Environmental Control of Flowering in Barley (Hordeum vulgare L.). II. Rate of Developement as a Function of Temperature and Photoperiod and its Modification by Low-temperature Vernalization

Abstract

Plants of six contrasting genotypes of barley were raised from vernalized (imbibed at 1 °C for 30 d) or nonvernalized seeds and grown in 12 different controlled environments comprising factorial combinations of three photoperiods (10, 13 and 16 h d-1), two day temperatures (18 and 28 °C) and two night temperatures (5 and 13 °C). Except at longer days for Athenais or Arabi Abiad, the 28 °C day temperature was generally supra-optimal and delayed awn emergence. At lower temperatures and in photoperiods shorter than the critical value, Pct which delay awn emergence, the time from sowing to awn emergence for five of the genotypes conformed to the equation '/f = a + bT+cP where / is the time to awn emergence (d), T is mean diurnal temperature (°C), P is photoperiod (h d1) and a , b and c are genotypespecific constants. In Arabi Abiad, however, significant responses to temperature were not detected. The low temperature pre-treatment of the seeds reduced the subsequent time to awn emergence in Athenais and the autumn-sown genotypes Ager, Arabi Abiad and Gerbel B, especially in longer days, but either had no effect or tended to delay awn emergence in the spring-sown types Emir and Mona. In the springsown types Pc was outside the range investigated (i.e. > 16 h d1), but in Ager it was approx. 13 h d1 and in Gerbel B just over 13 hd1. For plants of Arabi Abiad grown from vernalized seeds Pc was almost 15 h, but ^ 13 h in plants from nonvernalized seeds. In Athenais, whether or not the seeds had been vernalized, Pc varied with mean diurnal temperature, from about 12-5 h d1 at 10 °C to about 15 h d1 at 20 °C. These results are discussed in relation to field predictions and the development of simple procedures for screening germplasm for sensitivity to temperature and photoperiod.