New research might pave the way to SDS resistance

November 24, 2020

Overexpression of soybean gene might lead to resistance from SDS and more

No matter if it is 50 acres or 50,000, crop producers must hone their management practices to maximize yield while minimizing costs. Any number of different pathogens or pests can derail a good season. Soybean farmers in Iowa know how devastating they can be, with some causing millions in losses each year.

Now, new research, recently published in “Plant Biotechnology Journal” by Iowa State University’s agronomy professor Madan Bhattacharyya suggests that there could be hope of future immunity against some of the worst offenders, like sudden death syndrome (SDS) in soybeans.

Enhancing SDS resistance was Bhattacharyya’s initial goal in manipulating soybean genetics.

SDS is caused by a fungus in the soil that attacks a soybean plant’s roots called Fusarium virguliforme. The symptoms of SDS are typically seen on leaves after flowering. Leaves of infected plants will likely show scattered yellow spots between veins. These spots grow to form large chlorotic and necrotic blotches between the leaf veins, while the midvein and major lateral veins remain green.  Diseased plants will have rotted taproots and lateral roots, so by the time a farmer sees discolored leaves, it is already too late.

SDS is typically is one of the leading causes of yield loss for soybeans, and that’s no different in Iowa.

“Sudden death syndrome regularly finishes as one of the most destructive soybean diseases across the north central region and a disease that soybean farmers have been battling since the 1970s,” said Daren Mueller, coordinator of the Integrated Pest Management program at Iowa State and co-director of the Crop Protection Network.

In the last 20 years, there have been over 167 million bushels lost with an average of a $72.8 million loss each year just in Iowa. On average, it kills about 1.6% of soybeans each year, and went up to 5% losses in 2010.

This is why Bhattacharyya’s work might be a game changer for some farmers. He and his team were able to identify a gene, that once overexpressed, could provide immunity against SDS.

“This gene has only been found in legumes, and a limited number of other crops like cocoa, jute and cotton,” Bhattacharyya said.

He and his team tested the transgenic lines with the overexpressed gene from 2015 to 2018 in the field, and found that up to 91% showed SDS resistance. This could save farmers millions of dollars each year in lost yield.

“Managing SDS is very complicated, and often involves using a lot of different management tactics to tackle it,” Mueller said. “But the most reliable management strategy should center around resistance.”

Mueller said that researchers like Bhattacharyya who are studying how to improve resistance gives soybean breeders a fighting chance to develop better lines which is the most sustainable foundation for SDS management strategies for farmers. 

“The expression of this gene is very rapidly suppressed by an F. virguliforme infection. To overexpress the gene during infection, we swapped a part of the gene with that of three other genes that are induced during infection,” Bhattacharyya said. “We were very surprised to see that the transgenic soybean plants exhibited resistance not only against F. virguliforme, but also against spider mites, soybean aphids and soybean cyst nematode.”

Soybean cyst nematode is the number one pathogen in soybean that causes yield suppression valued at over $1.2 billion annually in the U.S.

Bhattacharyya’s team has been studying the mechanisms used by the overexpressed gene in inducing broad-spectrum resistance against multiple pathogens and pests in transgenic soybean lines. They have observed that over 20 putative signaling genes for defense responses are regulated by this gene. Further research and testing might establish that this gene could be a “master switch” for defense pathways against multiple pathogens and pests.

This research develops a better understanding of how the mechanisms of resistance work, and soybean breeders can learn from and use it to help develop lines to combat serious diseases and pests.

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