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Luteoviruses (family Tombusviridae ) and poleroviruses (family Solemoviridae ) are economically important pathogens of cereals such as wheat ( Triticum aestivum ), barley ( Hordeum vulgare ) and oat ( Avena sativa ). In Australia, the luteoviruses barley yellow dwarf virus PAV (BYDV PAV) and barley yellow dwarf virus MAV (BYDV MAV), along with the poleroviruses cereal yellow dwarf virus RPV (CYDV RPV) and maize yellow dwarf virus RMV (MYDV RMV), were distinguished from each other and reported in the 1980s (Sward and Lister 1988; Waterhouse and Helms 1985). The poleroviruses barley virus G (BVG) and cereal yellow dwarf virus RPS (CYDV RPS) were reported in Australia more recently (Nancarrow et al. 2019; Nancarrow et al. 2023), while the luteovirus barley yellow dwarf virus PAS (BYDV PAS) has not previously been reported in Australia. During 2010, an oat plant exhibiting yellow/ red leaf discoloration and stunted growth was collected from a roadside in Horsham, Victoria, Australia. The plant tested positive for BYDV PAV and negative for BYDV MAV, CYDV RPV and MYDV RMV by tissue blot immunoassay (TBIA) as described by Trębicki et al (2017). The virus isolate has since been continuously maintained in a glasshouse in live wheat plants using aphids ( Rhopalosiphum padi ). In 2021, total RNA extracted from a wheat plant infected with this isolate (Nancarrow et al. 2023) tested positive for BYDV PAV by RT-PCR using the primers BYDV-1/BYDV-2 (Rastgou et al. 2005), but negative for BYDV PAV, CYDV RPV and MYDV RMV using other published primers (Deb and Anderson 2008). A high-throughput sequencing (HTS) library was prepared from the total RNA with the NEBNext Ultra II RNA Library Prep Kit for Illumina (NEB) without ribosomal RNA depletion and sequenced on a NovaSeq 6000 (Illumina). Raw reads were trimmed and filtered using fastp v0.20.0 (Chen et al. 2018) while de novo assembly of all of the resulting 5,049,052 reads was done using SPAdes v3.15.3 (Nurk et al. 2017). BLASTn analysis of the resulting 4,067 contigs (128- 12,457 bp in length) revealed only one large virus-like contig (5,649 bp) which was most similar to BYDV PAS isolates on NCBI GenBank, sharing 87% nucleotide (nt) identity with BYDV PAS isolate OH2 (MN128939), 86% nt identity with the BYDV PAS reference sequence (NC_002160) and 82% nt identity with the BYDV PAV reference sequence (NC_004750). Additionally, 4,008 HTS reads were mapped to the assembled genome sequence with Bowtie2 v2.4.5. (Langmead and Salzberg 2012) with 100% genome coverage and an average coverage depth of 101X. Primers were designed to the assembled genome sequence to generate overlapping amplicons across the genome, and the resulting amplicons were Sanger sequenced. This confirmed the genome sequence of BYDV PAS isolate PT from Australia (5649 bp, GC content 47.9%), which was deposited in GenBank (LC782749). Ten additional plant samples collected from western Victoria, Australia, all tested positive for BYDV PAS by RT-PCR using the primers PASF and PASR (Laney et al. 2018). The additional samples consisted of one oat sample collected in 2005, one barley sample collected in 2007, three wheat samples collected in 2016 and one barley, one brome grass ( Bromus sp.) and three wheat samples collected in 2020. BYDV PAS is also efficiently transmitted by R. padi but is often more prevalent and severe than BYDV PAV; it can also overcome some sources of virus resistance that are effective against BYDV PAV (Chay et al. 1996, Robertson and French 2007). To our knowledge, this is the first report of BYDV PAS in Australia. Further work is needed to determine the extent of its distribution, incidence, impacts and epidemiology in Australia, along with its relationship to other BYDV PAS isolates.

