Role of Botryosphaeria Species in Peach Tree Gummosis on the Basis of Differential Isolation from Outer and Inner Bark. P. L. Pusey, Plant Pathologist, USDA-ARS, Southeastern Fruit and Tree Nut Research Laboratory, P.O. Box 87, Byron, GA 31008. . Plant Dis. 77:170-174. Accepted for publication 25 August 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993. DOI: 10.1094/PD-77-0170.

Nonwounded stems of 1-yr-old peach trees were inoculated with Botryosphaeria spp. in May, and fungal colonization of outer bark (rhytidome), inner bark (living secondary phloem), and xylem were evaluated after 18 mo. Trees inoculated with an isolate of B. obtusa or B. rhodina from peach or an isolate of B. dothidea from apple were symptomless, whereas trees inoculated with an isolate of B. dothidea from peach were dead (69%) or severely diseased. The same fungal species used in inoculations were isolated from the outer bark of symptomless stems (following surface-sterilization with 70% ethanol) at frequencies of 35–100% but from inner bark or xylem at frequencies of 0–13%. Sequential isolations were made from outer to inner bark of commercially grown peach trees that varied in age (4–18 yr) and symptom expression in central Georgia. The progression from outer to inner bark usually resulted in an increase in the proportion of B. dothidea isolated on potato-dextrose agar relative to B. obtusa. B. dothidea was consistently predominant in diseased inner bark associated with lenticels. Botryosphaeria spp., which inhabit only dead outer bark as saprophytes, may have been disproportionately represented in previous studies on the cause of peach tree gummosis.