Tonga's mangoes - a treat for pesky pekas and fearsome fungus [1]
Monday, December 19, 2011 - 14:14. Updated on Wednesday, September 11, 2013 - 09:54.
Mangoes are slowly ripening-up on trees under the hot December sun, but despite what appears to be an abundant mango season, fewer mangoes will be left for humans after the C.g. fungus spoils flowers and premature fruit, and the flying foxes or fruit bats (pekas) take their share of what is left.
Agricultural expert, Semisi Pone, reveals why the season of fruitfulness in Tonga is not what it used to be, and the serious threat posed by a fruit fungus.
By Semisi Pone.
According to legend, Hina send two flying foxes (peka), from Samoa, as a present to her lover Sinilau who was living in Tonga. Sinilau kept the pekas on a tree near his house. They multiplied over the years and became a serious pest. I guess Sinilau had to run away to Samoa because the pekas ate all the food. Perhaps it was a cunning ploy by Hina to get Sinilau to come to her? In Tonga the pekas are still eating the mangoes but now they have been out maneuvered by a more serious threat, a fungus.
The scientific name of the fungus is Glomerella cingulata. That is the sexual state of the fungus or more commonly known as a telemorph. But it does not seem to cause too much trouble. It is the asexual state of the fungus or anamorph that is causing all the problems. Called Colletotrichum gloeospororioides (C.g.), it affects the flowers of most fruit trees in Tonga.
Called a "flower blight", it happens in the wet season. That is why a lot of mango trees lose their flowers and fruits, because the fungus causes them to rot and fall off. C.g. also affects yams, bananas, vanilla, kava, vegetables, and can be found on a lot of other plants.
Most people have noticed that fruit trees usually bear fruit if it is dry during the flowering season. But if it is wet the flowers fall off, and they refer to them as "'auhia".
I was in Tonga recently and talked to a lot of locals, who all seemed to have the same conclusion. My feeling is that there may be a shift in the local weather pattern, which makes it wetter during the flowering season, causing the fungus to multiply quickly and destroy the flowers. Global Warming, perhaps? The fungus is not a problem during the dry season.
There is another fungus called Oidium mangiferae, or powdery mildew, which attacks mango flowers during the dry season, but it is not in Tonga yet.
As far as I know, C.g. causes 100% loss of mango fruits every wet year. I think this may be the case with the other fruits. A former school mate told me that he has not seen a tava tree fruiting in the past few years. It may be timely to find out what is going on with the fruit trees. Buying containers of apples and oranges imported from New Zealand is expensive. However, a Tristeza virus has wiped out our oranges and mandarins totally. There are few citrus trees around but not many.
I have made a proposal to the University of Auckland to do a PhD programme on the Biocontrol of the flower blight in Tonga.
I believe the University will approve it, as the results will be useful to other Pacific Islands as well as New Zealand. New Zealand has a huge problem with the PSA (Pseudomonas syringae pv actinidae) bacteria on its $1.5 billion kiwifruit industry. They had to destroy $100 million worth of the golden kiwifruit, because it was too susceptible to PSA.
My results may also be useful to control C.g. and C. acutatum on Avocado and other crops in New Zealand.
So the only thing left to do now, if you want to enjoy those few juicy surviving mangoes, is to find a microorganism to knockout the pesky peka.