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

They attack many major crops in the Andean region and many
weed species, causing extensive damage to members of the
Solanaceae. Races differ in their ability to attack certain crops.
Resistance
Limited work has been done ol development of resistance to
N. aberrans. A native Solantr tu erosum ssp. amligena
cultivar shows a high level of resistance, and excellent resistance
exists in S. sparsipiluni.
Control
II In preliminary experiments in South America, economical
control has been achieved through the use of'organophosphates
and oxime carbamates.
2) Because of'a relatively wide host range, selection of suitable
crops for rotation schemes isdifficult, although members ofthe
Gramineae and most of the Leguminosae are no nhosts.
Populations decline rapidly in the absence of a suitable host:
therefore, rotations can be shorter than those required for the
potato cyst nematode.
3) Quarantine and restriction of potato seed tuber shipments
into disease-free areas should be strictly enforced.
Selected References
AI.AR)N. C., and I'. IA I ALA. 1977. Afecto de la temperatura en la
resistencia da Solanuon ardi,en a it Nacoblbu aherras.
Nematropica 7:2-3.
CLARK, S. A. 1967. [he development and life histor' of the false
root-knot nematode. 'ah, .serendipiticu.s. Ne'natologica
13:91-11).
IATAIA. P.. and M. de SC1R RAIl. 1975. Mode oftdissenlination
ol Nacotbu. spp. in certain potato-grossing areas of Peru and
Bolikia. I. Nenratol. 7:324-325. (Ahstr. .
,JAILA,IP.. and A. M. GOIL)EN. 1977. laxonomic status of
\acothrts species attacking potatoes i South America.
Nenatropica 7:9-10.
LaROSA, t). i., and I'. IA AI.A. 1977. Depth of penetration of
.\acobhu.aherran.s in potato tuhers. Ncratropica 7:11,
LORI)EI.I.O. I.. 6. F.. A. P).I.. ZAMITII. and 0. J. BOOCK. 1961.
f-No nematodes found attacking potato in Cochaha mba. Bolivia.
Ain.. Acad. Bras. Cienc. 33:2)9-215.
SIER. S.A. 1970. Revision of tile genus ,acoth-o Ihorne and Allen.
1944 (Nematode: lvlernchoidea). .1.Neniatol. 2:228-235.
Lesion Nematodes
Of the several Pratrhnchiuns spp. known to damage potatoes,
P. penetrans is the most important in North America and in
Europe. Species in other areas are P. crefratms, P. mittyu's, P.
thornei,and P. scribneri in Europe; P. crenatts, P. hractlvurts
and P. scribneri in North America: P. anclinus, P. scrihneri,P.
penetrans,and P thornei in South America: P.hrachvurusand
P. scrihneri in Africa: and P. vunus and P. coffeae inI Japan.
Symptoms
High populations of lksion nematodes cause areas of poor
growth: plants are less vigorous, turn yellow, ard cease to grow.
Damage is caused by direct feeding, and usually only cortical
tissues are affected. Large numbers of nematodes cause
extensive lesion formation and cortex destruction of
unsuberizcd feeder roots (Fig. 103A). Affected roots are
commonly invaded and damaged by other soil iicroorganisms,
thus increasing root destruction. Rhizomes are not attacked as
severely as roots.
In general, P. penetrans in primarily aroot pathogen, whereas
other species such as P. brachi.urtus and P. scribneri cause
serious tuber damage. Lesions on tubers become visible when
nematode numbers in a small area of the tuber are high enough
to cause a number of adjacent cells to die. In South Africa,
symptoms on tubers caused by P. brachyurutsare purple-brown
areas about 0.5 nim in depth, irregular in shape.and surrounded
by a slightly depressed border. Raised wartlike protuberances,
unsightly lesions, pimples, and weight loss and withering
in storage reduce tile market value of tubers and make infected
seed potatoes worthless (Plate 83).
Lesion nematodes are often associated with wilt-causing
fungi such as Fusaritjnrspp. and J'eriicillium spp. Other fungi
and bacteria are frequently present in potato tissue damaged by
these nematodes.
Disease Cycle of the Causal Organism
The first molt occurs in the egg, and the second-stage larva
emerges from the egg. All stages are wormlike and active. They
enter plant roots usually just behind the root cap but may enter
through other u,nsuberized surfaces of roots. rhizomes, and
tubers (Fig. 10313). Entry of, and movement through, roots may
be intercellular or intracellular. Entry is apparently
accomplished largely by mecha nical pressureaid cuttiig actioI
of tie stylet rather than by enzymatic action. lesion formation
and root death usually occur ahead of the area penetrated. In
tubers, cells surrounding nematodes are brown: cytoplasm is
granular: and nuclei are reduced in size.
Males are common in some species but not in others. Bisexual
reproduction occurs in species in which males are abundant.
Gravid females lay eggs in the soil and roots, either singly or in
small groups. (ieneration time is from four to eight weeks,
depending uponi factors such as temperature, nematode species,
and host.
Epidemiology
Soil temperature requirements vary greatly with species.
Optimum temperature for reproduction of P. petetrans is
16-20' C: it is anrimportant pest in regions of Europe and the
United States that have this temperature range. In warmer
climates, species with higher temperature optinia (25-28°C),
such as P. hractitrrus in Africa and R coffeae in southern
.Japan replace P. pe slerans.
Damage to potatoes by lesion nematodes is usually associated
with coarse-textured soils. This may be partly because some of
the species involved, e.g., P. penetrans, are favored by sandy
soils and partly because such soils are preferred for potato
culture.
Soil moisture influences movement and other activities of
Prat lenchusspp. In general, favorable soil moisture level isone
Fig. 103. Root-lesion nematode (Pratylenchus penetrans): A,
damage on the roots; B, adults, larvae, and eggs inside root.
(Courtesy W. F. Mai, B. B. Brodie, and M. B. Harrison)
AP