Sunday , 24 March 2019

Destroying Rainmaker Mushrooms

Nandkumar Kamat

There is a mycological dimension to rainfall which has been completely overlooked by meteorologists. Mushrooms produce 30 thousand tiny spores a second and these disperse in the atmosphere to act as nuclei for cloud formation. The spores carry a sugar called Mannitol traces of which are found in atmosphere. From Mannitol concentration scientists have estimated that annually 50 million tons of spores are released over earth and they play an important role over thick forest canopies to form rain bearing clouds.

States along Western Ghats from Kerala to Gujarat are destroying rainmaker mushrooms, some of the most dominant species in forests and grasslands due to their overexploitation to meet booming market demand. Along entire Western Ghats of India lies the largest gene pool of a unique fungus Termitomyces which cannot exist without its cultivator – the termites. Attempts to domesticate it have failed although I am the only scientist in the world to make it fruit in the laboratory during work done for my PhD.

This fungus which spends 10 months inside the dark underground chamber fruits with onset of monsoon. Thanks to total neglect and indifference from forest department and Goa state biodiversity board, from the beginning of this month wild edible mushrooms are being picked up in thousands at young, immature stages from their natural habitat – the termite hills and are sold at premium prices ranging from `500 to `1000 for a packet of 50.

Till October 2015, the role of such gilled mushrooms was unknown in formation of clouds and bringing rains. Then a paper was published and drew the attention of the world about the role mushrooms play as rainmakers (Hassett, Maribeth O, Mark W F Fischer, and Nicholas P Money. “Mushrooms as rainmakers: how spores act as nuclei for raindrops.” PloS one 10.10 (2015): e0140407.) The credit for this stupendous discovery goes to Nicholas Money, biologist at Miami University in Oxford, Ohio who specialises in the study of fungal growth and reproduction. He used environmental electron microscope to show that spores “grow water drops” in the lab in a way that makes it very likely that they would behave in the same fashion in the humid interior of a cloud.

This finding that the special properties of spores cause water vapour to condense into liquid water on their surface shows that they are unlike other airborne particulates. The astonishing numbers of airborne spores suggests that they may contribute to drop formation in clouds and stimulate rainfall. Relative to other particles in clouds, spores may be significant because they form droplets of a perfect size to stimulate rainfall.

Mushrooms are fascinating in their spore discharge mechanisms. Money provides an example of a fungus called Pilobolus which launches a capsule filled with 90,000 spores at a speed of 32 kilometres per hour over a distance of 2.5 metres. Scaled to human dimensions, this is equivalent to a 9 kilometres flight. Money explained the process: “The spores of mushrooms and related basidiomycete fungi that use the same launch mechanism (called a surface tension catapult) jump over a maximum distance of 1 millimeter. This does not seem very impressive, but it is a marvel of evolutionary engineering. In a mushroom, the discharged spore is shot into the air space between the gills and is stopped dead by the viscosity of the air (the microscopic spore has negligible inertia). It then falls between the gills and is swept away by air currents circulating around the cap of the fruit body. Convection and wind are responsible for lifting the spore into the atmosphere. The diversity and distribution patterns of mushroom-forming fungi are evidence of the effectiveness of this process as a dispersal mechanism. A single mushroom can release 30,000 spores per second from its gills, billions of particles in a day.”

These can be launched in air upto 30 kilometres but cloud formation takes place in troposphere where the density of these spores seems to be high. Now what relevance this has to mushrooms exploited from Western Ghats and especially from Goa? The edible Termitomyces mushrooms sold in Goa are not allowed to reach their spore formation stage. These mushrooms grow on termite hills. The density of termite hills ranges from 8 to 10 in forests and upto 68 in grasslands per hectare. If we take area under forests and grasslands in Goa we get about two million termite hills. Not all termite hills produce mushrooms every year. Not all mushrooms reach mature stage because there are snails, beetles, animals which damage and consume these species.

Each mushroom when fully mature and after attaining the open cap size produces upto four billion basidiospores. More than five to ten million such mushrooms are annually harvested in Goa before these reach the final stage. In nature when this stage decomposes the tissues as well as spores deposited on the mound are transported inside the underground chamber by worker termites to re-inoculate their fresh fungus garden. The fungus cultivator termites don’t get adequate number of spores. On the other side removal of these mushrooms at immature stages causes a net deficit in natural spore discharge budget which is beneficial for cloud formation and rainfall. The craving of Goans and others for these seasonal delicacies would have a heavy price in future – less rainfall in all Western Ghat talukas.

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