Abstract
Shoot fly (Atherigona naqvii) is one of the major insects affecting spring maize in North India and can cause yield loss up to 60 per cent. The genetics of insect resistance is complex as influenced by genotypic background, insect population and climatic conditions. Therefore, quantitative trait loci (QTL) mapping is a highly effective approach for studying genetically complex forms of insect resistance. The objective of the present study was to dissect the genetic basis of resistance and identification of genomic regions associated with shoot fly resistance. A total of 107 F2 population derived from the cross CM143 (resistant) x CM144 (susceptible) was genotyped with 120 SSR markers. Phenotypic data were recorded on replicated F2:3 progenies for various component traits imparting resistance to shoot fly at different time intervals. Resistance to shoot fly was observed to be under polygenic control as evidenced by the identification of 19 putative QTLs governed by overdominance to partial dominance and additive gene actions. The major QTLs conditioning shoot fly resistance viz., qDH9.1 (deadheart) and qEC9.1 (oviposition) explaining 15.03 and 18.89 per cent phenotypic variance, respectively were colocalized on chromosome 9. These QTLs are syntenic to regions of chromosome 10 of sorghum which were also accounted for deadheart and oviposition suggesting that the same gene block may be responsible for shoot fly resistance. The candidate genes such as cysteine protease, subtilisin-chymotrypsin inhibitor, cytochrome P450 involved in synthesis of alleochemicals, receptor kinases, glossy15 and ubiquitin-proteasome degradation pathway were identified within the predicted QTL regions. This is the first reported mapping of QTLs conferring resistance to shoot fly in maize, and the markers identified here will be a valuable resource for developing elite maize cultivars with resistance to shoot fly.
Highlights
Maize is the third most important cereal crop after wheat and rice in terms of area and production having diversified uses as food, feed and a range of industrial products
Plant morphology has a strong impact on shoot fly damage, especially seedling characteristics that physically reduce feeding, oviposition, and shelter
The distribution of leaf injury (LI) and DH data at 21 days after emergence (DAE) revealed that the response of F2:3 families followed a normal curve with transgressive segregation in both directions (Fig 1)
Summary
Maize is the third most important cereal crop after wheat and rice in terms of area and production having diversified uses as food, feed and a range of industrial products. The continuous planting of maize throughout the year has led to increased incidence of shoot fly (Atherigona species) at seedling stage [2]. Sixteen shoot fly species have been reported on maize in Africa and Asia [3], of which A. naqvii Steyskal (Muscidae: Diptera) is most prevalent in North India [4] and reported to cause a loss of about 28–45 per cent in grain yield during spring season in the Indian Punjab [2]. The maggots of shoot fly attack the whorl leaves of emerging seedlings causing deadheart while curled and distorted leaves are formed in bigger plants. Shoot fly is not exposed to insecticides in maize as the larvae feed inside the leaf whorls
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