European Journal of Plant Pathology最新文献

The present investigation was designed to assess how administering biocontrol agents (BCAs) made from the nematophagous endophytic fungus MR20 (Purpureocillium lilacinum) or a mixture of endophytic plant growth-promoting bacteria MR12 (Pseudomonas fluorescens), and MR25 (Serratia marcescens), could enhance tomato growth and resistance to Meloidogyne incognita under in vivo conditions. The three strains’ cell-free culture filtrates showed a strong nematocidal impact (P < 0.05) on M. incognita infective second-stage juveniles (J2s). The highest mortality rates by the three BCAs were at concentrations of 80%, followed by 60%, 40%, and 20%. The in vitro hatching of free eggs was found to be considerably (P < 0.05) reduced as the concentrations of the endophytic bacteria MR12, and MR25 were increased in the order 1 × 10⁵, 1 × 10⁶, 1 × 10⁷, 0.5 × 10⁸, to 1 × 10⁸ colony forming units (CFU)/mL, and the maximum nematicidal activity in killing M. incognita free eggs occurred at 1 × 10⁸ CFU/mL. A statistically significant (P < 0.05) reduction in the percentage of M. incognita-free eggs retrieved was seen in vitro when various concentrations of the endophytic fungus MR20 were applied compared to the negative control (distilled water). The endophytic fungus MR20 had the highest nematicidal activity against M. incognita free eggs at a concentration of 3 × 10⁶ CFU/mL. The application of P. lilacinum or a combination of P. fluorescens and S. marcescens to tomato plants in the presence of M. incognita under greenhouse conditions resulted in a significant increase (P < 0.05) in root and shoot fresh weight, number of leaves, weight of leaves, and stem diameter when compared to the positive control treatment that contained only M. incognita. Treatment with P. lilacinum was more effective (P < 0.05) than P. fluorescens and S. marcescens in reducing egg masses per root, J2s per 100 g of soil, egg masses per 100 g of soil, J2s + eggs of M. incognita per 100 g of soil, reproduction factor, and reduction percentage after 60 days under greenhouse conditions. Nevertheless, the reduction of M. incognita gall size categorization (> 4 mm, 2–4 mm, and < 2 mm) was more effectively achieved by treatment with P. fluorescens and S. marcescens than by treatment with P. lilacinum. Under in vivo conditions, the tested P. lilacinum or a mixture of P. fluorescens and S. marcescens effectively controlled nematode population densities below the economic threshold.

Cassava (Manihot esculenta Crantz) is a major staple food in many developing countries, including Brazil. However, it faces significant challenges due to diseases such as dry root rot (DRR) and black root rot (BRR) caused by soil-borne plant pathogenic fungi. This study explored the use of cover crops to suppress these diseases and to improve the agronomic traits of cassava. Over four cultivation cycles, various cover crops (sunn hemp, black oat, jack bean, maize, peanut and cowpea) were alternated with cassava varieties 'BRS Kiriris' (resistant) and 'BRS Formosa' (susceptible) in soil infested with DRR (Fusarium oxysporum, F. equiseti, F. verticillioides, F. solani, F. lateritium, F. chlamydosporum) and BRR (Lasiodiplodia theobramae, Neoscytalidium dimidiatum) pathogens. In the 2nd cycle, only germination showed significant differences, but by the 4th cycle, various agronomic parameters, including fresh weight (FW.AP), dry weight (DW.AP) of the aerial part, fresh weight (FW.Root), dry weight (DW.Root) of the roots, and plant vigor. Cowpea was identified as the most effective cover crop for reducing the disease index (DI %) by promoting healthier and taller cassava plants. Jack beans and peanuts also had positive effects on vigor, FW.AP, DW.AP, FW.root, and DW.root. In contrast, maize, black oats, Crotalaria ochroleuca, cassava, and fallow soils had minimal impacts. Throughout these cycles, the selected cover crops consistently contributed to disease reduction and improved the agronomic performance of the cassava. This study highlights the potential of holistic disease management strategies.

