. Recent research on foliage diseases : conference proceedings : Carlisle, Pennsylvania, May 29-June 2, 1989. Leaves Diseases and pests United States Congresses. Effect of wounding and inoculation site on infec- tion.—Wounding significantly increased infection of leaflets (fig. 4). The wounded leaflets inoculated at midrib and margin had 56% and 67% infection while the corresponding inoculated but nonwounded treat- ments inoculated had only 17% and 28% infection, re- spectively. Both nonwounded and wounded petioles showed 100% infection when inoculated with G. fraxini. The symptom of infection
. Recent research on foliage diseases : conference proceedings : Carlisle, Pennsylvania, May 29-June 2, 1989. Leaves Diseases and pests United States Congresses. Effect of wounding and inoculation site on infec- tion.—Wounding significantly increased infection of leaflets (fig. 4). The wounded leaflets inoculated at midrib and margin had 56% and 67% infection while the corresponding inoculated but nonwounded treat- ments inoculated had only 17% and 28% infection, re- spectively. Both nonwounded and wounded petioles showed 100% infection when inoculated with G. fraxini. The symptom of infection was necrosis of the area around the inoculation site. Incidence of infec- tion of leaflets and petioles was not influenced by the temperatures (16, 20, 25 C) used in these experiments. Gnomoniella fraxini was reisolated from petioles or leaflets showing symptoms. Figure 6.—Infected overwintered petioles. A. Shown in mia-June after leaves have expanded. The proximity of petioles to current leaves serves as an ideally placed souce of primary inoculum and new leaves are already infected. Terimnal bud of shoot with overwintered petioles has been killed by earlier infection. B. Petioles that are clinging to the previous year's growth on green ash before budbreak in the spring. The small, black, round to ellipitcal specks (arrows) are acervuli. When this set of isolates were compared for patho- genicity, all caused some infection. Isolates from the six sources did not differ significantly from each other in disease-causing ability (fig. 3). FIGURE 3. INFECTION OF GREEN ASH BY G FfiAXTNI ISOLATED FROM DIFFERENT PLANT PARTS 60 1 I SOURCE OF CULTURE ^1 NOT INOCULATED 11^ SPRING LEAF BLOTCH lH FALL LEAF BLOTCH 222 SUMMER PETIOLE jsH WINTER PETIOLE ^3 SMALL LEAFSPOT BRANCH CANKER FLSD .05 ill FIGURE 4. EFFECT OF POSITION OF WOUND ON INFECTION OF GREEN ASH LEAVES BY GNOMONIELLA FRAXINf TREATMENT / POSITION L~l NW - Nl IB A 9 MIDRIB - Nl I •*» 5 v-=; \ - \ BSE NW 4 GF «
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