Losses in productivity of subterranean clover swards caused by sowing cucumber mosaic virus‐infected seed

Abstract

Field trials were done in 1988 -89 at two sites to examine the effects of sowing seed stocks in which a low proportion (1.6 -7.0%) of the seed was carrying cucumber mosaic virus (CMV) infection ( = infected seed) and the subsequent CMV spread that results, on the productivity of swards of subterranean clover cvs Esperance, Green Range and Karridale. Except in irrigated plots of cv. Green Range, a variable proportion of the CMV-infected seedlings always failed to establish, so sowing infected seed normally resulted in plots containing fewer or far fewer seed-infected plants than expected. The rate of virus spread by aphids was faster and resulted in more extensive infection at maturity when the plots contained more seed-infected source plants. In two irrigated trials at South Perth, in which healthy and infected seed of cvs Esperance and Green Range was sown, CMV spread was extensive. When the plots were left undefoliated, herbage dry wt yields were decreased by 12 -30% and seed yields by 53 -64% due to infection. When they were mown, the herbage dry wt losses recorded were 17 -24%. In three trials at Mt Barker sown with healthy and infected seed, extensive spread of CMV occurred with cv. Green Range but not with cvs Esperance and Karridale. With cv. Green Range, losses of 25 -28% in herbage dry wt were recorded inside CMVaffected patches in mown or grazed plots, while losses were up to 13% when herbage was sampled at random. Seed yield losses were 40 -42% and 53% in infected mown and undefoliated cv. Green Range plots, respectively. In the mown or grazed plots of cvs Esperance and Karridale, herbage dry wt losses recorded were up to 7% while seed yield losses were 9 -16% in mown and 9% in undefoliated plots.The mean wtiseed of seed harvested from mown plots of cvs Green Range and Karridale sown with infected seed was 8 ~ 12% less than that of seed from mown control plots. CMV was detected in seed harvested from undefoliated cv. Green Range plots and mown plots of cvs Green Range and Karridale sown with infected seed but levels of seed infection with the mown plots were 3 -5 times less than in the seed sown.Field trials were done at two sites in 1987 -90 to examine the persistence of CMV in subterranean clover swards. CMV infection was established in 1987 and the plots were grazed in subsequent years. At Badgingarra, infection gradually decreased with little CMV being recovered by 1990. At Mt Barker, recovery of CMV was relatively poor in 1988 and even poorer in 1989, but there was some resurgence of CMV infection in 1990.

Alteration of plant species mixtures by virus infection: Managed pastures the forgotten dimension

“…(examples 8 and 9) pasture decline studies in simulated perennial pasture swards with introduced initial virus infection lasting for 2 years (Eagling et al, 1992;; and (example 10) regular monitoring over 6-7 years of sown annual pasture swards where viruses were deliberately introduced and pasture decline occurred due to weed invasion (two sites) or, competition with healthy pasture and weed plants eventually eliminated the virus-infected plants (one site) (Jones, 1991;Jones & Nicholas, 1992;McKirdy & Jones, 1994a, 1994b. Example 1 is described in greatest detail because of the magnitude of information it provides about (a) the influence of virus infection on plant fitness parameters, the plant species balance outcome arising from competition between virus-infected and partially resistant hosts or nonhost weeds, and the annual regeneration of pasture and weed species from seed; and (b) additional factors that promote changes to the plant species balance, and how pasture decline occurs.…”

“…In the south-west of Western Australia, T. subterraneum or annual Medicago spp. cultivars were sown in unreplicated square (5 × 5 m) field plots (one cultivar per plot; Jones, 1991;Jones & Nicholas, 1992). Seven T. subterraneum cultivars were sown at site 1 and six at site 2.…”

“…However, the former would not apply to any of the 13 main research papers describing the 10 examples of such studies cited in Sections 4-7 above. Similarly, because they are all readily available worldwide, the latter would not apply to any of the five research papers in the Annals of Applied Biology (Bain et al, 1998;Catherall & Potter, 1987;Coutts & Jones, 2002;Jones, 1991) or…”

“…In managed pasture, the terms “pasture decline” and “pasture deterioration” are both used to describe the alteration to plant species composition that takes place when invasive weed species outcompete and gradually replace sown pasture species (Barbetti et al, 2006; Barnett & Gibson, 1975; Boddey et al, 2004; Cocks, 1994; Ghanizadeh & Harrington, 2019; Gibson et al, 1981; Gillespie, 1983; Grice & Campbell, 2000; Jones, 2012; Lee et al, 2017; McKirdy & Jones, 1997; McLaughlin & Boykin, 1988; McLaughlin et al, 1992; Pratt, 1967; Taylor et al, 1995; Tozer et al, 2017). One of its main causes is the decreased competitive ability of pasture species when virus infection results in them being outcompeted by weed species of little value as livestock feed (Eagling et al, 1992; Jones, 1991, 1996, 2012, 2013a, 2013b; McKirdy & Jones, 1994a, 1994b; McLaughlin & Windham, 1996). A range of other biotic and abiotic factors also change pasture species composition, for example, overgrazing, poor soil fertility, soil compaction, waterlogging, drought and disease caused by fungal or nematode pathogens, all of which impair survival of pasture plant hosts (Barbetti et al, 1996, 2006, 2020; Boddey et al, 2004; Brink et al, 1996; Gillespie, 1983; Grice & Campbell, 2000; Nichols et al, 2014; Pratt, 1967; Reeve et al, 2000).…”

“…Research on the effects of virus infection upon the plant species balance in managed pastures was done over two decades (1980–1999) (Bain et al, 1998; Catherall, 1987; Catherall & Potter, 1987; Coutts & Jones, 2002; Eagling et al, 1992; Jones, 1991; Jones & Nicholas, 1992, 1998; McKirdy & Jones, 1994a, 1994b; McLaughlin et al, 1992; McLaughlin & Windham, 1996; Ragland et al, 1986). The subsequent environmentally based research that focused on the alteration to species composition resulting from virus infection of wild plants growing in natural ecosystems commenced in the following decade.…”