Submitted to: Australasian Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2010
Publication Date: 11/17/2010
Citation: Pokharel, R.R., Abawi, G.S., Duxbury, J.M., Smart, C.D., Wang, X., Brito, J.A. 2010. Variability and the recognition of two races in Meloidogyne graminicola. Australasian Plant Pathology. 39:326-333. Interpretive Summary: The rice root-knot nematode is widely distributed in rice-growing areas throughout Asia and also occurs in several states in the US. This species of root-knot nematode not only infects rice, but also wheat and some vegetables and weed species. Studies concerning differences between nematode isolates originated from Asian countries and the US are limited. In this paper we compared the morphological, molecular, and pathogenic characteristics of ten isolates of the rice root-knot nematode collected from Bangladesh, India, Nepal, and Florida. We found that the Florida isolate had similar morphological characteristics and ITS sequences but a different host range from isolates collected from Bangladesh, India, and Nepal, suggesting that the Florida isolate might represent a second race different from those originated from the three Asian countries. We also analyzed ITS sequences from the ten isolates and identified that multiple ITS sequences occurred within individual nematodes in some isolates. The rice root-knot nematode reported in the US can infect different plant species; therefore, a further study of the pest is needed.
Technical Abstract: The rice root-knot nematode, Meloidogyne graminicola, is an important pathogen, impacting rice, wheat and possibly vegetable production in South-East Asia. Ten isolates of M. graminicola from broad geographic areas were compared using traditional and molecular methods. Total body length, oesophageal length, maximum body width and tail length were measured in 40 juveniles and the perineal patterns of 10 females per isolate were compared. Pathogenicity was determined on a variety of hosts. The internally transcribed spacer (ITS) region was amplified and sequenced to confirm the identity and phylogenetic relationships of the isolates. Substantial variation observed in morphometric measurements among and within isolates did not correlate with the geographic source of the isolates. All the isolates were similar in host range, but the M. graminicola-Florida isolate differed from the other nine isolates in that it was not pathogenic to rice cvv. Labelle, LA 110, Cocodrie, BR 11, and Mansuli, suggesting that M. graminicola consists of more than one race. ITS sequences of all 10 isolates matched with those of M. graminicola in GenBank and formed a single clade in the phylogenetic analysis with minor variations among and within isolates. Multiple ITS sequences occurred within individual juveniles in some of the isolates.