Soybean Aphid, Aphis glycines Matsumura, a New Vector of Potato Virus Y in Potato

American Journal of Potato Research, May/Jun 2005 by Davis, Jeffrey A, Radcliffe, Edward B, Ragsdale, David W

ABSTRACT

Soybean aphid (Aphis glycines Matsumura), an exotic species first discovered in the North Central region of the United States in 2000, is a competent vector of several Potyviridae. Soybean aphid has high fecundity and produces alatae (winged morphs) readily, characteristics typical of proficient virus vectors. When soybean aphids were exposed to Potato virus Y (PVY)-infected potato plants and then clip-caged on healthy potato plants in groups of five or as single aphids, PVY transmission ranged from 14% to 75% across all experiments. PVY^sup O^, PVY^sup N^, and PVY^sup NTN^ strains were transmitted by soybean aphid.

RESUMEN

El �fido de la soya (Aphid glycines Matsumura), especie ex�tica que fuera descubierta en la regi�n norcentral de los Estados Unidos en el a�o 2000 es un vector de varios Potyviridae. El �fido de la soya tiene una alta fecundidad y produce r�pidamente formas aladas, caracter�stica t�pica de los vectores de virus. Cuando los �fidos de la soya se pusieron en contacto con el virus Y (PVY) en plantas de papa infectadas y luego se insertaron en plantas sanas en grupos de cinco o como �fidos solitarios, la trasmisi�n de PVY fue de 14% a 75% en todos los experimentos. Las variantes PVY^sup O^, PVY^sup N^ y PVY^sup NTN^ fueron trasmitidas por el �fido de la soya.

Accepted for publication 12 October 2004.

ADDITIONAL KEY WORDS: Solanum tuberosum, virus transmission efficiency

INTRODUCTION

Since its discovery in the North Central region of the United States in 2000, soybean aphid (Aphis glycines Matsumura) has spread to 21 states (Venette and Ragsdale 2004). This aphid can directly damage soybean (Glycine max L), causing early leaf senescence and reducing pod set, seed quality, and yield (Xibei et al. 1994; Wang et al. 1996,1998; Wu et al. 1999).

In addition to direct feeding damage to soybean, soybean aphid transmits several plant viruses including Alfalfa mosaic vwiis (AMV), Cucumber mosaic virus (CMV), Peanut mottle virus (PMV), Soybean mosaic virus (SMV), Tobacco ringspot virus (TRSV), and Tobacco vein-banding mosaic virus (TBMV) (Fang et al. 1985; Alleman et al. 2002; Clark and Perry 2002; Wang and Ghabrial 2002). Soybean aphid is a proficient vector of nonpersistent viruses in part because of its high fecundity, short generation time (McCornack et al. 2004), and propensity to form alatae (winged morphs) (Voegtlin and Onstad 2003). Soybean aphid is congeneric with two known Potato virus Y (PVY) vectors: buckthorn aphid (Aphis nasturtii Kaltenbach) and cotton aphid (Aphis gossypii Glover). Aphis glycines and A. gossypii have been reported to produce hybrids which, while viable, have reduced fecundity (Zhang and Zhong 1982). For these reasons, we hypothesized that soybean aphid could be a vector of PVY.

PVY exists as several strains that have been placed into groups based on their symptomology in potato (Solanum tuberosum L.) and tobacco (Nicotiana tabaccum L.) (de Bokx and Huttinga 1981; Kerlan et al. 1999). The common strain, PVY^sup O^, produces mosaic and leaf drop in potato and tobacco. A strain designated as tobacco veinal necrotic strain, PVY^sup N^, produces mottling and necrosis in potato (Chachulska et al. 1997; Kerlan et al. 1999) and severe necrosis in tobacco (de Bokx and Huttinga 1981). In potato, PVY^sup N^ tends to cause a milder mosaic than does PVY^sup O^ and in some cultivars is essentially asymptomatic (de Bokx and Huttinga 1981). A variant of PVY^sup N^ can produce tuber necrosis in potato and has been designated as PVY^sup NTN^. This variant causes typical mosaic symptoms on potato leaves, sunken necrotic rings on tubers, and leaf necrosis in tobacco (Le Romancer et al. 1994). Tubers may be infected with PVY^sup NTN^ but not show symptoms due to cultivar differences or lack of permissive environmental conditions. In addition, there are specific strains detected serologically as PVY^sup O^ that cause necrosis in tobacco (McDonald and Singh 1996; Chrzanowska 2001). These strains have been designated PVY^sup N:O^ and are recombinants between PVY^sup O^ and PVY^sup N^ (Nie and Singh 2002, 2003; Singh et al. 2003).

Preliminary experiments using a mass inoculation procedure similar to the arena tests described by Irwin and Ruesink (1986) suggested that soybean aphid can acquire and transmit PW (Davis et al. 2004). Objectives of this study were (i) to confirm that soybean aphid can transmit PVY from potato to potato and (ii) to measure transmission efficiency.

MATERIALS AND METHODS

Virus Strains and Maintenance

The PVY inoculum source used in these experiments originated from PVY-infected tubers (cvs Red La Soda and Chieftain) harvested at the University of Minnesota Outreach, Research and Education Park (UMore Park), Rosemount, MN, from field plots used to screen potato breeding lines for PVY resistance. In the field, this PVY source is maintained by annual harvesting of tubers from the "infector rows," which are blended with certified seed and planted as inoculum the next year. Thus, this source is representative of aphid-transmitted PVY strains found in Minnesota, a characteristic considered desirable in transmission efficiency trials (Irwin and Ruesink 1986; Power and Gray 1995; Gray et al. 1998; Lucio-Zavaleta et al. 2001). All three PVY strains and recombinant PVY^sup N:O^ were shown by reverse transcriptase polymerase chain reaction (RT-PCR) to be present in the inoculum source, but titer levels for each strain were not determined. In the greenhouse, transmissions to maintain the PVY source were by green peach aphid (Myzus persicae (Sulzer)), and potato aphid (Macrosiphum euphorbiae (Thomas)). Aphids were allowed to move freely from infected to healthy potatoes, transmitting PVY. This ensured that freshly infected plants were available to serve as virus sources for all experiments and that all PVY strains maintained were aphid transmitted.