Abstract
Nematode-resistant cover crops can suppress populations of plant-parasitic nematodes. Samples of a loamy and a sandy loam soil were collected from two sugar beet fields in Lower Saxonia, northern Germany (“Jeinsen” and “Gross Munzel”) to measure the effects of cover cropping on the population genetic structure and infectivity of Heterodera schachtii as well as the composition of soil microbial communities. These fields allowed for a comparison of cover cropping with Brassica species resistant to Heterodera schachtii to fallow. In a series of radish bioassays with H. schachtii populations from Jeinsen and Gross Munzel, ratios of second-stage juveniles in roots per eggs in soil were higher in soil from under Brassica cropping than from under fallow. In denaturing gradient gelelectrophoresis, profiles of the parasitism gene vap1 differed between Brassica and fallow treatments in both populations. At Gross Munzel, microbes of soils and within nematode cysts differed between Brassica and fallow areas. Specifically, the frequency and occurrence of isolates of Pochonia chlamydosporia and Exophiala salmonis were lower within the cysts from Brassica than from fallow treatments. Overall, cover cropping with resistant Brassica species affected the bacteria and fungi infecting the cysts and subsequently, the infectivity of the H. schachtii population. Cover crop effects on nematode virulence (vap1 gene) and microbial colonization of the cysts could affect long-term nematode population dynamics.
Highlights
Heterodera schachtii is one of the most important pests of sugar beet, and has been the subject of intensive investigations for over 150 years [1]
Treatments had been established as strips: (1) fallow: one pass of tillage after the cereal harvest in August 2011, fallow, and (2) cover crop of resistant oilseed radish Raphanus sativus ‘Colonel’ that was planted on 16 August 2011 at a planting density of 25 kg/ha, and cultivated until the end of November
Cover cropping with H. schachtii-resistant oilseed radish and mustard led to cysts with varying microbial communities and with a change in the virulence gene vap1
Summary
Heterodera schachtii is one of the most important pests of sugar beet, and has been the subject of intensive investigations for over 150 years [1]. The lemon-shaped cyst of H. schachtii contains the primary inoculum of up to 600 nematode eggs with the contained second-stage juvenile (J2). Or stimulated by root exudates, J2 hatch from the eggs and move through the soil to infect host plant roots. Nematodes become sedentary, and develop into adults after several molts. Management of H. schachtii relies on a wide rotation of host crops with non-hosts, cover cropping with resistant hosts, and cultivating resistant or tolerant sugar beet cultivars. Other management tactics (e.g., application of granular nematicides) lack economic feasibility or are not registered
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