Abstract
Photosynthates generated after heading contributes to 60% - 80% of grain yield in rice. Delay in leaf senescence can contribute to a long grain-filling period and thereby increased yield. The objective of this study was to identify genomic region(s) responsible for delayed leaf senescence (DLS) and validate the role of underlying candidate genes in controlling target traits. 302 BC2F4 backcross-derived lines (BILs) developed from a cross between Swarna and Moroberekan were phenotyped for two seasons (DS2016 and WS2017) for chlorophyll content and yield parameters. KASPar-SNP assays based genotyping data with 193 SNPs of mapping population was used to identify the targeted genomic region(s). Significant positive correlation was observed between the two most important determinants of DLS traits viz., RDCF (reduced decline degree of chlorophyll content of flag leaf) and RDCS (reduced decline degree of chlorophyll content of second leaf) with plant height (PH), grain number per panicle (GPN), panicle length (PL), number of tiller (NT) and grain yield (GY). A total of 41 and 29 QTLs with phenotypic variance (PVE) ranging from 8.2 to 25.1% were detected for six DLS traits during DS2016 and WS2017, respectively. Out of these identified QTLs, 19 were considered as stable QTLs detected across seasons. 17 of the identified stable QTLs were found to be novel. In-silico analysis revealed five key genes regulating chlorophyll metabolism. Expression analysis of these genes confirmed their strong association with the senescence pattern in leaf tissue of parents as well as selected phenotypically extreme lines. The identified stable QTLs regulating DLS traits and validation of potential candidate genes provides insight into genetic basis of delayed senescence and is expected to contribute in enhancing grain yield through genomics-assisted breeding (GAB).
Highlights
Rice is one of the world’s most important food crops, especially in the developing world
Phenotypic characterization of population for delayed senescence trait The SPAD value of flag leaf (FL) and second leaf (SL) was high at heading and thereafter decreased in parents and in the mapping population lines. This reduction was faster in FL of Moroberekan (30.7% reduction) as compared to Swarna (13.7% reduction), similar trend was observed in the case of SL viz. Moroberekan (30.3% reduction) and Swarna (18.5% reduction)
Ten stable QTL regions were identified for six delayed senescence traits
Summary
Rice is one of the world’s most important food crops, especially in the developing world. Rice production has steadily increased during the green revolution, but in recent years the rate of increase in grain yield has substantially reduced [1]. To increase grain yield in cereal crops, source strength needs to be increased so that sink organs can be more efficiently filled via efficient nutrient translocation. Delay in the onset of leaf senescence or slower degradation of chlorophyll content and photosynthetic activity is expected to extend the assimilatory capacity of the canopy thereby contributing to higher grain yield [2]. Due to its role in the efficient use of nutrients, which is essential for high crop yields, senescence has attracted special interest especially in monocarpic plants. Breeding for delayed leaf senescence (stay-green) traits could be of strong interest to crop breeders
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