) Formation of heterotic population complementary to each other, 3) Population improvement based on RRS, 4) Pedigree breeding based in elite x elite F2 populations and 5) Multilocation testing including stress environments. One of the most exciting accomplishment in germplasm development in CIMMYT's Subtropical Maize Subprogram has been the formation of population SIW-HG88A or Population 501 (subtropical intermediate white heterotic group "A") and SIW-HG88B or Population 502 (subtropical intermediate white hoterotic group "B"), which are highly heterotic to each other. These populations reflect our strategy of focusing on heterosis and complementarity between both parents, to ensure the usefulness of our products for hybrid development. To date, two cycles of RRS have been completed based on S2 x tester progenies evaluated at eight locations across the subtropical mega-environment; inbred parents from C1 were released in 1995. Further work on heterosis and combining ability of subtropical germplasm during 1993, 1994 and 1995 permitted the release of 19 new CML 's 1995 all of which were announced and made freely available to interested research partners, together with relevant information about their agronomic performance and combining ability. Many national programs and private seed companies are using this elite germplasm to assemble and release new hybrid combinations. Our strategy in breeding for stress environments has enhanced yield stability of the new subtropical hybrids. Single cross hybrid CML78xCML321 yielded 9.2 Mg ha-l across 20 locations from 1994 to 1996,20% more than the best seed industry checks. Hybrid CML216xMBR-Et(W)-14-Sg yielded 9.3 Mg ha-l outperforming the best seed industry check at individual locations and across location in Mexico, China, India and Zimbabwe during 1996-1997. This hybrid showed good resistance to SWCB, gray leaf spot, northern leaf blight, rust, ear and stalk rot, and maize streak virus. A new set of subtropical elite inbred parents (CML's) will be released in 1998.

English

0208|AGRIS 0201|AL-Maize Program|R01PROCE

CIMMYT Staff Publications Collection