|
|
Home
> Plant
Diseases
>
The Genus Meloidogyne Goeldi
>
Morphology
Morphology
The species of
Meloidogyne are usually differentiated on the basis of the
morphological and morphometric characters of stylet, second-stage
larvae, females and males. The perineal pattern of the females however,
has been traditionally depended upon for identification of species. The
four most common species, viz., M. incognita, M. javanica, M. arewia
and ,M. hapla have been differentiated additionally on the
basis of female, male and larval morphology.
|
In
addition to conventional morphological characters, recent emphasis
has shifted to the use of electro phoretic analysis _of enzyme
phenotvpe for the identification of species or biological races.
Three of the four major species have been identified with a high
degree of accuracy on their esterase phenotype. For instance, all
the populations of M. javanica are characterized in having
three esterase bands which are unquestionably highly
speoies-3pecific. M. incognita
exhibits a
distinct phenotype designated. Likewise, all the populations
of M. hapla have esterase phenotype designated as Hi. The
fourth major species, M arenaria is not associated with any
particular esterase phenotype. Malate dehydrogenase and glutamate
oxaloaeetate transaminase phenotypes are also useful in separating
M. hapla from other major species.
|
|
There is a
strong sexual dimorphism exhibited by the members of the genus. The
males are vermiform, generally 1400 X 30um, while the adult females are
pear shaped (pyriform) and measure about 700x400Mm. The outermost layer
of the body wall is formed by non cellular, elastic, basically triple
layered cuticle, which is secreted by the underlying hypodermis. It
maintains the body shape against body turgot, helps in locomotion and
protects the internal systems from physical, chemical and biological
forces. Externally, the cuticle bears several markings which are helpful
in toxonomy.
In the female,
the transverse annules are present in the anterior region, become
shallow and sparse and gradually disappear in the anterior middle region
of the body. These reappear in the posterior portion forming finger
print like perineal pattern around the tail terminus, anus and vulva.
There patterns are typical of each species. Remnants of lateral fields
may be visible interrupting the transverse anoules in the anterior
regions.
The openings
of the phasmids in juveniles and females are usually hidden by the
annulations or aerolations in the lateral field. In females, the
phasmids are visible between tail tip and anus in the perineal pattern,
while in males the slit like phasmidial openings. are located within the
inner ridge of the lateral field, at I he level of cloacal openings.
The
oesophagus is typically tylenchoid with procorpus, valvated metacorpus,
isthmus and three'well developed oesophageal glands, usually extending
ventrally. Tbe duct from the dorsal gland joins the lumen of the
pracorpus close behind the knobs while those from subventral gUnds join
in the metacorpus. Tbe intestine joins the isthmus where pair of
specialized oesophago-intestinal cells (cardia) is present.
The
preparasitic larva has a small genital primordium comprised1
of two small flat somatic cells and two large spherical germinal cells.
The primordium enlarges after feeding begins and also during moults,
finally giving rise to a pair of prodelphic ovaries in females-and a
single testis in male. Two anteriorly directed testes may b&
present in some males formed after sex reversal under environmental
stress. Most species of Afeloidogyne are able to reproduce
pflrtheno-genetically as well.
The eggs are
about 40 pm in diameter and 90-100 pm long, ovoid bodies.
The egg shell is triple layered, outer vitelline, middle chiitinous and
inner glycolipid, which are secreted by the different parts of the
uterus. The eggs are highly resistant to chemicals and environmental
stress and have special significance in survival and persistence of the
population.
|
