First report of Albifimbria verrucaria causing leaf spot on Glycine latifolia

Authors: HERMAN, THERESA - Oak Ridge Institute For Science And Education (ORISE); PAWLOWSKI, MICHELLE - University Of Illinois; Domier, Leslie; Hartman, Glen

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2019
Publication Date: 10/10/2019
Citation: Herman, T.K., Pawlowski, M.L., Domier, L.L., Hartman, G.L. 2019. First report of Albifimbria verrucaria causing leaf spot on Glycine latifolia. Plant Disease. 104(2):576. https://doi.org/10.1094/PDIS-08-19-1677-PDN.
DOI: https://doi.org/10.1094/PDIS-08-19-1677-PDN

Interpretive Summary: Plants of two accessions of greenhouse grown Glycine latifolia were observed to be mildly to severely affected with leaf spot symptoms that included moderate defoliation. Spots were irregularly shaped, approximately 2 to 5 mm by 4 to 8 mm in size, pale, gray or light brown in color. Symptomatic leaflets were detached, rinsed with tap water for one minute, and incubated in the dark at 24° C. After one-week, spore bodies called sporodochia were observed forming in and around the leaf spots. Spores were released in sterile water, spread on potato dextrose agar and isolates were white with dark green to black stroma. Spores were harvested from a 2-week-old culture via flooding with sterile deionized water and misted onto six 5-week old soybean and nine G. latifolia plants with a hand-held spray bottle. Necrotic lesions similar to those on the original plants were visible 2 days after inoculation and severely affected leaflets dropped off within two weeks. DNA was extracted from a mycelial plug 8 mm diameter and a specific region of DNA was sequenced and had 100% identity to the fungus, Albifimbria verrucaria. To our knowledge, this is the first confirmed report of A. verrucaria causing leaf spot on G. latifolia or any perennial Glycine species in natural or controlled environments. This information is important to those working with perennial Glycine species and those working on disease monitoring in soybean to determine the possible distribution and importance of this disease to soybean.

Technical Abstract: Plants of two accessions of greenhouse grown Glycine latifolia were observed to be mildly to severely affected with leaf spot symptoms that included moderate defoliation. Spots were irregularly shaped, approximately 2 to 5 mm by 4 to 8 mm in size, pale, gray or light brown in color and not bounded by veins, but often surrounded by chlorotic haloes and delimited by dark brown or reddish lines within or outside the haloes. Symptomatic leaflets were detached, rinsed with tap water for one minute, and incubated in the dark at 24° C. After one-week, sporodochia were observed forming in and around the leaf spots, at first light green, then turning dark green to black. Spores were released in sterile water, spread on potato dextrose agar (PDA), and incubated at 25°C in the dark for one week. Resulting isolates were white with dark green to black stroma and appeared morphologically to be Myrothecium or Paramyrothecium. Spores were harvested from a 2-week-old culture via flooding with sterile deionized water. The spore solution was added to 250 ml sterile deionized water amended with 0.04% Tween 20 and misted onto six 5-week old soybean and nine G. latifolia plants with a hand-held spray bottle. Necrotic lesions similar to those on the original plants were visible 2 days after inoculation and severely affected leaflets dropped off within two weeks. DNA was extracted from a mycelial plug 8 mm diameter and were subjected to PCR using ITS primers producing 500 bp amplicons. Using BLAST, the first nine alignments for the ITS region had 100% coverage and 100% identity for Albifimbria verrucaria. To our knowledge, this is the first confirmed report of A. verrucaria causing leaf spot on G. latifolia or any perennial Glycine species in natural or controlled environments.