Survey and assessment of the major fungal diseases of Eucalyptus spp. in seedling production system

Abstract

The survey and assessment of the major eucalyptus fungal diseases under seedling production system of Siam Forestry Company, Nampong District, Khon Kaen Province were carried out during March – September 2018. Seven clones of eucalyptus seedlings (H4, H26, H28, H32, H36, H38 and P6) were produced in the production year. There were 3 disease symptoms always found along the period, i.e., leaf blight, leaf spot and dieback. The disease severity index (DSI) of leaf blight and leaf spot including percent disease incidence (DI) of dieback were evaluated once monthly. In March, average DSI and DI were the lowest (9.56, 10.55 and 1.50%, respectively). The average maximum DSI of leaf blight (20.70) and DI of dieback (28.39%) were detected in September, also DSI of leaf spot (21.50) in August. The eucalyptus clone P6 showed the lowest average DSI and DI of all symptoms. But clone H32 exhibited the highest of leaf blight DSI (18.30) and dieback DI of 22.35%. For leaf spot, the clone H28 was the maximum DSI (19.67). Whereas, 61 isolates of fungal causal agents were obtained from pure culture isolation. These isolates were tested on the pathogenicity using detached leaf technique under laboratory condition. Result indicated that 58 isolates were pathogenic causing symptoms on detached leaves. In addition, top 10 virulent isolates were investigated on their pathogenicity tested on eucalyptus clone H4 seedlings under greenhouse condition. It was clearly that all isolates caused the disease symptoms on leaves. The isolate 39DBH32 caused the biggest average lesion diameter (3.23 cm), however the isolate 37LBH38 led to the smallest average diameter (0.40 cm). All of these 58 isolates were identified into 4 genera using morphological characteristics. The result revealed that there were Coniella sp., Pestalotiopsis sp., Cylindrocladium sp. and Curvularia sp.