Environmental Control of Flowering in Barley (Hordeum vulgare). III. Analysis of Potential Vernalization Responses, and Methods of Screening Germplasm for Sensitivity to Photoperiod and Temperature

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Abstract
Three genotypes of barley were subjected to 18 potentially vernalizing pre-treatments, comprising constant temperatures of 1, 5 or 9 °C in factorial combination with photoperiods of 8 or 16 h d−1 for 10, 30 or 60 d−1. These pre-treated seeds or seedlings, together with non-pre-treated seeds as controls, were then transferred to each of four growing-on regimes, namely day/night temperatures of 18/5 °C or 24/3 °C in factorial combination with photoperiods of 11 or 16 h d−1. The times from sowing to awn emergence were recorded. The warmer growing-on regime (mean 19 °C) was not supra-optimal in long days, but in short days it considerably delayed awn emergence in all three genotypes. In cv. Athenais there was no specific response to the potentially vernalizing pre-trcatments: the rate of progress towards awn emergence could be treated as a linear function of the integrated responses to temperature and photoperiod acting independently throughout development. In addition to these responses, cv. Gerbel B and the land-race Arabi Abiad also responded to low-temperature vernalization and the response became saturated during the longer-duration pre-treatments. In Arabi Abiad, the rate at which vernalization occurred, and the period required to saturate the response, were not greatly influenced by difference in pre-treatment temperature between 1 and 9 °C. In contrast, in Gerbel B the cooler the temperature of pre-treatment the greater the saturated response to vernalization, the greater the effect of each day of pre-treatment, and the shorter the period required to saturate the response. Models of the photothennal and vernalization responses were combined in a single entity which described the influence of environment on rate of development. Simple germplasm-screening techniques are proposed for genotype characterization so that the phenotypic flowering response can be estimated for any environment