RELATIVE WATER CONTENT AS AN INDEX OF PERMANENT WILTING IN GROUNDNUT UNDER PROGRESSIVE WATER DEFICIT STRESS

Abstract

The relationship between relative water content (RWC) and permanent wilting was studied in 21 Spanish groundnut cultivars by imposing 60 days of progressive stress (DPS) by withholding irrigation 24 days after emergence (DAE) and periodical recording of soil moisture content, soil temperature, leaf RWC and wilting symptoms and then re-watering and recording of rejuvenation during Summer season. With increasing water deficit stress, the leaf RWC declined progressively in all cultivars with mean values of 92, 85, 77, 69 and 61 at 10, 25, 35, 50 and 60 DPS, respectively. Amazingly, even after 60 DPS, the RWC was above 60 in 13 out of 21 cultivars of which 11 cultivars showed <25% visual wilting (VWP) and of these seven cultivars i.e. TPG 41, ICGV 86590, TG 37A, Girnar 3, AK 159, GG 4 and DRG 12 showing <10% permanent wilting (PWP) are promising. The study conclude that lower limit of RWC in groundnut leaves causing permanent wilting though varied with cultivars, the groundnut plants could survive moisture deficit up to 60% RWC and further reduction enhanced permanent wilting. A strong inverse relation between RWC at 60 DPS and VWP (r= -0.74* *) and RWC at 60 DPS and PWP (r= -0.76* *) respectively, indicate that RWC at the 60 DPS determines the mortality of groundnut plants undergoing severe moisture deficit stress.