Australasian Plant Pathology最新文献

Cucurbits are an important crop grown across peri-urban, coastal and inland regions of New South Wales, Australia. Viral infection is a persistent issue across cucurbit commodities, different production methods and production regions. In this study, 34 cucurbit growing properties across five production regions of New South Wales were surveyed and sampled repeatedly from 2018 to 2021. Samples were tested for the presence of known endemic viruses using both serological and molecular diagnostic methods. Viral pathogens were detected on 22 of the 34 properties sampled, and in 44% of samples tested. Annual disease incidence ranged from 0 to 90%, typically increasing towards the end of the summer growing season. Papaya ringspot virus, watermelon mosaic virus, and cucumber mosaic virus, were identified as the most frequently detected viruses. Melon necrotic spot virus and beet pseudo yellows virus were detected at low rates. Cases of mixed infections of papaya ringspot virus and watermelon mosaic virus were also detected in some samples. Furthermore, cucumber green mottle mosaic virus, a “notifiable disease”, was detected for the first time in New South Wales. A newly described virus, watermelon crinkle leaf associated virus-1, was also detected using next- generation sequencing technology. The latter two virus records represent a geographic range expansion and first report for Australia respectively.

Identifying the causative agent of a disease provides key information for diagnosis and management. Here, we identified the causative agent of a leaf spot disease prevalent in water spinach (Ipomoea aquatica) in Fujian Province, China. Ninety bacterial isolates were recovered from symptomatic leaves of water spinach collected across six growing areas in Fujian Province. Completion of Koch’s postulates confirmed that 60 yellow mucoid isolates were the causative agents of the disease. PCR amplification of 16S ribosomal RNA gene sequences demonstrated that the isolates belonged to the genus Xanthomonas. We then PCR-amplified and sequenced the recA, dnaK, gyrB, and rpoD genes of the isolated pathogens for multilocus sequence analysis. In the resulting phylogenetic tree, the isolated pathogens grouped with X. euvesicatoria pv. perforans strain TC2-1. Biological and chemical tests performed on 60 isolates showed that all of them were positive in hydrogen sulfide, litmus milk, starch hydrolysis and bile-esculin tests, but negative in nitrate reduction, pectinase activity, and oxidase activity tests. The isolates could also cause disease symptoms on tomato (Solanum lycopersicum) leaves and stems but not on pepper (Capsicum annuum) plants. Based on DNA characteristics, physiological and chemical properties, and pathogenicity test results, we propose that the leaf spot disease in water spinach is caused by X. euvesicatoria pv. perforans.

Medicago sativa is a good fodder crop in Pakistan. Its continuous cultivation and sustainable production is important for the better growth and yield of animals. Phytoplasma is an important well spread disease worldwide which has been reporting from more than 150 years ago on different plants including Lucerne or Alfalfa (Medicago sativa). The study was conducted to identify phytoplasma and potential insect vectors responsible for its transmission. The sampling of infected plants and sucking insects was done from Multan, RY Khan and Faisalabad, Punjab during 2017–2020. The 50 symptomatic samples were observed for the detection of phytoplasma initially through staining and electron microscope. It was further confirmed by Nested Polymerase Chain Reaction (Nested-PCR), Sequencing and Phylogenetic Analysis. The results indicated the presence of phytoplasma bodies in sieve tube cells of the infected plants that were further confirmed by the amplification of 1.8 kb and 1.2 kb fragment of 16 S rRNA gene using the primer pairs P1/P7 and RI6F2n/R2 respectively. Restriction fragment length polymorphism (RFLP) analysis also showed a similar pattern of bands formation associating with 16 S rRNA of 16SrII-D subgroup linked with sesame phyllody (16SrIID) group. The obtained DNA sequences of Pakistani isolates were submitted on NCBI (MT614018.1 and MT614019.1). The phylogenetic analysis using Clustal W and MEGA6 software showed that submitted sequences have > 99% nucleotide identity with phytoplasma strain “Ca. P. australasia” of 16SrII-D subgroup. The potential insect vectors, Orosius orientalis, Orosius argentatus, and Laudelphax striatellus captured from infected plants were detected positive as well as transmission study confirmed their vector status for alfalfa phyllody diseases transmission. To our information, this is first detection of phytoplasma infestation and its insect vectors associated with Medicago sativa in Pakistan. The 16Sr-II D group of phytoplasma is spreading widely in many crops so, control is essential to stop it into other economically important crops.

