2002 Volume 40 Issue 3 Pages 259-268
The effects of shade (C: unshaded control, S1: 48% shading and S2: 76% shading) at different growth stages (stage-I: vegetative to beginning of tuber initiation, stage-II: tuber initiation to initial tuber bulking and stage-III: tuber bulking to maturity) on nitrate reductase (NR) activity, plant growth and yield of field grown potatoes (Solanum tuberosum L.; cv. May Queen and Dejima) under two levels of spacing were studied. Main stem length was increased by higher intensity of shading and denser plant spacing at all stages of growth. Denser plant spacing also increased the leaf area index (LAI) . Shading at early stage delayed tuber initiation. Increasing shading intensity consistently decreased dry matter production and marketable tuber weight and decreased the tuber yield. The yield reduction was greatest (41%) in S2 plants at stage-II and smallest (15%) in S1 plants at stage-III. On an average (cultivar, spacing and growth stages) 19 and 30% yield reduction was observed for the reduction of 48 and 76% solar radiation, respectively. The NR activity in leaves decreased by shading. On an average, 16 and 25% reduction in NR activity was observed for the reduction of 48 and 76% solar energy, respectively. The reduction coefficient of yield or NR activity for light was 0.40 and 0.33 respectively for both levels of shade applied. From this study it could be concluded that shading at stage-II is very critical for tuber yield and is directly related to the reduction of NR activity and yield.
