Results and Discussion Phenological development

When considering all the lines together, the average time taken by the plants to mature increased from 127 to 165 days, as the light intensity was reduced from full sunlight to 20% of that value (Fig. 40.1). This trend was obvious in four of the lines (i.e. Springsure, Toowoomba, Warwick and Coonabarabran), less apparent in the Narrabri line and not apparent in the Moree line. The delay in plant development time, observed under the reduced light intensities, may be the result of reduced photosynthesis, which in turn led to a reduction in the plant growth rate (Monteith and Elson, 1969). The delay in reaching maturity under the 80% light intensity reduction conditions could have a bearing on the survival of A. fatua in the field. Such delays would extend the life of the plant to a period well beyond the time of crop harvest, thus not allowing seed from these plants to be returned to the seed bank. The response observed between the lines was variable, with the Narrabri line showing the shortest delay in plant maturity time (10 days at 80% light intensity reduction), compared with the Toowoomba, Warwick and Coonabarabran lines (~70 days). The overall time taken to mature in full sunlight (—127 days) was comparable with that seen in earlier field-grown plants of the same lines (Armstrong, 1994).

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