Evaluation of Sunflower Genotypes for Terminal Heat Stress Tolerance Using Yield-Based Indices and Multivariate Analysis

• Hussein Tuama Abbood

  Author

Heat stress (HS) is a major problem for sunflower production at the global level due to the effects of climate change. In this study, ten sunflower genotypes were compared to determine elite heat-tolerant ideotypes and gain insight into the association between traits under terminal heat stress. The experiment was carried out at the Karbala Research Station/Extension Farm, Iraq, in 25^th July of 2025. The evaluated genotypes, comprising elite hybrids, commercial varieties, and breeding lines, included AKSF-9 (T1), COSFV-5 (T2), CMS-234A (T3), KBSH-44 (T4), PAC-36 (T5), EC-68414 (T6), DRSH-1 (T7), ARM-248B (T8), RHA-274 (T9), and CMS-108B (T10). The two contrasting sowing environments were used to subject the plants to terminal heat stress at the reproductive stage in a Randomized Complete Block Design. The ANOVA, Pearson correlation, PCA, and hierarchical clustering were used for the analysis of morpho-physiological, yield, and stress-tolerance indices. There was considerable genotypic variation between the environments tested. Under stress, the vegetative vigor, the earliest phenological development (heat escape), and the oil yield (60.5 g/plant) were significantly greater between the two genotypes, T7 (DRSH-1) and T4 (KBSH-44), than the other genotype under the three stress levels. Under stress, vegetative vigor, earliest phenological development (heat escape), and highest seed (127.0 g/plant) and oil yield (60.5 g/plant) were significantly higher in the two genotypes T7 (DRSH-1) and T4 (KBSH-44) than in the other genotype at all stress levels. They had the lowest SSI (0.407 and 0.527) and the highest Heat Tolerance Index. On the other hand, T6, T10, and T3 were very sensitive. Good positive correlations were observed between yield and tolerance traits, with negative correlations with stress penalty metrics, using Pearson correlations. The PCA and hierarchical clustering showed similar results and well clustered the genotypes into tolerant, moderate, and susceptible groups, with T7 having the highest heat-tolerant score based on composite response. Based on this, two genetic materials (T7 and T4) were identified as potential and resilient germplasm for direct cultivation in heat-sensitive agroecosystems and as parental lines in breeding programs, and thus require further testing in multi-environment trials.

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