: Causal Agent of Leaf Blight in Southern China.

Calonectria leaf blight caused by spp. is among the most serious diseases affecting the health and sustainability of plantations in southern China. Recent outbreaks of this disease in GuangDong Province prompted a need to identify the species involved. Typical symptoms of Calonectria leaf blight were observed on 2-year-old × trees in a plantation in the ZhaoQing region. In total, 38 isolates were collected from 32 diseased trees. All isolates were identified using DNA sequence analyses of the translation elongation factor 1-α (), β-tubulin (), calmodulin (), and histone H3 () gene regions. Phylogenetic analyses revealed that was the dominant species, accounting for 81.6% of the isolates collected. Other species isolated included (10.5%), (5.3%), and (2.6%). This is the first report of in China and all isolates had identical sequences in all four gene regions. PCR amplification using primers targeting the and genes in all isolates revealed that only the idiomorph was present. The results suggest that was introduced into the sampled area with very limited genetic diversity. Pathogenicity tests were conducted on two genotypes widely planted in the GuangDong Province using isolates representing all species collected. The results showed that these species could all cause disease but the predominance of on infected trees suggests that it is the major driver of the disease problem studied. Different genotypes used in the pathogenicity tests differed in susceptibility to infection by the spp. tested, providing opportunities to avoid leaf blight by deploying disease-tolerant planting stock.