DEVELOPMENT OF VENTURIA INAEQUALIS ON APPLE LEAVES OBSERVED BY ELECTRON MICROSCOPE
黑星病菌在苹果叶片上的发育过程研究

Development of apple scab pathogen, Venturia inaequalis, on the leaves were examined by means of scanning and transmission electron microscopy. The results showed that the conidia of V. inaequalis germinated and developed appressoria within 12 h after inoculation. The germination percentages of conidia examined at 6 h and 12 h after inoculation were 83% and 95% respectively. The frequency of appressorium formation of the germinated conidia were 93% and 95% 12 h and 24 h after inoculation respectively. The TEM observations revealed that after penetration of the cuticle growth of the pathogen was entirely subcuticular during the stages of parasitism. The sporulation of the fungus started with the formation of conidia 12 days after inoculation in the apple leaves. With the initiation of the conidiogenesis the enlarged stroma forced the cuticle outward until rupture. Each new proliferation lengthens the annellide and normally produces a single terminal conidium. Production of annelids and conidia occurs in narrow thread-like lines which radiate irregularly from one or more centers of origin (site of initial infections) and branch repeatedly, forming a network over the leaf surface , often paralleling a leaf vein. The typical scab symptom was observed at this sampling time.