Journal of Plant Pathology最新文献

This research investigated the inhibitory effects of essential oils (EOs) extracted from four Citrus sinensis cultivars (Thomson navel, Jaffa sweet, Sanguine blood, and Valencia) against Alternaria spp., a pathogen affecting oranges. Among the cultivars studied, the EO from the Sanguine blood cultivar exhibited the highest antifungal activity when added into the culture medium and it was selected for further investigations. Sanguine blood EO reduced melanin in the fungal hyphae and completely inhibited vegetative growth of Alternaria species at 550–750 μg mL⁻¹ concentrations and inhibited spore germination at 800–1000 μg mL⁻¹ concentrations, which were similar to the fungicide Mancozeb. Separation of cytoplasm from cell wall, hyphal emptying, destruction of cell wall, plasma membrane, organelles such as nucleus and mitochondria, hyphal lysis and cell death were observed in all three fungal species tested. Activities of cell wall degrading enzymes produced by the pathogens were significantly reduced in the fungi treated with the EO. Reduction of the disease index was observed in all four cultivars, similar to the effect of fungicide. Gas chromatography-mass spectrometry analysis revealed presence of D-limonene, β-myrcene, and β-linalool as the main components of the EO obtained from the Sanguine blood cultivar. In conclusion, the EOs as natural plant protectants could control Alternaria spp. on orange under both in vitro and in vivo conditions.

Abstract

Pigeaonpea is attacked by various diseases, including the wilt disease of pigeonpea caused by Fusarium udum. This disease is a severe pathogen to this crop. This study aims to identify the potential biocontrol agent against wilt disease as a fungicide alternative. Forty-seven isolates were evaluated for antagonistic activity against F. udum by dual culture method. Interaction of F. udum and antagonistic bacteria was studied in potato dextrose agar (PDA) under in vitro conditions and lysis of fungal hyphae was observed by using Scanning Electron Microscope. Dry weight of F. udum mycelium was recorded after 3 days of co-inoculation with the rhizobacteria in PDB. Potential antagonistic bacterial isolates were further used for enzymatic assay in vitro conditions. Molecular characterization of bacteria was done by using primers based on hydrolytic genes like chitinase and 1,3-glucanase related genes, amplified at 402 and 750 bp, respectively. Out of forty-seven bacterial isolates used to assess their antagonistic activity, only eight isolates, viz., Bacillus amyloliquefaciens CFLB 31, Bacillus velezensis CFLB 24, Bacillus subtilis CFLB 11, Stenotrophomonas rhizophila CFLB 26, S. matalophila CFLB 47, Microbacteria sp. CFLB 28, G.nicotiana CFLB 18 and Pseudoarthrobacter sp. CFLB 36 showed the promising antagonistic activity against F. udum with 70–84% inhibition in a dual culture plate assay. Among them, three Bacillus species (B. amyloliquefaciens, B. velezensis, B. subtilis) and S. maltophilia CFLB 47 were found to be the most effective biocontrol agent against F. udum under in vitro conditions. Lysis of fungal hyphae was also noted during interaction of fungus and bacteria on PDA. These isolates were screened for production of hydrolytic enzymes activities and they showed positive for production of pectinase, protease and cellulase under in vitro conditions. These isolates amplified chitinase and β-1, 3-glucanase-related genes at 402 and 750 bp, respectively. In addition, bacterial strains reduced the mycelium weight of F. udum with the range of 58.42 − 86.84% during co-inoculation in PDB. However, B. amyloliquefaciens had the highest percentage of biomass reduction, up to 86.84%. Bacterial treatments are considered beneficial and nature-friendly. The results propose that the eight potential strains and their hydrolytic enzymatic properties made them promise to manage wilt disease of pigeonpea.

Cotton crops are routinely threatened by emerging fungal diseases. Fungal endophytes also can be considered latent phytopathogens. In this study we tested the hypothesis that an endophytic strain of Diaporthe, isolated from chlorotic leaves of cotton (Gossypium hirsutum), could trigger physiological effects of biotic stress in this oilseed plant. We also assessed the histopathological aspects of the mycelial interaction of the endophyte with the adaxial surface of G. hirsutum leaves. Thus, we studied the synthesis of photosynthetic pigments, pattern of gas exchange, and photochemistry of cotton plants subjected to inoculation with Diaporthe ueckerae via root and leaf at three different phenological stages (vegetative, reproductive, and maturation). Additionally, we histopathologically analyzed infected leaves using electron microscopy to study the process of leaf colonization by this endophytic fungus. We evidenced that D. ueckerae inoculation negatively affected the synthesis of photosynthetic pigments in plants at vegetative and reproductive stages. Moreover, inoculation also negatively affected the photosynthetic rate and carboxylation efficiency of these plants. We also found that the presence of the endophyte increased transpiration and decreased water use efficiency in the plants. Furthermore, foliar inoculation negatively affected stomatal conductance, whereas inoculation via leaf or root reduced the photochemical performance of cotton. We also observed that D. ueckerae colonizes the leaf tissues of G. hirsutum via glandular trichomes and forces penetration into the epidermis using appressoria, and the plant responds by closing the stomata. The observed physiological alterations are indicative of biotic stress, confirming the hypothesis that D. ueckerae may be an opportunistic phytopathogen for cotton plants.