Previously, we reported that endophytic Pseudomonas aeruginosa PC5 isolated from Prosopis cineraria, abundantly produced antimicrobial volatile organic compounds (VOCs) and significantly suppressed the growth of Pythium aphanidermatum which causes damping-off in cucumber in in vitro assays. However, under pot culture conditions, no significant effect of this bacterium on cucumber damping-off was noticed under salt water irrigation (100 mM NaCl), while the antagonistic bacterium Acinetobacter johnsonii PC3 isolated from the same host which produced low levels of antimicrobial VOCs was effective in reducing the disease incidence under salt water irrigation. In this in vitro study, the effect of NaCl on the growth P. aphanidermatum and VOC composition of these two endophytic bacterial strains was evaluated. NaCl had inhibitory effects on the growth of both P. aeruginosa PC5 and A. johnsonii PC3. Gas chromatography-mass spectrometry analysis of the VOCs produced by these endophytes revealed that dimethyl disulfide (DMDS), a well-known antimicrobial compound, was the major compound (33.82%) released by P. aeruginosa PC5 in the absence of NaCl, whereas the production of DMDS was completely inhibited when it was cultured in a medium containing high concentrations of NaCl. Trimethylsilanol was released abundantly by A. johnsonii PC3 when grown in the salt-amended medium compared to control, suggesting possible involvement of this compound in the suppression of P. aphanidermatum by this bacterium under salt-stress conditions.

In the spring of 2021, Current Season Needle Necrosis (CSNN) symptoms were observed on about 60% of the needles together with needle cast on Trojan Fir (Abies equi-trojani) growing in Aladağ Mountain range near Bolu province of Turkey. From the 200 symptomatic needles, obtained from 10 branch samples collected from 10 different trees in the years 2021 and 2022 each, the following eight fungi were recovered in the respective percentages; Didymella sp. (25.5%), Sydowia polyspora (25%), Alternaria alternata (14.5%), Aureobasidium sp. (1.5%), Epicoccum sp. (1.5%), Colletotrichum fioriniae (0.5%), Botrytis cinerea (0.5%) and Rhizosphaera macrospora (0.5%). Isolations were made from 200 asymptomatic needles collected from Kastamonu (150) and Bolu (50) provinces and the following fungi were recovered; Didymella sp. (30%), A. alternata (8.5%), S. polyspora (1%), Epicoccum sp. (1%) and Rhizopus sp. (0.5%). S. polyspora was recovered from only the asymptomatic fir needles collected from Bolu province. Pathogenicity of the three potential pathogenic fungi were tested on the needles of healthy fir saplings by spraying spore suspensions and S. polyspora produced necrosis on 37% of the intact needles, following Didymella sp. with 23% and C. fioriniae 21%. Mix inoculum of the three fungi formed necrosis on 30.5% of the fir needles. Pathogenicity of S. polyspora was also tested on wounded needles and it produced higher rates of infection than the healthy ones. Pathogenicity of S. polyspora, Didymella sp., C. fioriniae were tested on barks of 3 years old fir saplings and only the former produced significant size of necrosis, 3.16 cm in 28 days. Occurrence of CSNN on Trojan fir was first recorded in Bolu province of Turkey with this study.

Chickpea is one of the sources of plant protein with a yield capacity of about 6 tons per hectare. Because of cultivation in rainfed lands this plant has a very low average yield in most countries of the world. However, in the autumn cultivation of chickpeas, the amount of production increases significantly which is due to the increase in the use of winter rainfall. Nowadays, the introduction of cold tolerant cultivars and the identification of genotypes have provided the conditions for welcoming the chickpea winter cultivations. The main limiting factor for autumn cultivation of chickpeas is the increasing damage caused by Ascochyta blight (AB) due to the availability of suitable humidity and temperature for the growth of the fungus Ascochyta rabiei. The main aim of the present study was to determine the resistance pattern of selected MCC741 line and cold tolerant cultivar Saral against three pathotypes of A. rabiei named PI, PIII and PVI. For this purpose, a pathogenicity test method was designed and the effectiveness of this method was evaluated on different chickpea genotypes with different reported resistance levels and also by the pathogenicity test in green house. The results showed that the in vitro pathogenicity test method is well able to differentiate resistant and susceptible cultivars based on the symptoms of the disease. Furthermore, the virulence of the aforementioned pathotypes can be distinguished from each other. These results showed that this method can be used as a nondestructive method in prescreening studies and evaluation of resistance levels of a unique plant genotypes. This method is also recommended for pathotyping of new fungal isolates. In vitro assay on the resistance pattern of cold tolerant chickpea accessions showed that the Saral cultivar presented an appropriate resistance against pathotypes I and III but did not show a resistance against pathotype VI. The resistant pattern was confirmed by greenhouse pathogenicity test. It is necessary to evaluate more cold tolerant chickpea samples in other studies to identify sources of resistance to this pathotype.

