Mycovirome of Diaporthe helianthi and D. gulyae, causal agents of Phomopsis stem canker of sunflower

Diaporthe helianthi and D. gulyae cause Phomopsis stem canker, which is a yield-limiting fungal disease of sunflower (Helianthus annuus L.) in the United States. In this study the mycovirus was characterized in D. gulyae and D. helianthi using 52 and 42 isolates respectively that were recovered from diseased sunflower plants randomly sampled from commercial fields in the U.S. states of Minnesota, Nebraska, North Dakota, and South Dakota. Total RNA extracts depleted of rRNA from each fungus were pooled to construct one library for sequencing to obtain 20GB per library of raw reads using a metatranscriptomics approach. Between the two libraries, they only share one mycovirus in a high amount. Twenty-one novel viral contigs and 10 viral contigs were discovered infecting D. gulyae and D. helianthi, respectively, along with a plant virus contig that was detected as Cucumber green mosaic virus coat protein, indicating trans-kingdom transmission of the same viruses. Among the viruses infecting D. helianthi, we detected two of the same viruses, Helianthus annus leaf-associated partitivirus 3 and 5, that were detected in a direct sunflower virome reported before. Interestingly, Qinvirus which is mostly known as a group of insect viruses, was found in a contig. There was also a circular ssDNA virus contig detected in the D. gulyae library aside from ss (+)RNA, ss (-)RNA, and dsRNA viruses. Surprisingly, a short contig of Fusarium graminearum virus-1 SD4 was also detected, indicating that intergeneric transmission of the viruses may exist. Besides an understanding in the virome diversity, the mycovirome survey provides the first clue of biological molecules that can be further developed for antifungal purposes.