I - --ii

eduction in the size of the crop's pod-bearing structure and the level of
stored photosynthate. available for pod filling. The influence of both factors
is integrated in the water-use efficiency values which we have shown in the
previous section to be severely reduced in the drier locations.
2. It has been also: indicated in an earlier section that ILC 482 is an earlier
maturing cultivar than ILC 72. This early-maturing characteristic will generally
confer upon IfC 4.82 a yield advantage over ILC 72 under northern
Syrian Mediterrnmean environmental conditions for two reasons. First, early
maturation is achieved without a reduction in the duration of the reproductive
phase which is critical in a crop with a potentially indeterminate growth
habit. Second, as crop evaporative demand increases significantly in the late
spring-early summer period (the period of crop reproductive development),
an early-maturing cultivar will be exposed to less extreme levels of moisture
stress and these will be deferred to a later stage in its phenological developmerit.
Accumulated totals of pan evaporation for the reproductive phases of
the two cultivars (Table 1) show that there was significantly greater potential
evapotranspiration during the reproductive phase of ILC 72 than that
experienced by tLC 482 at all sites.
The beneficial effect of this early maturing characteristic on seed yield was
most clearly demonstrated at B3rida where seed yields in ILC 72 were much
reduced below the values of 0.7--1.00 t/ha which might have been expected to be
obtained from the maximum dryrnotter production achieved (Tables 2 and 7).
This is illustrated by the atypical harvest index values shown by both density
Ireatments. The likely caus, of this reduced seed yields appears to have been
moisture stress induced flower and seed abortion which seems to have been at
supercritical values during the sensitive flowering and early pod formation phase.
Winter-sown ILC 482 appears to have been less affected by this stress as it
retained a higher number of pods per plant and managed to fill almost a0! the
pods set which was quite clearly not the case in ILC 72 (percentage of empty
pods, Table 7). However, the reduction in harvest index in winter-sown ILC 482
at Brida from the values of greater than 0.5 achieved at the other two sites
suggests that a 20% yield reduction occurred even in this cultivar from specific
stresses imposed in Ihe reproductive phase of development. In ILC 72 the data
shown for 100-seed weight in Table 7 further suggest that moisture stress effects
at Brida restricted the adequate filling of pods from either concurrently derived
or translocated photosynthate. As this was not the case in winter-sown ILC 482 it
appears to be further evidence to suggest the beneficial effects of early maturity
which allows escape from the most severe effects of moisture stress.
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