Zebra Chip, Phosphorus, PVY"O"

Potato Association of America meeting highlights

Published in the November 2012 Issue Published online: Nov 08, 2012
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Denver, Colo., was the site for the 96th Annual Meeting of the Potato Association of America, held at the Crowne Plaza Hotel in August. Here are some of the highlights:

P.E. Fixen, International Plant Nutrition Institute.

Potato Management Challenges Created by Phosphorus Chemistry and Plant Roots. Due to a combination of factors, potato plants have higher solution P concentration needs and critical soil test levels than most other common crop plants. When soluble P is added to soils as commercial fertilizers, the properties of the specific fertilizer dominate the initial reactions but with time soil properties become more influential. During the reaction series, P solubility declines as fertilizer P gradually transforms to "soil P." Efficient management of P for potato production, perhaps more than for most crops, requires that right source, rate, time and place decisions be made to facilitate plant P uptake during this transformation process.


Carl J. Rosen, University of Minnesota.

Optimizing Phosphorus Fertilizer Management in Potato Production. Most research shows that P fertilizer is efficiently used when band-applied at planting (eg. 5 cm to each side of the seed piece); however, some western U.S. work shows increased yields and petiole P levels with preplant broadcast applications. Potato fertilizer best management practices include: 1) apply the fertilizer P rate calibrated for your soil; 2) band-apply fertilizer P at least 5 cm from the seed piece, especially on sandy soils or where DAP or urea-phosphates are used; 3) use petiole P tests to determine the need for in-season applications; 4) account for all P sources applied including animal manures; and 5) utilize the best soil conservation practices possible to reduce P losses to surface waters.


Jolyn R. Rasmussen, Simplot Plant Science.

Simplot Plant Sciences Introduces First Innate Products. Innate technology is a patented plant biotechnology process that works with a plant's own genes to enhance desirable traits and to decrease less desirable traits. Simplot's first application of Innate Technology includes the following traits: 1) reduced black-spot bruising through PPO silencing; 2) reduced degradation of starch to sugars during storage; and 3) reduced free asparagine levels. The first petition submitted to the USDA for regulatory review includes these traits in Russet Burbank, Ranger Russet and Atlantic. Larger trials with these products are being grown under commercial growing conditions in 2012.


Robert D. Davidson, Colorado State University, SLV Research Center.

Cultivar improvements for powdery scab resistance in the Colorado Cultivar Development Program. Powdery scab caused by the pathogen Spongospora subterranean has become a significant pest of concern for many Colorado potato producers. Because of this situation, the Colorado Cultivar Development Program has embarked on an approach to build resistance into many of the newer releases to both root galling and tuber symptom development. Using a greenhouse screening technique, numerous advanced selections have been evaluated for disease development. Currently, four of the newest russet selections have demonstrated excellent resistance to both root galling and tuber symptoms. These russets have shown essentially zero root galling incidence and no tuber symptoms.


Charles R. Brown, USDA/ARS.

General Performance and Resistance to Tuber Infection by Columbia Root-knot Nematode Derived from Solanum bulbocastanum in Fumigated and Un-fumigated Ground. The Columbia Root-Knot Nematode (CRKN) is an important pest in the Columbia Basin and is present in most potato-producing states west of the Mississippi. Resistance to the nematode was discovered in Solanum bulbocastanum and bred into the potato-breeding population. In the backcross 5 generation, a resistant breeding line PA99N82-4 (82-4) was selected to compare to Russet Burbank with diverse nematicidal treatments and no control. Nematode numbers were significantly increased in RB control plots while the increase was negligible to very small in the 82-4 control plots. The breeding line 82-4 can be grown in CRKN-infested ground without fumigation and it lowers the numbers of nematodes dramatically compared to RB.


Walter R. Stevenson, University of Wisconsin-Madison.

STORECAST Storage Potato Disease Risk Indexing-Assessing the decay potential of potato crops. In a typical season, soft rot, leak and pink rot represent the dominant storage rot diseases in most production regions. Studies were initiated at the UW-Madison in 2003 to determine the potential for adapting RT-PCR methodologies for assessing the decay potential of potatoes before harvest. There was excellent agreement between the decay forecast and eventual decay incidence with 90 percent RB storages and 75 percent chipping storages showing full or close agreement between predicted and observed decay. More decay than predicted was observed in 2 percent of both chipping and RB storages, respectively. Less decay than predicted was recorded in 23 percent and 8 percent of chipping and RB storages, respectively. The decay forecasting system was registered as STORECAST "Storage Potato Disease Risk Indexing" and provides growers with a valuable tool for improving tuber storage.


Joseph E. Munyaneza, USDA-ARS, Yakima Agricultural Research Laboratory.

Effects of Potato Psyllid and Zebra Chip Disease on Potato Seed and Postharvest. Zebra chip (ZC), a new and economically important disease of potato in the United States, Mexico, Central America and New Zealand, is associated with the new bacterium Candidatus Liberibacter solanacearum transmitted to potato by the psyllid Bactericera cockerelli. Studies were conducted to investigate the role of the potato seed in ZC spread and whether the disease can develop in storage following a late liberibacter infection. Results provide evidence that ZC-infected potatoes generally do not germinate and do not play a significant role in ZC spread to new areas where the disease and potato psyllid are absent. Furthermore, results of our preliminary studies indicate that ZC appears to readily develop in storage.


Jazeem Wahab, Canada-Saskatchewan Irrigation Diversification Centre.

