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Poster: Diseases of Plants: New & Emerging Diseases


Diaporthe and spruce decline: incidence, pathogenicity, and population genetics
C. MCTAVISH (1), D. Fulbright (2), A. Jarosz (1) (1) Michigan State University, U.S.A.; (2) Michigan State University, U.S.A.; (3) Michigan State University, U.S.A.

Spruce decline, characterized by needle loss and branch dieback, is found throughout Michigan. A survey of fungi from cankers in the Lower Peninsula of Michigan found Diaporthe (formerly Phomopsis) to be the most common, disease-causing fungus. Sequencing Diaporthe isolates using ITS1 and ITS4 established 5 different groups. Pathogenicity studies were performed on these groups by inserting mycelial agar plugs containing a representative isolate of each group into a small wound, sealing the wound with Parafilm, and measuring the canker area 9 weeks post-inoculation. Groups 4 and 5 were the most virulent, while group 3 was the least virulent group. Groups 1 and 2 were intermediate on the virulence spectrum. Colorado blue spruce (Picea pungens) was the most susceptible species, and 9 different seed sources of P. pungens did not differ in susceptibility. Other tree taxa tested, in order from most to least susceptible, were Norway (P. abies), white (P. glauca), Black Hills (P. glauca var. densata), Serbian (P. omorika), and Meyer (P. meyeri) spruce. Group 1 was more common in the eastern Michigan, and fell into a Diaporthe eres clade. Group 3 was more common in the central region, and also fell into a D. eres clade. Group 2 was most common in the central region, and was unresolved taxonomically. Groups 4 and 5 were common throughout the Lower Peninsula and were also unresolved. Future work includes sequencing more gene regions to resolve Diaporthe groups.