RA 00015.pdf - OAR@ICRISAT

Nitrogen fixation by the nodules is apparently
adequate for the yield potential of this cultivar at
ICRISAT Center. Farmyard manure treatment
enhanced nodule activity in the early stages, but
had no significant effect on growth or yield.
Seed Size a n d S e e d l i n g Size
The influence of cultivar differences in seed size
on seedling growth were investigated with twenty
cultivars from seeds with 100-seed weights ranging
from 4.5 to 22.2 g. At first there was a close
relationship between seed size and seedling size
with 100-seed weights of up to about 16 g, but as
time went on size of the young plants bore less
relation to the size of the seeds from which they
were derived (Fig 31). The greater "seedling
vigor" of the larger-seeded cultivars could be of
importance when seedlings face adverse conditions-such
as, for example, surface crusts on
Alfisol.
Ovule and Seed A b o r t i o n
The extent of ovule and seed abortion during pod
development in a range of genotypes was estimated.
In some small-seeded cultivars, up to 90
percent of the ovules developed into mature
seeds, but in other cultivars more than half of the
ovules or young seeds aborted. There was a
negative correlation (r = - 0.81**) between the
percentage realization of the potential seed number
and 100-seed weight.
Pod-set
In previous years we found that pods formed in
the later reproductive phase were the same size as
those formed earlier. This suggested that pod-set
was suboptimal. Cultivars in which pod-set is not
limiting yield might be expected to show a decline
in the average weight of late-formed pods, which
would indicate a limitation of nutrient or assimilate
supply. We have compared weights of early
and late-formed pods in more than 30 cultivars;
so far we have found none in which the weight of
the later-formed pods shows a distinct and
significant decline. This type of measurement
seems to be sufficiently simple and reliable for use
in screening large numbers of plants from the
germplasm collection in an attempt to find
cultivars in which pod-set is not limiting the
yield, if such cultivars exist.
Source-sink Relationships
Flower Removal
Experiments were carried out in the field to
extend last year's observations of the effects of
experimentally delayed pod-set on yield. Using
the early and medium-duration cultivars, we
found that when all flowers were removed from
the plants for 1 to 7 weeks, there was no
significant reduction in yield in any of the
cultivars. This ability to compensate so well for
the loss of early formed flowers and pods is
probably of considerable importance in enabling
0.6
0.5
0.4
0.3
0.2
0.1
35
30
26
22
18
14
10
A. 14 days after sowing
B. 56 days after sowing
4 6 8 10 12 14 16 18 20 22 24
Seed weight ( g / 100 seeds)
Figure 31. Relationship between 100-seed weight
and total dry weight of seedling shoots
of 20 pigeonpea cultivars.
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