EFFECTS OF TEMPERATURE AND PHOTOPERIOD ON EARLY GROWTH AND FINAL NUMBER OF TUBERS IN POTATO (SOLANUM-TUBEROSUM L)

A phytotron experiment with all combinations of two photoperiod (12 or 18 h) and four temperature (18/12. 22/16, 26/20 or 30/24 degrees C; 1 2 h/12 h) treatments was carried out to analyse quantitative effects o n early tuber growth, dry-matter partitioning and number of tubers of two cultivars. Higher temperatures and longer photoperiod delayed the onset of expolinear tuber growth and the onset of linear tuber bulking . Higher temperatures also gave lower absolute tuber growth rates. Pho toperiod did not affect absolute tuber growth rate at lower temperatur es. Higher temperature and longer photoperiod gave lower relative rate s of partitioning of dry matter to the tubers. Differences between tre atments in numbers of tubers initiated were inconsistent. This quantit ative analysis of the effects of temperature and photoperiod on charac teristics of tuber growth should prove useful in potato modelling.