Small Potato' Production: Seed-Tuber Size and Seed Spacing Effects on Growth and Yield. A study was conducted to examine the effects of seed-tuber size, seed spacing and top-kill timing on growth parameters and yield characteristics for `Small' potato cultivars Baby Boomer, Blushing Belle and Piccolo under irrigated production. Larger seed produced higher Leaf Area Indices (LAI) and higher tuber yields than smaller seed. The relationship between seed-tuber size vs LAI, and seed-tuber size vs. tuber yield were variable for the different cultivars. Generally, closer spacing produced higher marketable yields than wider spacing. Delaying top-kill resulted in a higher yield of oversized tubers relative to marketable grade tubers.

Tina Brandt, University of Idaho.

Acrylamide Concentrations in Six Potato Cultivars at Harvest and in Storage. The objectives of this study were to evaluate acrylamide levels of currently grown cultivars as it relates to growing season, storage temperature and duration and tuber characteristics. Six cultivars, Russet Burbank, Ranger Russet, Alturas, Russet Norkotah, Western Russet and Premier Russet, were grown. Within a cultivar, the warmer the storage temperature, the lower the acrylamide concentrations in processed french fries. Results from this study indicate acrylamide concentrations vary significantly between cultivars, change with time and temperature in storage and do not vary greatly by growing season. Acrylamide concentrations significantly correlated with the non-blanched method of fry color determination and glucose concentrations and may be a means to predict acrylamide levels within a given cultivar.


Felix M. Navarro, University of Wisconsin-Madison.

Lelah: A new potato chipping variety with excellent long storage ability. Lelah was named in 2011 in honor of the late Lelah Starks, from Stark Farms, a benefactor that provided land for the breeding maintenance farm, and State Foundation Seed, both in Rhinelander, Wis. Lelah develops attractive round-oval tubers with smooth-skin finish, resulting in appeal for both fresh market and chip production. Tubers are very uniform in size profile, possessing high specific gravity and can be stored through nine months under proper conditions with excellent chip color when stored at 47 degrees F. Yield is lower than Snowden. We expect that Lelah provides a good choice for a long storage chipper with the potential to extend the cold storage season for about a month after Snowden fry quality is not commercially acceptable.


Joe Guenthner, University of Idaho.

Use and costs of insecticides to control Zebra Chip and psyllids.
Zebra chip has become a serious problem in North America. Researchers in Texas developed a sampling and reporting program for cooperating growers in three states. Data from this project enabled us to document insecticide use and costs for ZC control in commercial potato fields. The number of different insecticides used in Texas declined from 17 in 2009 to 10 in 2011. The most commonly used insecticides in all three states were Admire and Movento. Costs varied significantly among fields in the same locations. Issues raised but not covered by this study include: yield loss, quality loss, ZC management strategies, control of other insects and the impact of ZC on the competitive positions of potato growing areas.


Pankaj Banik, Department of Plant Sciences, University of Saskatchewan.

Resistance of potato genotypes to drought stress
. A study was undertaken to examine the drought stress resistance in contrasting potato genotypes using 11 litre pots in a greenhouse held around 17 percent relative humidity. Plants were exposed to cyclic acclimation by withholding water until soil moisture content reached 10 percent. U1002 treatments with a previous drought stress history induced more tubers in the 5-50g category in the subsequent generation compared to treatments with no drought stress history. RB, Fu12 and U1002 showed high resistance, moderate resistance and sensitivity, respectively, though leaf water loss over as little as 15 minutes. Other parameters are being evaluated and will be presented.


X. Nie, Agriculture and Agri-Food Canada, Potato Research Centre.

Molecular and pathological characterization of Potato virus Y isolates belonging to PVY"O" strain group. Previous studies have revealed the existence of several PVY"O" variants in potatoes in New Brunswick, Canada. Sequence analysis of the complete genome revealed that NB7 was closely related to other O5 isolates. Pathogenetic analysis using potato cv Jemseg revealed that all isolates incited local and systemic lesions on the plants, but with varying degrees of severity. Further pathological analysis was carried out on Physalis floridana. Previously we have demonstrated that PVYO-CP gene plays a pivotal role in induction of leaf necrosis/leaf drop and plant death in P. floridana. As expected, all isolates incited necrotic responses on the plants. However, unlike other isolates, NB7 did not cause plant death on the plants.


Andrew Jensen, Idaho, Oregon, and Washington State Potato Commissions.

Field studies of potato psyllid on bittersweet nightshade, Solanum dulcamara, in western Idaho. The outbreak of `zebra chip' (ZC) in Washington, Oregon and Idaho in 2011 prompted new field studies of the potato psyllid, the vector of the putative causal agent of ZC. Solanum dulcamara, also known as bittersweet nightshade, is a deciduous vine, sometimes forming dense thickets. Psyllids collected in March were placed on this plant in the lab at room temperature. Copulation and egg laying were observed during early March on this plant. Overwintering in the field was not conclusively determined as of this writing, but these studies have shown that S. dulcamara could be an important non-crop host for the potato psyllid in the Pacific Northwest.


Philip B. Hamm, Oregon State University, Hermiston Agricultural Research and Extension Center.

Zebra Chip, the Columbia Basin experience in Oregon and Washington in 2011. Infrared photography identified patches of ZC-infected plants had appeared in random locations in fields, suggesting adult insects originated from a distance away from field edges and that spread occurred to adjacent plants as eggs hatch and nymphs/adults moved. Insects most likely moved into the region carrying the bacterium June 20-25, at least six weeks prior to when the insects were found in some traps. ZC incidence was high in a few fields due to the fact that no insecticides had been used for three-plus months following planting because economic thresholds of insects commonly controlled had not been reached. Tubers infected with ZC were apparently more susceptible to shatter bruising, were dark following steam peeling and could be removed at the grading line prior to making french fries.