First report of Alternaria longipes causing kiwifruit leaf spot in China and screening of potentially fungicidal active substances

Abstract

Kiwifruit, which is known for its unique flavour and high value, is extensively cultivated in the world, especially in China. In 2022, a unique case of leaf spot disease was discovered in Xifeng, Guizhou Province, China, with symptoms deviating from those reported in previous studies. We isolated the pathogenic fungal strain YYK-A and YYK-F using the tissue isolation method and verified them using Koch’s postulates. The colony appeared white during early growth and gradually turned black at later stages. The conidia exhibited 3–8 transverse septa, 0–2 longitudinal septa and measured 10.0–53.0 × 5.0–13 µm in size. The strain was identified as Alternaria longipes, which was supported by phylogenetic analyses based on multigene sequences. The inhibitory activity of five fungicidal active substances against A. longipes was investigated using the mycelium growth method to formulate an effective disease management strategy. Honokiol displayed the highest inhibitory activity against A. longipes with an EC₅₀ of 9.57 mg L⁻¹. To our knowledge, this is the first report of A. longipes causing kiwifruit leaf spot in China.