Cyst nematodes of the genus Heterodera are a major group of sedentary plant parasites causing a significant economic impact, restricting production and market access globally (Moens et al. 2018). The ryegrass cyst nematode Heterodera mani is in the Avenae group and is found predominantly in pastures and grasslands in Europe, California, and South Africa. It was first described by Mathews (1971) from Northern Ireland. Known hosts are grasses (family Poaceae), principally Lolium perenne (perennial ryegrass), but also Dactylis glomerata (cat grass) and Festuca pratensis (meadow fescue) (Subbotin et al. 2010). Mowat (1974) reported that H. mani causes negligible damage to the yield of L. perenne in pot trials; however, Maas & Brinkman (1982) determined that it may cause significant damage to spring and autumn-sown perennial ryegrass in field conditions. During a routine examination for potato cyst nematode from a farm near Mawbanna in north-west Tasmania, Australia, several pale to dark brown Heterodera cysts were extracted that were lemon shaped with the presence of a small vulval cone at the posterior end and a distinct neck. The J2 (n=20) stylet length ranged from 24-26 µm with round knobs deeply concave anteriorly, hyaline tail length was 37-42 µm, true tail length ranged from 59-68 µm and total body length varied from 526-559 µm. All the above characters match those described for H. mani (Subbotin et al. 2010). To verify this identification, DNA was extracted from five individual J2 juveniles from a single cyst using QIAamp DNA micro kit (Qiagen®), and two gene regions amplified: internal transcribed spacer region of ribosomal RNA (ITS-rRNA) with primer pair AB28 and TW81 and cytochrome oxidase 1 (CO1) with primer pair JB3 and JB5 (Bowles et al. 1992; Curran et al. 1994; Derycke et al. 2005). One PCR reaction contained 10 µM (1 µl each) of each primer, 12.5 µl of OneTaq® DNA Polymerase and 5 µl of DNA template with a final volume of 25 µl. PCR products were sent for purification and Sanger sequencing at Macrogen (Seoul, Rep. of Korea). All resulting sequences were trimmed, aligned, and analysed using Geneious Prime® 2022.0.1 (www.geneious.com). Five ITS sequences (accessions ON402852-ON402856) and five CO1 sequences (accessions ON402857-ON402861) were submitted to GenBank. These ITS sequences were very similar to each other and exhibited 99.16-100% similarity with that of H. mani isolate from Hamminkeln, Germany (AY148377) (Subbotin et al. 2018). The CO1 sequences exhibited 98.96-100% similarity with that of H. mani isolate from Washington, USA (MG523097) (Subbotin et al. 2003). Obtained sequences were mapped to reference sequences downloaded from NCBI GenBank and maximum likelihood phylogenetic trees were calculated. Due to the lack of further living nematode material, pot experiments were not performed. Such experiments are not feasible in Tasmania currently and transfer of live nematode material to the Australian mainland presents logistic and legal issues. However, morphological and molecular evidence for species determination of H. mani was unequivocal and contributes to the list of cyst nematode species present in Australia. This is the first detection of H. mani in Australia and is a range extension of the species from North America, Africa, and Europe to Australia. The nematode may cause damage to perennial ryegrass in Australia, however, impact on yield still needs to be investigated.

