Ultrastructure of potato tubers infected with potato virus X

The ultrastructure of Katahdin tubers infected with potato virus X (PVX) is compared with PVX-free tubers by electron microscopy. Electron-dense globules surrounding the inner periphery of the tonoplast were observed in PVX-infected tubers, while PVX-free tubers did not show such bodies. Other organelles were comparable in PVX-infected and PVX-free tubers     

Eradication of potato virus X from potato by ribavirin treatment of cultured potato shoot tips

Ribavirin treatment of cultured potato shoot tips was tested as a means of eradicating potato virus X (PVX) from two potato cultivars. Shoot tips were cultured on liquid medium containing 0, 1, 10 or 100μg/ml ribavirin. Cultures were evaluated periodically for viability, and scored for vigor on a relative growth scale. Developed plantlets were assayed for PVX by transmission tests toGomphrena globosa. Ribavirin treatment was phytotoxic at all tested concentrations, and lethal to all cultivars treated at 100 μg/ml. Treatment also delayed plantlet development by up to 2 months at 1 and 10 μg/ml as compared with nontreated controls. PVX assays indicated that 80 and 83% of the plantlets were free of PVX following treatment with 10 μg/ml for cultivars Russet Burbank and Red McClure, respectively. Five and 6% of the plantlets developed from the 1 μg/ml treatment were PVX-free, whereas 0 and 2% of the controls were PVX-free for the same cultivars. Six to 8 months were required to develop plants from shoot-tip cultures treated with 10 μg/ml ribavirin.     

Reinfection of potato seed stocks with potato virus S and potato virus X in Wisconsin

Reinfection of potato seed stocks with the potato viruses S (PVS) and X (PVX) varied with cultivar, virus, and grower. Rapid recontamination was observed for the cultivars Norgold Russet and Ontario with PVS and for the cultivars LaChipper, Norchip, and Norgold Russet with PVX. Recontamination was low for the cultivars LaChipper and Monona with PVS and for the cultivars Kennebec, Monona, Norland, and Superior with PVX. Survey results suggest that PVS and/or PVX can be eliminated from cultivars which appear to possess field resistance to infection, but that further evaluation of cultivars which are very susceptible to reinfection will be necessary.     

Volunteer potatoes as a source of potato leafroll virus and potato virus X

Volunteer potatoes were investigated as infection sources for potato leafroll virus (PLRV) and potato virus X (PVX) in a high elevation seed potato growing area of eastern Idaho. Population densities ofMyzus persicae were assessed. Percentage of PLRV and PVX infection of the volunteers and seed potato crops was determined, as well as density of volunteers and certain parameters of volunteer growth and reproduction. Volunteers apparently harbored no more PLRV than the potato crop from which they originated. But they were found to be an important reservoir of PVX with the infection increasing as much as 12.43% in one year. No aphids capable of transmitting PLRV were found although one species that can transmit potato virus Y was recorded. The mean density of volunteers varied from 0 to 84,880 stems/ha. The number of tubers remaining in the field after harvest and winter weather conditions appeared to be the only factors affecting volunteer density. Volunteer plants arising from seed pieces at an average depth of 6.1 cm were found to set an average of 2.1 new tubers per plant at an average depth of 4.0 cm. These results suggest that volunteer potatoes are a significant source of PVX infection in subsequent seed potato crops.     

Potato virus X infection of Netted Gem potato

When Netted Gem potato plants were inoculated with potato virus X 7 to 31 days before defoliation the tubers were not uniformly infected. Testing of a single germinating eye chosen at random from each tuber detected fewer than half of the tubers from which stem-end, mid, or apical-end sections produced infected plants. The number of completely and partially infected tubers increased as the length of time between inoculation and defoliation was increased. Infection was not correlated with tuber size. Partially infected tubers produced equal numbers of infected plants from stem-end and apical-end sections.     

The effect of potato virus X on the yield of the potato variety Hudson

The effect of a mild strain of PVX on the yield of the recently released potato variety Hudson was determined in split-plot experiments at three locations in New York. Two other varieties, Katahdin and Bake-King, were included for comparison. The yield data compared were total tuber yield, tuber yield > 2 1/4 in. and > 1 7/8 in. diameter and tuber number> 2 1/4 in. and > l 7/8 in. diameter. The effect of the mild strain was not great. Hudson appeared to be more tolerant to the mild strain of PVX than the other two varieties although the variety X virus interaction was very low.     

An enhanced multiplication of potato virus X is not related to a synergistic reaction between the potato viruses X and Y

Summary Greenhouse experiments demonstrated a differential interaction between potato viruses X and Y in two potato cultivars. Enhancement of PVX synthesis in doubly infected plants occurred only in the PVY-susceptible potato cv. Ulla, whereas PVX multiplication was almost completely inhibited in the doubly infected PVY-resistant cv. Franzi. However, a synergistic effect was also evident in the latter cultivar in the form of a growth inhibition of the plants. An increased multiplication of one or both of the viruses is, therefore, not related to a synergistic reaction.     

