| dc.description.abstract | Drought, which is a major constraint to maize production in Kenya, is a difficult trait to breed for
in this crop. Conventionally, it takes 10-15 years of breeding to develop homozygous and
homogeneous inbred lines. Additionally, heavy funding and inputs are required to develop new
varieties. Doubled haploid (DR) technology which requires only 1-2 years to reach
homozygosity, is gaining rapid adoption in modem maize breeding programs. DR germplasm is
available in eastern and southern Africa awaiting commercial exploitation by the National
Agricultural Research Systems. This study was designed to i) evaluate the performance of maize
DH inbred lines under stress and non-stress conditions, ii) classify the DR lines into respective
heterotic groups iii) estimate combining abilities, heritability and correlation coefficients for
grain yield and yield associated traits in DR hybrids made from these lines and iv) assess
stability of performance of three-way DR hybrids. One hundred DR lines obtained from
International Maize and Wheat Improvement Center (CIMMYT) gene pool were test-crossed to
two single cross parents (CML312/CML442) and (CML395/CML444) in a North Carolina
design II fashion to generate 200 DR hybrids. Screening for good agronomic traits reduced these
harvested testcrosses to 160. An alpha-lattice design of 15xll with two replications was used to
evaluate the 160 DR hybrids together with three commercial checks and two local checks across
6 locations in Kenya under optimum, nanaged drought and random drought conditions during
2012-2013 growing seasons. Each two-row plot measured 5 m long spaced at 0.75 m between
rows and 0.25 m between hills. Data were collected on grain yield, days to anthesis, ear and plant
heights, ear and plant aspects, number of ears per plant, foliar diseases and grain moisture at
harvest and analyzed using SAS software. Ten DR inbred lines L36,L4, Ll3, Lll, Ls, L71, L9, L6S,
L64and LSI had positive and significant (p<0.001; 0.05) GCA effects for grain yield while best
sea estimates for grain yield were observed in thirteen DH testcross hybrids. The top ten DH
hybrids yielded 16 % higher grain than the best commercial check (7.7 tlha) under non-stress
conditions, while under drought stress these hybrids out yielded the best commercial check
(3.43 t/ha) by 62 %; a highly significant (p<0.001) amount. Outstanding DH hybrids across
various moisture regimes included entries 91, 116, 120,26 and 23. Significant location, genotype
and genotype x location effects were observed for grain yield, days to anthesis and anthesissilking
interval (ASI) under well-watered conditions. Although high heritability estimates were
observed under optimum conditions, heritability was greatly reduced under drought. However,
selection under drought could be greatly enhanced by using the secondary traits. The two single
cross testers successfully classified 24 DH inbred lines into heterotic group A, 47 to heterotic
groupB and nine (9) to HGAIB. It was concluded from these studies that DH lines have ability
to produce high grain yield and acceptable agronomic traits for commercial use. Further, the
identified best ten DH lines offer good parental sources for improved yield in hybrids under
drought conditions for commercial exploitation. It was therefore recommended that these lines
should be introduced into Kenyan breeding programs. | en_US |
