In a significant study to find out why sandalwood spike disease (SSD) has almost wiped out sandalwood from forests of southern India, scientists from National Centre for Cell Science (NCCS) and Bengaluru’s Institute of Wood Science and Technology have reported that the disease was spreading through sandalwood seedlings.
While it is known that sap-sucking insect vectors transmit phytoplasmas, this team found SSD was spreading through seeds too. In the last three years, over 200 seeds from SSD-affected trees and over 500 seedlings generated using commercially purchased seeds were screened for the presence of SSD phytoplasma.
Dr Amit Yadav and his team at Pune’s NCCS in collaboration with Dr R Sundarraj from the Bengaluru-based institute were behind the study that has been published recently in Biology – an international, peer-reviewed journal.
For their research, the scientists grew sandalwood seedlings in an insect-free greenhouse and found one-month and four-month-old seedlings testing positive for SSD phytoplasma.
Phytoplasmas are recently discovered bacterial plant pathogens causing severe yield losses in many crops. Caused by phytoplasmas, SSD has threatened the existence of sandalwood in India.
“The epidemiology of SSD is still poorly understood despite the efforts to understand the involvement of insect vectors in SSD transmission over the last two decades,” Dr Yadav said.
(Express sourced)
Apart from the transmission of SSD phytoplasma through insect vectors, the information on vertical transmission through seeds was entirely unknown, scientists pointed out.
SSD has been known for over 100 years and has adversely affected the natural population of sandalwood in the southern states, leading to a severe shortage of sandalwood-based products. The production of this wood has decreased annually in the country by 20 per cent since 1995. The decline in natural population has pushed sandalwood into the International Union for Conservation of Nature (IUCN) “red list” of threatened species in 1998 and listed as “vulnerable (vu)” in 2019, according to researchers.
In India, nursery-raised seedlings have been a primary source of sandalwood saplings distributed to the private and state forest departments.
“We used advanced and highly sensitive real-time PCR assays to detect the phytoplasma DNA. The real-time nested PCR-based screening revealed an alarming rate of 38.66 per cent and 23.23 per cent phytoplasma positivity in one-month and four-month-old seedlings, respectively. Usually, embryos (which give rise to seedlings) are considered sterile. These results were further validated by visualising the phytoplasma cells in sandalwood tissues using scanning electron microscopy,” Dr Yadav added.
The presence of phytoplasmas in the seeds and seedlings is a concern for the commercial distribution of sandalwood seedlings. This also poses a fear of spreading the disease to newer areas where efforts to re-establish the healthy sandalwood population are underway.
