Witches’ Broom and Biodiversity

Throughout history Humans have been quite fond of the cacao tree and in the past couple hundred years we have facilitated its spread in lands far from its home in South America. There is a stark contrast between the fate of the genetically stale cacao tree and the rest of South America’s cornucopia of biodiversity. In modern times we go to great lengths to preserve and even increase the genetic diversity of the cacao trees while steadily chipped away at the diversity of South America through deforestation and climate change factors. The lack of genetic diversity of the cacao tree makes it very vulnerable to fungi like Witches’ Broom which hits cacao production hard and consistently devastates the production of regions it spreads to by 50%-90% (Meinhardt 577). For some fungi, Frosty Pod for instance, there has been some breakthroughs in building the cacao trees’ resistance, but Witches’ Broom has had very little in the way of breakthroughs. A short 2014 article in The Plant Cell stated that “there is no known treatment for witches’ broom disease” (Farquharson). This statement is perhaps a little too sweeping since there have been ways of removing the disease from a tree for over 100 years. Nonetheless, those methods are work intensive and do not guarantee the disease will not return. The cacao tree represents the risks which a lack of genetic diversity brings. As species and subspecies are eliminated one by one from South America it becomes easier to see how the challenges we face with the cacao tree will be similar to future challenges in maintaining a non-biodiverse environment as a whole.

The first documentation of Witches’ Broom, Moniliophthora perniciosa, was by a man named Alexandre Rodrigues Ferreira in 1785 (Purdy 579). Ferreira was born in Brazil in 1756 and went to the University of Coimbra (Martins 242). In 1783 he was tasked by the portuguese to lead an expedition into Brazil for the purpose of documenting both the nature and the people they come across (Martins 242), and it was during that expedition that he describes what is thought to be Witches’ Broom (Meinhardt 577).

Witches’ Broom has previously existed in Bolivia, Brazil, Peru, and Venezuela for a long time, but in the past couple of hundred years it has spread (Purdy 579). In 1895 arrived in Surinam and proceeded to devastate plantations reducing the production by 80% (Money 73). After that it has over the past century infected “Guyana (1906); Colombia (1917); Ecuador (1921); Trinidad (1928); Tobago (1939); Grenada (1948); St. Vincent (1988); Panama (1989); and Brazil, the state of Bahia (1989)” (Purdy 579). In short it has touched large portions of South America and the Caribbean inevitably results in a region’s chocolate producing power relative to the rest of the world dropping precipitously. Luckily for countries outside South America harboring cacao trees the range of the fungus is around 100-150km, but this does not mean someone couldn’t accidentally or intentionally bring it in, and a great deal of money could be earned if an investor happened to know which countries will have their cacao trees devastated by Witches’ Broom  (Money 75-76).

The fungus’ spread through a plant begins by consuming the living material of its victim, but after a couple of weeks it begins to rapidly kill and then consume dead tissue in the 0415-pink-mushrooms296x460plant (Money 70). Finally it will sprout small mushroom-ish growths, seen on the left (Bowers: image), from the infected area and release spores (Money 70). With intervention affected trees are recoverable, but once the fungus arrives the owners of the trees must keep on lookout as the fungus is relentless in its attempts to reinfect.

 

 

In Dr. Constant Johan Jacob van Hall’s book Cocoa written in 1914 he mentions that the number of fungi and insects that afflict the Cacao tree are large and the number of fungia and insects that actually cause harm to the cocoa tree as relatively small, but that the harmful ones can devastate entire plantations (Hall 233). He states that Witches’ Broom causes losses that “probably surpass those of any other disease of the cocoa plant” (Hall 254). An example solution that van Hall proposes is to remove and burn all the leaf bearing branches of the infected tree as seen below, then place black tar on the wounds, after that to treat the trees with a chemical solution to remove any remaining spores (Hall 257). Finally another chemical solution must be reapplied yearly to stop reinfection of the crops (Hall 257). This system of controlling the fungus stops the trees from producing entirely for a whole year and takes several more years for the trees to regain their full production value (Hall 257). However, van Hall does mention in passing that there are experiments where the tree is not completely removing every leaf bearing branch which is a precursor to more modern treatments (Hall 257).

