Australian Cool-Season Pulse Seed-Borne Virus Research: 1. Alfalfa and Cucumber Mosaic Viruses and Less Important Viruses.

Here, we review the research undertaken since the 1950s in Australia's grain cropping regions on seed-borne virus diseases of cool-season pulses caused by alfalfa mosaic virus (AMV) and cucumber mosaic virus (CMV). We present brief background information about the continent's pulse industry, virus epidemiology, management principles and future threats to virus disease management. We then take a historical approach towards all past investigations with these two seed-borne pulse viruses in the principal cool-season pulse crops grown: chickpea, faba bean, field pea, lentil, narrow-leafed lupin and white lupin. With each pathosystem, the main focus is on its biology, epidemiology and management, placing particular emphasis on describing field and glasshouse experimentation that enabled the development of effective phytosanitary, cultural and host resistance control strategies. Past Australian cool-season pulse investigations with AMV and CMV in the less commonly grown species (vetches, narbon bean, fenugreek, yellow and pearl lupin, grass pea and other Lathyrus species) and those with the five less important seed-borne pulse viruses also present (broad bean stain virus, broad bean true mosaic virus, broad bean wilt virus, cowpea mild mottle virus and peanut mottle virus) are also summarized. The need for future research is emphasized, and recommendations are made regarding what is required.

P450-mediated resistance in Myzus persicae (Sulzer) (Hemiptera: Aphididae) reduces the efficacy of neonicotinoid seed treatments in Brassica napus.

BACKGROUND: The prophylactic use of seeds treated with neonicotinoid insecticides remains an important means of controlling aphid pests in canola (Brassica napus) crops in many countries. Yet, one of the most economically important aphid species worldwide, the peach potato aphid (Myzus persicae), has evolved mechanisms which confer resistance to neonicotinoids, including amplification of the cytochrome P450 gene, CYP6CY3. While CYP6CY3 amplification has been associated with low-level resistance to several neonicotinoids in laboratory acute toxicity bioassays, its impact on insecticide efficacy in the field remains unresolved. In this study, we investigated the impact of CYP6CY3 amplification on the ability of M. persicae to survive neonicotinoid exposure under laboratory and semi-field conditions. RESULTS: Three M. persicae clones, possessing different copy numbers of CYP6CY3, were shown to respond differently when exposed to the neonicotinoids, imidacloprid and thiamethoxam, in laboratory bioassays. Two clones, EastNaernup209 and Osborne171, displayed low levels of resistance (3-20-fold), which is consistent with previous studies. However, in a large-scale semi-field trial, both clones showed a surprising ability to survive and reproduce on B. napus seedlings grown from commercial rates of neonicotinoid-treated seed. In contrast, an insecticide-susceptible clone, of wild-type CYP6CY3 copy number, was unable to survive on seedlings treated in the same manner. CONCLUSION: Our findings suggest that amplification of CYP6CY3 in M. persicae clones substantially impairs the efficacy of neonicotinoid seed treatments when applied to B. napus. These findings highlight the potentially important real-world implications of resistances typically considered to be 'low level' as defined through laboratory bioassays. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Virus Diseases of Cereal and Oilseed Crops in Australia: Current Position and Future Challenges.

This review summarizes research on virus diseases of cereals and oilseeds in Australia since the 1950s. All viruses known to infect the diverse range of cereal and oilseed crops grown in the continent's temperate, Mediterranean, subtropical and tropical cropping regions are included. Viruses that occur commonly and have potential to cause the greatest seed yield and quality losses are described in detail, focusing on their biology, epidemiology and management. These are: barley yellow dwarf virus, cereal yellow dwarf virus and wheat streak mosaic virus in wheat, barley, oats, triticale and rye; Johnsongrass mosaic virus in sorghum, maize, sweet corn and pearl millet; turnip yellows virus and turnip mosaic virus in canola and Indian mustard; tobacco streak virus in sunflower; and cotton bunchy top virus in cotton. The currently less important viruses covered number nine infecting nine cereal crops and 14 infecting eight oilseed crops (none recorded for rice or linseed). Brief background information on the scope of the Australian cereal and oilseed industries, virus epidemiology and management and yield loss quantification is provided. Major future threats to managing virus diseases effectively include damaging viruses and virus vector species spreading from elsewhere, the increasing spectrum of insecticide resistance in insect and mite vectors, resistance-breaking virus strains, changes in epidemiology, virus and vectors impacts arising from climate instability and extreme weather events, and insufficient industry awareness of virus diseases. The pressing need for more resources to focus on addressing these threats is emphasized and recommendations over future research priorities provided.

