Breakdown of sweetpotato (Ipomoea batatas) bedding roots: investigating plant pathogenic bacteria and fungi and implications for their management in Australia and Papua New Guinea

Breakdown of sweetpotato (Ipomoea batatas) bedding roots: investigating plant pathogenic bacteria and fungi and implications for their management in Australia and Papua New Guinea

The breakdown of storage roots in sweetpotato (Ipomoea batatas) plant beds at commercial production sites in Australia and Papua New Guinea (PNG) poses a significant concern, as it adversely affects the productivity, quality, and quantity of premium sprouts intended for field planting. This decline in productivity is linked to issues such as sprout wilt and death, and premature breakdown of storage roots, irregular vine growth, delayed sprout emergence, extended time to achieve optimal sprout length, and a reduced number of viable sprouts. Biotic factors, including soilborne pathogens and endophytic bacteria and fungi, are suspected contributors to these problems. Pathogens such as Erwinia spp., Fusarium spp. and Sclerotium rolfsii have been previously implicated in storage root rots and sprout wilting in Australia. However, it is still unclear which of these microorganisms are associated with or are the cause of the breakdown of sweetpotato storage roots in Australia and PNG. This study aimed to isolate, characterise, and identify both pathogenic and endophytic fungi and bacteria at the species-level that may be responsible for the premature breakdown of sweetpotato storage roots in the plant beds. Samples of diseased and healthy storage roots and sprouts were collected from various sweetpotato cultivars in Bundaberg, Australia, and the Highlands of PNG. Morphological characterisation was performed through visual and microscopic assessments, while molecular characterisation included genomic DNA extraction, PCR, and sequencing. A candidate pathogen was identified (Diaporthe batatas), and pathogenicity tests were conducted under controlled conditions using glasshouse trials and a Conviron growth cabinet, confirming Koch’s postulates. The study revealed a diverse range of endophytic and pathogenic fungi present in both diseased and healthy storage roots and sprouts, including novel findings such as the presence of D. batatas. These results provide new insights into the biological factors driving disease in sweetpotato plant beds and establish a comprehensive understanding of the pathogenic and endophytic microbial communities associated with sweetpotato storage roots breakdown. The findings offer practical implications for disease management, equipping sweetpotato growers with critical information to improve farming practices, minimise disease losses, and enhance sustainable production. Furthermore, the outcomes contribute to the commercialisation of sweetpotato in Australia and PNG, and globally, while laying the foundation for future research into sustainable disease management strategies.