Photo 1. Spots, light brown with yellow haloes, on leaf of passionfruit caused by Alternaria alternata.
Photo 2. Spots on passionfruit caused by Alternaria passiflora; they are generally larger than those of Alternaria alternata, especially on the fruits and stems.
Photo 3. Deeply sunken spots on a granadilla fruit, covered with dark spore masses of Alternaria passiflorae.
Brown spot and Alternata spot
Alternaria passiflorae (brown spot) and Alternaria alternata (Alternata spot).
Worldwide. It is recorded from Australia, Fiji, New Caledonia, New Zealand, Niue, Papua New Guinea, and Tonga (Alternaria passiflorae), and Australia, Niue, Samoa, and Vanuatu (Alternaria alternata).
Passionfruit, granadilla and weed relatives (e.g., stinking passion flower, Passiflora foetida).
Symptoms of both species are similar and it would be difficult to tell them apart without microscopic examination of the fungi involved.
On the leaves, the spots are 6-10 mm wide, brown at first, becoming light brown later. Yellow haloes surround the spots of Alternaria alternata (Photo 1). Leaves fall after developing only a few spots. Spots also occur on the stems; those of Alternaria passiflorae are larger, up to 30 mm, and sometimes girdle and kill the stems (Photo 2). Stem spots of Alternaria alternata rarely kill the stems.
Similar symptoms occur on granadilla (Photo 3).
On the fruits, the spots start as tiny greyish spots, and then become light brown, and finally dark brown (Photo 4), with wrinkled, sunken centres (Alternaria alternata), usually less than 10 mm diameter. Spots of Alternaria alternata are generally larger, and may cover one side of the fruit.
Spores produced on the fruit, leaves and stems are spread in wind and rain.
Two fungi are the cause of these two closely related diseases. They are especially severe in warm, wet weather. In Samoa, it is estimated that losses from Alternaria alternata can reach 30% in the higher areas where the crop is grown. There are, however, differences between varieties in their resistance to the disease. Spots less than 10 mm on the fruits can still be used for juice, but, if more than that, the fruits usually have internal rots and cannot be processed.
Alternaria alternata and Alternaria passiflorae are both serious diseases in Australia. They can cause significant loss of yield due to leaf damage, and in the case of infection by Alternaria alternata, damage to the fruit, so that it is only fit for processing.
Look for brown spots with light centres on the fruit, leaves and stem. Look for the wrinkled spots on the fruits; those of Alternaria passiflorae are sunken, rotting the flesh beneath the skin.
Cultural control is particularly important in the management of this disease:
Yellow passionfruit is tolerant, but purple passion fruit and hybrids between purple and yellow are very susceptible.
Where these diseases are present, in countries that are hot and have high rainfall, chemical control may be required to obtain an acceptable crop. If fungicides are needed, use sprays of copper or mancozeb.
AUTHOR Grahame Jackson
Information from Gerlach WWP (1988) Plant diseases of Western Samoa. Samoan German Crop Protection Project, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) Gmbh, Germany; and information (and Photos 1,2&4) from Diseases of fruit crops in Australia (2009). Editors, Tony Cooke, Denis Persley, Susan House. CSIRO Publishing. Photo 3 Kohler F, Pellegrin F, Jackson G, McKenzie E (1997) Diseases of cultivated crops in Pacific Island countries. South Pacific Commission. Pirie Printers Pty Limited, Canberra, Australia.
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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