Distribution and Virulence Phenotypes of Heterodera Glycines in Missouri

Authors: NIBLACK, T - UNIV OF ILLINOIS; WRATHER, J - UNIV OF MO, DELTA CENTER; HEINZ, R - UNIV OF MO, COLUMBIA; Donald, Patricia

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2003
Publication Date: 10/1/2003
Citation: Niblack, T.L., Wrather, J.A., Heinz, R.D., Donald, P.A. 2003. Distribution and Virulence Phenotypes of Heterodera Glycines in Missouri. Plant Disease. 87:929-932.

Interpretive Summary: A survey was conducted to determine the distribution and diversity of soybean cyst nematode in Missouri soybean production fields. The statistically sound random survey results were compared with data from the nematology diagnostic laboratory to determine if samples submitted to such laboratories provide a skewed estimate of distribution and losses of this pest. Random soil samples were collected in a statistically sound manner using the methodology of the Agriculture Statistical Service to locate fields and collect samples. The nematode distribution described by the random samples was similar to the distribution described by samples submitted to the nematology diagnostic laboratory indicating that data from diagnostic laboratories is not necessarily flawed or skewed. One major finding of the study, however, was that the importance of the pest based on the number of samples submitted by county or region was not valid. The number of samples submitted in a county or region was a better reflection of the educational effort in that area. Using a race test to measure the diversity of the nematode populations, it was found that a majority of the populations were able to reproduce on sources of plant resistance germplasm currently in use. This finding suggests that sources of different plant resistance should be identified and incorporated into commercially available varieties more aggressively than has been done in the past. It also indicates that without new plant germplasm, yield losses due to soybean cyst nematode are likely to start increasing instead of decreasing. Losses in Missouri in the year of the study, 1999, were $58 million.

Technical Abstract: The soybean cyst nematode, Heterodera glycines, is the most economically important pathogen of soybean (Glycine max) in Missouri. Knowledge of the nematode's distribution and ability to adapt to resistant varieties is important for determining crop losses and establishing research priorities. No previous surveys of Missouri have provided reliable population density and phenotypic diversity data; therefore, we conducted a random survey to obtain both. Two samples from each of 200 fields were collected; 392 samples were processed for extractions of cysts and eggs. Two hundred forty seven (63%) of the samples had detectable cyst nematode populations, which ranged from 15 to 149,700 eggs/250 cm3 soil. The lowest average population densities were observed in the east central region of Missouri (2,260 eggs/250 cm3 soil) and the highest were observed in the northeast (9,238 eggs/250 cm3 soil), but among the eight regions sampled, mean population densities did not differ significantly. These population densities were potentially responsible for losses worth over $58 million in 1999 in Missouri. Race tests were conducted on populations from 183 samples. In order of frequency, races 3,1, and 2 accounted for 86% of the H. glycines populations. Nearly 60% of the populations were virulent (able to produce females) on Plant Introduction (PI) 88788, which is one of the sources of resistance for most H. glycines-resistant cultivars. More than a third of the populations were virulent on the cultivar Peking, another common resistance source. Very few populations were virulent on PI 90763 or PI 437654, suggesting that these sources of resistance should be exploited more frequently.