What nematode is responsible for root knot disease in carrots?

Meloidogyne incognita is the nematode species primarily responsible for root knot disease in carrots. This type of nematode is a plant-parasitic organism that specifically targets the roots of various plants, including carrots. When Meloidogyne incognita invades carrot roots, it induces the formation of galls or "knots," which can disrupt the vascular system of the plant, leading to nutrient and water uptake issues. This condition often results in stunted growth, yellowing leaves, and reduced yield.

The other nematodes listed, such as Paratrichodorus spp. and Longidorus africanus, are associated with different plant pathologies and do not specifically cause root knot disease. Pythium sulcatum, on the other hand, is a water mold that causes damping-off disease in seedlings and young plants but is also unrelated to root knot disease. Understanding the specific roles of these organisms can help in managing and preventing disease in agricultural practices.