First Report of Pratylenchus neglectus and P. thornei Infecting Canola and Weeds in Iran

Abstract

Cultivation of canola (Brassica napus L.) is relatively new in Iran. Because nearly 90% of Iran's edible oil is imported, farmers are subsidized and encouraged to grow this crop. Except for the sugar beet cyst nematode, Heterodera schachtii, to which susceptibility of some canola cultivars has been established (1), information on other nematode pests of canola is lacking. During a survey from April-May 2002 and repeated in 2003, soil and root samples of winter canola and weeds were collected at harvest of canola from research stations and farmers' fields in the south, west, and northwest of Tehran Province. Each sample was a composite of 25 roots and 2 kg of soil per hectare, collected from the rhizosphere of canola with a 2.5-cm-diameter soil corer. Samples were put in plastic bags and kept at 5°C until they were processed, within 2 weeks from sampling. Samples were sieved through a 0.840-cm aperture sieveand mixed thoroughly. Nematodes were extracted from subsamples of 5 g of roots and 250 g of soil with a modification of the sugar centrifugal flotation method (2), counted, and identified. Two species of root lesion nematodes, Pratylenchus neglectus and P. thornei, were found. When they were present in the same field, they occurred in the roots of both Regents × Cobra and Orient cultivars. Averages of 28 and 321 P. thornei per gram were found in the roots of cvs. Regents × Cobra and Orient, respectively. Averages of 30, 1,026, 626, and 450 P. neglectus per gram of roots of cvs. Regents × Cobra, Orient, Ocapi, and GLSIO were detected, respectively, in different fields. Heavily infected plants were stunted and had roots with dark lesions, a symptom typical of the attacks by these nematodes. Generally, greater nematode densities were in the roots than in the soil and both nematode species were more abundant in cooler than in warmer areas of the province. Since these nematodes are also severe pests of wheat, which is also grown in the province, they could pose a potential threat to both crops. Weeds that were present in the sampled fields belonged to the botanical families Scrophulariaceae, Gramineae, Euphorbiaceae, Crucifereae, and Compositeae. Between 22 and 1,500 P. thornei and 17 P. neglectus per gram of roots of Crucifereae and 280 P. thornei per gram of roots of Gramineae were found. To our knowledge, this is the first report of lesion nematodes infecting canola plants in Iran.