In vitro Evaluation of Heat Stress Tolerance in Some Tomato Cultivars

Twenty locally grown tomato cultivars were evaluated for their in vitro heat tolerance. Leaf discs were collected during vegetative, flowering and fruiting stages and incubated in water bath at 40°C for 1, 2 and 3 hours. Electrical conductivity (EC) was measured as an indication of cell injury due to electrolytes leakage. The results indicated that cultivars can be classified into three groups according to their heat stress tolerance: (a): heat stress tolerant cultivars (EC ranged from 27.75 to 41.69 μmho/cm) which include Queen, Indian, Super Strain B, Pearson and Strain-B; (b): moderately heat stress tolerant cultivars (EC ranged from 43.80 to 50.70 μmho/cm). This group consisted of nine cultivars Pacmore, Tnshet Star, Rocky, Shohba, Raad VF, VFN8, Moneymaker, Imperial and Pearson Imperoved; and (c): heat stress sensitive cultivars (EC ranged from 53.12 to 72.20 μmho/cm) and included Malica, Castle Rock, Edkawi, Chico, Pakmore VF and Super Marmand. Correlation coefficients among the three growth stages were positive and significant or highly significant which indicated that this method is effective in selecting genotypes at early growth stages. The incubation period of 2 hours was optimum for this test. This method is a useful tool for plant breeders to screen for heat stress tolerance of genotypes during early growth stages in breeding programs in addition to field evaluation in various agricultural production areas.