earliness, yield, and yield components of bread wheat under well-watered and rain-fed conditions: the role of the ppd-d1a gene

Objective: earliness is a critical trait for wheat grown under conditions of end-season heat and drought stress. heading time is influenced by three groups of genes, including photoperiod (ppd), vernalization (vrn), and earliness per se (eps). ppd-d1 is an important tool for marker-assisted selection and backcrossing programs. although the effect of ppd-d1a on earliness is well-documented, its impact on yield, yield components, and other key agronomic traits remains a subject of debate. in this study, near-isogenic lines for ppd-d1a were developed in two genetic backgrounds: roshan and kalheydari cultivars. the primary aim was to examine the effect of ppd-d1a on earliness, yield, and yield components.methods: isogenic lines from the kalheydari and roshan cultivars were evaluated under both well-watered and rain-fed conditions in two distinct locations of kerman and sepidan, iran, during two successive growing seasons (2020-2022). at each location, the experimental design was a randomized complete block design with four replications. then, several agronomic characteristics such as days to heading, days to maturity, grain filling period, plant height, peduncle length, grain yield, spike number per square meter, grain number per spike, 1000-grain weight, and spike length, were measured.  results: when compared to the ppd-d1b allele, which is photoperiod-sensitive, the ppd-d1a allele, which is photoperiod-insensitive, reduced days to heading and maturity by 5.14 and 7.53 days, respectively. the results also indicated that ppd-d1a led to a 14% decrease in grain number per spike, while it increased 1000-grain weight by 17% and grain yield by 13% under rain-fed conditions. however, the effects of ppd-d1a differed significantly under well-watered conditions, where it decreased 1000-grain weight by 18% but increased grain number per spike by 10%, with no significant effect on the grain yield.conclusion: these findings suggest that the impact of ppd-d1a on yield and yield components is strongly influenced by the specific environmental conditions in which the wheat is cultivated.