UV-B Orchestration of Growth, Yield and Grain Quality Traits Highlights Modifications of Source-to-sink Relationship in Pearl Millet Cultivars

Climate change and stratospheric ozone layer dynamics have altered the intensity of ultraviolet B (UV-B) radiation, affecting the growth, yield, and metabolic responses of major cereal crops. As a result, to meet the future demand scenario for growing population and health concerns, millets have been recognized as important substitutes. Among them, pearl millet has shown resilience against various abiotic stresses, but its response to UV-B radiation has not yet been explored. Recognizing its importance in present global food systems, the present investigation aimed to analyse the effect of elevated UV-B (eUV-B; ambient+7.2 kJmd) on four cultivars (HHB-272, HHB-67, MPMH-21, and MPMH-17) of pearl millet during panicle development stage and grain filling stage under natural field conditions. The results indicated that UV-B stress altered growth morphology (plant height, number of leaves, leaf area, and panicle length) at both stages, with less pronounced effects on cultivars HHB-272 and HHB-67. Declined growth indices [relative growth rate (RGR), absolute growth rate (AGR), net assimilation rate (NAR), and leaf area ratio (LAR)] at panicle stage revealed predominance of UV-B stress. Grain yield was positively affected in all the cultivars, indicating better resource allocation to different important needs, thereby altering the trade-offs between growth and development as reported in our present study. The grain quality (total soluble sugars, reducing sugars, total free amino acids, starch content, soluble protein) of harvested seeds exhibited a decreased quality response index, and metabolic pathway analysis of the metabolites identified through UHPLC-HRMS indicated a shift in photoassimilates towards fatty acid biosynthesis. These findings help to understand various plant metabolic pathways, potentially revealing the resilience mechanism involved in pearl millet under eUV-B exposure.