First report of Alternaria black spot disease caused by Alternaria alternata on the invasive weed Solanum rostratum in Xinjiang, China.
In August 2015, foliar symptoms of yellowish to black spots were observed on plants of Solanum rostratum near an agricultural plantation in Changji, Xinjiang, China. The following year, about 17% of the 206 plants surveyed on about 0.2 ha of deserted farmland were infected from July to September. Symptoms of the disease appeared on about 70% of leaves on all the infected plants. Initially, some yellowish spots were observed on the abaxial dorsal leaves, which subsequently turned white, and some dark spots appeared on the front and dorsal sections of the infected leaves; the spots gradually joined to some irregular larger spots, and finally entire leaves fell or withered. After heavy rainfall, the adaxial region of some infected leaves, flowers, and stems were observed to produce some dark spots. The causal pathogen was isolated and identified as Alternaria alternata based on morphological characteristics, molecular data (sequence analysis of the internal transcribed spacer (ITS), glyceraldehyde 3-phosphate dehydrogenase (gpd) gene, Alternaria allergen a 1 (Alt a 1), and 28S large subunit ribosomal RNA (LSU) gene) and pathogenicity test. This is thought to be the first report of A. alternata causing Alternaria black spot disease of S. rostratum in China or elsewhere.