Worldwide in tropical and sub-tropical countries. Asia, Africa, North, South and Central America, Erope, Oceania. It is recorded from American Samoa, Australia, Federated States of Micronesia, Fiji, French Polynesia, New Caledonia, Northern Mariana Islands, Palau, Papua New Guinea, Samoa, Solomon Islands, Tonga, and Vanuatu. Commonly, it occurs on cocoa, coconut and papaya. Only in American Samoa, Federated States of Micronesia, and Samoa has it been recorded from breadfruit.
It is recorded from Samoa (breadfruit, cocoa and coconut); Fiji (cocoa, coconut, papaya, rubber); Solomon Islands (cocoa, coconut); and Tonga (coconut).
Phytophthora is not a fungus, although much of its biology and life cycle is fungus-like. It is a water mould or an oomycete, related to algae.
The disease on breadfruit usually starts on the lower fruit; this is because heavy rain splashes soil up to a metre above ground level, and soil can contain spores of the water mould. Infection of the fruit causes a brown spot at first, which turns white as it becomes covered with growth of the mould. Spores are formed in this growth. After a few more days, when the spot has grown to about 8-10 cm, the fruit is completely rotten and falls off the tree.
The disease spreads when spores are moved from the spots in wind-driven rain. The spores - called sporangia (a single one is a sporangium) - do not germinate directly; most often they form small swimming spores called zoospores that travel in the water on the fruit surface or wherever they land. There are about 20 zoospores in each sporangium. After a short swim, the zoospores stop moving, germinate and infect the fruit. Fruits can have more than one infection.
On breadfruit, it is only the fruit that is affected (Photo 1), not the leaves or the branches. The disease is not common in Samoa, although in times of prolonged wet weather it can cause large losses on certain varieties. The disease often starts on the lower fruit, and then, depending on the weather and the maturity of the other fruit, spreads to the rest of the fruit. About one week after infection the rotten fruit fall off the tree.
Look for the cottony white growth on the side of the fruit, or perhaps at the bottom. Cut the fruit open to see the brown rot inside. The lemon-shaped spores can be seen with the use of a x10 hand lens.
In Samoa, the variety Puou is said to be more susceptible.
It is unlikely that chemicals would be used against Phytophthora fruit rot, but if they were, perhaps on fruit that is sold on domestic or export markets, protectant fungicides containing copper or mancozeb would be suitable, or systemic products, e.g., metalaxyl, potassium phosphonate or fosetyl-aluminium.
AUTHOR Grahame Jackson
Information (and Photo 1) is from Gerlach WWP (1988) Plant diseases of Western Samoa. Samoan German Crop Protection Project, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) Gmbh, Germany.
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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