Photo 3. Late-stage infection of jackfruit fruit by Rhizopus stolonifer, showing the groups of spores (sporangia) on long stalks (sporangiophores).
Jackfruit Rhizopus fruit rot
Rhizopus stolonifer; previous names are Mucor stolifer, Rhizopus artocarpi, Rhizopus nigricans.
Worldwide. In the tropics and sub-tropics. It is reported from Cook Islands, Fiji, French Polynesia, Niue, Samoa, and Solomon Islands
Jackfruit, and many other plants are hosts. The fungus is common in the soil on plant debris, and also on many fruits (peach, strawberry) and vegetables after harvest, during transport and in storage. In the Pacific islands, Rhizopus has been recorded on sweet potato, breadfruit, passionfruit, citrus (mandarin and tangerine), and eggplant.
Rhizopus rot is a common disease of jackfruit flowers and young fruit. It causes a soft, watery, brown spot on the fruit (Photo 1) that soon becomes covered in a grey-brown, later black, furry mould (Photos 3&4). Fruit symptoms occur on the tree and in storage.
On jackfruit, it is a primary pathogen, affecting the fruits at all stages of development whereas, on most other fruits and vegetables, Rhizopus infects through wounds caused by insects and weather events, or through cracks caused by abnormal growth. Infections also occur at the stem end of fruits when they are harvested.
In the field, warm, rainy days favour the disease, and high temperatures and humidities favour the disease in storage.
Spread is by large number of spores in the air. Survival occurs as thick-walled spores (black spore masses on top of long stalks (Photo 4), in the soil, on plant debris, and on seed. The spores can withstand long periods of drying and cold. Seed infection occurs after damage by insects or rots of the seed head, or fruit.
Probably a minor disease of little economic impact on jackfruit. However, total loss of fruit and vegetables can occur if there are long periods of warm, rainy weather. In storage, damage is likely if hygiene is poor, and temperatures and humidities are high.
Look for the soft, rapidly development fruit rots on the tree or in storage. Look for the grey fungal growth, turning black as the spores develop.
In most instances, management will not be required as the impact of the disease is low. If environmental conditions are such that they favour the disease, do the following:
If fungicides are required, apply a protectant product, e.g., mancozeb, or a systemic benzimidazole, e.g., thiophanate-methyl or a triazole, e.g., propiconazole. If a systemic product is used, alternate these with sprays of mancozeb.
If the concern is only to protect the fruit in storage, spray once 10 days before harvest.
AUTHORS Grahame Jackson & Eric McKenzie
Information from Plantwide Knowledge Bank. (http://www.plantwise.org/KnowledgeBank/SearchResults.aspx?q=rhizopus&cb=2043). Photos 1,2&4 (taken by Eric McKenzie), and used in this fact sheet, appeared previously in McKenzie E (2013) Rhizopus stolonifer PaDIL - (http://www.padil.gov.au). Photo 3 Ellen Iramu, Honiara, Solomon Isalnds.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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