Reduction in potato growth at high temperature: role of photosynthesis and dark respiration

The relationship of photosynthesis and dark respiration to reduced potato growth at temperatures above 20°C was determined. Ten potato clones were propagated in vitro from sterile plandets and grown in a growth chamber at 20/15°C and 30/25°C (day/night) with an 18 hr. daylength. Plants were harvested 26 to 30 days after transplanting. Daylength was decreased to 12 hrs. to induce tuberization and plants were harvested at 45-51 and 75-79 days after transplanting. At each harvest one plant from each cultivar was chosen from each of five blocks and selected growth (tuber number and dry weight of leaves, stems, roots and stolons, and tubers) and physiological variates leaf area, net photosynthesis, maintenance dark respiration, and chlorophyll fluorescence parameters 0 (Initial), P (Peak), T (Terminal), P-O (Variable fluorescence) and P-T (Fluorescence quenching)] were measured. The high temperature decreased root and stolon, tuber and total dry weight and increased stem dry weight. Amongst physiological variates, the higher temperature decreased leaf area, net photosynthesis and maintenance dark respiration. The chlorophyll fluorescence parameter 0 significantly increased, which also increased the P and T parameters. Variable fluorescence (P-O) and fluorescence quenching (PT) were not significantly affected by the growth temperature. The analyses of covariance, in which physiological variates were used as covariates to remove significant differences in growth variates, indicated that the most effective covariate was the T chlorophyll fluorescence parameter. The least effective covariates were leaf dark respiration and the chlorophyll fluorescence parameters P-O and P-T. The changes in 0 fluorescence suggest that reduced photosynthetic efficiency, particularly in Photosystem II, plays a major role in reduced potato production at high temperatures.