Abstract
The current perspective of increasing global temperature makes heat stress as a major threat to wheat production worldwide. In order to identify quantitative trait loci (QTLs) associated with heat tolerance, 251 recombinant inbred lines (RILs) derived from a cross between HD2808 (heat tolerant) and HUW510 (heat susceptible) were evaluated under timely sown (normal) and late sown (heat stress) conditions for two consecutive crop seasons; 2013–14 and 2014–15. Grain yield (GY) and its components namely, grain weight/spike (GWS), grain number/spike (GNS), thousand grain weight (TGW), grain filling rate (GFR) and grain filling duration (GFD) were recorded for both conditions and years. The data collected for both timely and late sown conditions and heat susceptibility index (HSI) of these traits were used as phenotypic data for QTL identification. The frequency distribution of HSI for all the studied traits was continuous during both the years and also included transgressive segregants. Composite interval mapping identified total 24 QTLs viz., 9 (timely sown traits), 6 (late sown traits) and 9 (HSI of traits) mapped on linkage groups 2A, 2B, and 6D during both the crop seasons 2013–14 and 2014–15. The QTLs were detected for GWS (6), GNS (6), GFR (4), TGW (3), GY (3) and GFD (2). The LOD score of identified QTLs varied from 3.03 (Qtgns.iiwbr-6D) to 21.01 (Qhsitgw.iiwbr-2A) during 2014–15, explaining 11.2 and 30.6% phenotypic variance, respectively. Maximum no of QTLs were detected in chromosome 2A followed by 6D and 2B. All the QTL detected under late sown and HSI traits were identified on chromosome 2A except for QTLs associated with GFD. Fifteen out of 17 QTL detected on chromosome 2A were clustered within the marker interval between gwm448 and wmc296 and showed tight linkage with gwm122 and these were localized in 49–52 cM region of Somers consensus map of chromosome 2A i.e. within 18–59.56 cM region of chromosome 2A where no QTL related to heat stress were reported earlier. Besides, three consistent QTLs, Qgws.iiwbr-2A, Qgns.iiwbr-2A and Qgns.iiwbr-2A were also detected in all the environments in this region. The nearest QTL detected in earlier studies, QFv/Fm.cgb-2A was approximately 6cM below the presently identified QTLs region, respectively Additionally, QTLs for physiological and phenological traits and plant height under late sown and HSI of these traits were also detected on chromosome 2A. QTL for HSI of plant height and physiological maturity were located in the same genomic region of chromosome 2Awhereas QTLs for physiological and phonological traits under late sown were located 8cM and 33.5 cM below the genomic location associated with grain traits, respectively in consensus map of Somers. This QTL hot-spot region with consistent QTLs could be used to improve heat tolerance after validation.
Highlights
Since 1980s global wheat productivity has reduced by as much as 5% due to increase in temperature roughly by 0.13 ̊C per decade since 1950[1,2]
The mean minimum and maximum temperature under late sown condition were higher from timely sown conditions by 2.7 and 4.2 ̊C (2013–14) and 1.1 and 0.9 ̊C (2014–15), respectively (S1 Fig)
Analysis of variance based on heat susceptibility index showed significant (p < 0.01) main effects due to genotypes for all traits studied during both the crop seasons 2013–14 and 2014–15 (Table 1)
Summary
Since 1980s global wheat productivity has reduced by as much as 5% due to increase in temperature roughly by 0.13 ̊C per decade since 1950[1,2]. IPCC predicted in 2012 [3] that the world daily maximum temperature will rise approximately 1.3 ̊C by middle and 2–5 ̊C by the end of 21st century. South Asia will face an increase of 1.54 ̊C in maximum and 1.08 ̊C in minimum temperature during rabi (wheat) season by 2020. It has been reported that eachC rise in temperature above cardinal causes reduction in grain filling duration by 2.8 days [8], grain numbers by 4% [9], gain weight by 5% [10] and grain yield by 3–4% [11]. In 2004, the country suffered a yield loss of 4.6 Mt due to the sudden increase in temperature during February [12]
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