Intracellular Salivation Is the Mechanism Involved in the Inoculation of Cauliflower Mosaic Virus by Its Major Vectors <I>Brevicoryne brassicae</I> and <I>Myzus persicae</I>

Abstract

Cauliflower mosaic virus (CaMV) is transmitted to crucifers in a noncirculative manner by several aphid species. CaMV is preferentially acquired from the phloem, although acquisition also occurs after brief intracellular stylet punctures of aphid vectors in nonvascular leaf tissues. In the present work, we used the electrical penetration graph technique to study the specific aphid stylet activities and behavioral events leading to the inoculation of CaMV to turnip plants by its two major vectors, Brevicoryne brassicae (L.) and Myzus persicae (Sulzer). Aphids subjected to an 8-h acquisition access time on infected plants were transferred to test plants and removed immediately after specific behavioral events were recorded. CaMV was readily inoculated after the first intracellular puncture in nonvascular tissues by both vector species. Inoculation rate of CaMV by B. brassicae was the highest after a 3-h inoculation access period, regardless of whether aphids had reached the phloem phase during that period. Consistent interspecific differences also were found in the ability of both aphid vectors to retain CaMV. B. brassicae could retain the virus after several intracellular punctures, whereas M. persicae readily lost the virus after performing the same number of intracellular stylet punctures. We concluded that salivation by aphids during successive intracellular stylet punctures in the epidermal and mesophyll cells before reaching the phloem phase are the key behavioral events associated to the inoculation of Cauliflower mosaic virus. The likely location of the viral retention site inside the aphid mouthparts is discussed.