Use of beneficial microorganisms as an alternative to resistance of Botrytis spp. to fungicides controlling gray mold on strawberry (Fragaria x ananassa)

The effect of four fungicides frequently used against gray mold in strawberry was evaluated on mycelial growth of two Botrytis cinerea isolates (Bt.MB and Bt.L) collected from two Moroccan regions. The results obtained showed that B. cinerea isolates were resistant and less sensitive to the active ingredient of each treatment at different degrees. At the pH 5.6, The chlorothalonil-carbendazim combination was very effective on Bt.L isolate (IC₅₀ ¼ HD et CI90 HD) while the mancozeb was very effective on Bt.MB isolate (IC50 ¼ HD) .On the other hand, the azoxystrobin treatment has no effect on the Bt.L isolate (IC₅₀ and IC₉₀ 2HD) unlike mancozeb that inhibits totaly the vegetative growth to Bt.L isolate (IC₅₀and IC₉₀ HD) whereas, the propanocarb HCL was moderately effective on Bt.MB isolate (IC₅₀ HD and IC₉₀ HD). At pH 7.5, the chlorothalonil-carbendazim inhibits completely the growth of Botrytis cinerea isolates (IC₅₀ and IC₉₀ ¼ HD) while the other three fungicides are moderately effective on Bt.L isolate (IC₅₀ HD and IC₉₀ HD). Antagonists of the pathogenic of strawberry plants, B. cinerea (Bt.L and Bt.MB), were isolated, selecting two bacterial isolates belonging to the genus Bacillus (Bacillus sp. B1 and Bacillus sp. B2). During in vitro confrontations, the isolate produced inhibition zone by producing antibiotics. The radial growth of the pathogen was reduced. After 7 days the antagonist had completely invaded the pathogenic colony fragmenting it and sporulating throughout it. Bacillus sp. B1 gives a great inhibition for the two pathogenic isolate than Bacillus sp. B2.