A cytological and ultrastructural study on the maturation and germination of oospores of Plasmopara viticola from overwintering vine leaves

Abstract

Observations on cytological and ultrastructural changes in Plasmopara viticola oospores were carried out during the overwintering period. Three types of oospores were observed. Type I, characterized by a thin inner oospore wall (IOW), large lipid globules and two nuclei, was recovered only in samples collected in October. These oospores were considered to be immature. Maturation occurred during November and involved a noticeable increase in thickness of the IOW, fusion of nuclei, formation of an ooplast and break up of large lipid globules into smaller ones (type II oospores). A few oospores (type III) showed abnormal organization with very large lipid globules and less frequently discernible nuclei. IOW solubilization, dissolution of the ooplast and lipid globules and nuclear division were the first detectable events during oospore germination. Germinating oospores produce a germ tube which was terminated by a sporangium. In its young stage, the sporangium had a thick wall and an unusual multi-layered membrane. During this phase, nuclear divisions took place in the sporangium. While sporangium development progressed, the ribosome density in the cytoplasm decreased and mitochondria, initially roundish with evident cristae, became their usual tubular profile. The plasma membrane had a typical structure and storage organelles, such as finger print vacuoles and lipid globules, became more numerous in the cytoplasm. Larger vacuoles contained the flagella of differentiating zoospores.

A new approach to modelling the dynamics of oospore germination in Plasmopara viticola

“…Calcium, and, consequently, germination rate exhibit an oscillating behaviour nutritional reserves. Ultrastructural studies have shown that P. viticola oospores are mature by the middle of November (Vercesi et al 1999). In fact the germination of the oospores overwintered in natural conditions occurs from the end of November onwards, continuously until mid May and then sporadically until mid June.…”

The host guides morphogenesis and stomatal targeting in the grapevine pathogen Plasmopara viticola

“…Sexual propagation exists prior to overwintering of infectious spores, which are of agronomic importance as they provide the first source of inoculum in the year. However, it is the rapid sequence of asexual propagation cycles (sometimes as short as 4 days) that is responsible for the efficient spread of this oomycete during the growing season (Vercesi et al 1999).…”

Estimating germinability ofPlasmopara viticola oospores by means of neural networks

“…Moreover, knowledge of the amount of the previous germination percentage G~ 1 is useful to achieve a more satisfactory correlation. The previous germination percentages assessed in the current year include a precocious climatic influence, probably affecting oospore maturation (VERCESI et al, 1999). BURRUANO et al (1994a) observed that the oospore germination rate is strictly dependent on the number of mononucleate (e.g.…”