Differences in growth properties between near-isogenic wheat lines carrying different types of vrn-d1 in the genetic background of two early cultivars

Near-isogenic wheat lines NILs, carrying different alleles of vernalization response gene Vrn-D1 spring-type and wintertype NILs in the genetic background of two early wheat cultivars, were grown in early, normal and late seasons. Spring-type NILs reached the double ridge formation stage 109-112°C days earlier than the winter-type NILs in early-sown fields, and 88-102°C days earlier in normal-sown fields. Spring-type NILS reached the terminal spikelet formation stage 113-214°C days earlier than the winter-type NILs in early-sown fields, and 30-98°C days earlier in normal-sown fields. However, the time of young spikelet development was the same in both winter-and spring-type NILs in late-sown fields, where the temperature after sowing was under 12°C. The absolute value of the slope of the regression line showing the relationship between the number of days and average temperature from sowing to the double ridge formation stage was lower in the winter-type NILs than in the spring-type NILs, though the absolute value from the double ridge formation to terminal spikelet formation stage was the same. In early and normal-sown fields, the jointing stage of spring-type NILs was earlier than that of winter-type NILs, but there were no such differences in the flowering and maturity stages. Therefore, the acceleration effects of Vrn-D1 were prominent until around the terminal spikelet formation stage and jointing stage but became unremarkable from the heading to maturity stages under early and normal-sown field conditions, where the temperature after sowing was roughly over 12°C.