Australasian Plant Pathology最新文献

Vegetatively propagated plants like yam are prone to yield losses by viruses as infection tends to build up in successive cycles of propagation. This study aimed to eliminate yam mosaic virus (YMV) from yam using an optimized combination of thermotherapy and meristem culture. A protocol was optimized for shoot initiation, multiplication, and rooting from shoots of four yam varieties using Murashige and Skoog (MS) medium with growth regulators. A control at 26 ℃ and a thermo-treatment at 36, and 40 ℃ followed by meristem culture was used to eliminate YMV and verified using double antibody sandwich ELISA (DAS-ELISA) and reverse transcription (RT)-PCR. Results showed that the highest explant initiation rate of 87.5% and 83.3% were obtained for variety Bulcha and Aw/Ar/005, respectively, on MS medium with 1.0 mg/L 6-benzylaminopurine (BAP) + 0.5 mg/L naphthaleneacetic acid (NAA). While the MS medium with BAP (0.5 mg/L) + NAA (0.25 mg/L) produced the highest initiation rate of 91.7% in variety Aw/Ar/001. The longest mean shoot length of 9.0 ± 0.37 cm was recorded in Bulcha on MS medium with BAP (0.5 mg/L) + NAA (0.25 mg/L). The highest percentage of rooting was obtained on MS medium with 1.5 mg/L indole-3-butyric acid (IBA) + 0.5 mg/L NAA for variety Bulcha and variety Aw/Wo/011. The maximum YMV elimination (93.3–100.0%) was noted at 40 ˚C thermo-treatment for 20 days followed by meristem culture. No amplification of the 586 bp fragment of YMV was obtained by RT-PCR in all the plants that went through 40 ˚C thermotherapy. The results make significant contribution in improving yam production in many countries, particularly in Africa where YMV is a significant constraint.

Allium crops are commonly grown in South Africa and harvested as either fresh produce for the domestic and export markets or as seed. Apart from occasional outbreaks on garlic, rust is problematic as a cosmetic disease with unappealing uredinia regularly observed on freshly packed produce of bunching onion and leek in supermarkets. Spore morphology and phylogenetic analysis of five rust samples collected from A. fistulosum (bunching onion) confirmed the causal organism as Puccinia porri. Garlic and bunching onion varieties were mostly susceptible to P. porri, whereas leek varieties were either susceptible or segregating in their response, with bulb onions being resistant. Microscopy of early infection structures showed appressorium formation, stomatal penetration, and a substomatal structure which differentiated into infection hyphae and haustorium mother cells. At microscopy level differences in host response became visible from 48 h post-inoculation onwards with prehaustorial and early hypersensitivity observed as resistance mechanisms in onions.

Fusarium brachygibbosum Padwick is a phytopathogen with a widespread distribution, infecting various host plants. In South Africa, there is a limited number of studies on the genetic diversity of fusaria, particularly in undisturbed soils. In the current study, the genetic diversity of F. brachygibbosum was investigated using inter-simple sequence repeat (ISSR) and mating type genes. The F. brachygibbosum isolates were collected from four different geographic regions within the grassland biome of South Africa. A total of ten ISSR primers produced 64 distinct and reproducible amplicons, with 100% polymorphism. The ISSR markers revealed high levels of intraspecific variation, which is depicted by various genetic diversity indexes. In the analysis of mating type genes, the MAT1-1-2 gene was found among the four populations, but the MAT1-2-1 gene was only present in the population from the Groenkloof Nature Reserve. The data from this study will contribute substantially to knowledge of grassland fusaria of South Africa and their population structure in the grassland biome.

Nematodes are highly abundant soil organisms, and their presence can have profound effects on soil health and plant growth. Among them, Rotylenchus species are known for their economic importance as root ectoparasites or semi-endoparasites, inflicting damage on a wide variety of economically important plants. Their impact on agricultural crops, ornamentals, and fruit and forest trees makes them significant subjects for study. In this paper, we present an updated species list of Rotylenchus spp., a genus of spiral plant-parasitic nematodes belonging to the family Hoplolaimidae. As of the current research, 107 species within the Rotylenchus genus have been recognized. To facilitate the identification of Rotylenchus species, we introduce a novel browser-based interactive key for the identification of such huge number of species. This web-assisted tool utilizes a list of 48 diagnostic character-states belonging to 11 characters for identifying 107 Rotylenchus species, providing an easy and accurate method for the identification of these plant-parasitic nematodes. This paper contributes to the understanding of Rotylenchus species’ diversity and their taxonomy while offering a valuable tool to aid researchers, agricultural professionals, and plant pathologists in accurate species identification and subsequent management strategies.

