Screening tomato genotypes for adaptation to high temperature in West Africa

Tomato is an important vegetable widely grown in the tropics due to its nutritional value and financial benefits for farmers. In Ghana, there is an undersupply caused by production ceasing entirely from October to May due to high temperatures. Heat stress has been reported to cause excessive flower drop leading to drastic reduction in yield; however, genotypic differences in heat tolerance exist in tomato. A greenhouse experiment was conducted to screen 19 different tomato genotypes for their tolerance to heat stress. The genotypes were selected because they were the commercial varieties widely available to farmers. The average day and night temperatures recorded were 33.8 degrees C and 25.9 degrees C, respectively. Cultivars were evaluated for heat adaptation traits such as flower drop and number of fruits. There were highly significant differences between the genotypes for numbers of fruits per plant, ranging from 1 to 27. Fruit yield per plant ranged from 26.7 to 571.8 g. The locally developed open pollinated cultivar Nkansah' had the highest fruit number and fruit yield per plant, but produced the smallest sized fruits of only 25.2 g. Cultivars with large size fruits were Queen', DV 2962' and Wosowoso' with a combined average of 85.7 g. The first two principal components (PCs) accounted for 79.7% of total variation. The first PC had positive weights for number of flowers per truss, number of fruits per plant, total number of flowers, yield per plant and number of trusses. PC2 explained 11% of the total variability among genotypes and had positive weights for all traits except number of days to flowering and weight per fruit. The highly contrasting material on traits such as flower and fruit production under high temperatures can be used for further research to elucidate the physiological responses conferring adaptation to heat stress.