Symptoms
Root-knot nematodes are sedentary endoparasites. This means they enter plant roots as juveniles then become stationary, feeding on adjacent plant cells as they grow. This stimulates the root tissue to enlarge and form a gall which is a typical sign of infection. These galls should not be confused with rhizobium nodules found on legumes. These nodules are caused by beneficial nitrogen-fixing bacteria and present as an outgrowth from the root rather than a swelling or gall.
As root-knot nematode numbers increase and plant root systems become more damaged, the plant’s ability to uptake nutrients and water is affected. This leads to stunted growth, yellowing of leaves, wilting despite adequate water and decreased yield.
The stress associated with root damage also makes plants more prone to other diseases. Therefore, losses caused by root-knot nematodes often go unidentified because symptoms are difficult to identify above the ground.
Infestations are often misdiagnosed and are regularly attributed to nutrient or water deficiencies, poor soil or soil-borne diseases. Symptoms usually occur in patches of the crop, with impacted areas often becoming weedy.
Affected potato tubers blister and carrots have galls on the tap or lateral roots and are often forked. Crops are more likely to show symptoms late in the season after nematode populations have had time to build-up.
Meloidogyne fallax can cause more severe external symptoms on potato tubers than other root-knot nematode species and can penetrate the flesh more deeply, causing internal spotting.
