Discussion
Ten species of root lesion nematodes have been found associated with roots and soils of vegetables crops, but P. loosi (Fig 2) is the predominate species found in Guilan province and also the south-west region of Caspian Sea. At a high soil infestation density, lesion nematodes have been proven to cause significant yield loss. Damage by lesion nematodes to host crops is greater in sandy soils where water and nutrients are generally limited. In addition, lesion nematodes interact with other pathogens in causing increased damage those results in disease. The most common symptom on susceptible trees is a slow decline as the nematodes increase to very high numbers over the years. The foliage of diseased trees may appear lighter green or chlorotic (Fig 3). Once inside the root, lesion nematodes feed and move only cortical cells.
This sort of feeding does not greatly disturb the plant function. However, if population build up to high levels, the nematodes will begin to feed on tissues and plants may show visual sign of injury such as yellowing. Flowers or fruit may be reduced substantially in number and quality. The vigor of the host is reduced, and the plant may be predisposed to winter injury or other infectious diseases. The symptoms on infected roots initially are small, light to dark brown lesions (Fig 8A). These lesions tend to expand and to merge as the growing season progresses, giving the roots a discolored appearance overall. Nematode feeding causes cortical tissue disintegration and girdling (Fig 8B), resulting in the sloughing off of the epidermis and remaining cortex and a reduction in the size of the root system.
P. loosi and P. neglectus were the most frequently encountered species; however, mean population, distribution in the zone P. loosi was more than the other species. The effect of these nematodes on citrus trees in these regions in not known. Due to economical importance of P. loosi and its introduction as a new host for citrus in the zone, it is suggested that further investigations be