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Average height of top tiller (Plant height)
Plant height was depressed in Mn deficient plants and
removal of stress increased it significantly (Table
3). The maximum height was obtained in taller cultivars
HD 2009 and C 306. Thus potential tallness appeared to be
related to Mn stress tolerance in wheat. Effect of Mn was
more pronouned on the growth of the top tiller in comparison
to younger tillers. However in different Mn rates, the
differences were insignificant except in highly susceptible
cultivars DWL 5023 and KSML 3 which had significant increase
even with 20 mg Mh kg-1. The plant height was
positively related to grain and straw yields (r =
0.84** and 0.80** respectively).
The height of tillers, likely to contiribute towards
increased assimilate production for grain, seemed to have
acted as a secondary sink for assimilates, contributing more
towards straw yields.
Sink capacity
If the assimilates are not limiting the sink capacity
determines the ultimate grain yield. The sink capacity
comprised of the interaction of the following factors:
Number of spikes (ears)
The spike number (number of fertile tillers) was very low in
control plants of DWL 5023 - the only spike produced was
devoid of grains (Table 4). The
spike number was poorly related to straw and grain yields
and thus did not serve as a good indicator of grain yield as
the size of the spike and grain number in each differed
widely.
Average spike length
Under Mn stress the spike length was very small in DWL 5023
but increased significantly with 5 mg Mn/kg application, but
the differences between Mn rates were non-significant
(Table 4). The grain yield was
poorly related to spike length in control, implying
possibilities of both impaired grain development as well as
grain filling. However, in 5 and 10 mg Mn kg-1
supplied plants the grain yield was related to average spike
length.
Number of grains in the top spike (Number of flowers
fertilized)
The average number of grains was very significantly
decreased with Mn stress, and these strikingly and
significantly increased when Mn stress was removed
(Table 5). All the cultivars
produced maximum number of grains at 10 mg kg-1
Mn rate of application except DWL 5023, KSML 3 and C 306
which gave maximum grain number at 20 mg kg-1 Mn
rate. The average grain number was highest in cultivar WG
377 followed by WL 711, WL 410, HD 2009, TL 419, WL 1562, C
306, KSML 3, WG 357 and DWL 5023 in decreasing order.
The highly susceptible DWL 5023 and moderately susceptible
WL 1562 did not produce any grains under Mn stress. Failure
to set grains in these cultivars could be ascribed to a
single or a combination of the following factors:
a) Interruption of sink capacity
b) Improper translocation mechanism
c) Scarcity of leaf photosynthates
d) Infertile pollen/nondehiscence of anthers
e) Non-receptive stigmas
f) Absence of fertilization
g) Non-viability of embryos
h) Deficiency of growth regulators/ accumulation of
inhibitors of cell division
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