Abstract
The responses of two potato (Solanum tuberosum L.) cultivars to different levels of soil moisture stress at three growth stages (stage-I: vegetative to beginning of tuberization, stage-II: tuberization to initial tuber enlargement and stage-III: tuber enlargement to maturity) were studied in pot experiments in a naturally lit glasshouse. At 60% and 45% field capacity (FC), the cultivars May Queen and Dejima produced a smaller amount of dry matter than at 75%FC at all stages of growth. Dry matter production decreased relatively more in Dejima than in May Queen. The maximum reduction in Dejima (59%) was observed at stage-I and in May Queen (33%) at Stage-II at 45%FC. Plant height, leaf area, number of stolons and tubers per plant also decreased at lower moisture levels (45%FC) . Water-soluble carbohydrate (WSC) content in leaves increased due to the decrease of the moisture level, while the starch content decreased and the amount of total nonstructural carbohydrates (TNC) did not vary appreciably. Starch content of the tubers increased and leaf water potential (ψw) decreased at lower moisture levels. Nitrate reductase (NR) activity was also suppressed at these levels and the reduction rate was comparatively higher at 10 days after treatment (DAT) than at 20 DAT in both cultivars. Lower moisture level decreased the tuber yield too, and the maximum yield reduction was observed at stage-II in both cultivars at 45%FC. Depending on the severity of the treatments, stage-II at 45%FC was found to be most critical for potato yield. It was suggested that the decrease in tuberization and tuber enlargement due to moisture stress may be related to the decrease in the NR activity, leaf starch content and ψw.
