Compendium of Potato Diseases - (PDF, 101 mb) - USAID

cultivars. Symptoms are slight deepening of veins and rugosity
of leaves and possibly stunting and a more open type of growth.
Some strains may cause mottling or bronzing in certain cultivars
and, when severe, may cause necrotic spots oti the upper
surfaces. Older leaves in the shade may develop greenish spots
instead of turning uniformly yellow. Controversy exists as to
whether PVS alone consistently reduces yield, but losses of
10-207 have been reported.
CatLsal Agent
PVS particles are straight to slightly curved filaments,
approximately 650 X 12 nm. Thermal inactivation is 55-6 0 ' Q
dilution end point in crUde potato sap is about 10 U;and
longevity in vitro at 20'C is about four days.
PVS isstrongly antigenic, and for convenience and reliabdlity
in diagnosis, serology is generally used. Plants in the field are
best tested just before flowering by sampling lower and middle
leaves. Viru:s concentration may be low early or late in the
season.
In tube tests, the precipitate is flocculent. The simple slideagglutination
test can be used under ideal conditions, but
inicroprecipitin, bentonite, or latexflocculationorgel-diffusion
tests are preferred.
Epidemiology
PVS is tuber-perpetuated, readily transmitted mechanically
by infective sap, and reputed to be spread in nature primarily
by contact with diseased plants. Certain strains are transmitted
by the aphid I' :rs persicae in a nonpersistent manner.
Transmission tests with true seed have been negative.
Other Hosts
Ir. Nicotiana dehne'vi, systemic vein clearing occurs after 20
days, spreading from the leaf tip toward the base (Fig. 80A).
Later, leaves develop interveinal or veinbanding mottle at 200 C
with a 16-hr day at 1,000 FC. Andean isolates give mild mosaic
or are sy(ptomless.
So/anum rostratunm and Saracha un/re/lata (affected by sone
strains only) show necrotic spotting on inoculated leaves in 20
days, and later, on systemically invaded leaves. Andean strains
do not cause necrotic spotting.
Datura meteI, Pi.vsalis philadelptica.aind P. puhescens are
systemically infected without symptoms.
Capsicum annuurm, Lycopersicon esctuh'nltun, Nicandra
pnhrsalode is,N o aa glutinu, A'. sar'eesris, N. abacu,
and Ph/'Vsa/is floridlata are immune to infection.
Local lesions occur in Chenopoditim album and C.
amaranticolor after 40 days (Fig. 80B and C), in C. quiroa
16-20 days), and in C'antopsis tetragonoloha(6-10 days).
Most Andean strains (but not all) are systemic in C. quinoa
and C. amaranticolor.
Resistance
Well-defined mature plant resistance is present in potato, so
ransissionmst occur relatively early in the season if tuhcrs
are to become infected.
Certain cultivars, including Bintje, Katahdin, aid Kennebec,
are moderately resistant to reinfection. [he cultivar Saco and
some of its progeny hiave' strong general resistance, which is
inherited as a simple recessive: this resistancc can be overcome
by grafting, and plants carry the virus virtually without
symplams.
Resistance ofthe hypersensitive type ispresent in a cultivar of
Solanumt tuberosum ssp. antdigena this characteristic has been
brought through several crosses with S. tuerosum. A similar
type of resistance has been reported in the diploid S.
11egistacrolohbtum.
Control
o) VS-fr e clones (f susceptible cultivars have been
esta blished by rneristcm tip culture. In some regions these can be
maintained relatively free from reinfection, but in other regions
this is rlot so. possibly due to an insect vector. Indexing tubers
and testing mother plants intended for production of stem
cuttings, followed by release of elite seed. are the accepted
practices.
2) Roguing is not effective.
Selected References
BAFRE(KE, M. .. 1967. t'"berempfindlichkeit gegen das S-Virus der
Kartoffel i.i cineh boliviarischcn Andigena-Kion. Ziichter
37:281-286.
BAGNAI.I., R. II.. C. W- ILR.art'l R. Il. LARSON. 1959. I)ifferential
and host
carnat and serological relationships i n late n
of
t
potato \ irus
\i
10, potato virus S,
I\ h\ topa tho logy 49:435
BAiNAI.I.. R. -442.
H.,and I). A. YOt NG. 1972. Resistance to virus Sin the
potato. Am. Potato .l. 49:196-201.
de ()KX. .1 A.. ed. 1972. Viruses of Potatoes and Seed-Potato
Production. Pudoc. Wagcningei. Ihe Netherlands. 233 pp.
MacKIN)NON. I. P.. aid R. H. BA6iNA1.1. 1972. Use of Vicotiana
dehoevii to detect \iruses S. X. and Y in potato •d stocks, and
relative susoe,,Ihibility of six cointion varieties to potato virus S.
Potato Res. 15:81-85.
SII IPA R1). .1.I.. and I..
principles
F. (.A I-I.
ol seed
N. 1975.
potato
Critical
certification.
analses of
Ana.i.
the
Re. PIhitropathol.
13:271-293.
STACF-SMIr11. R.,and F. C. MEI.OR. 1968. Eradication of potato
viruses X and S by ihermotherapv and axillar' bud culture.
Plrytopathology 58:199-203.
Fig. 80. Potato virus S: A, systemic vein clearing in young leaves of Nicotiana dobneyi; B, local lesions in young and old leaves of
Chenopodium amaranticolor. (A,Courtesy R. H. Bagnall)
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