Witches' broom disease on cocoa in Rondonia, Brazil: pod infection in relation to pod susceptibility, wetness, inoculum, and phytosanitation

Abstract

Infection of cocoa pods by Crinipellis perniciosa was examined in the field in relation to pod susceptibility and variations in inoculum and climate over 2 years. The disease was incubated for 13 or 14 weeks in pods inoculated when 2 and 4 weeks old, and for 12 weeks in pods inoculated 6-12 weeks old. Pods were uniformly susceptible to natural infection during the 12 weeks after pollination. Over 75% of rain showers started between 12.00 and 02.00 h, providing sufficient water to rehydrate basidiocarps as well as to wet pods. Pods remained wet after rainfall for decreasing periods when rain occurred after 13.00 h. Incidence of pod disease was shown to be related to the number of wetness periods longer than 4 h, and to the number of open turgid basidiocarps occurring 12 weeks earlier. Wetness periods had a greater influence on disease. Pod infection was modelled by assuming that infection was limited by either wetness periods or turgid basidiocarp numbers; critical numbers of wetness periods when both factors were of equal weight were defined by an exponential equation. The model was used to predict reductions in pod disease associated with different amounts of broom removal in each year.

Moniliophthora perniciosa, the causal agent of witches’ broom disease of cacao: what's new from this old foe?

“…Phytosanitation, i.e. the removal and destruction of diseased plant parts, has been shown to reduce pod loss and delay disease epiphytotics of WBD (Rudgard and Butler, 1987; Soberanis et al ., 1999). However, this strategy is tedious and expensive, and in one study it was shown that 95% removal was required to achieve 50% reduction in pod loss (Rudgard and Butler, 1987).…”

The Impact of Plant Diseases on World Chocolate Production

“…Broadly, there are four major strategies that may be adopted: phytosanitation, chemical control, genetic resistance, and biological control (18). Phytosanitation, by removal and destruction of diseased plant parts, has been shown to reduce pod loss and delay disease epidemics (32,34). However, this strategy is tedious and in one study it has been shown that 95% removal is required to achieve 50% reduction in pod loss (32).…”

Plant pathology in a developing world

“…And this has highlighted a more general problem, a lack of sound epidemiological data from the various areas of South America where this disease is devastating. At least for Rondonia, this deficiency has been alleviated by the studies of Rudgard (1986aRudgard ( , 1987 and Rudgard & Butler (1987).…”