Saturday, 15 July 2006

Effects of Combined Cultural Practices on Suppression of Soilborne Pathogens and Microbial Community Patterns in a Plainfield Sandy Loam.

Mafmudije Selimi, Teresa Balser, Douglas I. Rouse, and Ann MacGuidwin. Univ of Wisconsin - Madison, Dept of Plant Pathology, 1630 Linden Dr., Madison, WI 53706

A four-year field experiment was conducted in Central Wisconsin to evaluate the effect of individual and combined cultural practices on Potato Early Dying a disease complex caused by a synergistic interaction between a soilborne fungus Verticillium dahliae and a migratory endoparasitic nematode Pratylenchus penetrans. The cultural practices evaluated in this study were manure-straw based compost (0, 3 and 9 T/a), fallow, rye and soybean cover crops, and sanitation through the removal of infested plant material (+/-).The experiment consisted of a two-year rotation of potato and snap beans. Beginning with potatoes in 2001, compost was applied in early spring before planting, and vines were removed in late summer at the time of vine killing operations. In 2002, snap beans were planted as a short-season crop, harvested, and the cover crops were established in late July. This allowed us to examine interactions between compost and cover crops. We were able to evaluate the full factorial of compost, cover crops and vine removal on disease beginning in 2003. The identical experimental design was established adjacent to the first experiment beginning in 2002. Therefore, the first time we were able to observe the complete factorial of treatments on potatoes on this repeat of the experiment was in 2004. Bulk soil samples were taken in spring and fall of each year from both sides of the field for Verticillium analysis. Pratylenchus counts were obtained only from soil planted to potatoes. Since little is known about the ecological environment in which this interaction takes place, another objective of this study was to evaluate whether certain microbial community patterns could be associated with disease. A subset of the treatments was chosen based on their impact on disease and information in the literature pertaining to changes in community profiles. Therefore, we selected the compost treatments with/without vine removal, and the two controls fumigation and continuous potatoes. Bulk soil samples were taken in spring and fall of each year where potatoes were planted, and in 2003 rhizosphere soil was obtained from plants in which stem sampling for Verticillium was done. Vine removal reduced Verticillium in both 2003 and 2004. Vine removal also had lower values for all levels of compost, and there was a combined effect of low compost and vine removal on Verticillium in 2004. Interestingly, while high compost treatments did the best job in maintaining yield, they also maintained the highest populations of Verticillium. Pratylenchus populations were highest in soybean treatments in 2003 and there was a combined effect of no compost and soybean on Pratylenchus populations in both 2002 and 2004. While soybean treatments had higher populations than rye or fallow in the compost treatments, these populations were significantly lower than the no compost treatments, thus indicating that compost had a mitigating effect on Pratylenchus populations. Principal components analysis distinguished each sampling date, with gram (-) and fungal lipids characterizing the first and second principle components respectively. Pairwise correlations of the principal components, and pathogen data indicated that gram (-) bacteria were negatively correlated with Verticillium in bulk soil and in the rhizosphere, while Pratylenchus was negatively correlated with fungi and gram (-) bacteria. Rhizosphere soil had greater absolute abundance of lipid biomass, gram (+), gram (-), and fungal lipids than bulk soil. The continuous potato control had lower absolute abundance of gram (+) bacteria, gram (-) bacteria, and fungal lipids in rhizosphere soil than compost and fumigation treatments. Subsequent analysis using canonical correspondence analysis and path analysis is planned in order to further investigate these relationships.

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