Effects of postinfection applications of ergosterol biosynthesis-inhibiting fungicides on lesion formation and Pseudothecial development of Venturia inaequalis and influence of temperature and moisture on the quantitative production of Pseudothecia (Malus Domestica Bork., Apple Scab)
O'leary, Ann Lackner.
Thesis of Ph.D., North Carolina State University, 1985, 57 pages.
1985
บทคัดย่อ
The influence of temperature and moisture on the quantitative production of Venturia inaequalis pseudothecia in sterilized, inoculated leaf discs and in naturally-infected leaf discs was studied by exposing discs in a factorial design to seven temperatures (0, 4, 8, 12, 16, 20, 24 C), four moistures (wet, 95% RH, 88% RH, dry), two treatment durations (3, 7 da) at five stages (st) of pseudothecial development. More pseudothecia were produced in leaf discs in the wet treatment than in the 95% RH treatment; few pseudothecia were produced in the 88% RH and dry treatments. The optimum temperatures for pseudothecial production at stages 2, 3, 5, 7 and 9 were 4, 8, 8, 16, and 20 C, respectively. Number of pseudothecia produced in inoculated leaf discs was significantly correlated with inoculum concentration and length of initial incubation at 20 C.
The ergosterol biosynthesis-inhibiting (EBI) fungicides, bitertanol, etaconazole, fenarimol and triforine, applied 120 hr after inoculation with V. inaequalis resulted in the formation of chlorotic lesions 2 wk after application. Normal sporulating lesions were observed in the bitertanol and triforine treatments after 2 wk and in all fungicide treatments 5 wk after applications. Sporulation was also observed around the edges of chlorotic lesions after 5 wk. A postsymptom application of benomyl was more effective than the EBI fungicides in reducing recovery of V. inaequalis on acidified potato dextrose agar from lesions 5 wk after application. All postsymptom fungicide treatments failed to prevent continued sporulation from treated lesions. Few conidia recovered from treated lesions germinated compared to conidia recovered from untreated lesions. A single postharvest application of the EBI fungicides resulted in the production of fewer pseudothecia in overwintered leaves. Pseudothecia that develope
d in treated leaves were smaller and contained fewer ascospores compared to pseudothecia from untreated leaves. Histological studies indicated that fewer pseudothecia were initiated in treated leaves.