Abstract

The take-all disease is one of the most important maladies in cereals and grasses, being caused by the fungus Gaeumannomyces tritici. Secondary metabolites are known to perform critical functions during the infection process of various phytopathogens. However, the current understanding of the biosynthesis of secondary metabolites in G. tritici is limited. Similarly, comprehensive analyses of the expression, conservation, and evolution of these biosynthesis-related genes are crucial for enhancing our knowledge of the molecular mechanisms that drive the development of the take-all disease. Here we have performed a deep survey and description of secondary metabolite biosynthetic gene clusters in G. tritici, analyzed a previously published RNA-seq of a mimicked infection condition, and assessed the conservation among 10 different Magnaporthales order members. Notably, the majority of the 35 putative gene clusters identified were conserved among these species, with GtPKS1, GtPKS3, and GtTERP4 uniquely identified in G. tritici. In the mimicked infection condition, seven gene clusters, including the GtPKS1 cluster, exhibited upregulated expression. Through comparative genomic analysis, GtPKS1 was associated with the production of dichlorodiaporthin, a metabolite with cytotoxic and antifungal activity. In addition, GtPKS10 and GtPKSNRPS3 showed similarities to already characterized biosynthetic pathways involved in the synthesis of ACR-toxin (phytotoxic) and trichosetin (phytotoxic and antibiotic), respectively. These three gene clusters were further scrutinized through phylogenetic inference, which revealed the distribution of orthologous sequences across various plant-associated fungi. Finally, the detailed identification of several genes enrolled in secondary metabolite biosynthesis provides the foundation for future in-depth research, supporting the potential impact of several small molecules on G. tritici lifecycle and host interactions.

The last few years have been a huge challenge for every farmer in Europe and Hungary because of the increase in hot days and the decrease in precipitation. These facts induced the farmer’s interest in sorghum because it has better stress tolerance than many other cereales, but little is known about mycotoxin-producing fungi, which can infect this crop. Mycotoxins are secondary metabolites of filamentous fungi, and they are not only phytotoxic but also harmful to humans and animals. This study aimed to determine the internal infection caused by Alternaria spp., Fusarium spp., and Aspergillus spp., which are known as mycotoxin-producing fungi in food raw material. In our study in the case of sorghum, the presence of various mycotoxin-producing fungi was detected on Fusarium selective media (Nash and Snyder media), and the results indicate that these genera are present in sorghum grains as potential mycotoxin producers. To determine which Fusarium species is occurring in our sorghum grain samples, a molecular genetic study was performed on isolated fungi using the TEF region primer pairs to identify the occurring Fusarium species. We mainly identified Fusarium proliferatum in our conventional sorghum samples. The results show that the mentioned mycotoxin-producing fungi are in the sorghum grains and may pose a risk to the safety of feed and food because they may produce mycotoxins in the field or while being stored.

Helminthosporium leaf spot disease caused by Helminthosporium sesami is one of the most serious foliar diseases of sesame (Sesamum indicum L.), which causes a significant loss in yield and oil percentage. This study aims to investigate the effect of castor (Ricinus communis L.) essential oil and sodium bicarbonate (SBC) on the causal pathogen of leaf spot disease as well as the growth and yield of sesame. A gas chromatography-mass spectrometry (GC-MS) analysis of castor essential oil identified a number of bioactive components. Ricinoleic acid (19.15%) and squalene (9.82%) are two of the most bioactive components in castor oil. In laboratory experiments, castor oil at different concentrations (100, 250, 500, 750 and 1000 µl/L) and SBC at concentrations of 20, 40, 60, 80 and 100 mM were assessed on the mycelium growth of H. sesami. Castor oil at a concentration of 1000 µl/L resulted in the greatest reduction in pathogen mycelial growth (66.67%), while SBC at a concentration of 100 mM gave a high percentage of inhibition (82.96%). Data also show that foliar applications of castor oil and SBC reduced the disease severity of Helminthosporium leaf spot disease of sesame in both greenhouse and field experiments, with SBC being the most effective in reducing the disease severity compared to the control. The agronomic traits of sesame, such as plant height, capsules plant^− 1, weight of 1000 seeds (g), quantity of seeds produced per feddan (kg), and oil % in seeds, were also improved by the treatments.

