Submitted to: National Fusarium Head Blight Forum Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 12/8/2001
Publication Date: N/A
Technical Abstract: To investigate the role of mycelial colonies on floret surfaces in head blight infection, we mapped the location and number of colonies for 1-12 days after field plots were inoculated with Fusarium graminearum. Four plots of Robust barley were inoculated June 25, 2001. At 1, 2, 3, 4, 5, 6, 8, 10, and 12 days after inoculation (DAI), florets were harvested. Each day, 60 fresh (unfixed) florets were dissected and examined for presence of chlorotic or necrotic lesions; 80 additional florets were examined microscopically for presence of mycelium on floret surfaces. At 4-6 DAI, mycelial colonies were noted on 13% of awns, 13% of lemma exteriors, 9% of lemma interiors, 57% of palea exteriors, 3% of palea interiors, and 6% of caryopses. At 4-6 DAI, chlorotic lesions were present on the lemma and palea in 8-13% of florets, and on the awn and/or caryopsis in 3-4% of florets. By 6-8 DAI, colonies on the palea surface often spread laterally into the crevice between the palea and lemma, sometimes extending to the interior surfaces of the palea and lemma as well as to the caryopsis. A second pathway to the interior of the floret was through the apical floret mouth. By 5 DAI and thereafter, colonies extended basally on the interior surfaces of the lemma and palea. By 8-12 DAI, discrete chlorotic or necrotic lesions were present on the apex of 14% of lemmas and 13% of paleas. The results indicate that under warm, mist-irrigated field conditions, colonies on the abaxial (exterior) surface of the palea (near the keel) and on adaxial (interior) surfaces of the palea and lemma facing the floret mouth serve as starting points for floret invasion.