Effect of sugar alcohols, antioxidants and activators of systemically acquired resistance on severity of bacterial angular leaf spot (Xanthomonas fragariae) of strawberry in controlled environment conditions

Abstract

Bacterial angular leaf spot of strawberry caused by Xanthomonas fragariae is an increasingly important disease for which few management strategies are available. The resistance status of most cultivars is unknown and of those cultivars tested, few have significant levels of resistance. Copper formulations are available and have limited effectiveness but phytotoxicity is a problem with repeated applications. This controlled environment study examined the efficacy of foliar applications of various antioxidants, such as α-tocopherol and mannitol, along with the plant activators acetylsalicylic acid and acibenzolar-S-methyl, and the fungicide fosetyl-Al, for disease control. Mannitol and acibenzolar-S-methyl consistently provided excellent control of disease, while fosetyl-Al and α-tocopherol were significantly less effective. Other antioxidants and sugar alcohols similar to mannitol did not provide the same level of angular leaf spot control. Interestingly, interactions were observed between various sugar alcohols and strawberry cultivars in suppressing disease. The mode of action of sugar alcohols against angular leaf spot is likely not related to their antioxidant activity. Sugar alcohols, especially mannitol, may represent a new and non-toxic approach to bacterial angular leaf spot control.