Geographical Distribution of Botryosphaeriaceae and Phomopsis/Diaporthe Canker Pathogens of Avocado in California

B and Phomopsis/Diaporthe (P/D) spp. are fungal pathogens known to cause cankers on a variety of woody hosts such as avocado, grapevine, almond, citrus, cherry, plum, mango, and coast live oak. On avocado (Persea americana Mill.), the disease came to be known as Dothiorella canker because the pathogen most often isolated at the time was known as Dothiorella gregaria (2). However, new research has shown that avocado canker is due to a complex of fungal species, of which the most common belong to the family Botryosphaeriaceae and to a lesser extent, the genera P/D. Cankers are localized areas of dead bark caused by fungal infection that can occur on trees and other woody hosts (Figure 1). Symptoms of canker disease also include dead or dying shoots and branches, sometimes with dead leaves still attached, scattered among healthy foliage (Figure 2). On trees, cankers are usually found on branches, but can also occur on the trunk. The bark of a tree is composed of several layers of tissue surrounding its woody core. The outer bark consists of corky, dead plant cells which serve as a barrier to reduce water loss and to protect the inner bark tissue and sapwood. When the outer bark is not compromised, it prevents the entrance of most pathogens. Entry points through the outer bark can be caused by injuries such as pruning, grafting, girdling, phosphonate injections or insect wounds, split branches from sunburn, wind or frost damage (8). Once the outer bark layer is breached by a canker pathogen, other bark tissue, such as the phloem and vascular cambium, can be colonized. The resulting infection can lead to disruption of nutrients, assimilates and water movement Geographical Distribution of Botryosphaeriaceae and Phomopsis/Diaporthe Canker Pathogens of Avocado in California Akif Eskalen Extension Subtropical Plant Pathology Specialist