Development of High-Yielding and Stable Maize (Zea Mays L.) Hybrids Tolerant To Low Soil Nitrogen
Date
2015-12
Authors
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Publisher
University of Ghana
Abstract
Maize is Ghana’s most important cereal crop and is grown by the vast majority of
rural households. It is widely consumed throughout the country, and is the second
most important staple food in Ghana, after cassava. Low soil nitrogen (N) impedes
maize production in the small-scale farming sector in Ghana. Development of
improved maize varieties that are tolerant to low soil N will reduce the need for
nitrogen inputs and enhance production. The objectives of this study were to (1)
assess maize production constraints of Ghanaian maize farmers, and their
perceptions and knowledge on soil fertility, (2) determine heterotic groups and
combining ability of grain yield for intermediate maturing maize inbred lines under
low and high soil N environments, (3) determine the mode of gene action
conditioning grain yield under low N, (4) evaluate the testcrosses (single cross
hybrids) for high yield, stability and tolerance to low and high soil N and (5)
identify and map Quantitative Trait Loci (QTL) for grain yield (GY) and secondary
traits under high N and low soil N.
A Participatory Rural Appraisal (PRA) was conducted among 120 farmers in six
communities in the forest savanna transition agro-ecological zone of Ghana using
Focus Group Discussion (FGD) and semi-structured interview. Thirty-two inbreds
received from Institute of Agricultural Research for Development (IRAD),
International Institute of Tropical Agriculture (IITA) and International Maize and
Wheat Improvement Center (CIMMYT) were crossed to three elite testers (87036,
1368 and 9071) in a line x tester scheme to generate 96 F1 hybrids. The 96 F1
hybrids along with 4 checks were evaluated under low N (30 kg ha-1) and high N(90 kg ha-1 N) soil environments at three locations in Ghana in 2013 and 2014. One
hundred and fifty BC2F1 families in a mapping population (CML 444 x CML 494)
were used to identify SNP markers associated with quantitative trait loci (QTLs) for
yield and yield related traits under low N and high N environments.
The PRA revealed low soil fertility, drought, pests and diseases as the major maize
production constraints. Most farmers grow improved varieties but, have very little
knowledge about hybrids. Farmers preferred low N and drought tolerant varieties
with good storability that are disease and insect resistant and require low inputs.
They also indicated preference for slender cobs, light in weight with lots of grains.
Evaluation of hybrids and inbreds showed genetic variability for grain yield and
secondary traits. Significant GCA and SCA effects for grain yield and most
measured traits were detected with predominance of GCA effects over SCA effects,
indicating that most traits were controlled predominantly by additive gene action.
Hybrids CLWN 247 x 9071, ZM523B-29-2-1-1-B*6 x 9071, TZD II 68 x 1368, and
P43SCRq Fs100-1-1-8 x 9071 were identified as high yielding, and low N tolerant.
These are recommended for further testing for potential release to farmers in low
soil N environments. Seven hybrids (CZL 00001 x 9071, LapostaseqC7-F18-3-2-1
x 9071, CLWN 364 x 9071, CLWN 247 x 9071, CLWN 247 X 87036, TZD II 68 x
1368, and CML 395/CML 444 x 9071) were among the 20 best yielding hybrids
across environments. These are candidates for further testing for commercialization.
Based on SCA of grain yield, HGCAMT and HSGCA methods for heterotic
classification, the lines were classified into three heterotic groups for each
environment. The inbreds in each heterotic group may be recombined to form
populations which could be improved through recurrent selection. Subsequently,
inbred lines could be extracted from each population for the production of superior
hybrids and synthetics by selfing and crossing onto an inbred tester of opposing
heterotic group. The GGE biplot analysis revealed CML 395/ CML 444 x 9071 and
TZDII 68 x 1368 as the most high yielding and stable hybrids. These hybrids should
also be further tested in multi-location trials and promoted for release. A total of 13
QTLs were identified with 158 SNP markers for six different traits (grain yield,
days to silking, stay green characteristic, ears per plant, anthesis silking interval and
plant height) under low N environment (9 QTLs) and high N environment (4
QTLs). Five QTLs (qgy-1, qts-1, qsg-1, qsg-4 and qasi-6) for GY, DTS, SG, ASI
and EPP, respectively, were close to their adjacent markers, with an interval of 0.7
to 5.2 cM between them and explained phenotypic variance of 9% to 21%.
Description
Thesis(PhD)- University of Ghana, 2015
Keywords
Maize, High-Yieldin, Hybrid, Hybrid