A fungal disease may threaten chocolate - or at least the plants it comes from. The fungus causes frosty pod rot, which can decimate cacao plantations. Now, researchers have found that this fungus actually clones itself rather than reproducing sexually.
The fungus itself is called Moniliophthora roreri. In the past, many researchers and cacao breeders believed the fungus produced sexually. This is largely because the fungus belongs to a group of fungi that produces mushrooms, which are the fruit of fungal sex.
Cocoa is one of the few major crops that's produced entirely by small farms. Due to the instability of cocoa prices, fungicides are often a risky investment for growers. Instead, many growers monitor their crop for symptoms of frosty pod rot, and then bury the pods that display telltale dark lesions or white dusting.
The disease itself has spread over the past 60 years. This is probably due to the fact that people have accidentally transported infected pods. In some areas, frosty pod rot has dropped cocoa yields by a staggering 100 percent. This, in turn, has caused growers to abandon their plantations altogether. That's why researchers have taken a closer look at the fungus to understand a bit more about it in order to combat it.
In this latest study, the researchers looked at the genomics and populations genetics of the fungus. This revealed that while the fungus may be able to sexually reproduce, they also found no evidence that mushrooms exist, which would be a sign that the fungus was undergoing sexual reproduction.
"This fungus is phenomenally unusual - it has mating types but doesn't undergo sexual reproduction," said Jorge Díaz-Valderrama, a doctoral student in mycology at Purdue. "This knowledge is biologically and economically valuable as we seek better insights into how mushrooms come about and how we can reduce this disease's damage to the cocoa industry."
The findings show that this fungus is cloning itself rather than reproducing sexually. In addition, the researchers found different variations in the two mating types, which may open the door for breeding programs to figure out which mating type is more virulent and, possibly, develop resistant cacao cultivars.
"We're working on identifying biochemical components that could be useful for controlling frosty pod rot and protecting vulnerable cacao-growing regions," Díaz-Valderrama said.
The findings were published in the March journal Heredity.
