First detection of silverleaf {Chondrostereum purpureum) on rabbiteye blueberry (Vaccinium virgatum) and disease damages

摘要

Silverleaf of blueberry was described for the first time in Vaccinium corymbosum Brigitta Blue' in the 2005 season in the southern area of Chile. The disease is caused by the fungus Chondrostereum purpureum and the symptoms are the silvering of the foliage, necrosis of the wood center and plant death. Since the first detection, a new cultivar of V. corymbosum has been detected every year as susceptible to this disease. Moreover, during the 2014 season, Silverleaf was detected for the first time in the 'Brightwell' rabbiteye blueberry [V. virgatum Aiton). The objective of this study was to describe the disease and its causal agent, and to determine the level of damage to plants and berries. The fungus was consistently isolated from necrotic wooden tissue, collected from plants with silver foliage. It developed white and cottony colonies on PDA, covering a 9-cm petri plate after 7 days at 24°C. Healthy rabbiteye potted plants were inoculated by placing mycelial plugs on pruned stems, in order to fulfill Koch's postulates. The developing disease was monitored for a year, where leaf symptom occurrence and wood necrosis were recorded. Symptomatic wood fragments were collected from the necrotic area and cultured on PDA. The re-isolated fungus exhibitedidentical morphometric features as the one which was originally isolated. Mycelium from a pure culture was used for DNA extraction and sequence analysis of the ITS 4 and 5 regions, and the APN1 marker for species identification. The fungus was identified as C. purpureum (Pers.) Pouzar. Furthermore, the disease decreased stomatal conductance, xylem water potential and photosynthesis. Fruit yield and quality were severely reduced by silverleaf, becoming unsuitable for fresh market.