Graduate Thesis Or Dissertation
 

Lodging control and yield enhancement in Morex spring barley with paclobutrazol treatment

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  • Lodging in cereals can cause significant decreases in yield. It is both a problem in susceptible cereal cultivars with a tall-stemmed, weak-strawed growing habit and in lodging-resistant cereal cultivars when they are grown under high-nitrogen, high-moisture regimes. Plant growth regulators (PGR's) are chemical growth retardants that offer a method of lodging control. For the susceptible cultivars that are not amenable to genetic shortening through plant breeding, PGR's accomplish on a seasonal basis what has not been possible through gene manipulation. For cultivars that become susceptible in the high-intensive systems of modern agriculture, PGR's can be integrated into the chemical regime to control the lodging-promoting conditions created by yield-promotion practices. Morex spring barley is a lodging-susceptible cultivar that is tall-stemmed and weak-strawed. This growth habit aggravates the lodging problem when Morex is grown under intensive yield-promoting conditions. In greenhouse and field experiments, chemical control of the Morex lodging tendency was tested with an experimental chemical, Paclobutrazol. Paclobutrazol acts on the endogenous gibberellin hormone system in the plant by inhibiting its synthesis. The chemical's effect on the cereal plant is reported to occur in the internodes which Paclobutrazol shortens by decreasing longitudinal growth and strengthens by increasing transverse growth. Lodging control is realized through height reduction which lessens the torque effect created by the weather conditions that actually cause the event of lodging to occur. Paclobutrazol caused significant shortening of the basal internodes in the greenhouse and field experiments. Uncharacteristic of the expected effect, the PGR did not strengthen the shortened internodes. Specific stem weight and breaking strength values for the treated plants were significantly lower than the corresponding control values. In the field, Paclobutrazol delayed lodging until after the critical lodging period that occurs from approximately 15 days before anthesis to 15 days after anthesis. Lodging control was reflected in yield increases. Treated plots yielded significantly higher than did the control plots. The two high treatments of 800 and 1000 g/ha also yielded significantly higher than did the low treatments of 400 and 600 g/ha. Yield increases in the treated plots can be attributed to improved seed filling given the fact that lodging in the control plots occurred during the period when yield losses are caused by poor seed development. Unfortunately, the data did not give any clear indication of other possible sources of yield enhancement. Beneficial effects of Paclobutrazol on the tillering and inflorescence development that several researchers have reported for the PGR, Chlormequat, were not evident. The experiments showed that Paclobutrazol is effective on Morex spring barley as a chemical lodging control agent and yield enhancer. A clear association of reduced height with lodging control and concomitantly with yield increases was shown by the data. The absence of improved stem strength raised questions concerning the mechanism of Paclobutrazol's effect on the barley species and the possible mechanism of its effect in combination with nitrogen fertility.
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