First report of atypical scab on apples in China

Apple cv. Huangtaiping (Malus pumila) is grown widely in northern China for the production of jellies, preserves, and cider. In 2018, atypical scab symptoms were observed on fruits of Huangtaiping in Heilongjiang Province of China. The disease incidence was estimated at approximately 0.4%. Symptoms were scab-like black spots distinct from scab caused by Venturia inaequalis.

Symptoms of atypical scab observed consist in light black spots of 3 to 5 mm on surface of fruits.

Conidia were generally produced on lesions, were cylindrical to fusiform, 0 to 1 septate, yellowish and 19.7 (13.5 to 25.8) × 5.7 (3.6 to 6.9) μm (n = 10) in size. DNA of three selected isolates were extracted and sequenced.

The scientists at Huazhong Agricultural University (Wuhan, China) found that the tested isolates resulted very close to Venturia asperata. In July 2019, pathogenicity of the isolate VAHLJ3-1-1 was evaluated on Huangtaiping. A conidia suspension with a concentration of 5×105/ml was sprayed evenly on the surface of six fruits. In order to maintain high humidity, inoculated fruits were wrapped with a plastic bag (a cotton ball with water was placed in the plastic bag) to maintain wetness for 3 days. Six fruits sprayed with water were used as a control. Four weeks after inoculation, similar symptom of atypical scab was observed on fruits of Huangtaiping, and V. asperata was isolated again from six inoculated fruits with reisolation frequency of 100% by the single spore isolation, while no symptom was observed on the control fruits.

"Based on the morphological and molecular identifications, the causal agent of atypical scab on Huangtaiping was identified as V. asperata. Apple scab is usually caused by V. inaequalis. However, apple scab has also been caused by V. asperata in Italy and France. To the best of our knowledge, this is the first report of V. asperata associated with apple scab-like lesions in China. This information increases our knowledge of the spectrum of Venturia species associated with disease on apple fruit and will be a valuable foundation underpinning management strategies for this cultivar", the scientists conclude.

Source: Yang Zhou, Haidong Bu, Chingchai Chaisiri, Qin Tan, Li Wang, Liangfen Yin, Weixiao Yin, Chaoxi Luo, 'First Report of Atypical Scab Caused by Venturia asperata on Apple in China', 2021, Plant Disease.