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ARS Home » Midwest Area » Urbana, Illinois » Soybean/maize Germplasm, Pathology, and Genetics Research » Research » Publications at this Location » Publication #78474
Title: REGULATION OF HETERODERA GLYCINES POPULATION BY PASTEURIA SP. IN NATURALLY INFESTED SOIL

Author
item ATIBALENTJA, NDEME - UNIV OF ILLINOIS
item Noel, Gregory
item LIAO, TIM - UNIV OF ILLINOIS
item GERTNER, GEORGE - UNIV OF ILLINOIS

Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Soybean cyst nematode is a serious pest of soybean throughout soybean production areas in the United States, causing losses of approximately $325 million annually in the North Central Region. These large annual losses to soybean cyst nematode are deceptive in that much progress has been made in reducing yield loss by following an integrated pest management (IPM) approach. The primary control practices utilized in IPM of soybean cyst nematode at present are the use of crop rotation with nonhost crops and planting of resistant cultivars. Another control practice that also is a component of IPM is the use of biological control. Biological control of plant-parasitic nematodes is a difficult area in which to do research, but progress is being made. In this paper, the population dynamics of soybean cyst nematode and a recently discovered obligate bacterial parasite, Pasteuria sp., is reported. Various mathematical models were evaluated to find the one that best describes the interrelationships of the nematode and Pasteuria sp. In naturally infested field soil, Pasteuria sp. was able to maintain soybean cyst nematode below damage thresholds. Pasteuria is the most promising organism discovered thus far for the biological control of soybean cyst nematode, and may be used as a component of IPM to control this pest.

Technical Abstract: During the 1994 and 1995 growing seasons, soil samples were collected in microplots to determine densities of Heterodera glycines cysts, numbers of eggs per cyst, densities of second-stage juveniles (J2) numbers of Pasteuria endospores per J2, and percentages of endospore-encumbered J2 in 250 cm3 of soil. Although the bi-weekly means of J2 densities climaxed every summer, the fluctuations of the nematode population were not significant (P > 0.05) except for cyst densities. In contrast, the numbers of endospores per J2 and the percentages of endospore-encumbered J2 varied significantly (P < 0.001) over time. The numbers of Pasteuria endospores per J2 followed a negative binomial distribution showing that there was a 0.42 probability for at least one endospore to attach to a J2. Typically, climaxes in population densities of J2 coincided with the decline in the numbers of endospores per J2 and the percentages of endospore-encumbered J2, indicating a regulation of the H. glycines population by Pasteuria sp. The regulation hypothesis was substantiated by the fit of an exponential decay model to the relationship between J2 densities and numbers of endospores per J2. This model demonstrated that J2 densities declined with increasing numbers of endospores per J2 from 287.5 # 5.2 to 67.4 # 3.3 at a rate of 1.2 # 0.1. The steady densities of J2 derived from the exponential decay model were consistent with the predictions of the Lotka-Volterra model of population dynamics based on the equation 0.0195ln(y) - 0.000336y = 0.000049x - 0.00285ln(x) + 0.06589, where x and y represent the bi-weekly means of J2 densities and the percentages of endospore-encumbered J2, respectively.