Elimination of Tobacco rattle virus from viruliferous Paratrichodorus allius in greenhouse pot experiments through cultivation of castle russet

Abstract

Corky ringspot (CRS) is a widespread potato tuber necrotic disease caused by Tobacco rattle virus (TRV) infection. In the Pacific Northwest, this virus is transmitted by the stubby root nematode (SRN) within the genus Paratrichodorus. Remediating CRS affected fields is a major challenge that can be mitigated by growing plant varieties that are resistant to TRV infection. Growing alfalfa has been shown to reduce TRV levels in CRS infested fields over time but the development of a potato cultivar with these same capabilities would be of great economic benefit to potato growers. Castle Russet is a new potato clone that does not develop symptoms of CRS disease. To assess its ability to reduce soil virus load, Castle Russet, tobacco var. "Samsun NN", alfalfa var. "Vernema", and Russet Burbank potato were grown for a period of 1 to 3 months in soils containing viruliferous SRN populations at two different inoculation pressures (60 nematodes/pot and 1060 nematodes/pot) in greenhouse pot experiments. SRN population size and the presence of TRV were assessed over several months post inoculation. Results indicate that plant host and length of exposure significantly influence SRN population dynamics, whereas the TRV infection status of bait plants was significantly affected by both of these factors as well as inoculation pressure. These results suggest that both alfalfa var. "Vernema" and Castle Russet are resistant to TRV infection and may potentially be used to eliminate the virus from fields affected by CRS.

Corky ringspot (CRS) is a widespread potato tuber necrotic disease caused by Tobacco rattle virus (TRV) infection. In the Pacific Northwest, this virus is transmitted by the stubby root nematode (SRN) within the genus Paratrichodorus. Remediating CRS affected fields is a major challenge that can be mitigated by growing plant varieties that are resistant to TRV infection. Growing alfalfa has been shown to reduce TRV levels in CRS infested fields over time but the development of a potato cultivar with these same capabilities would be of great economic benefit to potato growers. Castle Russet is a new potato clone that does not develop symptoms of CRS disease. To assess its ability to reduce soil virus load, Castle Russet, tobacco var. “Samsun NN”, alfalfa var. “Vernema”, and Russet Burbank potato were grown for a period of 1 to 3 months in soils containing viruliferous SRN populations at two different inoculation pressures (60 nematodes/pot and 1060 nematodes/pot) in greenhouse pot experiments. SRN population size and the presence of TRV were assessed over several months post inoculation. Results indicate that plant host and length of exposure significantly influence SRN population dynamics, whereas the TRV infection status of bait plants was significantly affected by both of these factors as well as inoculation pressure. These results suggest that both alfalfa var. “Vernema” and Castle Russet are resistant to TRV infection and may potentially be used to eliminate the virus from fields affected by CRS.

Figure 1:

Two weeks post-transplant, plant hosts were inoculated to evaluate their ability to host Stubby root nematodes (SRN) and Tobacco rattle virus (TRV). At month zero, test hosts were transplanted into pots containing viruliferous SRNs and cultured for one to three months. Each month a subset of hosts is sacrificed, nematode counts are taken, and a tobacco bait plant is transplanted into the test pot. After one month the tobacco bait plant is harvested and both foliar and root tissue was tested for the presence of TRV using RT-PCR.

Figure 2:

Population counts of stubby root nematode, Paratrichodorus allius, across three months in pots grown with alfalfa, Russet Burbank potato, Castle Russet potato and tobacco; inoculated with 60 and 1,060 nematodes/10 L soil in Experiment 1 and 2, respectively.

Figure 3:

Number of bait plant tissue samples that tested positive and negative for the presence of TRV by RT-PCR. (A) Foliage tissue in Experiment 1 (B) Root tissue in Experiment 1 (C) Foliage tissue in Experiment 2 (D) Root tissue in Experiment 2.

Figure A1:

Nematode reproduction factor (Rf) estimates calculated from 250 cm³ soil samples collected from four plant genotypes, across three months, in two independent experiments. Individual data points are plotted as circular dots, whereas the population mean is plotted using an “X” symbol and standard error of the mean is denoted by the error bars. Experiments are differentiated by inoculation pressure. (A) Experiment 1 (60 nematodes/10 L) is plotted in orange (B) Experiment 2 (1,060 nematodes/10 L) plotted in red.

Figure A1:

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