Winter cover crops as reservoirs of tobacco rattle virus (TRV) and hosts of root-lesion, root knot and stubby-root nematodes
Elmhirst, J.F., Forge, T.A. (2021). Winter cover crops as reservoirs of tobacco rattle virus (TRV) and hosts of root-lesion, root knot and stubby-root nematodes. Canadian Journal of Plant Pathology, [online] 43(4), 631-640. http://dx.doi.org/10.1080/07060661.2020.1867898
Plain language summary
Corky ringspot is an important disease of potato that is caused by virus (Tobacco Rattle Virus, TRV) that is transmitted from plant-to-plant belowground by a group of plant-parasitic nematodes, or roundworms, called stubby root nematodes. Fall-winter cover crops that are grown between successive potato crops may differ in their ability to host stubby root nematodes or TRV, thereby affecting the likelihood that TRV inoculum will be carried through to the next year’s potato crop. In order to compare the efficiency of several potential cover crops as hosts for stubby root nematodes, and the ability of the nematodes to obtain TRV from roots of infected plants and re-transmit to healthy plants, a greenhouse pot study was conducted on four potential fall-winter cover crops (annual ryegrass, perennial tetraploid ryegrass, winter wheat and sorghum-sudangrass) and one rotation crop (sweet corn). Annual ryegrass, perennial ryegrass, and winter wheat were then evaluated in two years of field studies where two additional groups of nematodes that are pests of potato, root-lesion nematodes and root-knot nematodes, were present in addition to stubby root nematodes. Results of the greenhouse experiment indicated that annual ryegrass, perennial ryegrass and winter wheat each suppressed re-transmission of TRV via stubby root nematodes. Results of the field experiment indicated that neither of those crops would foster the buildup of populations of either stubby root, root-lesion or root-knot nematodes, suggesting that they would be good choices for fall-winter cover crops in potato rotations where corky ringspot and these nematodes are present.
A greenhouse pot study was conducted on four cover crops (annual ryegrass, perennial tetraploid ryegrass, winter wheat cv. ‘Caledonia’ and sorghum-sudangrass) and one rotation crop (sweet corn cv. ‘Sheba’) to compare the efficiency of these crop species as hosts of Paratrichodorus minor (Colbran) Siddiqi, and the ability of the nematodes to acquire tobacco rattle virus (TRV) from roots of infected plants and re-transmit it to healthy plants. P. minor reproduced rapidly on sorghum-sudangrass and sweet corn and re-transmitted the virus to indicator plants. Annual ryegrass, perennial ryegrass, and winter wheat cv. ‘Caledonia’, all of which re-transmitted TRV poorly in the greenhouse, were evaluated in two years of field studies for fall establishment and soil coverage, nutrient sequestration, effect on parasitic nematode populations and on subsequent potato crops. Annual ryegrass performed best overall in terms of establishment, ground cover, overwintering survival and foliar biomass production. None of the cover crops had a consistently significant effect on populations of parasitic nematodes in field plots, including Pratylenchus, Paratrichodorus, and Meloidogyne. Both ryegrass cover crops appeared to provide a favourable environment for survival of root knot nematodes (Meloidogyne spp.), although they are not considered to be hosts of this nematode. There was no difference in soil carbon, nitrogen or potato yield following any cover crop. Symptoms of corky ringspot were not observed in the field and TRV was not detected in potato plants by RT-PCR.