Pseudomonas syringae pv. coronafaciens (Ps-c) is a pathogenic bacterium species that can be found in agricultural environments and causes diseases in plants. During a survey in 2019–2020 of different areas, bacterial halo blight (BHB) caused by Ps-c in oat (Avena sativa L.) was observed in many oat fields in Huan county, Gansu Province of China. Average leaf disease incidence was approximately 1 to 14%. The symptoms of BHB were mainly observed on leaves of oat and appeared as white to yellow streaks. After 20–30 d, the streaks became yellow necrotic lesions and spread over whole leaves, eventually causing leaves to wilt and senesce. Symptomatic leaves of affected oats were collected to investigate the etiology of BHB disease. A group of 32 bacterial isolates (HK7) phenotypically similar were isolated from the necrotic lesion margins. Pathogenicity tests of this group of isolates by wounding and injection demonstrated that the symptoms induced by them on oat were similar to those observed in the field. HK7 isolates were identified as Ps-c based on Biolog Gen III MicroStation, morphological, physiological and biochemical characterization, 16S rRNA and gyrB gene sequence analysis, which compared with a reference strain (Ps-c ATCC 19608). Furthermore, Ps-c was host specific. After inoculation of Ps-c on A. sativa (B7) and A. nuda (B2) in greenhouse by Completely Randomized Design (CRD), number of tillers, plant height, flag-leaf length, flag-leaf width, fresh weight, dry weight, panicle length, grains per spike, reproductive branche number and thousand grains weight of infected oat decreased by 19.44%, 11.49%, 11.34%, 9.23%, 11.61%, 7.57%, 6.11%, 9.73%, 9.31% and 4.15% compared with that of healthy oat, respectively. BHB (Ps-c) is a new bacterial disease on oat in China and has a negative effect on plant growth, forage and grain yield of oat, and these negative effects increased with the increase of disease severity.

Exserohilum rostratum has been recorded as an emerging pathogen causing rice leaf spot in many countries, and it is also implicated as one of the factors contributing to rice seed discoloration, which affects grain quality. However, there is currently insufficient understanding of the biological aspects of foliar symptoms and pathogen development during the interaction between rice and E. rostratum, particularly under varying temperatures. Additionally, there is limited information available regarding the sensitivity of E. rostratum to fungicidal treatment. Therefore, this study aims to address these gaps and gain insights into these areas. Herein, 29 selected fungal isolates recovered from rice leaves with tiny-spot symptoms from different paddies in Thailand were morphologically and molecularly characterized (based on the sequences of three loci: rDNA-ITS, Tef1a, and GAPDH), which subsequently were identified as E. rostratum. The investigation of symptom development on rice leaves after artificial infection with these isolates under greenhouse conditions (temperature range between 30–35 °C) and high humidity (> 80% RH) conditions revealed that the fungal isolates developed reddish-brown, irregular ellipsoidal spots, along with merging lesions resulting in chlorosis and necrotic tissue. Tiny black spots were observed under growth room conditions of 27 °C and > 80% RH. Experiments conducted on detached rice leaves infected under controlled conditions, with the only variable being temperature variation (33 °C and 27 °C) at constant RH, demonstrated that leaves treated at 33 °C exhibited greater symptom progression compared to those treated at 27 °C. This suggests that temperature influences the expression of symptoms related to rice leaf spot. Additionally, histopathological examination of rice leaf sheaths infected with E. rostratum confirmed the parasitic lifestyle of the fungus and could aid in tracking the pathogen development during exposure to different temperatures. Inhibition assays using flusilazole, azoxystrobin, tricyclazole, and mancozeb against E. rostratum mycelial growth showed that flusilazole had the strongest inhibition effect against all the isolates tested. Overall, our study contributes to a better understanding of the biological responses during E. rostratum infection in rice, particularly during distinct temperature exposure, as well as the response to fungicides of this pathogen, providing insights for future research and management practices in combating E. rostratum.

