Temperature as a component of the expression of developmental responses in wheat

Summary Studies were made of days to ear emergence under the constant temperatures of 9, 14, 19 and 25°C and 16 h photoperiod in three sets of wheat lines each possessing genotypes differing for developmental responses.Days to ear emergence in three near-isogenic lines of the wheat cultivar Triple Dirk, which differed for vernalization response, increased as the strength of the response increased. At the four temperatures Triple Dirk D (Vrn 1 vrn 2) was not significantly different from normal Triple Dirk (Vrn 1 Vrn 2) but Triple Dirk B (vrn 1 Vrn 2) was significantly (P=0.01) later than normal Triple Dirk at each temperature. This indicates that the vrn 1 allele confers stronger vernalization response than vrn 2 over the range of temperatures (9–24°C). However, Triple Dirk C (vrn 1 vrn 2) failed to head after 120 days at each temperature indicating strong interaction between vrn 1 and vrn 2 with each other (and possibly the Triple Dirk back-ground) to give a much stronger vernalization response than predictions from additivity of their individual effects.The second set comprised the four Chinese Spring/Thatcher chromosome substitution lines CS/T 3B, 6B, 7B and 5D, plus Chinese Spring and Thatcher, and were grown in the unvernalized condition. CS/T 5D was similar in days to ear emergence as Chinese Spring at all four temperatures but the other three lines were earlier to ear emergence, particularly as the temperature increased. Days to ear emergence was fastest at 14°C in all lines, except CS/T 3B, in which it decreased progressively from 9 to 24°C.The third set of Chinese Spring and Thatcher and the homoeologous group 2 chromosomes of Thatcher substituted in Chinese Spring, the group which is considered to be involved in the control of photoperiod sensitivity. The three substitution lines responded differently to temperature compared with Chinese Spring and with each other, with chromosome 2D being the least, and chromosome 2B the most, responsive to temperature.