SPORULATION OF FUSARIUM-OXYSPORUM F-SP LYCOPERSICI ON STEM SURFACES OF TOMATO PLANTS AND AERIAL DISSEMINATION OF INOCULUM

Plants exhibiting symptoms of wilt and xylem discoloration typical of Fusarium wilt caused by Fusarium oxysporum f. sp, lycopersici were obs erved in greenhouses of cherry tomatoes at various sites in Israel. Ho wever, the lower stems of some of these plants were covered with a pin k layer of macroconidia of F. oxysporum. This sign resembles the sporu lating layer on stems of tomato plants infected with F. oxysporum f. s p. radicis-lycopersici, which causes the crown and root rot disease. M onoconidial isolates of F. oxysporum from diseased plants were assigne d to vegetative compatibility group 0030 of F. oxysporum f. sp. lycope rsici and identified as belonging to race 1 of F. oxysporum f. sp. lyc opersici. The possibility of coinfection with F. oxysporum f. sp. lyco persici and F. oxysporum f. sp. radicis-lycopersici was excluded by te sting several macroconidia from each plant. Airborne propagules of F. oxysporum f. sp. lycopersici were trapped on selective medium in green houses in which plants with a sporulating layer had been growing. Spor ulation on stems was reproduced by inoculating tomato plants with race s 1 and 2 of F. oxysporum f. sp. lycopersici. This phenomenon has not been reported previously with F. oxysporum f. sp, lycopersici and migh t be connected to specific environmental conditions, e.g., high humidi ty. The sporulation of F. oxysporum f. sp. lycopersici on plant stems and the resultant aerial dissemination of macroconidia may have seriou s epidemiological consequences. Sanitation of the greenhouse structure , as part of a holistic disease management approach, is necessary to e nsure effective disease control.