APPLICATION OF A MODIFIED COMPREHENSIVE BREEDING SYSTEM FOR MAIZE (ZEA-MAYS L) IN CAMEROON

A modified form of the ''comprehensive breeding system'' was implement ed in the mid-altitude zone of Cameroon for the formation of single-cr oss hybrid and open-pollinated synthetic cultivars of maize (Zea mays L.). Reciprocal source synthetics were formed from segregating inbred lines selected for combining ability for yield and ether agronomic tra its, and for line per se performance. New lines were extracted from th e source synthetics and from their crosses with introductions. Lines w ere evaluated in testcrosses with 1 single-cross testers at the S3 sta ge of inbreeding, and in single-cross hybrids at the S4-S6 stages. The best single-crosses were further evaluated for commercial release. Li nes selected per se and from combining ability trials were recycled th rough the reciprocal synthetics. A synthetic cultivar was formed each year by intermating selected inbreds from bath reciprocal groups. The principal modifications to the comprehensive breeding system were to i ncorporate new germplasm annually into the reciprocal synthetics as in breds preselected for combining ability and line per se performance, a nd to re-form the reciprocal synthetics on an annual rather than full- cycle basis, permitting new groups of inbreds to be extracted and test ed each year. Results indicated that: 1) Single-cross hybrids equal or superior to the best available check in all agronomic traits were obt ained. 2) The performance of synthetic cultivars exceeded or equalled the best alternative open-pollinated cultivars for all traits evaluate d. 3) The formation of superior hybrid and open-pollinated cultivars f rom a common selection program indicates that it is not necessary to m aintain separate selection populations for the two cultivar types.