Fungal diseases of macadamia fruit in South Africa have the potential to cause notable economic damage in this rapidly growing industry. To improve our understanding of the species involved in husk rot in macadamia orchards, a survey was conducted over two consecutive growing seasons to identify Colletotrichum, Diaporthe and Calonectria spp. that are associated with husk rot-infected macadamia fruits, and to investigate the occurrence of these fungi in asymptomatic and symptomatic fruits at the four stages of fruit development. Of the 425 fungal isolates obtained from the survey, Colletotrichum and Diaporthe were the most frequently isolated genera confirming the important role that these causal agents play in the husk rot epidemics. The detection of Calonectria species was low, only from symptomatic fruits and limited to a few locations in the main macadamia-producing provinces in South Africa. Colletotrichum and Diaporthe species were detected throughout the season at different stages of fruit development and in both symptomatic and asymptomatic fruits. The study confirmed that three fungal pathogens cause husk rot of macadamia in South Africa, with Colletotrichum and Diaporthe species that may have a latent phase in macadamia fruit. Studies of the growth characteristics of the husk rot pathogens revealed varied optimal growth temperatures, which may influence their prevalence in the different provinces in South Africa where macadamia is grown. The significance of the varied prevalence and biology of the causal agents in husk rot epidemics are discussed, which may be helpful management strategies.

The study of plant–rhizosphere microorganism associations has become an important knowledge resource for sustainable agriculture. However, little has been achieved in the replacement of synthetic fertilization because most of these studies have been carried out under controlled conditions and not in experimental fields. In this study, we evaluated the effect of inoculating plants of two common bean cultivars at the vegetative and reproductive stages of the crop cycle with Alternaria solani native strain IA300 under field conditions. Results showed that A. solani is capable of increasing the production of common bean cultivars, reflected over different vegetative and reproductive response variables: leaf area, plant length (cm), fresh weight (g), dry weight (g), number of leaves, flowers, seedpods, and seed yield. The findings showed that Alternaria solani native strain IA300 may be considered a growth-promoting microorganism under field conditions. The effects on leaf area after inoculating bean plants with Alternaria were cultivar-dependent.

Clubroot disease, caused by Plasmodiophora brassicae, ranks among the most significant diseases affecting rapeseed cultivars, leading to substantial annual yield losses. Current control methods are limited to a small selection of chemical or biological treatments. Using biocontrol organisms presents a promising strategy for reducing disease severity and promoting plant vigour. However, their efficacy is strongly dependent on biotic and abiotic factors during the growing season, as well as the specific application conditions. In the present study, we evaluated the efficacy of the biocontrol fungus Acremonium alternatum in reducing clubroot disease symptoms across different susceptible and resistant rapeseed cultivars (Brassica napus) under various experimental greenhouse settings employing different types of P. brassicae inoculum: a uniform single spore isolate e3 and two German field isolates P1 and P1 ( +). We found that A. alternatum can reduce clubroot disease symptoms in susceptible rapeseed cultivars Visby, Ability and Jenifer, but not cv. Jumbo, when inoculated with the aggressive single spore isolate P. brassicae e3 at moderate (10⁶ spores mL⁻¹) and high (10⁷ spores mL⁻¹) densities. A. alternatum enhanced plant vitality and shoot biomass in cv. Visby inoculated with field isolates P1 or P1 ( +) but did not considerably reduce clubroot severity there. The clubroot-resistant cv. Mentor displayed a reduction in clubroot symptoms after A. alternatum treatment. In conclusion, A. alternatum holds some promise in managing moderate P. brassicae levels in the soil and could serve as an option in integrated pest management of clubroot disease when combined with resistant cultivars.

