The lustrous green that usually emanates from the many sturdy leaves of the hemp plant was nowhere to be seen. Instead, from this patch of agricultural land in mainland China rose small drab plants whose leaves easily unweaved under the slightest breeze. The roots, onced dug out of the earth, showed numerous swollen vesicles.
Researchers from the Hunan Agricultural University in Changsha city carefully extracted female worm-like bugs and eggs that were lodged in the sickened roots. Back in the laboratory they waited three days for the eggs to hatch and then analyzed the female bugs.
The shape and size of the body matched perfectly with those of the Meloidogyne javanica (M. javanica) roundworm. To definitely confirm the identity of the bugs, the researchers extracted DNA from a newly hatched offspring for analysis. As expected, it contained a string of 517 base pairs in all—identical to M. javanica.
To confirm that the bug was responsible for the sickening of the hemp plants, the team then inserted 400 newly hatched bugs into the pots of 12 hemp plants grown in a greenhouse. Another dozen plants were kept free from bugs as controls. Sixty days later, the plants infested with the M. javanica exhibited the same symptoms as those found initially in the field. The bugs were once again extracted from the plant, and morphological and DNA analyses confirmed for the last time the identity of the species.
A single M. javanica worm can deposit up to 200 eggs on the roots of a plant. In a few days the larvae enclose and start sucking up water and nutrients from the roots of the plants, which start to writhe and swell, forming conspicuous tumorous vesicles. In one to two months the larvae become sexually active and can start the cycle all over again. Such infections can lead directly to the death of the plant, or indirectly, through acquired vulnerability to fungal and bacterial attacks.
This tropical pathogen is capable of infecting a plethora of plants, and is one of the major studied agricultural pests. Over two thousand plants are vulnerable to the wider family of root-knot nematodes to which M. javanica belongs and, together, they are responsible for an estimated 5% of all crops lost worldwide.
Previous reports from South Africa had already evidenced the ability of the M. javanica to infest the hemp plant, but this was the first time such a phenomenon was observed in China. The country shares a history of over 6000 years of hemp cultivation, and today it contains half of the world’s area devoted to hemp fiber and seed plantations. Hopefully, the discovery of M. javanica bug infestations will allow for a timely counter-response and secure the future protection of these crops.
The report is available for free in the journal Plant Disease.
Featured image by Ryan Somma.