Identification of Quantitative Trait Loci for Anthesis_Silking Interval under Flowering Water Stress using SSR Markers in selected Kenyan Maize

Abstract

Drought is an important climatic phenomenon, which is the most severe limitation to maize production in developing countries. Maize (Zea mays L.) is particularly sensitive to water stress at reproductive stages, and breeding to improve drought tolerance has been a challenge. When drought occurs just before or during the flowering period, it results in delayed silking and a consequent increase in the length of anthesis-silking interval (ASI). Selection for a reduced ASI has shown correlated response to improved grain yields under drought. However, conventional selection has been limited by the difficulty in managing uniform experimental conditions to eliminate environmental effects and their possible interactions with the genotype. In this study, SSR (Microsatellite) molecular markers were used to identify genomic regions responsible for the expression of ASI using bulked segregant analysis (BSA). This would enable develop marker assisted selection (MAS) strategies. An F; population of 203 individuals was developed from a cross between drought susceptible (KCB) and drought tolerant maize landraces (GBK 032357) and they were screened under drought to categorize into drought tolerant and drought susceptible. Based on the BSA procedure, the DNA from l0 most drought tolerant and 10 most drought susceptible plants based on ASI values were used to make DNA pools. These DNA pools and DNA from parents were assayed at 109 loci. A confirmation of polymorphic candidate markers on these 20 individuals revealed four genomic regions associated with ASI. These were regions near markers p-umc2l89, p-bnlgl179 and p“bnlglOl4 on chromosome l and p-urncl542 on chromosome 2. Together, the candidate QTLs accounted for about 65% of the observed variation for ASI. Significant phenotypic correlations among flowering parameters, grain yield and yield components were observed. Overlaps between the corresponding candidate QTLs were observed. For instance, markers, p-umc2l89 and p-bnlg10l4 showed significant association with days to silking (DS) whereas markers, p-bnlgl 179 and p-umcl542 showed significant association with both kemel number (KN) and grain yield (GY). This finding indicated pleiotropism between loci for ASI and DS, KN and GY. The generated information will enable formulation of Marker Assisted Selection for drought tolerance in maize.