The Effect of Environmental pH during Trichothecium roseum (Pers.:Fr.) Link Inoculation of Apple Fruits on the Host Differential Reactive Oxygen Species Metabolism

Trichothecium roseum is an important postharvest pathogen, belonging to an alkalizing group of pathogens secreting ammonia during fungal growth and colonization of apple fruits. Fungal pH modulation is usually considered a factor for improving fungal gene expression, contributing to its pathogenicity. However, the effects of inoculation with T. roseum spore suspensions at increasing pH levels from pH 3 up to pH 7, on the reactive oxygen species (ROS) production and scavenging capability of the apple fruits, affecting host susceptibility, indicate that the pH regulation by the pathogens also affects host response and may contribute to colonization. The present results indicate that the inoculation of T. roseum spores at pH 3 caused the lowest cell membrane permeability, and reduced malondialdehyde content, NADPH oxidases activity, O2●− and H2O2 production in the colonized fruit. Observations of the colonized area on the 9th day after inoculation at pH 3, showed that the rate of O2●− production and H2O2 content was reduced by 57% and 25%, compared to their activities at pH 7. In contrast, antioxidative activities of superoxide dismutase, catalase and peroxidases of fruit tissue inoculated with spores’ suspension in the presence of a solution at pH 3.0 showed their highest activity. The catalase and peroxidases activities in the colonized tissue at pH 3 were higher by almost 58% and 55.9%, respectively, on the 6th day after inoculation compared to inoculation at pH 7. The activities of key enzymes of the ascorbate-glutathione (AsA-GSH) cycle and their substrates and products by the 9th day after fruit inoculation at pH 3 showed 150%, 31%, 16%, and 110% higher activities of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase, respectively, compared to pH 7. A similar pattern of response was also observed in the accumulation of ascorbic acid and dehydroascorbate which showed a higher accumulation at pH 3 compared to the colonization at pH 7. The present results indicate that the metabolic regulation of the pH environment by the T. roseum not only modulates the fungal pathogenicity factors reported before, but it induces metabolic host changes contributing both together to fungal colonization.

INFLUENCE OF COLOR OF GRAIN DOURA ON THEIR COLONIZATION BY PATHOGENIC MICROFLORA

akes it possible to determine the infestation of plants and seeds with pathogens, as well as to save a high yield and improve the quality of grain, among other things. The aim of our research was to identify pathogenic microflora on sorghum seeds and determine the degree of their distribution. Place of research: Samara region. According to the phytopathological expertise of 2018-2020, it was found that the mold of grain sorghum seeds is caused by many types of mold fungi, but the most common were Cladosporium sp., Trichothecium roseum, Mucor sp., Penicillium sp. To a lesser extent, fungi of the genus Aspergillus were found. Pathogenic fungi from the genus Alternaria were observed on the surface of 2.0% of sorghum seeds, Fusarium sp. - 2.0 %. Among the two varieties of grain sorghum, the most susceptible to infection with pathogens was a sample with a yellowish-white color of seeds compared to orange-red, respectively, 49.3 % and 33.5 % of seeds infected with pathogens. In our opinion, this difference in seed damage may be due to the absence of tannins in the yellowish-white grain and its presence in the orange-red grain, which corresponds to the data of many authors. The number of healthy seeds in the sample with yellowish-white grain color was 50.7% and 66.5% with orange-red. The variety with a yellowish-white seed color was more strongly affected by mold fungi from the genus Cladosporium sp., Trichothecium roseum, Mucor sp., Penicillium sp. - on average, about 40.3 %. The interaction of pathogens in the community of mycobiota of grain undoubtedly affects their vital activity, which ultimately affects the relationship with the host plant. The results obtained will make a significant contribution to local technologies, to the environmentally reasonable integrated protection of sorghum from pathogens.

