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

Syncytia usually are elongate, with ends merging with normal
tissue, and each syncytium is generally associated with one
larva. When multiple infections occur within a small area of root
tissue, syncytia may coalesce. Nuclear hypertrophv is followed
by decrease in size and number of plastids, breakdown of
chond riosomes (mi tochondi ra). polyploid y of nuclei, and
nuclear disintegration,
Ingrowths or protuberances d'eslop next to xylem vessels;
"boundary formations" and microtubules are associated with
the ends of these protuberances. Ihey serve to increase the
surface area of the syncytial cell wall relative to its volume and to
allow for increased flow of solutes across the plasmalemma. The
cell wall becomes tip to 10 times its normal thickness.
Epidemiology
Although populations of cyst nematodes do not increase as
rapidly as do fungal and bacterial pathogens of potatoes, once
well established in a potato-growing area, they arc. with present
technology, inipossihlc to eradicate. The environmental
conditons providing successful cotomLr'iAl potato production
also provide optimum conditions for their multiplication and
survival. Potato cyst neniatodes flourish where soil
temperatures are cool. Although they have been found in
tropical and warmer temperate climates, they. do not generally
become established and are of lesser economic importance than
in cool climates, larvae become active at IO C. and maximum
invasion of roots occurs at 160 C. Soil temperatures of 260 C for
prolonged periods of time reduce development and limit
reproduction.
Cyst nernatodes develop well in soils suited for surviva! and
movement of wormlike stages, such as medium to heavy clay
soils and well-drained and aerated sands, silts, and peat soils
with a moisture content of 50-75(i of water capacity. Soil pH
valles that are tolerable to the potato plant can apparently be
tolerated by the nematodes. Nutritional status of the soil
.pp.
_l •
Fig. 100. Potato cyst nematode (Globodera rostochiensis): A,
mature cyst with enclosed eggs; B,sectien of potato root showing
syncytia. (Courtesy W.F. Mai, B. B. Brodie, and M. B. Harrison)
96
;10
appears to have little or no effect on nematodes other than that
caused by crop performance.
Encysted eggs withstand desiccation and can remain viable 20
years or more in soil under severe environmental extremes.
Moving infested soil such as that clinging to equipment, seed, or
storage containers is the most important means of local and long
distance spread. Planting contaminated tubers provides ideal
conditions for spread and is thought to be a primary factor in
nematode dissemination throughout the world. Birds are not
considered important in long-distance spread.
Other Hosts
These include tomato, eggplant, and a number of
Solanaceous weeds.
Resistance
Resistant cultivars and nonhost crops cause an average of 95
and 50i reduction in populations, respectively. Excellent
sources of resistance to G. rostochiensis(race R A) are available
in commercial varieties in Europe and North America. Good
resistance has been found to some, but not all, races of G.
pallida. Resistance to G.pallida (race P 4A) is available in some
ne%%er Dutch varieties.
Control
I) Restrict shipments of seed tubers and plants of other types
from infested areas.
2) Except for high dosages of soil fumigants, chemical
treatments usually reduce densities only slightly, if at all.
Although some organic phosphate and carbamate nematicides
provide good protection against infection by active larvae,
nematode density in treated soil usually remains the same or
slightly increases during growth of a potato crop.
3) Crop rotation has been widely used but is often
uneconomical because ofthe length of rotation required. When
nematode densities are high, rotation with potatoes grown once
in five years is necessary to assure profitable potato yields.
Resistant potato cultivars in rotation with susceptible cultivars
and nonhosts considerably reduce the required length of
rotation.
4) Combining different control mcasures is necessary for
keeping populations below damaging levels and for preventing
establishment of nematodes in new areas. Key components of
nematode management are: extensive surveys to determine
distribution of cyst nematodes, soil fumigants to reduce
numbers of nematodes in the soil, resistant cultivars to prevent
density increase, carbamate nematicides to suppress density
increases, prohibition of potato seed production in known
infested or exposed land, and regulation of reuseable containers
and movement of farm machinery, top soil, and plant material.
Selected References
C111TWOOD. B.Gand E.M. BUIIRER. 1946. The life historyofthe
golden nematode of potatoes, leterodera rostochiensis
Wollenweber. under Long Islana. New York, conditions.
Phytopathology 36:180-189.
ENDO, 13.Y. 1971. Nematode-induced svncvtia (giant cells). Pages
91-117 in: B. M. Zuckerman. W. F. Mai. and R. A. Rohde, eds.
Plant Parasitic Nematodes, Vol. 2.Academic Press. New York. 347
EVANS, K., .1. FRANCO. and M. M. de SCURRAII. 1975.
)istribution of species of potato cyst-nematodes in South America.
Nemnatologica 21:365-369.
HOOPES, R.W. 1977. [he internal response of several resistant and
susceptible potato clones to invasion by the potato cyst nematode
IUniversity. I'ieroderarostochiensis 61 pp.
Woilenweber. NIS thesis. Cornell
MULVEY, R. II.. and A. R. STONE'.. 1976. Description of Punctodera
maladorensis n. gen.. n. sp. (Nematoda: fleteroderidae) from
Saskatchewan with lists of species and generic diagnosis of
(ilobodera In. rank). Ileterodera and Sarisodera. Can .1.Zool.
54:772-785.
SPEARS, .1. F. 1968. The Golden Nematode Handbook: Survey,