Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2002
Publication Date: 8/31/2003
Citation: ALDERMAN, S.C., BILSLAND, D.M., GRIESBACH, J.A., MILBRATH, G.M., SCHAAD, N.W., POSTNIKOVA, E. USE OF A SEED SCARIFIER FOR DETECTION AND ENUMERATION OF GALLS OF ANGUINA AND RATHAYIBACTER SPECIES IN ORCHARD GRASS SEED. PLANT DISEASE. 2003. v.87. p. 375-379.
Interpretive Summary: Anguina is a nematode that replaces orchard grass seed with galls. The nematode is associated with the bacterial pathogen Rathayibacter, which destroys the panicle and reduces seed yields. Presence of the galls is of concern in the export of grass seed. There is no quantitative information available on the level of galls present in seed and studies have been hindered by lack of galls for biological and epidemiological studies. In this paper a method for detection and enumeration of galls within orchard grass seed samples was developed and quantitative data on occurrence of galls in orchard grass provided. This is also the first confirmed report of Rathayibacter in the US and the first report that Rathayibacter also replaces seed with galls in orchard grass.
Technical Abstract: Seed galls, caused by Anguina spp. leaf and stem nematodes, are normally easily detected visually in cereals such as wheat and barley. However, in grasses such as orchard grass, the presence of galls induced by Anguina spp. or Rathayibacter (Clavibacter) spp. are difficult to detect visually due to their low occurrence and covering by lemma and palea. To develop improved seed assays for the presence of nematode and bacterial galls, a small scarifier was fabricated to remove the lemma and palea, without causing major damage to the seeds or galls. The galls can then be visually identified and manually counted under a dissecting microscope. Using the new scarifier, several orchard grass seed lots were screened for Anguina and Rathayibacter spp. Percentage of samples of orchard grass seed harvested in Oregon from 1996, 1997, and 2000 containing galls of Anguina spp. were 37, 46 and 48, respectively; percentage of bacterial galls with Rathayibacter spp. from the same samples were 27, 31, and 40, respectively. Total galls with Anguina spp. per 25 g sample ranged from 1 to 24; mean galls per sample in 1996, 1997, and 2000 were 4.0, 4.5, and 4.8, respectively. Total galls with bacteria per 25 g sample ranged from 27 to 40; mean number of galls per sample in 1996, 1997, and 2000 were, 5.6, 4.8, and 11.0, respectively. This is the first report confirming the presence of Rathayibacter spp. galls in orchard grass in Oregon.