Species disease composition of sorghum crops in forest steppe of the Middle Volga region

The paper presents the results of field and laboratory studies on the disease diversity in sorghum and Sudan grass. It is found that leaf spotting in sorghum in the wooded-steppe of the Middle Volga region is caused by a broader range of pathogens than previously assumed, whilst the symptoms of damage caused by different types of fungi might be similar in occurrence. It is of paramount importance to proceed with phyto-examination of the seeds with further identification of the accumulated infection sources in the seed material under field conditions, at the time of harvest and during subsequent processing of the seed material in seed refiners, etc. For that to happen, the leaves with distinct spotting occurrence are collected and, given the preliminary storage of the material in humidity cabinet, are examined in the laboratory employing microscopic techniques. On the leaves of grain sorghum collected over the vegetation season of 2018 and dried up to be preserved as herbarium, the dark purple coming near to black spots of various sizes and shapes were predominantly observed. When identifying leaf pathogens, the fungi were largely detected and identified, i.e.: Alternaria tenuissima, Botrytis cenerea, Trichothecium roseum. In 2019, the leaves touched by spotting were already picked from different specimen varieties of sorghum and Sudan grass; and their identification was carried out with regard to dissimilar occurrence of symptoms during the period of plant vegetation. In the spotted areas of the infected leaves, there were mycelium and sporulation revealed of the fungi as follows: Cladosporium herbarum genera (82.1% of all specimens studied), Alternaria sp. (71.1%) and Verticillium sp. (71.4%). The midrange frequency of occurrence was estimated for Trichothecium roseum (53.6%), Helminthosporium sp. (42.9%), Cercospora sorghi (39.3%), Fusarium sp. (35.7%). Besides, the bacterial infection was discovered as well in 32.1% of the specimens.

Trichothecium roseum Enters ‘Fuji’ Apple Cores Through Stylar Fissures

Apple core rot, an economically important disease worldwide, appears both before and during harvest. Current gaps in understanding of the infection cycle impede progress toward more effective management of this disease. The fungus Trichothecium roseum is the main pathogen of core rot on apple in China. In this study, we used fluorescent labeling to trace colonization of T. roseum in floral tissues, characterizing routes of penetration to the core of ‘Fuji’ apples. T. roseum infected petals, anthers, filaments, stigmas and separated styles of flowers, and floral debris served as inoculum for core infection. In field inoculations, T. roseum entered styles initially through stylar fissures and colonized pluricellular hairs of these fissures during early stages of fruit development. Subsequently, hyphae grew along the extending fissures, which are continuations of stylar fissures located between stylar bases and carpel cavities. The hyphae remained in the extending fissures from mid-June to late July. When fruit developed an open sinus in late July, the sinus eventually fused with extending fissures and carpel cavities in late August, hyphae invaded carpel cavities, and ultimately fruit flesh via cracks on carpel cavity walls. Our results revealed for the first time the routes by which T. roseum penetrates apple fruit, and provided significant insights for strategic management of core rot.

Cuminal Inhibits Trichothecium roseum Growth by Triggering Cell Starvation: Transcriptome and Proteome Analysis

Trichothecium roseum is a harmful postharvest fungus causing serious damage, together with the secretion of insidious mycotoxins, on apples, melons, and other important fruits. Cuminal, a predominant component of Cuminum cyminum essential oil has proven to successfully inhibit the growth of T. roseum in vitro and in vivo. Electron microscopic observations revealed cuminal exposure impaired the fungal morphology and ultrastructure, particularly the plasmalemma. Transcriptome and proteome analysis was used to investigate the responses of T. roseum to exposure of cuminal. In total, 2825 differentially expressed transcripts (1516 up and 1309 down) and 225 differentially expressed proteins (90 up and 135 down) were determined. Overall, notable parts of these differentially expressed genes functionally belong to subcellular localities of the membrane system and cytosol, along with ribosomes, mitochondria and peroxisomes. According to the localization analysis and the biological annotation of these genes, carbohydrate and lipids metabolism, redox homeostasis, and asexual reproduction were among the most enriched gene ontology (GO) terms. Biological pathway enrichment analysis showed that lipids and amino acid degradation, ATP-binding cassette transporters, membrane reconstitution, mRNA surveillance pathway and peroxisome were elevated, whereas secondary metabolite biosynthesis, cell cycle, and glycolysis/gluconeogenesis were down regulated. Further integrated omics analysis showed that cuminal exposure first impaired the polarity of the cytoplasmic membrane and then triggered the reconstitution and dysfunction of fungal plasmalemma, resulting in handicapped nutrient procurement of the cells. Consequently, fungal cells showed starvation stress with limited carbohydrate metabolism, resulting a metabolic shift to catabolism of the cell’s own components in response to the stress. Additionally, these predicaments brought about oxidative stress, which, in collaboration with the starvation, damaged certain critical organelles such as mitochondria. Such degeneration, accompanied by energy deficiency, suppressed the biosynthesis of essential proteins and inhibited fungal growth.