ASCOSPORE GRADIENTS OF GIBBERELLA ZEAE FROM OVERWINTERED INOCULUM IN WHEAT FIELDS

Authors: DE LUNA, L - MCGILL UNIVERSITY; BUJOLD, I - MCGILL UNIVERSITY; CARISSE, O - AGRI & AGRI-FOOD CANADA; Paulitz, Timothy

Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2002
Publication Date: 12/20/2002
Citation: DE LUNA, L., BUJOLD, I., CARISSE, O., PAULITZ, T.C. ASCOSPORE GRADIENTS OF GIBBERELLA ZEAE FROM OVERWINTERED INOCULUM IN WHEAT FIELDS. CANADIAN JOURNAL OF PLANT PATHOLOGY. 2002.

Interpretive Summary: Ascospores of Gibberella zeae are the primary inoculum that causes Fusarium head blight, the most important foliar diseases of wheat in N. America. This study looks at gradients of ascospores arising from a infected plots with naturally overwintered inoculum. The spores were sampled at distances from 0 to 50 m away from the plots. The decrease in spore concentration over distance was described by three models. Ascospore concentrations declined by 50% within 18 m of the source, and by 90% within 60 m of the source. This is the first detailed study of ascospore gradients of G. zeae from naturally overwintered inoculum on a field scale. Although ascospore concentrations declined considerably within the 50 m transect, long-distance transport of spores beyond the field may occur.

Technical Abstract: Ascospore gradients of Gibberella zeae, causal agent of fusarium head blight of wheat, were measured over a three-month period in 1999 at two sites in Québec, Canada. At Macdonald Campus (MAC) and L'Acadie (LAC), spores were sampled daily with rotorod-type samplers along transects at intervals of 10 m up to 50 m away from plots of wheat inoculated at anthesis the previous summer and allowed to overwinter. At MAC, ascospore concentrations > 100 · m-3 were detected on 38 nights from 1 June to 20 August, in 16 separate release events that lasted from 1 to 3 nights. Most of the ascospore releases occurred 1 to 6 days after an initiating rainfall, and the ascospore concentration in subsequent evenings after the initiating rainfall decreased over time. Spore gradients were modeled with the inverse power model of Gregory, the negative exponential model of Kiyosawa and Shiyomi, and the general model of Lambert. The general model outperformed the other two models at both sites, with an adjusted R2 = 0.88 and 0.79 for MAC and LAC, respectively. The inverse power model outperformed the negative exponential model at MAC, and vice versa at LAC. Based on gradients that fit the negative exponential model, ascospore concentrations declined by 50% within 18 m of the source, and by 90% within 60 m of the source at MAC. This is the first detailed study of ascospore gradients of G. zeae from naturally overwintered inoculum on a field scale. Although ascospore concentrations declined considerably within the 50 m transect, long-distance transport of spores beyond the field may occur.