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Relationship of Botryosphaeria dothidea and Hendersonula toruloidea to a Canker Disease of Almond. Harley English, Department of Plant Pathology, University of California, Davis 95616; James R. Davis(2), and J. E. DeVay(3). (2)(3)Department of Plant Pathology, University of California, Davis 95616, (2)Present address: Branch Experiment Station, University of Idaho, Aberdeen 83210. Phytopathology 65:114-122. Accepted for publication 5 August 1974. DOI: 10.1094/Phyto-65-114.

An unusual canker disease of almond (Prunus amygdalus) caused by Botryosphaeria dothidea is described. Bandlike or irregular cankers are formed on the trunk or scaffold branches of vigorous young trees, occasionally causing death of the parts distal to the point of infection. A second fungus (Hendersonula toruloidea) was found in many of the cankers, but in nature it appears to be mainly, if not entirely, a secondary invader. Both fungi, however, were able to induce canker formation when mycelial inoculum was placed in cortical wounds on the cambium, or on xylem exposed by pruning. Natural infection by B. dothidea appeared to be through cortical growth cracks. The cankers induced by both organisms were largely annual rather than perennial, and there was no evidence of a synergistic relationship between these two fungi in the formation of cankers. The mycelium of both organisms was found principally in the lumen of cells in both xylem and phloem, and it passed from cell-to-cell mostly through pits. Since the sexual stage of B. dothidea was not found, the identification of the almond isolate as B. dothidea was based on asexual stage (Dothiorella) morphology, serology, and pathology. The almond cultivar Nonpareil was more susceptible to canker than either Ne Plus Ultra or Mission. Canker excision, with or without a wound protectant, was of no value in disease control.