A family of subsets of a set is called a $\sigma $-topology if it is closed under arbitrary countable unions and arbitrary finite intersections. A $\sigma $-topology is perfect if any its member (open set) is a countable union of complements of open sets. In this paper perfect $\sigma $-topologies are characterized in terms of inserting lower and upper measurable functions. This improves upon and extends a similar result concerning perfect topologies. Combining this characterization with a $\sigma $-topological version of Katětov-Tong insertion theorem yields a Michael insertion theorem for normal and perfect $\sigma $-topological spaces.
The aim of this study was to evaluate the photochemistry of Luffa cylindrica (L.) Roem in fungal biocontrol interacting treatments. Healthy plants were infected with Pythium aphanidermatum before the biocontrol application. Biocontrol agents were selected in preliminary Petri-plate experiment evaluation against causative agent P. aphanidermatum. Photosynthetic performance traits were studied. We found that P. aphanidermatum infection caused significant reduction in photosynthetic performance, pigments, and in maximum quantum yield of primary photochemistry, photochemical quenching, and electron transport rate with increase in nonphotochemical quenching as compared with non-infected control. However, application of biocontrol agents substantially improved maximum quantum yield of PSII, performance index, and total content of photosynthetic pigments in infected plants. The fluorescence intensity was used for quantifying the antagonist effect of biocontrol agents on infected plant leaves., H. Amrina, S. Shahzad, Z. S. Siddiqui., and Obsahuje bibliografii