Summer drought is a major factor limiting the regrowth of perennial ryegrass seed
crops. This phase of crop development has a strong influence on seed yield because most
of the tillers that contribute towards next season's seed crop are produced or regrown
during this period. In recent years many seed fields have exhibited premature decline
probably because of extensive drought after harvesting. Therefore, this study was
undertaken to (i) assess how post-harvest leaf and tiller development is impacted by the
timing and severity of water stress and (ii) identify potential relationships of water stress to
flowering and seed yield.
Rain-out shelters were used to exclude rainfall from two cultivars which received
either no irrigation or 2.5 cm of simulated rainfall in mid-August or mid-September or
both. These were compared to an ambient treatment. No rainfall decreased total tiller
production by approximately 30% in 1995 and 50% in 1996. There were also moderate
reductions in tiller dry weight, tiller height, and slight decreases in number of leaves and
the basal diameters. The trend showed that the cultivar Affinity responded quicker to an
early irrigation whereas the cultivar Buccaneer had a longer period of summer dormancy.
Total soluble sugars concentrations increased as tiller number decreased suggesting the
potential for rapid compensatory growth upon alleviation of drought. Limited irrigation
during the post-harvest period of regrowth did not generally affect fertile tiller number nor
seed yields. Fewer vegetative tillers as the stands aged, together with other changes in
plant parameters, may mark the beginning of the dieback problem.
In greenhouse studies, four cultivars were rapidly stressed using vermiculite as a
growth medium. Though little differences were observed among cultivars when
physiological responses were evaluated, stomata' diffusive resistance and leaf temperatures
increased, whereas plant water potential and leaf transpiration decreased as stress was
prolonged. Plant survival following water stress was largely dependent on cultivar and
gravimetric water content of vermiculite. This technique did not reasonably simulate
natural drought conditions in terms of plant physiological performances nor soil
characteristics, but it was useful to differentiate the ability of different genotypes to
survive a drought-induced dieback. / Graduation date: 1998
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33777 |
| Date | 04 November 1997 |
| Creators | Velloza, Theodosius Marmaduke |
| Contributors | Chastain, Thomas G. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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