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Stem canker research earns SDSU doctoral student recognition

Kashyap measuring fungal growth in petrie dish she is holding
Ruchika Kashyap, a doctoral student in SDSU’s Department of Agronomy, Horticulture and Plant Science, measures fungal growth to determine the fungicide sensitivity of Diaporthe gulyae, one of the pathogens that causes Phomopsis stem canker in sunflowers. She received second place in the oral competition when she presented her work at the recent virtual Northeastern Plant, Pest, and Soil Conference.

Research on using fungicides to manage stem canker in sunflowers earned South Dakota State University doctoral student Ruchika Kashyap second place in the oral competition at the recent virtual Northeastern Plant, Pest, and Soil Conference. Kashyap is evaluating the effectiveness of fungicides against Phomopsis stem canker under the tutelage of associate professor Febina Mathew in SDSU’s Department of Agronomy, Horticulture and Plant Science.

“This was the first time that I presented my research at a conference in the United States, so I was very surprised,” said Kashyap, noting she competed against students from Cornell University and Rutgers University. The conference was jointly organized by the Northeastern Weed Science Society, the Northeast Branch of the American Society of Agronomy, the Crop Science Society of America, the Soil Science Society of America and the Northern Region of American Society of Horticultural Science.

Kashyap received $200 for her second-place finish in the Jan. 6 oral competition. The India native earned her master’s degree at Punjab Agricultural University, the largest agricultural university in Asia, before coming to SDSU in fall 2019. Her research is supported by the National Sunflower Association and is a collaborative effort among the U.S. Department of Agriculture Agricultural Research Service Sunflower and Plant Biology Research Unit in Fargo, North Dakota; North Dakota State University; and University of Nebraska Panhandle Research and Extension Center.

‘I am proud of the work that Ruchika has done and her success presenting at her first big conference,” said Mathew, who has been at the forefront of efforts to manage stem canker since 2010 when an outbreak affected nearly 80% of the sunflower crop in Minnesota, North Dakota, and South Dakota. The fungal disease causes lodging and up to 40% yield loss.

Kashyap putting plug of pathogen on media plate
Ruchika Kashyap places an agar plug of a pathogen that cause Phomopsis stem canker in sunflowers on a media plate to study the sensitivity of the fungi to available fungicides.

Managing stem canker is challenging because the disease can be caused by several fungi from the Diaporthe family, Kashyap explained. “One of the important disease management strategies is use of fungicides, but no research had previously been done to study the sensitivity of these fungi to available fungicides.” The concern is that the more a product is used to control disease, the greater the chance the fungus will develop resistance, making the fungicide less effective.

Kashyap is examining three types of fungicides used to mitigate foliar diseases of sunflower which includes stem canker—tebuconazole, a triazole fungicide; succinate dehydrogenase inhibitors or SDHIs; and QoI fungicides. Her oral presentation described the tebuconazole experiments through which she also established test protocols. “This study will help continue monitoring of populations of Diaporthe for their sensitivity to available fungicides and to determine baseline sensitivity to new fungicide chemistries,” she added.

Kashyap used 104 isolates, 52 each of the two predominant pathogens—Diaporthe helianthi and Diaporthe gulyae—collected from sunflower fields affected by Phomopsis stem canker in Minnesota, Nebraska, North Dakota, and South Dakota. “We need to collect samples from different fields and different states to represent what is actually happening,” she said.

She placed each fungal isolate on an artificial media plate with different concentrations of the fungicide. Then she measured the fungal growth. “The goal is to determine the EC50 value, which means the fungicide concentration that inhibits fungal growth by 50%,” Kashyap said.

“When fungal strains become less susceptible, or less sensitive, to the fungicide, the EC50 value increases. That means the fungicide, when sprayed at the standard rate, will not effectively control growth of these fungal strains,” Mathew explained. The tests showed no shift in sensitivity to tebuconazole and, therefore, no changes in application rates are necessary.

Last semester, Kashyap completed the QoI fungicide experiments and this semester will begin testing the SDHI fungicide. Her research also involves genetic sequencing aimed at breeding sunflower varieties with resistance to Phomopsis stem canker.

“It is rewarding to know I am working on something that is so important to farmers,” Kashyap concluded.