Controlled deterioration and accelerated ageing tests to predict seedling emergence of watermelon under stressful conditions and seed longevity

Abstract

The emergence of 19 commercial seed lots (10 in 2005 and 9 in 2006) of watermelon (Citrullus lanatus Matsum and Nakai, Thunb.) with laboratory germination >90% were compared in stressful conditions of low temperature (LTE, early spring), mechanical stress (MSE, 6 cm deep sowing) and salt stress (SSE, 200 mM NaCl). The emergence percentage ranged between 12 54% for LTE, 19 -75%, for MSE and 43 91% in 2005 and 35 80% at LTE, 13 82% at MSE, 45 92% at SSE in 2006. The radicle emergence of the lots was determined after controlled deterioration (CD) at 40 and 45°C in 2005, or at 45 and 47°C in 2006, with 20% or 24% moisture content for 48, 72, 96, 120, 144 hours in 2005 and 48, 72, 96, 120, 144, 168 hours in 2006. The accelerated ageing test was also conducted at the same temperatures and ageing durations in both years. The germination range of the seed lots increased in both CD and AA as the ageing period was extended. Germination after all combinations of CD was positively and significantly (p<0.05) correlated with LTE, MSE and SSE. However, most very highly significant correlations (p<0.001) were observed after CD for between 48-96 hours at 45°C and at 24% in both years. Germination after the AA test was correlated with LTE, MSE and SSE. This was especially seen at 40 and 45°C. The highest number of very highly correlated combinations was found after AA at 47°C for 120 or 144 hours. The initial laboratory germination was significantly related to LTE, MSE and SSE, but the correlation values were much lower than those of both ageing tests. Laboratory germination after 6 month storage at 25°C and 12% seed mc was closely correlated with germination after both AA and CD tests (p<0.001). The results show that both ageing tests can be used to predict seedling emergence under stressful conditions. The optimum CD conditions of 48 hours and 24% mc at 45°C and AA conditions of 120-144 hours at 45°C are suggested as a routine predictive test of watermelon seed emergence and longevity.