Characterizing Potato Virus A Diversity and Host Range in Tamarillo Growing Regions in New Zealand

Abstract

Potato virus A (PVA) belongs to the family Potyviridae (genus Potyvirus), the largest and most economically important family of plant viruses in the world. PVA is known for its characteristic mosaic disease which varies considerably depending upon the environmental conditions, host infected and the strain of the virus involved. The known hosts of PVA are limited to the Solanaceae family of plants of which there are approximately 70 plant species recorded within New Zealand. Tamarillo, Solanum betaceum, a host of PVA, are grown in New Zealand with an annual market value of $1.8M. Diversity of PVA isolates has recently been identified in New Zealand grown tamarillo plants including two atypical isolates; a mild strain of the tamarillo-PVA isolate, Tamarillo mosaic virus (TamMV), and a potato-PVA isolate which causes severe symptoms on tamarillo. Prior to this research, no extensive review on the genetic diversity of PVA strains had occurred within New Zealand tamarillo plants or other Solanaceae. A survey of 687 Solanaceae plants revealed PVA incidence within tamarillo orchards has decreased from 100% to 56% over 20 years. Fifteen genetically distinct PVA isolate groups were identified; four by long open reading frame sequence analysis and 11 by analysis of only their coat protein genes. One recombinant PVA genome was identified. When inoculated to tamarillo, the newly identified PVA isolates were associated with symptoms that ranged from mild to severe. No symptoms were observed on black nightshade or potato infected with any of these PVA isolates. This research contributes to the further understanding of the PVA genetic diversity and will assist tamarillo growers with the knowledge needed to manage the virus within their orchards.