Economic yield in cereals results from the build up of dry matter
in the grains which depends upon potential assimilation Of
C02 and accumulation of photosynthates during the grain
filling period. This further depends upon absorption of solar
radiation by the green photosynthetic organs of the plant. In wheat
major photosynthetic structures are the leaves; specially the flag
leaf. Mostly the lower leaves are shaded by the upper leaves and thus
maximum solar absorption occurs in flag leaves.
Photosynthates deposited in wheat grain are translocated from major
sources which are closer to, i.e. from the nearest green parts
including awns and flag leaf. Then from other green leaves and
photosynthetic tissues including leaf sheath and stem itself. The
lower leaves supply the needs of lower parts; stem and roots (Lupton
1966; Wardlaw 1968). However, if the top leaves are removed, the
lower ones will supply assimilates to the grain, and similarly if the
lower leaves are removed, the flag leaf becomes the major transporter
of assimilates to stem and roots as well (Marshall and Wardlaw 1973).
How much these structures contribute to final grain weight depends
upon the environment and genetic potential of the species.
Awns, flag leaf and the very next lower leaf (which is generally a
3rd nodal leaf) are the potentially efficient photosynthetic organs
in terms of economic produce of the wheat plant. Of these maximum
contribution occurs from the flag leaf. Awns also contribute to the
spike, nevertheless, this contribution is not significant. The
photosynthetic output of the 3rd and other lower leaves is of
significance for the vegetative lower portion of the tiller. However,
if the upper leaf, the flag leaf, becomes non-functional (removed or
fallen) they also contribute to the grains in spike. The main
economic traits which are directly influenced by the non-functioning
of the photosynthetic organs include seed set, grain number and grain
weight which ultimately produce integrated effects on the total grain
yield.
Wheat developed with greater yield has an increased partitioning of
photosynthates from upper leaves (Evans and Dunstone 1970).
Increasing photosynthesis of small grain heads (spike of wheat) could
also increase yield. Therefore awned wheat lines will outyield the
awnletted lines under semi-arid or and environments (McDonough and
Gauch 1959). Therefore awn removal can also decrease yield as much as
21% (Saghir et al. 1968). However, awns have shown no yield advantage
in humid climates, possibly because of an increased susceptibility of
disease or lodging (Mckenzie 1972). Kramer and Didden (1981)
considered that awns did not contribute directly to yield but that
the effect was through linked genes.
Effect of flag leaf removal has been reported primarily in terms of
reduction in grain yield. Duwayri (1984) reported 10.7% reduction in
grain yield after flag leaf removal. Singh and Singh (1984) reported
that contribution of flag leaf towards grain yield is 17.3%. A loss
of grain yield up to 15-25% has been reported by Natt and Hofner
(1987) and 16.13% by Mahmood et al. (1991).
This study was conducted to determine the effect of the removal of
main photosynthetic parts of wheat plant on some of the yield related
characters in two cultivated varieties.