Multivariate Analysis of Heat Stress Indices to Assess Bread Wheat ( <scp> <i>Triticum aestivum</i> </scp> L.) Germplasm Under Timely and Late Sown Conditions

ABSTRACT Heat stress severely impairs wheat yields and poses significant challenges to food security. In the present investigation, 72 diverse bread wheat genotypes were evaluated in the completely randomised block design with two replicates at four locations under normal and heat stress conditions during Rabi , 2022–23. The mean maximum temperature was above congenial (&gt; 25°C) at 27.9°C, 28.8°C, 33.4°C and 33.3°C at Karnal, Hisar, Niphad and Pune locations, which imposed adverse effects at the heading and grain filling stages. Under heat stress, the pooled mean grain yield varied from 294.8 g (DHTW60) to 660.2 g/plot (RWP2017‐21). The genotype DBW173 showed an 8.07% yield reduction under heat stress, followed by DBW187 (9.51%), PBW826 (10.25%), 29 th SAWYT‐303 (10.36%), Raj3765 (11.41%), and RWP2017‐21 (11.54%). The 1000 grain weight (TKW) reduction was also low for these genotypes, except for 29 th SAWYT‐303 (19.80%). Here, the yield stability index (YSI) and heat susceptibility index (HSI) ranged from 0.56 to 1.02 and −0.09 to 1.95, respectively. In contrast, the relative heat index (RHI) and percent yield reduction (PYR) varied from 0.73 to 1.31 and −1.99 to 43.63, respectively. The low HSI values (&lt; 0.60) were recorded for NIAW1342, HI1605, DBW173, DBW187, PBW826, 29 th SAWYT‐303, 20 th HTWYT‐2, Raj3765, RWP2017‐21, K7903 and K9465. PCA clustered 13 heat stress indices into three clusters, where TOL, HSPI, HSI and PYR were grouped into a single segment. The genotypes DBW173, DBW187, HI1531, HI1605, NIAW1342, PBW826, Raj3765, RWP2017‐21, 20 th HTWYT‐2, 20 th HTWYT‐13, 20 th HTWYT‐41, 29 th SAWYT‐303 and WAP96 appeared as heat tolerant. The higher TKW, grains/spike, coupled with higher NDVI values, can be used as selection criteria under heat stress breeding. The indices HSI, PYR, HRI, YI and YSI can be employed effectively in future studies.