Studies of Erwinia early dying, an uncontrolled, bacterial disease of potato common in Kern County, has again claimed a large share of the budget of the California Potato Research Advisory Board.
At a recent meeting in Fresno, the board allocated $29,500 for studies in 2004-05 aimed at learning how the disease is spread and seeking ways to control it.
Mike Davis, plant pathologist at the University of California, Davis, will continue his board-funded investigations in progress.
Erwinia carotovora and E. chrysanthemi are associated with early dying, in which bacterial cells block the potato plant’s vascular system, prevent water from reaching the leaves, and kill the plant. The bacteria are always in the soil.
Davis told the board there is a connection between the disorder and the age, either chronologically or physiologically, of potato seed. "Older" seed is prey to the disorder, but he said he has no way to measure the physiological age.
Thus far, he has been able to isolate compounds from decayed seed and use them in trials to bring on the disease in clean potato plants.
"We think the disease is worse in Kern County because of the high temperatures there which hasten decay of the seed," he said.
He suspects that Erwinia, even though it is highly toxic to potato plants and kills them almost immediately, is not directly responsible for the early dying. Instead, something in the decaying seed tissue causes the cells to expand to block circulation in the plant.
In related studies, Davis is investigating mycorrhizal fungi in Kern County fields in 2003 and 2004 to see if they have some relationship to early dying.
Growers say they’ve "tried everything in the book," including treatment of seed with antibiotics, to bridle the disease, but they’ve had no success.
Few things known
Davis said a few things are known at this point. Although these may be help to a degree, they are not a cure. Some benefit may come from treatment of mother plants with calcium. "That gives a firmer seed piece that comes out of the ground more vigorously."
Davis also examined planting depth. "Some growers are planting pretty deep, and this can worsen the problem," he said, adding that the shallower the planting, within permissible depth, the less chance for moisture to surround seed pieces and promote decay.
Among the research projects totaling $89,700 and approved by the board is $22,500 for continuing development of varieties by Harry Carlson, superintendent of the UC Intermountain Research and Extension Center, Tulelake. Those multi-year efforts also involve other UC researchers and their collaborating counterparts at universities and USDA stations in Idaho, Texas, and Oregon.
Varieties, either new or improved, among russet, white, red, chip processing, and specialty potatoes are being selected and evaluated.
Along with yields, quality, and other traits, selections are screened for glycoalkaloid content. Glycoalkaloids are plant toxicants that occur in all solanaceous plants, particularly in potato vines and sprouts. They are governed by genetics and activated by light and temperatures to cause greening of tubers. The least amount of these compounds is desirable, and excessive amounts can cause marketing problems for potatoes.
Carlson is also running trials on evaluation of fungicide application techniques funded for $14,500 by the board. The work involves reconfiguration of solid set sprinkler systems for better uniformity of fungicides applied with them.
Joe Nunez, Kern County farm advisor, is leading a project with $20,200 for variety selection and development in his county. Nunez also is in charge of a project funded with $3,000 for trials with cover crops to suppress soil borne pests.
According to board manager Ken Melban, the board’s 2004-05 budget is $192,500, based on a mandatory assessment of growers of one cent per hundredweight on an estimated crop of 13 million cwt, plus 2003-04 carryover funds and interest.
California has 180 potato producers, including 100 in the Tulelake district, 71 in the Kern district, eight in the Stockton district, and one in Los Angeles County. The industry has been valued at about $160 million in recent years.
The eight-member board, established in 1974 under the California Marketing Act, was earlier this year authorized for another five years by the California Department of Food and Agriculture following public hearings producing no testimony objecting to the potato research program.
Monfort Management Services, which has represented the board since 1983, was again approved to manage the board for the 2004-05 year.