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Format:
Print
Author:
Bao, Yong
Dept./Program:
Plant and Soil Science
Year:
2010
Degree:
MS
Abstract:
Plant-parasitic nematodes are distributed worldwide, and cause yield and quality losses for most vegetable and field crops. Although crop damage due to nematodes in Vermont vegetable fields has been suspected, no formal statewide nematode survey has been conducted to date. The first objective of this study was to determine the frequency, abundance and distribution of nematodes associated with mixed vegetable production in Vermont. Sixty-six soil samples were collected from tomato, green bean and lettuce fields on 36 vegetable farms across Vermont at the beginning and end ofthe growing season 2008. Root lesion nematode (Pratylenchus penetrans) was encountered most frequently, with detection being 97% of the fields sampled.
Northern root knot nematode (Meloidogyne hapla) was only observed with low abundance in a few fields, but only one field contained abundance that exceeded the established economic threshold (100 individuals/100 cm³ dry soil). More vegetable fields were infested heavily by P. penetrans throughout more counties at the end than beginning of season. A soil bioassay with soybean plants suggested that the number of lesions cause by lesion nematodes on primary roots was correlated positively to soil infestation levels of P. penetrans. All cover crops commonly planted in vegetable fields reduced abundance of root lesion nematodes, especially clover as an over-winter cover crop (p=0.0072).
This survey indicated that root lesion nematode is prevalent and likely an economic concern that may cause vegetable yield loss in Vermont. The second objective of this study was to determine the effect of tillage and biocides on nematode community and extracellular enzyme activities in the soybean cyst nematode (SCN)-suppressive soil in a greenhouse experiment. SCN Guvenile stage 2) J2 population tended to decline when the soils were tilled, however increased rapidly when treated with biocides in the descending order of streptomycin and captan, captan, and streptomycin.
Tillage reduced nematode community diversity and richness index values, and increased dominance and maturity index values. Values ofa maturity index increased with the application of biocides. With tillage, the activity of the extracellular enzyme, L-proline aminopeptidase, was reduced to less than half of that under no-till practice. This experiment suggests that both bacteria and fungi were involved in the soil suppressiveness to SCN; intensive tillage and biocides application may diminish the soil suppressiveness by reducing soil community biodiversity and richness.