Potato virus X eradication in cultured potato meristem tips

Summary Potato virus X (PVX) infectivity of three series of axillary potato meristem tips, each including the apical dome plus one, two and four leaflets respectively, was compared statistically with the infectivity of three series of plantlets developed from meristem tips of corresponding sizes, cultured in vitro. PVX eradication depends on the size of meristem tips. The difference between the percentage of PVX-infected plantlets and the percentage of PVX-infected meristem tips was found statistically significant when one and two leaflet meristem tips were considered. This result gives experimental evidence of an active role of meristem tips development in the virus eradication process.     

Retention of infectious potato virus X on common surfaces

Potato virus X in sap from potato leaves was applied by atomizer to surfaces commonly contacted during potato planting, growth, harvesting, grading and storage. The virus retained its infectivity toGomphrena globosa L. or Netted Gem potato for 10 seconds on leather, 3 hours on unpainted wood, iron, rubber and human skin, 6 hours on painted wood, jute and cotton, and 24 hours on soil.     

The effect of separate infections by potato viruses X and S on Netted Gem potato

Numbers and specific gravity of Netted Gem potato tubers were unaffected by mottle and latent strains of potato virus X (PVX) and by potato virus S (PVS). Neither latent PVX nor PVS affected yield but mottle PVX alone and latent PVX combined with PVS reduced tuber size and yield (P = 0.05).     

The incidence of potato viruses X,Y and S in the Chilota potato collection

The 530 potato clones of the Chilota collection of the germplasm bank from the Universidad Austral de Chile were tested for potato viruses X (PVX), Y (PVY) and S (PVS) by means of NCM-ELISA (nitrocellulose membrane enzyme-linked immunosorbent assay). Four clones (0.8%) healthy for all 3 viruses simultaneously were detected. These clones could be resistant to the above mentioned viruses.     

In vitro shoot regeneration and chromosome doubling in 2X and 3X potato clones

The possibility of scaling ploidy levels up and down offers several advantages for genetic studies and breeding work in potato. Shoot regeneration and chromosome doubling in plants regenerated fromin vitro cultures were investigated in 4 diploid (2n=2x=24) and 2 triploid (2n=3x=36) clones. Internode and leaf expiants were taken from plants propagated eitherin vitro as shoot cultures, orin vivo in a greenhouse. Two regeneration procedures were compared. Regeneration frequencies were significantly higher using a two-step regeneration protocol and from leaf explants, while doubling was more efficient starting fromin vivo grown plants. No doubling was observed in triploid clones. Considering altogether the percentage of regeneration and doubling, and the number of shoots regenerated per explant, the most efficient conditions were considered leaf explants taken fromin vivo grown plants, and cultured according to a two-step regeneration protocol.     

Detection of potato viruses S and X in dormant potato tubers by the latex agglutination test

A simple procedure for detection of potato viruses S and X from dormant tubers by a latex agglutination test was developed. Eyes were pricked with a toothpick after having been covered with 50μ1 of buffer. Approximately 20μ1 of buffer then were drawn into a capillary pipette containing 10μ1 of antibody-sensitized latex and a latex agglutination test was performed. Both viruses were detected in all infected tubers tested. For potato virus S, the mean agglutination value was shown to vary significantly among cultivars. Tests on one eye were sufficient for detection with some cultivars, but tests on three eyes were necessary for detection with other cultivars. Eye location on tubers did not appear to influence test results, but better results were obtained when eyes were tested than when other tuber locations were tested.     

The effect of potato virus X on susceptibility of potato tubers toFusarium roseum ‘Avenaceum’

Potato virus X (PVX)-free and mild PVX-infected tuber lines originating from the same Katahdin clone were compared for susceptibility to tuber rot incited byFusarium roseum (Lk.) Synd. and Hans. ‘Avenaceum’. The effect of interval between top-kill and harvest on development ofFusarium tuber rot was also determined. A series of tubers from both PVX-free and PVX-infected tuber lines was either (i) mechanically bruised and inoculated by immersion in a spore suspension ofF. roseum ‘Avenaceum’, (ii) mechanically bruised but not inoculated, (iii) inoculated only or (iv) neither bruised nor inoculated. Tubers from all treatments were then stored at temperatures of 18–21 C (65–70 F) for a 3-week period prior to being placed at 4 C (39 F) for the remainder of the storage period. The amount of rot was determined after a 5–6 month storage period at the latter temperature. In a 4-year study PVX-free tubers were significantly (1% level) more susceptible to infection byF. roseum ‘Avenaceum’ than tubers infected with mild PVX. PVX-free tubers left in the ground for 2 or 3 weeks after top-kill were significantly (1% level) more susceptible toFusarium dry rot than those infected with the virus; however, there was no significant difference in disease incidence between PVX-free and PVX-infected tubers when harvested 4–5 weeks after top-kill. Tubers, both PVX-free and PVX-infected, remaining in the ground for a 2 week period following top-kill were significantly (1% level) more susceptible toFusarium tuber rot than those harvested 3 weeks after top-kill; similarly, both PVX-free and PVX-infected tubers harvested 3 weeks after top-kill were significantly (1% level) more susceptible than those left in the ground for a 4–5 week interval.