Prevalence and importance of the necrotrophic effector gene ToxA in Bipolaris sorokiniana populations collected from spring wheat and barley

Authors: MANAN, FAZAL - North Dakota State University; SHI, GONGJUN - North Dakota State University; GONG, HONGMEI - North Dakota State University; HOU, HONGYAN - Minnesota State University; KHAN, HANNAH - North Dakota State University; LENG, YUEQIANG - North Dakota State University; CASTELL-MILLER, CLAUDIA - University Of Minnesota; ALI, SHAUKAT - South Dakota State University; Faris, Justin; ZHONG, SHAOBIN - North Dakota State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2023
Publication Date: 2/1/2023
Citation: Manan, F., Shi, G., Gong, H., Hou, H., Khan, H., Leng, Y., Castell-Miller, C., Ali, S., Faris, J.D., Zhong, S. 2023. Prevalence and importance of the necrotrophic effector gene ToxA in Bipolaris sorokiniana populations collected from spring wheat and barley. Plant Disease. https://doi.org/10.1094/PDIS-08-22-2011-RE.
DOI: https://doi.org/10.1094/PDIS-08-22-2011-RE

Interpretive Summary: There are numerous fungal pathogens of wheat and barley that cause disease leading to significant losses in grain yield. One such fungal pathogen, known as Bipolaris sorokiniana, infects the leaves and roots of wheat and barley to cause the disease known as spot blotch. Previous research has revealed that some strains of the spot blotch fungus carry a gene known as ToxA that aids the fungus in causing disease on plants that carry a gene known as Tsn1. in this study, researchers collected over 300 strains of the spot blotch fungus from roots and leaves of infected wheat plants and leaves of infected barley plants, and they evaluated the strains for the presence of the ToxA gene to determine its prevalence among the strains. The ToxA gene was not present among the strains collected from barley. Strains that harbored the ToxA gene produced more disease on wheat plants that had the Tsn1 gene than strains that lacked the ToxA gene, thereby confirming that the ToxA gene increased virulence of the spot blotch pathogen. The results of this research show that wheat breeders should strive to eliminate the Tsn1 gene from their breeding lines to gain increased resistance to spot blotch disease.

Technical Abstract: The necrotrophic fungus Bipolaris sorokiniana causes foliar and root diseases on wheat and barley. Those diseases are common in all wheat- and barley-growing regions with more severe outbreaks occurring in warm and humid areas. The fungus can also infect a wide range of grass species in Poaceae. ToxA is an important effector gene that has been identified in several wheat fungal pathogens including B. sorokiniana. In this study, we investigated the prevalence and virulence role of ToxA in B. sorokiniana populations that were mainly collected from spring wheat and barley in the Upper Midwest of the United States. A total of 278 B. sorokiniana isolates were evaluated including 169 from wheat leaves, 75 from wheat roots, 30 from barley leaves and four from wild quack grass leaves. ToxA was detected in the isolates from wheat leaves, wheat roots and wild grass leaves, but not in those from barley leaves. Prevalence of ToxA in wheat leaf isolates (34.3%) was much higher than that in wheat root isolates (16%). Sequencing analysis revealed two haplotypes with the majority being BsH2. All ToxA+ isolates produced the functional effector in liquid cultures. Pathogenicity assays revealed that ToxA+ isolates caused significantly more disease on spring wheat lines harboring Tsn1 than their tsn1 mutants, suggesting the ToxA-Tsn1 interaction plays an important role in spot blotch development. This work confirms the presence and importance of ToxA in B. sorokiniana populations from wheat and thus, the breeding of Tsn1 out from spring wheat cultivars can reduce susceptibility to spot blotch.