First Report of Target Spot of Flue-cured Tobacco Caused by Rhizoctonia solani AG-3 in China

摘要

In early August 2006, a disease caused severe losses in a 1,400-ha field of 5-month-old tobacco plants in Kuandian and Fengcheng Counties, Dandong City of Liaoning in northeast China. Symptoms were observed on almost every plant. Disease symptoms were subsequently observed at nearly 100% incidence in 2,000 ha of fields from three towns in Kaiyuan County and two towns in Xifeng County, Tieling City, Liaoning Province in the second half of August 2006. Symptoms first appeared on leaves as small (2 mm) water soaked spots, and developed into expanded, dark brown lesions (2 cm) on the middle to lower leaves. Each lesion exhibited concentric rings, a necrotic center, and a tear in the center and margin that often resulted in a shot-hole appearance. Fungal isolates were obtained from the margins of lesions that were surface-sterilized by dipping each leaf section into 75% ethyl alcohol for 3 sec, then in 0.1% HgCl2 for 15 sec, rinsing in sterilized distilled water three times, and plating the leaf section onto half-strength potato dextrose agar (PDA).