Chocolate Crisis by Dale Walters

Author:Dale Walters
Language: eng
Format: epub
Publisher: University of Florida Press
Published: 2020-12-15T00:00:00+00:00

9

Vascular Trouble

Papua New Guinea (PNG) occupies the eastern half of the island of New Guinea and includes the neighboring islands of New Britain and Bougainville. The western half of the island forms the Indonesian provinces of Papua and West Papua. Cacao was introduced to PNG around 1900 when Trinitario-type seed was brought to the country, most likely from Samoa (Wood and Lass 1985, 578). At the time the northern part of the country was under German rule, while the south of the country had been colonized by the British since 1884. Both parts ended up under Australian administration until its independence in 1975. PNG exported its first cacao beans in 1905, but production was small and did not increase much over the subsequent years, so that by 1940 only 200 tonnes were exported. Most of the crop was grown on the island of New Britain, and much of the cacao planting there was badly damaged during the war. The end of the war saw a rapid expansion in production, with 1,000 tonnes produced in 1950 increasing to 30,000 tonnes in 1970 (Wood and Lass 1985, 578). Production levels have stayed much the same since, and in 2017 output was 40,000 tonnes (Statista.com n.d.).

Two major problems continue to affect cacao in PNG: pod borers, which we will look at in the next chapter, and a fungal disease known as vascular-streak dieback (VSD). In the early 1960s, a serious dieback was affecting cacao trees in the Gazelle Peninsula on New Britain. Cacao was long known to suffer from dieback, with gradual loss of leaves and death of branch tips. This dieback is caused by several factors, including lack of shade, nutrient stress, and damage from insects—ideal conditions for invasion by a range of pathogens just waiting for an easy way into the cacao tree. The dieback in New Britain was attributed to infection of weakened stems of the cacao tree by the fungus Lasiodiplodia theobromae, because this pathogen was regularly isolated from diseased samples (McMahon and Purwantara 2016, 310–311). But a young Australian PhD student, Philip Keane, working at the Lowlands Agricultural Experiment Station at Keravat on New Britain, noticed that the first symptoms of the disease occurred well before the branches invaded by Lasiodiplodia died. These initial symptoms occurred on leaves behind the branch tip, and, unlike the dieback caused by stresses, this version affected young healthy trees. Together with his PhD supervisors Ken Lamb and Noel Flentje, Keane found a fungus growing in the xylem or water-conducting vessels of affected trees on which the leaves had begun to turn yellow prior to falling off. The fungus was subsequently found to be a new pathogen of cacao, a basidiomycete eventually given the name Ceratobasidium theobromae. It produced its fruiting bodies during wet weather, with its spores appearing at night following an afternoon of rain. The fungus is a real night-lover, since the majority of spores are released between 1 and 3 a.m. Once liberated from their fruiting bodies, the spores are carried on the wind and are able to infect young cacao leaves.

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