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Phyllosticta species associated with diseases of four commercial Citrus species grown in China are reported. Totally, 496 Phyllosticta strains were isolated from mandarins (Citrus reticulata), pomeloes (C. maxima), oranges (C. sinensis) and lemons (C. limon) in the main citrus producing regions across China, and 74 strains were selected for phylogenetic analysis. Analyses inferred from the sequences of internal transcribed spacer region (ITS1, 5.8S nrDNA and ITS2), partial translation elongation factor 1-alpha (TEF1) and partial actin gene (ACT), showed these representative Phyllosticta isolates clustered in four distinct clades corresponding to three known, and one undescribed species. The newly resolved taxon, Phyllosticta citrichinaensis was isolated from leaves and fruits of all four Citrus species and is introduced in this paper. This taxon caused minor damage, showing irregular spots or freckles. Phyllosticta citriasiana, associated with tan spot of pomeloes, was isolated only from pomeloes, and never from lemons, mandarins and oranges. Phyllosticta citricarpa, the citrus black spot pathogen, which is presently subjected to phytosanitary legislation in the EU and United States, was isolated from lemons, mandarins and oranges, but never from pomeloes. The isolates of P. citricarpa clustered in two subclades, one from mandarins, the other from oranges and lemons. P. capitalensis was isolated from all four Citrus species as an endophyte, causing false melanose, or together with P. citricarpa or P. citriasiana. Morphological, cultural and biochemical characters were consistent with the results of phylogenetic analysis. In addition, a specific primer pair Pca8/ITS4 was designed and selected, and its corresponding PCR procedure was developed for the detection of P. citriasiana in this study.

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Nitrogen is one of the most important nutrients needed for plants and algae to survive, and the photosynthetic ability of algae is related to nitrogen abundance. Red algae are unique photosynthetic eukaryotic organisms in the evolution of algae, as they contain phycobilisomes (PBSs) on their thylakoid membranes. In this report, the in vivo chlorophyll (Chl) a fluorescence kinetics of nitrogen-starved Porphyridium cruentum were analyzed to determine the effects of nitrogen deficiency on photosynthetic performance using a multi-color pulse amplitude modulation (PAM) chlorophyll fluorometer. Due to nitrogen starvation, the photochemical efficiency of PSII and the activity of PSII reaction centers (RCs) decreased, and photoinhibition of PSII occurred. The water-splitting system on the donor side of PSII was seriously impacted by nitrogen deficiency, leading to the inactivation of the oxygen-evolving complex (OEC) and decreased light energy conversion efficiency. In nitrogen-starved cells, a higher proportion of energy was used for photochemical reactions, and thermal dissipation was reduced, as shown by qP and qN. The ability of nitrogen-starved cells to tolerate and resist high photon flux densities was weakened. Our results showed that the photosynthetic performance of P. cruentum was severely impacted by nitrogen deficiency.