Variation in physiological parameters of coffee cultivars under different soil moisture regimes

Assessment on physiological parameters was carried out using two arabica (Sln. 9 and Sln. 3) and one robusta (Sln. 1R) coffee cultivars under different soil moisture regimes i. e., before stress, at stress and after alleviation of stress under field conditions for two seasons. The results indicated that considerable reduction in net photosynthesis (Pn), transpiration rate (E), stomatal conductance (g_s), sub-stomatal CO₂ concentration (Ci), carboxylation efficiency (CE) (Pn/Ci), relative water content (RWC), physiological water use efficiency (pWUE) (Pn/E) and higher stomatal resistance (rs) was observed during soil moisture stress in all the cultivars. The less reduction of physiological parameters in Sln. 9 at stress might be associated with an increase in the epicuticular wax content (ECW) and relative water content (RWC). The pWUE was maintained high in Sln. 9 under different soil moisture regimes. Significant (P>0.01) positive correlations between Pn and E, rs with E and Ci were observed at beforerstress in all the cultivars. The rs showed highly significant negative relationship with Pn and E under water stress. The Ci had significant positive correlation with Pn and E in arabica cultivars at stress, whereas such a relationship could not be observed in robusta coffee. The significance of the relationship of physiological parameters for drought tolerance in coffee is discussed. Thus, high Pn/Ci, rs, pWUE, ECW and less reduction in Pn and maintenance of RWC with low E and g_s during moisture stress period might be the contributing factors for drought tolerance in Sln. 9 arabica cultivar.