Groundnut bud necrosis virus (GBNV), a member of the genus Orthotospovirus, is the most devastating pathogen causing bud blight of tomato and causes substantial crop losses in India. Current management strategies rely upon the use of virus tolerant cultivars, control of insect vectors, and other cultural practices. Under field conditions, these methods are ineffective in reducing the disease. Control can be achieved with RNA silencing, which regulates the homologous specific degradation of targeted genes, resulting in reduced virus multiplication. In the present study, virus infected tomato plant samples were collected from different parts of Tamil Nadu, and infection was confirmed through DAC-ELISA using a polyclonal antibody specific to GBNV. The virus inoculum was propagated on the local lesion host, cowpea (Vigna unguiculata), resulting in the production of chlorotic and necrotic spots on inoculated primary leaves. Our results demonstrated that the complete nucleotide sequence of the replicase gene identified using PCR shared an identity of 94.7 to 97.7% with other isolates of GBNV. To investigate the virus suppression mechanism, an effective RNAi construct was developed with the conserved sequence of the replicase gene for GBNV. A 3674 bp hpRNA cassette, comprising the sense and antisense fragments of 357 bp along with the flanking sequence, inserted in a pHANNIBAL vector, generated transgenic tomato plants using shoot apical meristem explants through Agrobacterium harboring the gene construct. The presence of the transgene in the developed putative transformants was assessed by PCR analysis using nptII and Rep genes and dot blot hybridization using a DIG luminescent detection kit. The expression of the replicase hpRNA construct revealed reduced symptom development upon artificial inoculation of GBNV. Further analysis of the transgenic tomato plants using DAC-ELISA confirmed the reduced level of virus titer. We propose that the RNAi construct, established with a conserved sequence of the replicase gene, showed a gene silencing mechanism as evidenced by reduced virus accumulation in putative transgenic lines, and this could be used as an effective strategy in the management of GNBV in tomato.

Blossom blight is the most destructive strawberry disease worldwide. Minerals play a significant role in the control of plant diseases. The antimicrobial effects of salt solutions have been widely documented for the management of various plant diseases. This study aims to evaluate the impact of mineral compounds on strawberry blossom blight caused by Botrytis cinerea. Ten mineral compounds were used to evaluate the inhibition of mycelial growth, mycelium deformation, and conidia production of B. cinerea in vitro. Five mineral compounds, aluminum chloride, aluminum sulfate, sodium metabisulfite, borax, and potassium sulfate, were chosen based on in vitro results for further study. Linseed oil, castor oil, and three inert materials were used to formulate these minerals. The number of infected and healthy flowers was used to evaluate the efficacy of the mineral compound formulations in the control of strawberry blossom blight under greenhouse conditions. The observed efficacy was between 33%—51%. The most effective formulations of mineral compounds were aluminum chloride and aluminum sulfate formulated with castor oil by two and one parts per thousand, respectively. The results show that these two mineral compounds can be used as alternative to fungicides for the control of B. cinerea especially in organic production of strawberry.

Ascospores discharged at rainfall and dispersed by wind can provide long-distance spread of the European canker fungus, Neonectria ditissima. Ascospores are produced by perithecia which are the sexual reproductive stage. Diffuse knowledge exists on the seasonal pattern of perithecium formation under different climatic conditions. Therefore, the development of perithecia was observed for several successive seasons at five sites in three Northern European countries. In Norway and Finland, ripe perithecia were commonly recorded throughout the year, and on individual cankers continuously for up to 28 months. In contrast, asexual reproductive structures (sporodochia) were confined to the growing season in both countries. In Northern Germany an average of 51% of cankers developed ripe perithecia by late winter, and perithecial senescence ensued in late spring. On average, ripe perithecia were present on cankers for 22 weeks. In contrast, sporodochia were observed all year round. The timing of perithecium maturation correlated with the number of days with > 2 mm rainfall in July–September. The presence of mature perithecia and sporodochia for different lengths of time in different countries has implications for regional disease management strategies.