Agriculture Reference
In-Depth Information
Steiner in Sherbakoff and Stanlet, 1943;
Praty-
lenchus andinus
Lordello, Zamith and Boock
,
1961;
Pratylenchus penetrans
(Cobb, 1917) Filipjev
and Schuurmans-Stekhoven, 1941;
Pratylen-
chus flakkensis
Seinhorst, 1968; and
Pratylenchus
vulnus
Allen and Jensen, 1951 (Scurrah
et al
.,
2005). In North America,
P. penetrans
is a severe
pest of potatoes, whereas in tropical regions only
P. brachyurus
and
P. coffeae
have a wide distribu-
tion, and both are known to damage potato.
Root-lesion nematodes cause damage by feeding
directly on roots or tubers and moving through
cortical tissues. They are often found associated
with bacterial and fungal infections, causing po-
tato early dying. Generally, plants parasitized by
root-lesion nematodes are stunted and exhibit
pronounced leaf chlorosis and root shedding.
Pratylenchus
spp. cause extensive root cortical le-
sions and produce cortex destruction. Initially,
reddish-brown lesions are caused on the roots,
but these later turn black. On tubers, lesion
nematodes can penetrate through lenticels,
parasitizing the adjacent tissue and producing
lesions of variable size, depending on the popu-
lation level. Small lesions may be confused with
lenticels, but large ones, although superficial,
can affect tuber quality. Infected tubers may
have pimples, pustules, or wart-like protuber-
ances affecting their marketability. Marketed
tubers have a shorter shelf life when infected by
Pratylenchus
spp.
All root-lesion nematodes are endopara-
sitic and migratory. Both juveniles and adults
enter and reproduce in the host roots and
tubers. In general, the
Pratylenchus
life cycle is
similar to that of other PPNs, comprising eggs,
four juvenile stages (J1 through J4), and adults
(Fig. 10.3
). Males are rare in those species that
reproduce by mitotic parthenogenesis, such as
P. brachyurus
, or abundant in amphimitic ones,
such as
P. coffeae
. Eggs are laid singly in the
roots or in the soil.
Kubo
et al
. (2001) reported that
P. brachyurus
,
Pratylenchus jaehni
(
P. coffeae
population K5),
and
P. coffeae
caused brown and round lesions
surrounding the lenticels of tubers of cultivar
Monalisa and cultivar Bintje
(Fig. 10.4
)
, and
reported several degrees of susceptibility in
potato cultivars. In Norway, Holgado
et al
. (2009)
reported that the yield of potato cultivar Satur-
na was reduced by 50% in the area of the field
affected by a large population of
P. penetrans
.
Transect sampling showed plant growth to
be correlated negatively with densities of
P. penetrans
, and suggested a damage threshold
of potato to the nematode of
100
specimens per
Fig. 10.3.
Stained
Pratylenchus coffeae
(n) and
eggs (e) inside the cortical tissues of potato
cultivar Atlantic. (Photo courtesy of C.M.G. Oliveira.)
Fig. 10.4.
Tubers of potato cultivar Monalisa. (a) Healthy, without nematodes; (b) lesions caused by
Pratylenchus coffeae
; (c) lesions caused by
Pratylenchus brachyurus
. (Photo courtesy of R.K. Kubo,
Instituto Biológico, Campinas, Brazil.)
