VARIABILITY IN NET PHOTOSYNTHETIC RATE, WATER USE EFFICIENCY AND CARBOXYLATION EFFICIENCY OF TOBACCO VARIETIES

Abstract

Increasing the photosynthetic efficiency is one of the most important ways to increase productivity. Understanding the variability in net photosynthetic rate and related traits among germplasm helps in selecting parents in breeding programmes. In the present study, 90 released varieties of different tobacco types were grown in experimental plots with recommended package of practices at the CTRI Research Farm, Katheru, East Godavari district, Andhra Pradesh were assessed for net photosynthetic rate (Pn), transpiration rate (E), stomatal conductance (SC) and intercellular CO2 concentration (Ci). From these observations intrinsic and instantaneous water use efficiency and carboxylation efficiency were computed. Non-FCV tobacco varieties recorded greater net photosynthetic rate and related traits compared to FCV tobacco varieties. The Photosynthetic rate (Pn) of FCV tobacco varieties varied from 8.95 to 28.80 mmol/m2/s with a mean of 18.61 mmol/m2/s. Among the non-FCV tobacco varieties Pn varied from 9.7 to 35.84 mmol/m2/s with a mean of 23.50 mmol/m2/s. Instantaneous water use efficiency varied between 2.330 to 4.930 μmol/mol among FCV tobacco varieties and 1.770 to 5.42 μmol/mol in non-FCV tobacco varieties with a mean of 3.23 and 3.557 μmol/mol, respectively. Mean intrinsic water use efficiency of FCV and non-FCV tobacco varieties were 68.69 and 71.86 μmol/mmol, respectively. Carboxylation efficiency ranged from 0.036 to 0.137 μmol/m2/ s2/(μl/l) in FCV and 0.037 to 0.160 μmol/m2/s2/ (μl/l) in non-FCV tobacco varieties. Among FCV tobacco varieties, Kanchan, Siri and Sahyadri recorded higher Pn, instantaneous and intrinsic water use efficiency and intrinsic carboxylation efficiency whereas, varieties viz., GCT-3, DD 437, GCT-2, HD-65-40, DP-401 and Bhagyalakshmi recorded higher efficiency among non-FCV tobacco varieties. The varieties which recorded greater photosynthetic rate, water use efficiency and carboxylation efficiency can be used in evolving physiologically efficient high productive varieties.