Off-road vehicles are potential vectors for the spread of destructive plant pathogens such as Phytophthora cinnamomi. However, the retention of Phytophthora species in soil on vehicles used off-road does not appear to have been assessed empirically. We sampled soil from 22 off-road vehicles used in conservation management in New South Wales and tested samples for the presence of Phytophthora species. Two species (P. cryptogea and P. aff. alticola) were detected from three vehicles. Two of these three vehicles were regarded as being clean externally and had not been used off-road for more than one week. Phytophthora species can therefore survive in small amounts of soil on vehicles for extended periods, potentially facilitating the spread of these destructive pathogens. Cleaning is required of management vehicles entering areas of high conservation value vegetation to minimise the risk of spreading Phytophthora species. However, research is needed to find the most effective methods for removing soil.

Numerous factors contribute to the decline in crop yields, including plant diseases caused by bacteria, fungi, and viruses. The management of these diseases with chemical fertilizers is not a sustainable approach. This review briefly summarizes the role, mechanisms, advantages, and disadvantages of using Streptomyces species in plant disease management as an alternative method is needed to address the problems of using chemicals. One promising alternative is to use microbes to manage plant diseases. Streptomyces, a gram-positive saprophytic bacterium, is particularly effective at combating plant diseases. They produce bioactive-rich antimicrobial metabolites and enzymes that can kill or inhibit the growth of plant pathogens. Streptomyces species are widely distributed in nature but are especially abundant in the rhizosphere, the soil region surrounding plant roots. Streptomyces can be used as bioinoculants to protect plants from diseases. In addition to their disease-fighting abilities, they can promote plant growth in many ways. They produce plant growth-promoting substances, such as indole-3-acetic acid (IAA), cytokinin, and siderophores. They also suppress diseases through antibiosis, mycoparasitism, and nutrient competition. Streptomyces can also supply plants with essential minerals, i.e., iron, copper, phosphorus, and sulfur. Therefore, it concluded that Streptomyces species can be used as an alternative to chemicals to control plant diseases.

To effectively combat parasitic weeds, it is essential to develop advanced biocontrol agents capable of thriving in diverse environmental conditions. The objectives of this study were to evaluate the potential of Fusarium oxysporum isolates as biocontrol agents against Egyptian broomrapes in tomato crops and to explore whether protoplast fusion could improve their biocontrol ability. Eleven F. oxysporum isolates significantly reduced the germination of Phelipanche aegyptiaca seeds. Consequently, these isolates were further evaluated for their potential as biological control agents against broomrapes through glasshouse and field experiments. The isolate KGh2-1 of F. oxysporum showed the highest reduction in the number of emerged broomrapes in both trials (p < 0.001). In order to enhance biocontrol activity against broomrapes, protoplast fusion was performed between F. oxysporum and F. equiseti. In comparison to KGh2-1, the fusant strains demonstrated superior ability in inhibiting the growth of broomrapes. The results also showed a clear host specificity of the selected pathogenic isolates and fusants. Protoplast fusion can be recommended as a valuable tool that can efficiently enhance the biocontrol ability of F. oxysporum against broomrapes.

Black locust (Robinia pseudoacacia L., Fabaceae) is a shade tree and commonly used in urban green spaces in Iran. In the current study, 13 symptomatic black locust samples showing withering and decline were collected within the campus of Shahid Bahonar University of Kerman (southeastern Iran) and sophora yellow stunt virus (SYSV, genus Nanovirus, family Nanoviridae) was detected in two samples using nanovirus degenerate primers by PCR assay and sequencing of amplicons. Subsequently, eight genome components of the Rob4 isolate were amplified using specific primer pairs and sequenced. Sequence analysis showed that the Rob4 isolate shared 93.3–99.8% nucleotide identity with the previously sequenced genome of isolate Ta1 from a plant of Sophora alopecuroides also growing at the university campus and 68.9–99.8% nucleotide identity with the other sequences of SYSV available in GenBank. To demonstrate the pathogenesis of SYSV in black locust seedlings, previously constructed clones of the SYSV genome components were used for agroinoculation resulting in the appearance of severe symptoms followed by wilting and death of seedlings. Based on the results of this study, black locust tree is identified as a permanent reservoir host of SYSV in Iran. To the best of our knowledge, this is the first report of the infection of a nanovirus with a symptomatic perennial tree having woody trunk.

