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Anguina Scopoli
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Biology
Nematode galls which fall in soil along with
the contaminated seed at the time of sowing or may be present already
from the previous season, absorb the soil moisture and become soft,
facilitating the release of the second stage larvae. Germination of
wheat seed is always preceded by release of the larvae in the soil7.
Normally, wheat seed starts sprouting within 3 days after planting and
the earliest release of larvae from galls is on the 4th day8.
The larvae enter the seed, both from the brush as well as the embryonic
ends.
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However, the larvae
entering the brush end are not able to reach the embryonic area from
this source. The larvae entering from the embryonic end reach the
embryo within 6 days and thereafter infest the growing point and are
carried mechanically upwards with the growth of the seedling. While
on the growing point, the larvae feed ectoparasitically and enter
endoparasitic mode of life, after about 90 days, invading the floral
primordia developing on the
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apical meristem. Within 3-5 days, the second-stage larvae, in the floral
tissues, become adult males and females through 3rd and 4tb moults. The
adult females lay eggs within 6-10 days and eggs in various
developmental stages as well as the next generation second-stage larvae,
along with males and females, are noticeable during the next 15-20 days
at the green gall stage. Subsequently, the green galls become brown and
later change to black hard galls. These galls may fall in the soil at
harvest and may serve as the source of new infection in the following
season, if wheat is taken in the same field. However, majority of the
galls remain as contaminant of the harvested seed and serve as the
source of new infestation with the use of the contaminated seed for
sowing. The total life cycle period, from second-stage larvae to second
generation second-stage larvae is between 105-113 days10.
Occasionally, the second-stage larvae present on the growing point of
the seedlings may enter the leaf tissues in the early stages or enter
the glumes or awn tissues at the flowering time. Small galls may be
formed in these tissues also but the number of larvae present in such
galls is few. A leaf gall may contain 25 nematodes which may be in
various developmental stages and may include egg-laying female’s also11.
The number of larvae present in the black hard galls ranges 3000 to
30,000 depending upon the size of the galls. The total number of adults
as well as the sex ratio is also affected by the size of the galls. In
large galls (4-6 mm), the maximum number of adults recorded was 81
comprising of 55 females and 26 males. In small galls (up to 2 mm) this
figure was 1I (7 females and 4 males) and in medium sized galls (2-4
mm), the number was 24 (16 females and 8 males). Irrespective of the
size of galls, the female; male ratio was 2:112. However, the
number of larvae "in a very large gall" has been reported up to 90,000".
The viability of the
larvae present in the nematode galls is reported to be quite long,
though actual experiments have not been conducted on this aspect. Live
nematodes from galls stored under
dry conditions for 28 years have been
recorded". According to some other reports, juveniles in the galls can
survive an exposure at -40°C for five minutes and ice embedding for
several days 11+16.
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