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Poster: Biology & Disease Mgmt: Mycology


Pathogenicity and Virulence of Alternaria alternata on ‘Alamo’ Switchgrass
S. COLLINS (1), B. Ownley (1) (1) University of Tennessee, U.S.A.

Alternaria alternata causes foliar disease in switchgrass (Panicum virgatum), and was the most frequently isolated fungus from a survey of 30 commercial switchgrass seed lots. The aims of this study were to determine 1) pathogenicity and virulence of A. alternata isolates recovered from commercial switchgrass seed, and 2) the impact of isolates on seed germination, plant health, and biomass. Tests were arranged in a completely randomized design and data were analyzed with mixed model ANOVA and F-LSD (SAS 9.4). Six isolates were screened for pathogenicity with a detached leaf assay using ‘Alamo’ switchgrass. All A. alternata isolates were pathogenic on detached leaves (P<0.05), with lesion areas ranging from 8.8% to 23.3%. Isolates of A. alternata were inoculated onto surface-sterilized ‘Alamo’ seed at 105 conidia/ml. Plant stand and health, and biomass yield were measured. Foliar disease ratings of plants from seed inoculated with all isolates was significantly greater than in untreated controls (P<0.0001). Isolates were inoculated (105 conidia/ml) on foliage of whole plants. All isolates caused greater foliar disease severity than untreated controls (P=0.10), and two isolates significantly reduced shoot fresh weight (P=0.05). Although A. alternata can cause foliar disease, isolates did not reduce plant stand, suggesting that this fungus may cause less economic losses than fungi that affect stand establishment, such as Bipolaris and Fusarium spp.