HypervirulentDiuraphis noxia(Hemiptera: Aphididae) Biotype Sam Avoids Triggering Defenses in Its Host (Triticum aestivum) (Poales: Poaceae) During Feeding

Abstract

In the molecular arms race between aphids and plants, both organisms rely on adaptive strategies to outcompete their evolutionary rival. In the current study, we investigated the difference in elicited defense responses of wheat (Triticum aestivum L.) near-isogenic lines with different Dn resistance genes, upon feeding by an avirulent and hypervirulent Diuraphis noxia Kurdjumov biotype. After measuring the activity of a suite of enzymes associated with plant defense, it became apparent that the host does not recognize the invasion by the hypervirulent aphid because none of these were induced, while feeding by the avirulent biotype did result in induction of enzyme activity. Genomic plasticity in D. noxia may be a likely explanation for the observed differences in virulence between D. noxia biotype SA1 and SAM, as demonstrated in the current study.

Profiling Diuraphis noxia (Hemiptera: Aphididae) Transcript Expression of the Biotypes SA1 and SAM Feeding on Various Triticum aestivum Varieties

“…Seemingly, biotype SAM escapes detection from resistant hosts, as it displays a comparable clustering configuration as D. noxia biotype SA1 4 hpi after feeding on susceptible cultivars, in that there is no association in the clustering of samples in regards to host genotype or by the type of Dn gene present. This again supports findings of the study conducted by Botha et al (2014a) where the defense response (measured in enzyme activity) in Dn-containing hosts fed on by D. noxia biotype SAM was similar to that of susceptible NIL hosts that were fed on by biotype SA1.…”

“…Diuraphis noxia biotype SA1 only expressed virulence against the susceptible wheat varieties as previously reported (Tolmay et al 2006, Jankielsohn 2011. The antixe-notic cultivars containing the Dn5 and Dn7 gene expressed the highest level of resistance against D. noxia biotype SAM and had a virulence score (VS) of 9/10 after the 6-wk screening period, but was still classified susceptible according to its virulence profile (VP), confirming the results of a previous study performed by Botha et al (2014a) All the other cultivars had expressed VSs of 10 and were classified as susceptible to feeding by D. noxia biotype SAM, including plants containing resistance genes (i.e., Dnl, Dn2, Dn4, Dn8, and Dn9).…”

“…Diuraphis noxia biotypes used during the study included SA1 and SAM, which were reared in insect BugDorm Insect cages (MegaView Science Co. Ltd, Taiwan) at 20 6 2 0 C to prevent crosscontamination with continuous artificial fluorescent lighting as described in Botha et al (2014a)…”

“…Plants were incubated in BugDorm Insect cages to prevent cross-contamination at 20 6 2 0 C with continuous artificial fluorescent lighting. Individual plants were infested with 10 apterous D. noxia adults (biotype SA1 or SAM) and incubated for 6 wk during which their scores were determined (Weiland et al 2008, Botha et al 2014a; Supp. File 1 [online only]).…”

Partial characterization of the X chromosome of Diuraphis noxia (Hemiptera: Aphididae)

“…This study made use of adult female aphids of the South African mutant D. noxia biotype (SAM) (Swanevelder et al 2010;Botha et al 2014), which derives from South African biotype 1 (SA1; Hewitt et al 1984). The female D. noxia specimens were obtained from the Department of Genetics, Stellenbosch University, Cereal Genomics Laboratory.…”