Genetic Diversity and Drought Stress Tolerance of a Global Collection of Pearl Millet at Germination and Early Seedling Growth Stages

Pearl millet {Pennisetum glaucum (L.) R. Br} is a C4 panicoid cereal millet crop grown in arid and semi-arid regions in Africa and Asia for food and fodder. This study involves the evaluation of the genetic diversity of 28 worldwide germplasm collection of pearl millet by genetic markers polymorphism and drought tolerance indices. The genetic diversity was expressed by 51 alleles of 9 ISSR markers that showed 96.43% total polymorphism and 11.76 alleles per marker. Cluster analysis of ISSR markers polymorphism divided the 28 genotypes into four clusters partially in agreement with their origin. The application of drought stress simulated by 20% PEG₆₀₀₀ treatment, retarded the germination percentage, and reduced shoot and root length, seedling fresh and dry weights. Drought tolerance indices (DTIs) were calculated based on the response of the seedling traits under drought stress compared to the control seedlings. ANOVA revealed statistically significant variation among the genotypes (P ≤ 0.05), except for seedling fresh weight (P = 0.17 > 0.05) under control conditions and seedling dry weight (P = 0.99 > 0.05) under drought conditions. Genotypes having higher DTIs for three traits are regarded drought resistant, i.e., those from India, Ethiopia, Pakistan, and Nigeria. The calculated heritability values indicated that seedlings dry weight is the least trait affected by drought stress whereas root length is the most influenced trait. Hierarchical clustering, based on the DTI values, also grouped the genotypes partially concomitant to their origin. The correlation analysis demonstrated a modest positive correlation between shoot length and root length. A low correlation of r ≤ 0.12 was observed between the morphological DTI matrix and the genetic matrix. Nevertheless, high levels of genetic diversity were identified among the examined genotypes that may face genetic erosion by climatic constraints, and a high potential for creating agronomically superior cultivars by crossing widely divergent genotypes.