Effect of Water Deficit Stress on Reproductive Stage of Durum Wheat Near Isogenic Lines Carrying the NAM-B1 Gene

In wheat, the NAC family plays a crucial role in conferring cellular responses to different abiotic stresses, particularly drought. The functional NAM-B1 allele in durum wheat accelerates senescence, while its homologous genes contribute to improved water deficit stress tolerance. Therefore, the main objective of this study was to investigate the role of the NAM-B1 gene in durum wheat subjected to water deficit stress at two reproductive stages.

Three Near-Isogenic Lines carrying a functional NAM-B1 allele and their recurrent parent, Langdon (LDN), were used in this study. The study assessed NILs and LDN performance under varied water conditions (well-watered, 60%, and 80% water deficit of pot capacity) during flag leaf and anthesis stages. The agronomic performance of the three NILs and LDN was assessed for 16 traits, including plant height, grain yield, and thousand kernel weight. Additionally, physiological measurements, including stomatal resistance, chlorophyll content (SPAD values), and chlorophyll fluorescence (Fv/Fm) were taken.

Significant genotypic effects were observed on seven agronomic traits, while 15 traits were influenced by the water stress treatment. The NILs exhibited accelerated maturity and a shorter grain-filling period, which were particularly pronounced under stress conditions. Severe water deficit resulted in reduced grain weight and thousand-grain weight in tested genotypes. Interestingly NILs carrying functional NAM-B1 showed taller plants and had higher tiller and spike numbers when compared to LND. Significant genotypic effects were observed for seven traits, and water stress treatments affected 15 traits. The NILs exhibited accelerated maturity and reduced grain weight under severe water deficit. Physiological measurements showed genotype and water-deficit differences, with NIL #504 displaying higher SPAD values, particularly under stress conditions, and a significant genotype X treatment effect was observed for stomatal resistance at the anthesis stage.

Limited treatment × genotype interactions for most traits highlight the complexity of drought tolerance in the tested lines, which might be attributed to its quantitative nature influenced by multiple genes. The study emphasizes the necessity for future research to explore the role of other NAM-related genes in response to water deficit stress and their interactive effects with the NAM-B1 gene at different growth stages in wheat plants subjected to diverse stress conditions.

In conclusion, this study reveals pronounced genotypic effects, particularly in agronomic traits, such as maturation rate and grain filling period, under severe water deficit stress. Future studies are needed to understand the genetic mechanisms mediated by NAM-B1 genes in accelerating maturity in response to stress.