Downy mildew of cucumber ( Cucumis sativus L.), caused by Pseudoperonospora cubensis(Berk. et Curt.) Rostovzev, is one of the most important foliar diseases of cucurbit crops. Two parental lines...

Summary: Dramatic increase in confocal microscopy observation output has been gained by optimization of a simple trypan blue and aniline blue dual-stain and its application to two model pathosystems: Pseudoperonospora cubensiscucumber and Phytophthora infestans-tomato. Comparison of two dual-stain methods for confocal microscopy studies of P. cubensis-challenged cucumber leaves indicated the 'mild' approach most successful. This methodology provides simultaneous detection of different pathogen structures layered with the plant defense reactions. Moreover, ImageJ-assisted quantification of plant defense responses renders this method useful for addressing the host plant resistance reactions, as well as investigating the given isolate's pathogenicity. Application of this method for the P. infestans-challenged tomato leaf samples resulted in detection of several fungal infection structures, along with plant defense responses. The dual-stain also enabled detection of a peculiar aniline blue-sensitive material in the pathogen cell walls at the area of its hyphae emerging through the leaf stomata. Results presented herein indicate this method is applicable for detailed (possibly quantitative) investigations of multiple plant-fungal pathosystems.

Late blight (LB) caused by the oomycete Phytophthora infestans continues to thwart global tomato production, while only few resistant cultivars have been introduced locally. In order to gain from the released tomato germplasm with LB resistance, we compared the 5-year field performance of LB resistance in several tomato cultigens, with the results of controlled conditions testing (i.e., detached leaflet/leaf, whole plant). In case of these artificial screening techniques, the effects of plant age and inoculum concentration were additionally considered. In the field trials, LA 1033, L 3707, L 3708 displayed the highest LB resistance, and could be used for cultivar development under Polish conditions. Of the three methods using controlled conditions, the detached leaf and the whole plant tests had the highest correlation with thefield experiments. The plant age effect on LB resistance in tomato reported here, irrespective of the cultigen tested or inoculum concentration used, makes it important to standardize the test parameters when screening for resistance. Our results help show why other reports disagree on LB resistance in tomato.

Downy mildew of cucumber (Cucumis sativus L.), caused by Pseudoperonospora cubensis (Berk. et Curt.) Rostovzev, is one of the most important foliar diseases of cucurbit crops. Two parental lines resistant PI 197085, susceptible PI 175695 and their F2 generation were used in our study. Inheritance of resistance to Pseudoperonospora cubensis in PI 197085 was quantitative. JoiMap 4.1 and MapQTL 6.0 software was used for a linkage groups construction and QTL mapping. Three QTL were detected: DM1, DM2, DM3. The loci were mapped on chromosome 5 of cucumber genome. Molecular analysis confirmed results of classical quantitative genetics indicating that resistance to Pseudoperonospora cubensis in PI 197085 is polygenic trait.