From seventy five yeast isolates, only eleven were selected as most effective isolates against the main causal fungal rot of tomato fruits, i.e. Alternaria alternata. These isolates which are considered biocontrol strains reduced A. alternata (1 x 10⁶ conidia/ml) infection by more than 90% . Five isolates from those eleven isolates were found to be the most effective ones since they inhibited the infection of the causal organism (1 x 10⁵ and 1 x 10⁶ conidia/ml ) after seven days of incubation at 21 ± 0.5^oC. The yeast isolate Ap638 (Arthroacus sp.) completely inhibited the rot infection causd by A. alternata (1 x 10⁵ conidia/ml) when this isolate was used at high concentration (1 x 10⁹ cfu/ml) after 18 days of incubation at 13 ± l^oC. In the test of different biocontrol agents (40 isolates) against the causal organism of grapes Penicillium crustosum and Botrytis cinerea, one bacterial isolate (Bacillus sp.) and about ten yeast isolates were found to be more effective in reducing the percentage of infection between 50-90%. Pre-and post harvest application of the above mentioned selected isolates were used to control and reduce the percentage of decay, weight loss, shatter, total wastage and frequency of the isolated fungi of  Flam and Thompson seedless grapes.