Several species of Venturia spp. cause scab disease on fruit trees: V. inaequalis on apple, V. pirina on pear, and V. nashicola on Asian pear that is listed as a quarantine pathogen in several countries in the world. An emerging disease caused by V. asperata on apple has very recently been reported in France, Italy and China. Fruit tree scab causes high economic losses and requires frequent fungicide treatments in orchards. Early detection of these pathogens is important in the management of this disease and—in the case of V. nashicola—to prevent its introduction and spread in disease-free areas. Using genomic resources available on these species, we identified polymorphic regions between them to develop a set of real-time PCR assays enabling detection of the four species on symptomatic fruits and leaves. We focused in particular on V. nashicola to establish a comprehensive validation procedure. The assay proved to be effective for targeting this quarantine species, thereby ensuring the reliability of analysis results in the context of regulatory monitoring.

Abstract

Losses in cereal crops caused by Fusarium species are controlled by using chemical fungicides, which also adversely affect human health and the environment. Therefore, in this study, zinc nanoparticles (ZnNPs) with strong antifungal activity were biosynthesized by the bacterium Paenibacillus polymyxa and then used as a green fungicide to manage root rot disease in wheat. The ZnNPs were 44 nm, spherical, and had a net surface charge of − 28.65 mV and with the active coating, provided significant antioxidant and antifungal activity. The ZnNPs scavenged 89% of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals and at 40 µg/mL, inhibited growth of the pathogenic fungi Fusarium culmorum (FC), F. oxysporum, Candida albicans, and C. gelberta. In an in vivo experiment with FC-infected wheat, ZnNPs in water at 160 µg/mL significantly (p = 0.006) reduced preemergent root rot disease by 86% and significantly prevented postemergent disease (p = 0.001). As a result, incidence and severity of crown and root rot disease decreased by 79% and 89%, respectively. With ZnNPs, root weight remained similar to that in the control, but shoot weight decreased by 33%. Treatment with ZnNPs increased grain yield by 10% in healthy wheat and maintained it in FC-infected plants. Compared with control plants, the 1,000-grain weight increased by 40%. Total chlorophyll, carotenoids, and antioxidant contents were similar between FC-infected wheat and control plants. Thus, on the basis of the results, ZnNPs are recommended as a new green and safe fungicide.

Phytophthora root rot is a major problem for avocado growers around the world. This review summarises the current control measures and their impact on the soil microbiome. The fungicide phosphite is widely used in the avocado industry, and reports from several countries indicate that Phytophthora cinnamomi is developing resistance. For this reason, alternative control measures have been investigated. Applying organic mulches and soil dressings of calcium or silicon provides a level of control. Biological control through the application of suppressive microbes has been actively investigated over many years, but reports of successful field deployment are rare. This review examines the effects on the soil microbiome of these control measures and assesses the future directions for research.

Grape production is seriously impacted by pests and diseases worldwide. Most producers rely heavily on the application of chemical pesticides to control pests and diseases of grapes and grapevines. With increasing rates of fungicide use, active ingredients may decrease in efficacy or become inefficacious due to the emergence of resistance in the organism targeted by the treatment. This research was conducted with the aim of assessing the sensitivity of Botrytis cinerea to five fungicide formulations (active ingredients: boscalid, cyprodinil + fludioxonil, fenpyrazamine, fenhexamid, and pyrimethanil), four of which have been registered and used for more than 10 years in Croatia. Even at the highest concentrations tested, pyrimethanil, boscalid and fenhexamid caused fungal inhibition at a rate significantly lower than 90%. Conversely, cyprodinil + fludioxonil had inhibition rates greater than 90% for 72% of the isolates. Finally, the fungicide fenpyrazamine, which is not registered for use in Croatian viticulture, resulted in fungal inhibition rates of less than 40%. To our knowledge, this is one of the few studies conducted in the Slavonia region of Croatia on the potential emergence of resistance to chemically active ingredients in B. cinerea populations. The results of the present study show that B. cinerea resistance to several active ingredients is of significant concern due to the small number of registered products available in Croatia to combat the disease this fungus causes on grapes.