Chemical and Biological Control of Botryosphaeria Species On Oriental Persimmon (Diospyros kaki)

Botryosphaeria spp. are ligninolytic ascomyceteous fungal organisms that incite diseases of Oriental persimmon, apple, pear, peach, nectarine, plum and Southern highbush blueberries in Florida. Botryosphaeria spp. have a very broad host range and there is no adequate chemical control. Disease manifestation in most crops is the formation of black cankers on the trunk and limbs, while it causes gummosis in stone fruit trees. Previously, the causal agent of Botryosphaeria cankers on deciduous fruit was thought to be B. dothidea; however, recent work in Florida has shown that B. obtusa, B.  rhodinia and B. ribis may be more common. We have chosen to study Botryosphaeria on Oriental persimmon because of an excellent market for the fruit, and because Botryosphaeria will often limit the tree lifespan to 5 to 10 years. Our objectives were to: 1) test the efficacy of fungicides against Botryosphaeria spp.; 2) survey phenolic compounds naturally occurring in plants for efficacy against Botryosphaeria spp.; 3) survey cultivated and native woody plant species for the presence of Botryosphaeria spp., and; 4) determine the influence of wounding and mode of inoculum entry on disease manifestation. The fungicides Tilt, Headline, Folicur, Domark and Topsin offered only partial control of Botryosphaeria species at relatively high (10 to 25 mM) concentrations, and the use of fungicides is not viewed as a promising tactic. We have made a serendipitous discovery concerning the efficacy of a bacterium, Bacillus subtillis against Botryosphaeria spp. in vitro, and this is an area of investigation. The effect of naturally occurring phenolic compounds (vanillic acid, syringic acid, catechol, veratric acid, 2,6-dimethoxy benzoic acid, ferulic acid, benzoic acid, 2,6-dimethoxy phenol, p-courmaric acid and guaiacol) varied with the compound and Botryosphaeria spp. in vitro. We have surveyed cultivated and native tree species for the presence of Botryosphaeria spp. using morphological indices and the polymerase chain reaction technique. B. rhodinia and B. ribis were the most common species surveyed. Lastly, we have compared the effect of mode of Botryosphaeria spp. entry into a plant by placing inoculum on stems and at the site of lenticels and by wounding (with a needle). Although lesion size increased with wounding, lesion size did not increase further with wounding at the site of lenticels.