bandicam 2018-03-09 23-41-30-259

Above: example of the methods described by van Hall. You can see the tree has had all its leaf bearing branches removed and is being sprayed down by the man on the right. (Hall 258)

Skip forward around 80 years later and the methods of dealing with the disease have branched out a tiny bit. In Purdy and Schmidt’s Status of Cacao Witches’ Broom they define four means of combating the disease. The first is a system of pruning that is similar to those being experimented with in 1914. The tree may not have every leaf bearing branch removed as in the above picture, but infected parts are trimmed and under dire circumstances it can be necessary to trim everything (Purdy 587-588). The second is the use of fungicides and chemicals to kill or prevent the infections from taking hold on the trees (Purdy 588-589). The third is timing the cacao pods to grow during the dry seasons (Purdy 589). Dryness makes a hostile environment for the spread of Witches’ Broom and the fungus has difficulty taking hold of plants (Purdy 589). And the fourth entails further developing the cacao tree genetic resistance to the fungus that is found in some of the trees (Purdy 589-590). This is what Purdy asd Schmidt propose as the future of combating Witches’ Broom (Purdy 589-590).

None of these solutions guarantee the disease won’t spread either. Purdy and Schmidt dismiss the idea of immunity entirely in favor of resistance as a more achievable goal (Purdy 589). A 2015 article in Scientific American titled The Race to Save Chocolate brings up the possibility of both bioterrorism as well as the risks of accidental spread inherent to global travel (Schmitz). And this is a worrying problem. As biodiversity falls it increases any and every nation’s vulnerability to accidental and intentional spreading of harmful fungi and pests.    

 

Sources:

“Chapter 4.” Cocoa, by Constant Johan Jacob Van. Hall, Macmillan and Co, 1914.

 

Bowers, J. H., et al. “The Impact of Plant Diseases on World Chocolate Production.” Plant Health Progress, 2001, doi:10.1094/php-2001-0709-01-rv

 

Farquharson, Kathleen L. “The Fungus, the Witches’ Broom, and the Chocolate Tree: Deciphering the Molecular Interplay Between Moniliophthora Perniciosa and Theobroma Cacao:” The Plant Cell Online, vol. 26, no. 11, 2014, pp. 4231–4231., doi:10.1105/tpc.114.133462.

 

Martins, Maria Do Rosário, et al. “Body Modification and Paleopathological Evidence in the Iconography from the ‘Philosophical Travel’ to Brazilian Amazonia by Alexandre Rodrigues Ferreira (1783 – 1792).” Antropologia Portuguesa, vol. 27, 2010, pp. 239–257., doi:10.14195/2182-7982_27_13.

 

Meinhardt, Lyndel W., et al. “Moniliophthora Perniciosa, the Causal Agent of Witches’ Broom Disease of Cacao: What’s New from This Old Foe?” Molecular Plant Pathology, vol. 9, no. 5, 2008, pp. 577–588. Wiley Online Library, doi:10.1111/j.1364-3703.2008.00496.x.

 

Money, Nicholas P. The Triumph of the Fungi: a Rotten History. Oxford University Press, 2007, www.oxfordscholarship.com.ezp-prod1.hul.harvard.edu/view/10.1093/acprof:oso/9780195189711.001.0001/acprof-9780195189711.

 

Purdy, Lh, and Ra Schmidt. “STATUS OF CACAO WITCHES’ BROOM: Biology, Epidemiology, and Management.” Annual Review of Phytopathology, vol. 34, no. 1, 1996, pp. 573–594., doi:10.1146/annurev.phyto.34.1.573.

 

Schmitz, Harold, and Howard-Yana Shapiro. “Scientific American.” Scientific American, 1 June 2015. https://www.scientificamerican.com/article/the-race-to-save-chocolate/

 

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