Biology and genetic diversity of phasey bean mild yellows virus, a common virus in legumes in Australia.

This study examined the natural and experimental host range and aphid and graft transmission of the tentative polerovirus phasey bean mild yellows virus (PBMYV). Eleven complete coding sequences from PBMYV isolates were determined from a range of hosts and locations. We found two genetically distinct variants of PBMYV. PBMYV-1 was the originally described variant, and PBMYV-2 had a large putative recombination in open reading frame 5 such that PBMYV-1 and PBMYV-2 shared only 65-66% amino acid sequence identity in the P5 protein. The virus was transmitted by a clonal colony of cowpea aphids (Aphis craccivora) and by grafting with infected scions but was not transmitted by a clonal colony of green peach aphids (Myzus persicae). PBMYV was found in natural infections in 11 host species with a range of symptoms and severity, including seven important grain legume crops from across a wide geographic area in Australia. PBMYV was common and widespread in the tropical weed phasey bean (Macroptilium lathyroides), but it is likely that there are other major alternative hosts for the virus in temperate regions of Australia. The experimental host range of PBMYV included the Fabaceae hosts chickpea (Cicer arietinum), faba bean (Vicia faba), pea (Pisum sativum), and phasey bean, but transmissions failed to infect several other members of the families Asteraceae, Cucurbitaceae, Fabaceae and Solanaceae. PBMYV was commonly found in grain legume crops in eastern and western Australia, sometimes at greater than 90% incidence. This new knowledge about PBMYV warrants further assessments of its economic impact on important grain legume crops.

Novel Sources of Turnip Yellows Virus Resistance in Brassica and Impacts of Temperature on Their Durability.

Turnip yellows virus (TuYV; family Solemoviridae, genus Polerovirus) is the most widespread and economically damaging virus of canola (Brassica napus L.) production in Australia. However, no Australian commercial seed companies market TuYV-resistant canola cultivars, and little information is available on the susceptibility of those available. To identify potential sources of TuYV resistance, 100 B. napus accessions from the ERANET ASSYST diversity set were screened in the field and five of these were selected for further phenotyping via aphid inoculation. Furthermore, 43 Australian canola cultivars, six B. napus genotypes with previously reported resistance, and 33 B. oleracea and B. rapa cultivars were phenotyped. All Australian cultivars were susceptible except for 'ATR Stingray'. Stronger resistance to systemic TuYV infection (IR) was identified in diversity set accessions 'Liraspa-A', 'SWU Chinese 3', and 'SWU Chinese 5'. As indicated by lower relative enzyme-linked immunosorbent assay absorbance values (R-E405) in infected plants, resistance to TuYV accumulation (AR) often accompanied IR. Moderate IR was identified in four B. oleracea cultivars and one B. rapa cultivar. Very strong AR was identified in four B. oleracea cultivars and AR of some degree was common across many cultivars of this species tested. The impact of temperature during the inoculation access period or post-inoculation incubation on the resistance identified was examined. Infection rates were significantly higher in resistant B. napus genotypes when inoculated at 16°C than at 26°C, suggesting an increase in aphid transmission efficiency. IR in B. napus genotypes was strong when incubated at 16°C, but weakened at elevated temperatures with almost total breakdown in most genotypes at 30°C. However, infected plants of B. napus and B. oleracea genotypes with AR maintained lower R-E405 values than susceptible controls at all temperatures tested. Novel sources of resistance identified in this study offer potential as breeding material in Australia and abroad.