Abstract
The doubled haploid (DH) technology enables maize breeders to develop a large number of homozygous lines rapidly and test them in hybrid combinations early in the breeding cycle. The objectives of this study were to evaluate testcross performance of 556 DH lines derived from 10 diverse tropical backcross (BC1) populations, and to estimate variance components and broad-sense heritability under both well-watered and managed drought-stress conditions in Kenya. The 556 DH testcrosses were divided into six trials, with each trial comprising 84 to 126 entries and six commercial checks developed through conventional pedigree method. Trials were evaluated at 3 or 4 well-watered (WW) and two managed drought-stress (WS) sites in 2012 using an alpha lattice design with three replications per environment. Test crosses of the DH lines showed significant differences in grain yield and other agronomic traits. In the combined analysis across the WW locations, the top 10 DH testcrosses from each trial gave 0.6 to 32.7% higher grain yield than the best commercial check. Under managed drought-stress condition, the top 10 DH testcrosses from each trial gave 11.8 to 40.9% more grain yield than the best check. The best DH lines identified in the study could be used in tropical maize breeding programs in Africa for improving grain yield and drought-tolerance. Following evaluation in advanced testing and national performance trials (NPT), a total of 36 hybrids involving DH lines from this study were recommended for commercial cultivation in east and southern Africa. Key words: Africa, heritability, managed drought-stress, testcrosses.
Highlights
Maize is among the most important food crops in the world
The top 10 doubled haploid (DH) testcrosses in each trial were either similar (e.g. Trial 2) or gave 17.5 to 32.7% higher grain yield than the best commercial check; but they all performed better (28.1 to 54.8%) than the mean of the commercial checks (Table 3)
The 10 highest yielding DH testcrosses in each trial showed a difference of -1.2 to 3.8 days to flowering as compared to the best commercial check and up to 4.4 days delay in anthesis as compared to the mean of the commercial checks (Table 3)
Summary
Maize is among the most important food crops in the world. Together with rice and wheat, maize provides at least 30% of the food calories to more than 4.5 billion people in 94 developing countries (Shiferaw et al, 2011). Even though maize is the most important staple food for over 300 million people in the region. Between 2005 and 2008, the average maize yield was estimated at 1.8 tons per hectare (t/ha) as compared to 2.5 t/ha in the Philippines, 3.1 t/ha in Mexico and 3.9 t/ha in Thailand (Smale et al, 2011). Several factors could contribute to this low production, drought has been cited as one of the major factors that frequently limits maize production in SSA. Heisey and Edmeades (1999) estimated that 20 to 25% of the global maize production area is affected by drought in any given year
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