Relationship between leaf scorch (diplocarpon earlianum) and yield in strawberry
Mutisya, J M
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The relationships between leaf scorch (Diplocarpon earlianum) and yield were determined on strawberry cultivars differing in their levels of resistance to leaf scorch. During the 1991 season, runner plants of 'Kent' were established in the waiting-bed (WB) system, consisting of twenty four small beds of 50 plants each. In the waiting-bed, plants were inoculated with Diplocarpon earlianum spores at six different concentrations ranging from 0 to 100,000 spores/ml. to produce six different levels of disease severity by the end of the season. Disease was estimated from 28 July to 28 October 1991 at biweekly intervals. Area under a disease progress curve was calculated for each treatment and growth analysis was done. Greenhouse and two field yield trials were conducted in 1992. Post-harvest regrowth was analyzed from the greenhouse plants. The results of this experiment indicated that leaf scorch linearly decreased all the vegetative components measured at the end of the season. Leaf area was the most affected vegetative component. The relationships between disease severity in 1991 and yield and yield components measured the following season on treated plants were quadratically significant and negative. A negative linear relationship was observed between leaf scorch severity and vegetative components measured after renovation. The experiment was repeated in 1992 using 'Kent', 'Jewel', 'Blomidon' and 'Vantage' which differ in their level of resistance to leaf scorch. The treatments were applied as in 1991 except for 'Vantage' which had control and disease level 6 as used on other cultivars. Disease in 1992 was estimated from 28 July to 6 November 1992 at biweekly intervals to establish disease progress curves and calculate area under disease progress curves for each treatment within cultivars. Growth analysis indicated that, in all cultivars except 'Vantage', vegetative components were significantly reduced by leaf scorch. Leaf scorch generally decreased vegetative and yield components of 'Vantage'. The relationship between leaf scorch and yield components was significant and negative in 'Kent', 'Jewel' and 'Blomidon' cultivars. Berry number was the most affected yield component. 'Blomidon' and 'Vantage' demonstrated a higher resistance to leaf scorch than both 'Kent' and 'Jewel' cultivars.