Zucchini plants with symptoms including twisted petioles, necrotic leaves, crown rot, and internal fruit rot were found in Bundaberg, Australia, at a commercial field for the first time during late autumn 2016, resulting in direct yield losses of 70 to 80%. Three Pseudomonas syringae strains isolated from symptomatic leaf (KL004-k1), crown (77-4C), and fruit (KFR003-1) were characterized and their pathogenicity evaluated on pumpkin, rockmelon, squash, and zucchini. Biochemical assays showed typical results for P. syringae . The three isolates differed, however, in that two produced fluorescent pigment (KFR003-1 and 77-4C) whereas the third, KL004-k1, was nonfluorescent. Multilocus sequence analysis classified the isolates to phylogroup 2b. The single-nucleotide polymorphism analysis of core genome from the Australian and closely related international isolates of P. syringae showed two separate clusters. The Australian isolates were clustered based on fluorescent phenotype. Pathogenicity tests demonstrated that all three isolates moved systemically within the inoculated plants and induced necrotic leaf symptoms in zucchini plants. Their identities were confirmed with specific PCR assays for P. syringae and phylogroup 2. Pathogenicity experiments also showed that the Eva variety of zucchini was more susceptible than the Rosa variety for all three isolates. Isolate KL004-k1 was more virulent than 77-4C on pumpkin, rockmelon, squash, and zucchini. This study expands the knowledge of P. syringae isolates that infect cucurbits and provides useful information for growers about the relative susceptibility of a range of cucurbit species.

The Chittering strain of potato spindle tuber viroid (PSTVd) infects solanaceous crops and wild plants in the subtropical Gascoyne Horticultural District of Western Australia. Classical PSTVd indicator hosts tomato cultivar Rutgers (R) and potato cultivar Russet Burbank (RB) and currently widely grown tomato cultivars Petula (P) and Swanson (S) and potato cultivars Nadine (N) and Atlantic (A) were inoculated with this strain to study its pathogenicity, quantify fruit or tuber yield losses, and establish whether tomato strains might threaten potato production. In potato foliage, infection caused spindly stems, an upright growth habit, leaves with ruffled margins and reduced size, and upward rolling and twisting of terminal leaflets (RB, A, and N); axillary shoot proliferation (A); severe plant stunting (N and RB); and necrotic spotting of petioles and stems (RB). Tubers from infected plants were tiny (N) or small and "spindle shaped" with (A) or without (RB) cracking. Potato foliage dry weight biomass was decreased by 30 to 44% in A and RB and 37% in N, whereas tuber yield was diminished by 50 to 89% in A, 69 to 71% in RB, and 90% in N. In tomato foliage, infection caused epinasty and rugosity in apical leaves, leaf chlorosis, and plant stunting (S, P, and N); cupped leaves (S and P); and reduced leaf size, flower abortion, and necrosis of midribs, petioles, and stems (R). Mean tomato fruit size was greatly decreased in all three cultivars. Tomato foliage dry weight biomass was diminished by 40 to 53% (P), 42% (S), and 37 to 51% (R). Tomato fruit yield was decreased by 60 to 76% (P), 52% (S), and 64 to 89% (R), respectively. Thus, the tomato strain studied was highly pathogenic to classical indicator and representative current tomato and potato cultivars, causing major losses in fruit and tuber yields. Tomato PSTVd strains, therefore, pose a threat to tomato and potato industries worldwide.

Yellow dwarf viruses (YDVs) form a complex of economically important pathogens that affect cereal production worldwide, reducing yield and quality. The prevalence and incidence of YDVs including barley yellow dwarf viruses (BYDV-PAV and BYDV-MAV) and cereal yellow dwarf virus (CYDV-RPV) in cereal fields in Victoria, Australia were measured. As temperature decreases and rainfall increases from north to south in Victoria, fields in three geographical regions were evaluated to determine potential differences in virus prevalence and incidence across the weather gradient. Cereal samples randomly collected from each field during spring for four consecutive years (2014-2017) were tested for BYDV-PAV, BYDV-MAV, and CYDV-RPV using tissue blot immunoassay. BYDV-PAV was the most prevalent YDV species overall and had the highest overall mean incidence. Higher temperature and lower rainfall were associated with reduced prevalence and incidence of YDVs as the northern region, which is hotter and drier, had a 17-fold decrease in virus incidence compared with the cooler and wetter regions. Considerable year-to-year variation in virus prevalence and incidence was observed. This study improves our understanding of virus epidemiology, which will aid the development of more targeted control measures and predictive models. It also highlights the need to monitor for YDVs and their vectors over multiple years to assess the level of risk and to make more informed and appropriate disease management decisions.