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

l.aboratory, Control. and Quarantine Procedures. U. S. Dept.
Agric. Handbook 353. 81 pp.
SIONE. A. R. 1972. Ilterod.ra pallida n. sp. (Neiiatoda:
Nfeteroeridae). a wcolg species 4 par-to cyst nerialatde.
Root-Knot Nematodes
One or more species of Meloido,'iyne are known to attack
almost all major crop plants and many weeds species. Vegetable
crops, inclhding potatoes. are extensi\ely damaged. with potato
losses reaching 2511 or more. Although species differ in their
abilitv to attack certain \cgetable crops, no vegetables go
Ln harned.
Root-k not ne matodes are wo rid wide in d isti but ion but are
limited in specific areas b\ tem perature and cropping practices,
lhe .Il. hi'ognitagroup is. perhaps. the most \widely distributed.
l. hapla is the dominant species on potato in Europe arnd North
America folhoscsd by .l. incognita and M. intog'niaacrita. InA
Africa and Asia. . /arvalicaand Al. iio, nlita are domi nalt.
follo\ed b\ . incognitaacrita and Ml. hap/a, tile latter being
found il .Japan. .1. itcogtital. incognta acrita, Al. [avanica.
and Ml. hap/a atrack potatoes in South America. 1 . arenari/
has been found ii potatoes ol most continents.
Symptoms
Aboveground syniptonis are not diagnostic. l)epending upon
nematode dcnsity, infected plants may show .arving degrees of
stuintinig arid a terideicy to \wilt under mnoisture stress.
K nots or galls of varying si/es and shapes are present on tile
roots (Fig. 101A). When neriatode densities are fiigh and
enirloniental conditions favorable. tubers are infected and
display galls that give themi a wart\ appearance (Fig. 101I).
Galls. containing white. pear-shaped. mature feriale
nemiatodes, range frori an almost spherical shape (in M.
arciraria) to averv rough arid irregular appearance (ilr M.
ha/il/a). Iidiidual gall si/ec(peids upiio neiiiatodedensityanid
species, root size. teriperiattire. and other environmental
factors. In :,dtition to galling . h01la caurses initiation of
extensi\e lateral root formltio,,.
Disease Cycle of Causal Organism
I lie disease cycle of root-knot nematodes on potato is similar
to thal on oitler crops arid plants. I lie first miolt occurs within
tile egg: the second-stage larsa emerges from the egg and invades
the host root near the rip. Iar\ac rligrate through the root to the
\ascular tissue. shere they become stationary. Feeding injury
and glandular sccretion by arsrae cause host cells surrounding
the reriatode head to undergo cell division a nd cell
enllargentcir. Ilnteraction of neriaolde anrid host causes
deselopniri ut mutiriucleate giant cells. fron which tie
neriaiode obtains its I od. After feeding, the larvae begin to
swkell. Sexes become distinguishable in fourth-stage larvae
within tile host tissue. I-eiiales continue to swell and at
riituritvare hrite. pear-shapedarid about I-2 rni long. After
the fourth stage, riales become \\ orrilike, about 1-1.5 riri flng.
al(n migrate out oftthc roots. Males are comrimon in some bot ri.t
all species and are functional in reproduction ill sWie bur not all
species. Feniah's remain in roots, and each may produce up to
I.000 eggs in a gelatinous matrix that is ofiten pushed out of tie
100t tissue. Eggs hatch inl the gelatinous matrix: young larvae
ererge arnd invade newv sites of tile silare root or new roots.
I)cpendi;, upon hosts, tempera ture, and nematodes species,
geecrathii time is usually 20-60 days.
Epidemiology
In ge.neral. root-knot nematodes reproduce most rapidly,
survive lInger. and cause tile most damage iii coarse-textured
soils. However. tile\t arcapparently limited more by
temperature requirements, which vary with species, than by soil
type. The "northern" root-knot nematode, AM.haplu, has an
optimum temperature of 200C. Other species have higher
temperature requirements and cannot withstand cold
temperature. Hence. root-knot nematodes are of greatest
economic importance in tropical and warm temperate climates
and of lesser importance in northern latitudes and high
elevations of tropical latitudes where soil temperatures are cool.
Because potatoes are predominately grown in tie cooler
climates, root knot of potato is not a major economic problem.
Potato culture in warmer climates could drastically change this
situation. Furthermore. environmental races exist in M.
javanica and possibly iii other species. Such strains could adapt
to cooler climates and cause severe damiage. For example, A'.
incognita has become well established in the nidhill elevations
of lIndia and causes severe damage to potato. Meloidogvnespp.
enhance disease development by other pathogens. On potato.
development of brown rot bacteria ( Pseudo/onaiotros solatracearum)
is enhanced by ,I. incognitaacrita.
,. /
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Fig. 101. Root-knot nematodes (Meloidogynespp.): gallson roots
(A) and tubers (B). (Courtesy P. Jatala)
'A,
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