A Quantitative Model of Reproductive Development in Cowpea [Vigna unguiculata (L) Walp.] in relation to Photoperiod and Temperature, and Implications for Screening Germplasm

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Abstract
Factorial combinations of four photoperiods (10 h, 11 h 40 min, 13 h 20 min and 15 h) and three night temperatures (14, 19 and 24 °C) combined with a single day temperature (30 °C) were imposed on nodulated plants of 11 cowpea accessions [Vigna unguiculata (L) Walp.] grown in pots in growth cabinets. The times to first appearance of flower buds, open flowers and mature pods were recorded. Linear relationships were established between the reciprocal of the times taken to flower and both mean diurnal temperature and photoperiod. When the equations describing these two responses are solved, the time to flower in any given photothermal regime is predicted by whichever solution calls for the greater delay in flowering. Thus in different circumstances flowering is controlled exclusively by either mean temperature or photoperiod. The value of the critical photoperiod is temperature-dependent and a further equation, derived from the first two, predicts this relationship. Considered together as a quantitative model these relationships suggest simple field methods for screening genotypes to determine photo-thermal response surfaces.