Yield-limiting potential of Beet western yellows virus in Brassica napus

Abstract

Losses in seed yield and quality caused by infection with Beet western yellows virus (BWYV) alone or in combination with direct feeding damage by Myzus persicae (green peach aphid) were quantified in field experiments with Brassica napus (canola, oilseed rape) in the ‘grainbelt’ region of south-western Australia. Plants infected with BWYV and infested with M. persicae were introduced into plots early to provide infection sources and spread BWYV to B. napus plants. Insecticides were applied as seed dressings and/or foliar applications to generate a wide range of BWYV incidences in plots. Colonisation by vector aphids and spread of BWYV infection were recorded in the plots of the different treatments. At sites A (Medina) and B (Badgingarra) in 2001, foliar insecticide applications were applied differentially at first, but, later, ‘blanket’ insecticide sprays were applied to all plots to exclude any direct feeding damage by aphids. When BWYV infection at sites A and B reached 96% and 100% of plants, it decreased seed yield by up to 46% and 37%, respectively. Also, variation in BWYV incidence explained 95% (site A) and 96% (site B) of the variation in yield gaps, where for each 1% increase in virus incidence there was a yield decrease of 12 (site A) and 6 (site B) kg/ha. At both sites, this yield decline was entirely because fewer seeds formed on infected plants. At site B, BWYV infection significantly diminished oil content of seeds (up to 3%), but significantly increased individual seed weight (up to 11%) and erucic acid content (up to 44%); significant increases in seed protein content (up to 6–11%) were recorded at both sites. In field experiments at sites B and C (Avondale) in 2002, insecticides were applied as seed dressings or foliar sprays. At site B, when BWYV incidence reached 98%, the overall yield loss caused by BWYV and direct M. persicae feeding damage combined was 50%. At site C, when BWYV incidence reached 97%, the overall combined yield decline caused by BWYV and direct feeding damage was 46%. This research under Australian conditions shows that, when aphids spread it to B. napus plantings such that many plants become infected at an early growth stage, BWYV has substantial yield-limiting potential in B. napus crops. Although the results represent a worst case scenario, the losses were greater than those reported previously in Europe and are cause for concern for the Australian B. napus industry. When applied at 525 g a.i./100 kg of seed, imidacloprid seed dressing controlled insecticide-resistant M. persicae and effectively suppressed spread of BWYV for 2.5 months and increased seed yield by 84% at site B and 88% at site C. Therefore, provided that mixing the insecticide with seed is sufficiently thorough, dressing seed with imidacloprid before sowing provides good prospects for control of BWYV and M. persicae in B. napus crops.

Identification and QTL mapping of resistance to Turnip yellows virus (TuYV) in oilseed rape, Brassica napus

“…Symptoms of TuYV infection are often reminiscent of abiotic stress, particularly nutrient deficiency, and can include reddening of leaves and stunted growth. In addition, TuYV infection has been shown to reduce seed yield in single OSR plants by 40-50% (Schroeder 1994) and cause yield losses in OSR crops of 11-46% (Graichen and Schliephake 1999;Jay et al 1999;Jones et al 2007). In the past, the most common strategy to control TuYV has been the use of chemical measures against the vector, in particular insecticide (neonicotinoid)-treated seeds, but most of these treatments are now banned for OSR in the EU, emphasising the need for alternative control measures such as natural plant resistance.…”

Effects of aphid feeding and associated virus injury on grain crops in Australia

“…BWYV transmitted by M. persicae caused a significant reduction on yield which averaged 34%. This result was based on three studies from WA, namely Jones and Hawkes (2002) and Jones et al (2003Jones et al ( , 2007, who found similar yield reductions in the range 30-39%, respectively (data extracted from publications), based on artificial aphid inoculations. Artificial inoculations used in virus trials may lead to a high and early incidence of disease (particularly as plants were inoculated at (Berlandier 2004).…”

“…Virus data from field assays were derived from artificial inoculations, whereas feeding data were derived from natural infestations, except in one study where a naturally infested crop was supplemented with aphids (Berlandier 2004). Canola yield tended to be affected more by virus injury than feeding injury; overall virus injury caused an average yield reduction of 34% (SD = 23) (Jones & Hawkes 2002;Jones et al 2003Jones et al , 2007 while feeding injury caused an average reduction of 23% (SD = 14) (Berlandier 2004;Jenkins et al 2011). All Australian data collated came from studies conducted in WA and NSW, despite canola being an important crop in VIC and SA with production averaging 331 000 and 260 000 tonnes, respectively, for 2009-2010 (sourced from Australian Bureau of Statistics (ABS)).…”

Electrical penetration graph studies to investigate the effects of cyantraniliprole on feeding behavior of Myzus persicae (Hemiptera: Aphididae) on Capsicum annuum

“…Imidacloprid has been shown to reduce incidence of persistently transmitted, aphid‐borne viruses, the transmission of which has been associated with phloem feeding (waveform E in EPG recordings) . For example, a reduction in feeding time and percentage of individuals that reached the phloem is believed to be responsible for reduced transmission of Barley yellow dwarf virus, a phloem‐borne virus, by Schizaphis graminum (Rondani) .…”