Genetic diversity, stability, and combining ability of maize genotypes for grain yield and resistance to NCLB in the mid-altitude sub-humid agro ecologies of Ethiopia.
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2013
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Abstract
Maize (Zea mays L.) is the third most important cereal crops in the world after wheat
and rice. In Ethiopia, maize remains the second largest food security crop after tef
[Eragrostis tef (Zucc.) Trotter.]. The mid-altitude, sub-humid agro-ecology (1000 to 1800
m above sea level) is the most important maize producing environment in Ethiopia.
However, productivity of maize is low, due to several biotic and abiotic constraints.
Among the biotic constraints, Turcicum leaf blight disease of maize caused by
Exserohilum turcicum Pass Leonard & Suggs shows high incidence of 95-100% and
inflicts significant grain losses in the country. Therefore, high yielding, Turcicum leaf
blight resistant and farmers-preferred maize varieties and their production technologies
should be developed and made available to growers to enhance maize production and
to achieve food security.
The objectives of this study were to: (1) assess farmer’s preferences, and production
constraints for maize in the mid-altitude, sub-humid agro-ecology of western Ethiopia,
(2) determine the genetic variability among elite maize inbred lines and select promising
parents for resistance to E. turcicum, (3) determine diversity among the elite germplasm
lines using SSR markers, (4) determine combining ability and heterosis among elite
maize inbred lines and their hybrids, and (5) investigate genotype x environment
interaction and yield stability of experimental maize hybrids developed for the midaltitude
sub-humid agro-ecology of Ethiopia.
A participatory rural appraisal (PRA) research was conducted involving 240 maize
farmers in three representative maize growing zones of western Ethiopia; West Shoa,
East Wollega and West Wollega, each represented by two districts and two subdistricts.
Maize was ranked number one both as food and cash crop by 82.9% of
respondents. Turcicum leaf blight was ranked as number one devastating leaf disease
by 46% of respondents. Breeding for improved disease resistance and grain yield,
enhancing the availability of crop input and stabilizing market price during harvest time
were recommended as the most important strategies to increase maize production by
small-scale farmers in western Ethiopia. Fifty inbred lines were evaluated for reaction to Turcicum leaf blight during the main
cropping seasons of 2011 and 2012. Inbred lines were clustered into resistant
(CML202, 144-7b, 136-a, 139-5j, 30H83-7-1, ILOO’E-1-9, SZYNA-99-F2, and 142-1-e),
and susceptible (CML197, CML464, A7033 , Kuleni C1-101-1-1, CML443, SC22-430
(63), (DRB-F2-60-1-2) – B-1-B-B-B, Pool9A-4-4-1-1-1). Inbred lines (CML312, CML445,
Gibe-1-158-1-1-1-1, CML395, and 124-b (113)) had intermediate response to the
disease. Overall, inbred lines such as CML202, 30H83-7-1, ILOO’E-1-9-1, CML312,
CML395 CML445 and 142-1-e were selected with better agronomic performance and
resistance to leaf blight for breeding. Twenty selected elite parental inbred lines were
genotyped with 20 polymorphic SSR markers. The genotypes used were clustered into
five groups consistent with the known pedigrees. The greatest genetic distance was
identified between the clusters of lines CML-202 and Gibe-1-91.
Eighteen selected inbred lines were crossed using the factorial mating scheme and 81
hybrids developed to determine combining ability effects and heterosis. Inbred lines with
high GCA effect (CML 202, CML395, 124-b (113), ILOO’E-1-9 and CML 197) were
selected as best combiners for hybrid development. Additionally five high yielding novel
single cross hybrids with grain yield of > 8 t ha-1 and high SCA effects were identified
such as CML395 X CML442, DE-78-Z-126-3-2-2-1-1 X CML442, ILOO’E-1-9-1-1-1-1-1
X CML312, X1264DW-1-2-2-2-2 X CML464 and SC22 X Gibe-1-91-1-1-1-1. These
experimental hybrids are recommended for direct production or as hybrid testers for
hybrid development.
Genotype x environment interaction (GEI) effects of 81 newly developed and three
check maize hybrids were evaluated across 10 locations in the mid-altitude sub-humid
agro-ecologies of Ethiopia. The AMMI-3 and GGE biplot models were used to determine
stability. Hybrids such as G68, G39, G37, G77, G34 and G2 were identified as the most
stable and high yielding at favorable environments such as Bako, Jima, Arsi Negelle
and Pawe in Ethiopia. The genotype and genotype by environment interaction (GGE)
biplot clustered the 10 environments into three unique mega-environments. Environment I included Bako, Jima, Asossa, Ambo, Finote Selam, Haramaya and Pawe
while environment II represented by Arsi-Negelle and environment III Areka and
Hawassa.
In general, the study identified valuable maize inbred lines with high combining ability
for breeding and novel single cross hybrids for large-scale production or as testers for
hybrid development at the mid-altitude, sub-humid agro-ecologies of Ethiopia or similar
environments in sub-Saharan Africa.
Description
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
Keywords
Corn--Breeding--Ethiopia., Corn--Diseases and pests--Ethiopia., Corn--Disease and pest resistance--Genetic aspects., Corn--Yields--Ethiopia., Corn--Varieties--Ethiopia., Fungal diseases of plants--Ethiopia., Theses--Plant breeding.