Developing shoots of grapevine ( Vitis vinifera cv. Kerner) were inoculated with conidia of the powdery mildew, Uncinula necator , at well‐defined phenological stages of the host to provoke the development of flag shoots in the field and to investigate these shoots as early as possible in the following growing season for the presence of the pathogen. The disease progress was monitored and fungal growth and development on samples from a field trial were analysed by means of low‐temperature scanning electron microscopy (LT–SEM). Mycelium was detected on the surface and in the interior parts of buds. The suitability of the field plot to analyse flag shoots was proven by the occurrence of such shoots in the following spring. Furthermore, early stages of cleistothecia development on berries were described for the first time. Establishment of U. necator in dormant buds of grapevine, giving rise to flag shoots in the following spring, is considered to play a significant role in overwintering of the pathogen in the vineyards of southern Germany.
This chapter contains sections titled: Introduction Resistance for which the Mechanism is Known and Molecular Detection Methods are Available Qo Site Inhibitors (QoIs) Benzimidazoles (MBCs) Demethylation Inhibitors (DMIs) Resistance for which the Mechanism is Known but Molecular Detection Methods are not Available Dicarboximides Carboxamides Phenylpyrroles Anilinopyrimidines Phenylamides Resistance Known in Field Populations but Resistance Mechanisms are Unknown Cinnamic Acids and Amino Acid Amide Carbamates Kasugamycin Polyoxins Pyrazophos Miscellaneous fungicides Outlook References
Mandipropamid is a new mandelic acid amide fungicide expressing high activity against foliar infecting oomycetes, including the grapevine downy mildew, Plasmopara viticola . Because cross‐resistance with the valinamide fungicides iprovalicarb and benthiavalicarb and the cinnamic acid amide fungicides dimethomorph and flumorph was postulated, all five compounds are classified as carboxylic acid amide (CAA) fungicides. To support this classification, cross‐resistance among these compounds with field isolates and the segregation of resistance in F 1 and F 2 progeny of P. viticola were evaluated. A bimodal distribution of sensitivity in field isolates and cross‐resistance among all CAAs for the vast majority of isolates were detected. Crosses between sensitive (s) and CAA‐resistant (r) isolates of opposite mating types, P1 and P2, yielded abundant oospores. All F 1 ‐progeny isolates were sensitive to CAAs (s:r segregation 1:0), whereas in F 2 progeny segregation of about 9:1 (s:r) was observed suggesting that resistance to CAA fungicides is controlled by two recessive nuclear genes. Mating type segregated in a ratio P1:P2 of c . 2:1 in F 1 and 1:1 in F 2 progeny. In the same crosses, resistance to the phenylamide fungicide mefenoxam segregated in a ratio of c . 1:3:2 (sensitive:intermediate:resistant), reflecting the monogenic, semidominant nature of resistance. The risk of resistance in P. viticola was classified as high for phenylamide and moderate for CAA fungicides. This is the first report on the inheritance of phenotypic traits in P. viticola .
