Two new species of fungus from the genus Ganoderma have been discovered in Kerala and are linked to coconut stem rot. They also genotyped and found genetic indicators in the two fungal species, Ganoderma keralense and G. pseudoapplanatum. The DNA barcodes have been made public in DNA sequence libraries so that future research might use them to identify the virus early. The findings were reported in the scientific journal Mycologia.
In various places of India, the butt rot or basal stem rot of coconut is known by several names: Ganoderma wilt (Andhra Pradesh), Anaberoga (Karnataka), and Thanjavur wilt (Tamil Nadu), to mention a few.
The illness starts in the roots, although discoloration and rotting of the stem and leaves are common signs. Flowering and nut set to decline in the latter phases, and the coconut palm (Cocos nucifera) eventually dies.
There is a reddish brown oozing. Only in India has this oozing been documented. The plants are unlikely to recover once infected. It’s hardly unexpected, therefore, that this results in a significant loss: According to certain estimates from 2017, over 12 million people in India rely on coconut cultivation.
Another indicator of infection is the appearance of shelf-like “basidiomata” on tree trunks, which are the fungus’ fruiting or reproductive structures. In an email, T.K. Arun Kumar of Zamorin’s Guruvayurappan College, Kohikode, who conducted this study, writes, “Although tiny, many fungus create macroscopic fruiting structures on the substrates where they thrive [for example, Ganoderma].” He goes on to say that Ganoderma’s basidiomata produce reproductive propagules (called spores), which are transported by wind and sometimes by insects. He continues, “That is how the disease transmits from one host to the next.”
Because the fungus is microscopic, it is not discovered until symptoms appear or reproductive structures are borne, which might be too late.
Surprisingly, the disease was previously assigned to the genus Ganoderma, and the exact species implicated had not been appropriately identified. One cause of this might be the scarcity of taxonomic investigations. Plant pathologists may be skilled in identifying diseases based on symptoms, devising disease prevention techniques, and even developing disease-resistant plants. However, among plant pathologists, there is a scarcity of fungal taxonomists who can accurately identify fungal infections, explains Dr. Arun Kumar.
During the years 2015 to 2019, the two-person team gathered data for their study. “A few years ago, there was a large-scale outbreak of the disease in Kerala’s Kozhikode district, and our examination of the collected fungal specimens, as well as collections [over many years] from plantations throughout Kerala, revealed that the identity of pathogenic species was previously unknown,” says Dr. Arun Kumar. As a result, he and Ph.D. student N. Vinjusha decided to dig further into the specimens, first visually and subsequently by genomic sequencing. Both species seemed to be new to science. Dr. Arun Kumar explains, “This finding was based on morphological features, DNA sequences from Kerala collections, and phylogenetic analysis by comparing DNA from all Ganoderma species known worldwide.” The pathogenic species linked to butt rot has been identified because of the research. As a result, disease prevention measures specific to each species may now be established.
Until now, scientists and farmers had to rely solely on visible symptoms of the disease [which appear only after complete colonisation, but now they can easily detect the presence of the pathogen much earlier by analysing plant extracts that can be obtained at any stage of growth, says Dr. Arun Kuma
Source: The Hindu