Photothermal Time for Flowering in Lentils (Lens culinaris) and the Analysis of Potential Vernalization Responses

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Abstract
Two cultivars of lentils, Laird and Precoz, were subjected to 18 potentially vernalizing treatments, comprising constant temperatures of 1, 5 or 9 °C in factorial combination with photoperiods of 8 or 16 h for 10, 30 or 60 d. These seeds or seedlings, together with non-vernalized seeds (as controls), were then transferred to four different growing regimes (‘day’/‘night’ temperatures of 18/5 °C or 24/13 °C, factorially combined with photoperiods of 11 or 16 h). Variation in the number of days from sowing to first flower (f) in the growing regimes for the controls conformed to the equation I/f = a+b+cP, where is mean temperature (°C), P is photoperiod (h) and a, b and c are genotype-specific constants. Accordingly, when the environment varies during development, the photothermal time required to flower in day-degrees (°C d) is given by 1/b above a base temperature defined as —(a+cP)/b. Most variation in time to flower could be accounted for by the photothermal time accumulated in the two successive environments. Therefore, there was no evidence of a specific low-temperature vernalization response in either cultivar. Neither was there evidence of ‘short-day’ vernalization, i.e. advancement of flowering resulting from preliminary short-day treatments. A potential error inherent in the predictive model described arises because it ignores the presence of a pre-inductive, photoperiod-insensitive phase; but agro-ecological considerations suggest that this error may not be important in practice.

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