Genetic Solution for Soybean SDS?

July 23, 2016 02:16 AM

In-plant protection could be the key to beating the disease

Soybean sudden death syndrome (SDS), identified 45 years ago in Arkansas, claims the No. 2 spot for soybean yield loss, second only to soybean cyst nematode. Across the country, university researchers and companies are searching for a solution for this devastating disease.

SDS is a tricky fungal disease. It infects soybean roots when the plant is young, but symptoms show up in the leaves when the plant is in early reproductive stages and conditions are warm and dry. Early diagnosis is difficult because the disease can sometimes be confused for other diseases or deficiencies. Unfortunately, once farmers see SDS symptoms it’s too late to save yield.

Research at Iowa State University (ISU) aims to beat the disease. Jiaoping Zhang, post-doctoral research associate in agronomy, and Asheesh Singh, ISU assistant agronomy professor and soybean breeder, have identified promising gene candidates they believe are responsible for genetic resistance to SDS.

Better breeding efficiency means farmers could potentially have access to resistant varieties faster. The team isn’t quite ready to release cultivars, but they’ve identified parent sources for potential new varieties. “Some germplasm lines are more resistant than others—that’s what we use for parent lines,” Zhang says.

Researchers are looking for a group of genes that contain resistant qualities. For SDS, the more genes, the better. “There might not be a way to make soybeans completely resistant [using genetics alone] but we could enhance the expression of resistance,” Singh says. 

Genetic resistance could help fight the disease with no additional cost to the farmer since protection is covered by the seed bill. Zhang appreciates that benefit—and farmers would too. “Some seed treatments may help control the disease, but breeders are always trying to find genetic resistance resources,” he says.

Seed treatments such as iLeVO from Bayer, and Clariva Complete Beans and Mertect 340-F from Syngenta, offer additional protection against SDS. Bayer’s iLeVO reduces the infection of Fusarium virguliforme on soybean seedling roots while Syngenta’s Clariva Complete Beans decrease nematode damage in roots, which Syngenta says reduces entrance for the Fusarium fungus responsible for SDS. 

Zhang and Singh recommend a systems approach to preventing SDS. “When no completely resistant soybean cultivar is available, there is a need to incorporate both genetics and chemical type controls to increase profitability,” Singh says. 

How to Identify SDS in Your Field

Since SDS can mimic other diseases it’s important to learn how to tell it apart. It’s a soilborne pathogen that overwinters in infected residue so pay special attention to fields with a history of the disease. Start scouting in June and keep scouting until mid-August.

Look for these symptoms:

  • Yellow, interveinal chlorosis and necrosis after R2
  • Leaflets turn brown and drop, leaving bare petioles
  • Lower stem cortex will have brown or gray streaks, but a normal pith (not to be confused with brown stem rot)

SDS requires cool, wet weather in early vegetative growth to promote infection. Symptoms appear during reproductive stages when wet conditions are followed by warm, dry weather. If SDS appears in fields this year, make note and plan to use seed treatment, resistant varieties or crop rotation to combat the disease.

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