Phytophthora palmivora: a serious threat to papaya production in South Africa

Abstract Phytophthora palmivora is an Oomycete pathogen widespread in tropical and subtropical regions, causing severe diseases such as fruit rot, bud rot, blight, cankers, and root rot. Papaya is grown in South Africa by smallholder and commercial farmers in the Limpopo and Mpumalanga provinces. In 2019, widespread symptoms of crown and root rot were observed in South African papaya orchards, leading to significant plant collapse. This study aimed to identify and characterize the pathogen causing papaya tree decline in South Africa, investigate their distribution, and evaluate their virulence. Samples were collected from six commercial orchards. Diseased stems and soil samples were analysed, resulting in isolation of Phytophthora palmivora . Molecular identification using rDNA-ITS, the translation elongation factor-1α (tef-1α), β-tubulin, Cox I and Cox II sequencing confirmed the pathogen, and pathogenicity tests revealed its aggressiveness on papaya fruits. This is the first disease report of P. palmivora in South Africa, where it is a regulated pathogen. Given its destructive potential, P. palmivora poses a serious threat to the papaya industry and possibly other crops such as macadamia, citrus, and avocado. Understanding its distribution and potential introduction routes is critical for implementing effective management strategies to protect South African agriculture from further damage.