Pantoea ananatis is a major pathogen that causes the new bacterial blight in rice, and its symptoms very similar to rice bacterial blight. Therefore, there is a dire need for an accurate and rapid method for detecting P. ananatis. In this study, an early and rapid visual detection method for P. ananatis was established. Using GyrB gene as the target sequence, an innovative recombinase-aided amplification detection system integrated with a lateral flow dipstick (RAA-LFD) was constructed. The optimized RAA-LFD detection method can be initiated at body temperature and does not rely on precise instruments. It does not require DNA extraction and can be used directly with plant tissue fluids. The results can be visualized after 10 minutes of amplification. The specificity and sensitivity tests showed that the RAA-LFD method could detect P. ananatis, whereas other common plant pathogens were not detected, and its detection sensitivity for P. ananatis DNA reached 100 copies/µL. The detection of diseased tissues indicated that this method could accurately detect P. ananatis in artificially inoculated rice tissues in the early stages of infection before symptoms. The RAA-LFD detection system established in this study is simple and fast, with visual results, excellent specificity, and high sensitivity. It is semi-quantitative and should be used for the early detection and rapid field diagnosis of new leaf blight, which provides technical support for the early warning and real-time detection of field samples.

Feijoa (Acca sellowiana), a native fruit tree of Brazil and Uruguay, has both a unique aroma and flavour. This species is widely cultivated in Colombia, New Zealand, and, to a lesser extent, in Georgia and Ukraine, amongst other countries. In its centre of diversity, Brazil and Uruguay, the cultivated area is increasing yearly. However, the occurrence of typical symptoms of anthracnose in feijoa plants has made fruit production difficult, or unfeasible, without the use of pesticides. Yet, little is known about the causal agent of anthracnose symptoms in feijoa fruit. Thus, this work aimed to analyse morphological and pathogenic characteristics of diseased fruit by using a multi-gene phylogenetic analysis based on DNA sequencing of six loci of 40 isolates in feijoa fruits collected in southern Brazil. Morphological data showed that mycelial radial growth rate ranged from 7.5 to 10.2 mm/day; length of conidia (L) ranged from 13.8 to 19.4 μm; width (W) ranged from 4.0 to 5.6 μm; and L/W ratio ranged from 2.5 to 4.2 μm. The size of appressoria ranged from 7.2 to 10.8 μm in length; 5.4 to 8.0 μm in width, and 1.1 to 1.5 μm for L/W. Isolates produced cylindrical or fusiform conidia and appressoria globules, nailed and irregular. Multigene phylogenetic analyses revealed the presence of anthracnose symptoms in both orchard-grown and natural populations of feijoa caused by Colletotrichum theobromicola assigned to the Gloeosporioides complex. All tested isolates showed that anthracnose symptoms caused pathogenicity in inoculated feijoa fruits. These results, together with data on lifestyle of the isolates, will lead to improved management and handling of commercial feijoa orchards.

Potato is the third most important crop. Its production and quality is greatly affected by various biotic stresses. In this study, 216 Solanum tuberosum subsp. tuberosum accessions were screened for late blight, viruses (PVY and PVX) and potato cyst nematodes (PCNs) resistance using robust molecular markers. Solitary or combined late blight resistant genes (R1, Rpi-abpt, R3a, R3b) presence was observed in 51 accessions. For PVY resistance, markers STM0003, RYSC3, and YES3-3 A were found in 38, 3, and 1 accession, respectively, and PVX resistance gene markers 1Rx1 and 106Rx2 were found in 19 and 10 accessions, respectively. The STM0003 marker was present in 38 accessions, of which 12 were resistant to PVY and 10 were susceptible. The genotype data on six markers for both the species of PCN showed 45 resistant accessions. A combined analysis of all markers for late blight identified six accessions with all the three resistance genes. Similarly, four accessions, i.e., CP 4226, CP 2049, CP 3696, and CP 3651 had both Rx1 and Rx2 genes for PVX resistance, while only one accession, viz., CP 2049 showed the presence of both H1 and HC genes along with the Gpa2 marker for PCN resistance. There were also seven resistance genes found in CP 2049 for late blight (2), PCN (4), and PVX (2), but none of the accession had genes for all four traits. The results revealed that developing potato varieties with combined resistance to late blight, viruses, and PCN requires concerted hybridization between different parental lines.

When the Grand Final of the Australian Football League (AFL) was played at the Brisbane Cricket Ground (the Gabba) in October 2020, small rolls of turf from Victoria were laid at the three player entrances. This turf was infested with southern sting nematode (Ibipora lolii) and so it was removed, the infested sites were fumigated, and nematicides were applied in an attempt to eliminate the nematode. Results published in September 2021 indicated that this appeared to have been successful, as I. lolii was not detected in a post-treatment monitoring program. This paper reports results from an ongoing monitoring program which show that the eradication program was ineffective. Consequently, the Gabba is currently the only Queensland location known to be infested with I. lolii. The paper finishes by listing the biosecurity issues that should be addressed to prevent further spread of the nematode.