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Grain yield
Mn stress reduced the grain yield to nil in cultivars DWL
5023 and WL 1562 and very poor in cultivars WL 711, WG 377,
KSML 3 and WG 357 (Table 1). Grain
filling was not complete in WG 377. As the differences among
these cultivars were non-significant these were susceptible
to Mn deficiency. Grain yield response increased
successively and significantly up to 20 mg Mn/kg rate in DWL
5023, upto 10 mg Mn/kg in KSML 3, WL 410 and TL 419 and upto
5 mg Mn/kg in WL 711, WG 377, WG 357, HD 2009 and C 306.
Straw yield
In control pots, the straw yield of DWL 5023, WL 711 and WL
1562 was very poor as compared to other cultivars (Table
1). The yield of TL 419 and HD 2009 increased
significantly upto 5 mg Mn/kg-1 but of rest of
cultivars upto 10 mg Mn kg-1.
Harvest index
Harvest index was considerably reduced in highly and
moderately susceptible cultivars which had higher index than
tolerant cultivars when adequate Mn fertilization was
supplied (Table 2). Optimum
harvest index in most cultivars was obtained with 5-10 mg Mn
kg-1 except in DWL 5023 where the response was
upto 20 mg Mn kg-1 indicating a higher
requirement of Mn for reaching the potential yield.
The previous studies also indicated that tolerant cultivars
were not necessarily the highest yielders when adequate
supply of plant nutrients was available (Wegrzyn et
al. 1980).
Increased assimilate production and reduction in
assimilate wastage
The cultivars which are able to reduce assimilate wastage
and have higher efficiencies to allocate assimilates are
likely to show higher harvest indices. Rate of
photosynthesis as measured by POE has already been reported
(Kaur et al. personal communication). The effect on
Mn deficiency on the following parameters was studied:
Number of infertile tillers
The number of infertile tillers is indicative of assimilate
wastage, its magnitude lowering the harvest index of the
plant. In highly susceptible cultivars, the 20 mg Mn
kg-1 application highly increased the number of
infertile tillers (Table 2). Thus
the applied Mn although contributed to increased assimilate
production but also resulted in its wastage because of the
failure of reproductive mechanism in the infertile tillers.
On the contrary, the tolerant cultivars had more infertile
tillers under Mn stress and its alliviation produced more
fertile tillers, thus increasing the ratio of
fertile/infertile tillers resulting in higher harvest
index.
Total number of tillers
The number of tillers formed were significantly less in Mn
Stressed plants of DWL 5023, WL 1562 and WL 711 (Table
3) possibly reducing assimilate production. Application
of even 5 mg Mn kg-1 significantly increased the
tiller number to the level of more tolerant cultivars. The
tiller number had a significant positive relationship in
control plants with straw yield (r = 0.90**) and
grain yield (r = 0.72**). The increased tiller
number obviously increased assimilate production capacity of
the plant.
Average Height of tillers
Tiller height increased significantly with Mn application
especially 10 mg Mn kg-1 rate. The tiller height
was minimum in DWL 5023 especially under Mn stress. It was
significantly related to grain yield in control and 5 mg Mn
kg-1 supplied plants (r = 0.81** and
0.72** respectively) and straw yield in control
and 10 mg Mn kg-1 supplied plants (r =
0.71** and 0.84** respectively).
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