Phylogenetic and pathogenic characterization of Phytophthora species associated with decline of horticultural crops in high humid tropic region of Western Ghats, India

Abstract

The aim of this study was to identify and characterize the Phytophthora species responsible for various diseases in horticultural crops, including avocado root rot, black pepper quick wilt, cacao black pod, guava fruit rot, and papaya root rot. Samples were collected from the Kodugu district of Karnataka, India, which falls within the Western Ghats. The favorable climatic conditions of the Western Ghats support the cultivation of diverse horticultural crops, encompassing fruits, spices, and plantation crops. However, this conducive environment also promotes the presence of Phytophthora species, which act as causative agents for various diseases in horticultural crops. Several recovered isolates exhibited typical colony morphology associated with Phytophthora, featuring a white cottony mycelium. Colonies displayed various patterns, ranging from non-distinctive to stellate with a chrysanthemum shape. Both sporangia and chlamydospores were observed upon induction in a sterile soil solution. The mycelial appearance and sporangial shape of the isolates resembled different Phytophthora species. Through a concatenated analysis of the internal transcribed spacer region (ITS), cytochrome c oxidase subunit I (COXI), and β-tubulin (β-tub) genes, three species infecting avocado were identified: P. cinnamomi (3 isolates), P. nicotianae (1 isolate), and P. tropicalis (1 isolate). Additionally, a species identified as P. tropicalis was found to infect black pepper (2 isolates) and cacao (1 isolate). The isolates causing disease in guava were identified as P. nicotianae (2 isolates), while those infecting papaya were identified as P. palmivora (2 isolates). Notably, this study reports the first instance of P. nicotianae and P. tropicalis infecting avocado in India, expanding our understanding of Phytophthora species distribution and host interactions.