Witches’ Broom Disease Outbreak in Brazil and Control Attempts: Success and Failure in Bahia, Brazil (1989–2009)
Cacao (Theobroma cacao L.), is a perennial crop cultivated mainly in small farms in the tropics, particularly Africa, Asia, and Latin America. It is estimated that 5 to 6 million farmers are involved in cocoa production worldwide and 40 to 50 million people depend on cocoa for their livelihood. Loss caused by diseases, which amounts to 30 percent of the total annual crop, is the major limiting factor to cocoa production.
One of the consequences of globalization is the increase in the movement of people and vegetative material between producer countries, a phenomenon that contributes to the spread of plant diseases in a very short time span (Lopes et al., 2007). One such disease is witches’ broom in cacao. The witches’ broom pathogen, Moniliophthora [Crinipellis] perniciosa, co-evolved with cacao in the diversity center of the Amazon Basin, in South America, and from there spread initially to the neighboring regions and more recently has been spreading to producing areas at farther distance. The first detection of the disease occurred in Surinam, in 1895 (Stahel, 1915), and in the next few decades years reached Bolivia, Colombia, Ecuador, The Guyanas, Grenada, Peru, Venezuela, and Trinidad and Tobago.
In 1989, witches’ broom was introduced in Bahia, the major cocoa producing region of Brazil. The disease consumed approximately 300,000 hectares of cacao in Bahia within three years. Losses as high as 100 percent of the crop were observed in many farms and the country lost 75 percent of its annual production, passing from 450 to less than 100 thousand metric tons per year and from an important exporter to importer of cocoa beans. As a result, many farms were abandoned and more than 200 thousand workers lost their jobs, resulting in an intensive migration from rural to urban areas. The cities in the region, extremely dependent on the cacao economy, were not prepared for that massive migration. They faced complex social problems for years after the introduction of the disease. The culture of cacao in Bahia was changed inextricably forever.
Strategies of Control
The first measure of control attempted was the eradication of the disease by eliminating and burning plants in the focus area (Pereira et al., 1996). However, while the first focus was being eradicated, another one was detected around 100 km apart from the first outbreak and so this measure was determined to be totally ineffective.
The second measure of control attempted was the use of fungicides and biological control agents. Both of them, despite the encouraging results in preliminary trials, did not result in an effective way of controlling the disease.
The third measure, which is most widely used in producer countries having the disease and attempted in Brazil, was the phytosanitary pruning. This is quite efficient when the outbreak of this fungal disease severity is low. However, in the first years of the disease in Bahia, the climate conditions to the disease development and the frequent flushing of the plant, resulted in high severity, many plants having hundreds of infected branches (brooms). Despite its efficiency, many farmers stopped doing it because of the high cost involved, aggravating the situation for neighboring farms that took total removal of brooms as their only hope to contain the disease. With the use of more resistant varieties of cacao (as cited below), the number of brooms per plant was reduced and the local epidemiological studies pointed to more regular periods of pruning. This measure of control became widely used in the region but has not proved sufficient to remove the massive disease pressure of the inoculums.
The fourth measure of control was the use of resistant germplasm; some of them were introduced or developed in the region a long time before the introduction of the disease in the region. However, these varieties despite resistance to witches’ broom, were either susceptible to other diseases introduced in the region after the witches’ broom (Ceratocystis wilt) or did not reach the levels of yield expected. Recently, new clones were developed and have been released to farmers, without those limitations. Today, around 150 thousand hectares of susceptible varieties were replaced by resistant ones. While this has shown some promise, over the last 20 years there has been little or no progress towards recovery in Bahia.
Lastly, with the overwhelming impact of the disease in Bahia, there is a very serious concern that witches’ broom potential to escape into areas where new planting of cacao has begun. The situation today is as dire as it was in 1989!