Researchers study tomatoes that may resist fungus ByBob Johnson
fields can havemultiple pathogens. “All of these diseases cause discolor- ation,” said Cassandra Swett, University of CaliforniaCooperativeExtensionplant pathology specialist. “There are noman- agement strategies for falciforme, while theotherdiseaseshave resistant varieties.” Once plants are infected, research- ers say there is little that can be done to save the crop. Pathogens remain viable in the soil for many years. Resistant va- rieties, therefore, are essential to man- aging fusarium. Swett made her remarks during the
February Sacramento Valley process- ing tomato production meeting as re- searchers discussedmanagement strat- egies for the challenging disease. While there are no varieties resistant to falciforme, some performedbetter un- der falciforme pressure, while others did poorly in a recent trial in a commercial field inFresno. “Wehave goodcandidates and ones to avoid,” Swett said. Once researchers discover why some cultivars did better than others, they can identify sources of genetic tolerance or resistance to falciforme that could be
bred into commercial varieties. A piece of sobering news from recent studies is that root knot nematodes ap- pear to weaken variety resistance to fu- sariumwilt race three. “About 63% of the (race three) fusar- ium wilt diagnoses had root knot nem- atode infections,” Swett said. “There is strong potential to identify race three resistant cultivars that also hold up un- der falciforme.” These nematodes al so stunt the plants and reduce yield and fruit qual- ity, she said. Researchers are screening non-fumi- gant nematicides that can be delivered through the buried drip lines. “Wi th fumigat ion being l imi ted, non-fumigant drip appliedmaterials are the future,” said Jaspreet Sidhu, UCCE vegetable crops farm advisor. Sidhu did a trial with encouraging re- sults of drip-applied Nimitz and Velum nematicides at the UC Shafter Research Station in Kern County. Another strategy for managing fusar- ium race three is to rotate ground out of tomatoes for a few years to reduce the pathogen load. Although fusariumwilt only damages tomatoes, some rotation crops are better than others at reducing pathogen levels. Among Sacramento Valley summer crops, corn, rice, lima beans, sunflow- ers and peppers are least likely to be colonized by fusarium, while melons and pumpkins are not promising rota- tion candidates. (Bob Johnson is a reporter in Monterey Coun t y . He may b e c on t a c t ed a t bjohn11135@gmail.com.) UC Davis to offer a symposium on red blotch disease University of California, Davis, is offer- ing a symposiumonmanaging grapevine red blotch disease. The March 16 event will be held from 9 a.m. to 3:30 p.m. at the UC Davis Conference Center. It will also be live streamed online. Registration is $250 for the in-person symposium and $150 for online. Red blotch disease in grapevines can dramatically reduce the value of wine- grapes and harm plants by inhibiting photosynthesis in the leaves. Infected vines are unable to conduct water ef- fectively, leaving sugar that is created by photosynthesis stuck in the leaves in- stead of in the berries. Presentations will cover the role of treehoppers, treatments,mitigation strat- egies and the impact of the disease on the composition of wine, andmore. For more information and to reg- ister, visit https ://ucanr.edu/sites/ ShortCourse17.
An evolving lethal soilborne fungus continues to challenge processing toma- to growers and researchers. Fusariumwilt causes affected leaves to yellow and wilt, and survives in the soil for many years. Resistant varieties are available toman- age races one, two, and three of this dis- ease. But there are no known resistant va- rieties for the recently identified fusarium falciforme. Root knot nematodes appear toweaken race three resistance, and vari- etychoice is complicatedbecause infested
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