Gray mold is a common and severe disease that affects strawberry production and storage. To clarify the occurrence and mechanism of Botrytis cinerea in strawberry resistance to boscalid [2-Chloro-N-(4'-chlorobiphenyl-2-yl) nicotinamide], a widely used fungicide, 137 isolates of Botrytis cinerea in strawberry were collected from Beibei, Xiema, and Changshou of Chongqing by random sampling method in 2021–2022 and monitored for resistance in the field by the discriminatory dosage method. The succinate dehydrogenase (SDH) related gene of 55 resistant strains was sequenced, and molecular docking was used to predict the binding mode of boscalid to wild-type and mutant SDH of B. cinerea. The results showed that the resistance frequency of B. cinerea to boscalid in Chongqing was 93.43%. Mutation sites on the B subunit of SDH were found in 45 of the 55 resistant strains, with three primary mutation types, P225F, N230I, and H272R, responsible for 43.6%, 16.4%, and 21.8% of mutations, respectively. Out of the 55 resistant strains, five were found to have mutation sites on the C subunit of SDH. Only one mutation type, G85A+I93V+M158V+V168I, was observed in these strains, where four amino acids were mutated simultaneously. However, no mutation sites were detected in the remaining five resistant strains. Molecular docking results predicted that the P225F mutation prevented boscalid from entering the binding pocket, which affects the formation of hydrogen bonds and other interaction forces and ultimately hinders the ability of boscalid to bind to SDH. The H272R mutation narrows the cavity bottom of the binding pocket and rotates part of the boscalid chemical bond, while the N230I mutation has no effect on boscalid binding. This study clarified the occurrence and mechanism of boscalid resistance in B. cinerea in the Chongqing region, and the results provide an experimental data for formulating strawberry gray mold management strategies and also provide some insights for the development of succinic dehydrogenase inhibitors (SDHIs) fungicides.

A total of one-hundred and fourteen Capsicum annum L. samples were collected from Qassim and Al-Baha regions, Saudi Arabia in the growing season of 2021–2022, showing virus like symptoms including, mottling, mosaic, chlorosis, leaf distortion, stunted growth, and necrotic lesions, dwarfing of leaves and fruits. These samples were tested against important viruses infecting pepper using ELISA kits. According to ELISA results, 80/114 (70%) samples were found to be infected with one or more of the tested viruses. However, incidence of the PMMoV was observed in 18/21 (85.7%) and 23/59 (38.98%) from Al-Baha and Qassim regions respectively. Based on highly positive ELISA samples of PMMoV three samples were selected for biological detection using mechanical inoculation with sap prepared and the results showed that systemic mosaic, mottling, necrotic spots, yellowing on N. tabacum, N. benthamiana, N. glutinosa, Solanum nigrum and necrotic and chlorotic spots on Chenopodium quinoa and C. amranticolor, while local lesions symptoms were produced on Datura stramonium. According to the ELISA results, positive samples from Qassim and Al-Baha regions were amplified by RT-PCR analysis, and 474-bp fragment was amplified using PMMoV specific primers. Two directional sequencing was done for the amplified products and the sequences of the virus isolates were submitted in the NCBI database with the following accession numbers, OP723368, OP723369, OP723370, OP723371, OP723372. The phylogenetic analysis showed the close relationship our isolates with other isolation of PMMoV and pairwise nucleotide sequence identity analysis revealed that these PMMoV isolates shared their identity between 92.5 and 100% with PMMoV isolates available in the databases. This study provides comprehensive report regarding the diagnosis of chili infecting viruses through serological and characterization of PMMoV through serological, biological, and molecular methods in the kingdom of Saudi Arabia.