Studies on utilization of tropical and subtropical maize germplasm --Liu, Z Four self-lines (Ye 107, Ye 8112, Huangying o2 and Qiqun 32) were crossed with tropical and subtropical maize germplasm (pool32, pool33, pool34 and population 70) ever since 1984. Exotic germplasms were introduced into temperate materials (above self-lines) according to different proportions (from 25% to 75%) for increasing genetic diversity, raising general combining ability (GCA) and resistance ability to disease and stress environments.

Three elite self-lines, YL1732, YL8234 and QIL3233, were bred by the above method in 1998. YL1732, a yellow semident self-line based on 75% subtropical germplasm and 25% temperate germplasm, was selected from 3 generations of inbreeding and 5 generations of self-inbreeding. Better performance was YL8234, an early maturing yellow flint self-line made up of 50% subtropical germplasm and 50% temperate germplasm. QIL3233, an intermediate to early maturing yellow dent material, was based upon inbreeding 4 generations and self-inbreeding 5 generations of temperate population 32 subtropical pool33. At present, these self-lines are used for breeding elite maize hybrids in summer planting corn region in China.

The evaluating experiments of selected self-lines in Jinan showed that disease indices of maize leaf blight (Helminthosporium turcicum Pass.) and leaf spot (Helminthosporium maydis Nisik.) decreased 61.5% to 78.9% and 53.8% to 69.4% respectively. Plant rates of maize stalk rots (Fusarium graminearum and moniliforme) and maize rough dwarf decreased 84.1% to 93.2% and 86.7% to 98.2%. Number of green leaves at maturity increased 2.6 to 4.4 times, and average grain yield also increased 20.0% to 55.6% respectively.
 
 


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