Clonal variation in temperature response of photosynthesis in tea

Abstract

The effect of temperature on the photosynthetic characteristics of six tea clones (viz., 6017, B/5/63, B/6/61, B/6/62, CCS-26 and T-78), originally from different agro-climatic zones in India, was studied to determine the clonal variation in photosynthesis, if any. The results clearly indicated significant clonal differences in relation to temperature. Of the six clones, B/5/63 and B/6/61 were found to be relatively thermotolerant. Both stomatal and mesophyll components seemed to be responsible for the differences in temperature dependence of photosynthesis, however, their magnitude varied with the tea clones. Differences in water use efficiency were also observed between clones. However, differences became less pronounced at the higher temperature. Clone B/5/63 showed higher water use efficiency and lower values for stomatal conductance and transpiration. Thus this clone may be suitable for relatively dry and exposed sites. A 2–10-fold increase in dark respiration with increase in temperature was also observed. However, higher increase was associated with clones having higher photosynthetic rates, indicating an association between photosynthetic and respiratory rates. The results provide a valuable indication regarding clonal variation in temperature responses of photosynthesis and may be used to offer useful suggestions to tea growers in the initial selection of tea clones.

Introduction

Tea (Camellia sinensis (L.) O. Kuntze) is a small tree but the plants are maintained in the form of bushes by continuous pruning. It is an important plantation crop of India and is grown in various agro-climatic zones. India is a major producer of tea both for the domestic and world market. The ever increasing demand for tea can be achieved, to a certain extent, by increasing the area under tea; a better option would be the use of high yielding clones and by growing clones most suitable for specific climatic regions.

Temperature is one of the major environmental factors determining the rate of growth and the natural geographic distribution of tea [1]. It has been demonstrated that temperatures above 30 and below 13°C are not conducive for the growth of tea bush [2]. Many high yielding tea clones are being used under tea plantation programmes in the Central Himalayan region which show considerable seasonal and diurnal variation in temperature. Therefore, the success in terms of yield would depend on the proper selection of clones which are better suited to the prevailing climatic conditions.

Photosynthesis, being one of the first physiological processes to be greatly affected by temperature [3]is widely used as a tool for indicating temperature stress [4]and for the rapid selection of plants most suitable for different habitats [5]. Existence of a close relationship between photosynthetic rates and yield in several plant species has also led many workers to use photosynthetic characteristics as criteria for selection of high yielding clones 6, 7. In the case of tea, with some exceptions 8, 9, studies have shown that the growth of the harvestable shoots (yield) depends on the photosynthetic rate of maintenance leaves and developing shoots 10, 11. Thus any existing variation in the photosynthesis may offer a greater potential for yield improvement in tea. Further, in many plant species genotypic and/or clonal variations in photosynthetic characteristics and yield in relation to temperature have been reported 6, 12. However, such information is lacking for tea clones [13]and therefore, the present investigation was undertaken to determine the clonal variation, if any, in photosynthesis in relation to temperature.