Histo-pathology study of the growth of Trichoderma harzianum, Phaeomoniella chlamydospora and Eutypa lata on grapevine pruning wounds
Protecting grapevine pruning wounds by inoculating them with Trichoderma spp. can prevent infection from trunk disease pathogens. The growth and interactions of both, the biological control agent Trichoderma spp. and the vine pathogens, are not well understood. Green fluorescent protein (GFP)-labelled Trichoderma harzianum and red fluorescent protein (DsRed)-labelled T. harzianum, were dual-inoculated with Phaeomoniella chlamydospora (DsRed) or Eutypa lata (GFP) on fresh pruning wounds of one-year-old Cabernet Sauvignon and Sauvignon blanc shoots. The inoculated fungi were recovered from varying depths within the shoots at 30-day-intervals for 90 days. Trichoderma harzianum suppressed the pathogens and grew deeper in the presence of the pathogens than when it was singly inoculated; possibly an indication of pathogen recognition and competitive response. Eutypa lata was completely eliminated from Sauvignon blanc in dual-inoculated canes after 90 days. The mycelium of P. chlamydospora (DsRed) grew extensively in the xylem vessels and possibly contributed to vessel occlusion. Phaeomoniella chlamydospora and E. lata caused blockage of the vessels and thickening of the vessel walls. Grapevine wood produced both tyloses and gums (gels) that blocked xylem vessels as a result of infection. A thickening of the cell walls of xylem fibres occurred only in E. lata-inoculated shoots, indicative of a different mode of pathogenesis from P. chlamydospora.