Runner plant production and the effect of light intensity on flower and fruit development in day-neutral strawberries

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Title: Runner plant production and the effect of light intensity on flower and fruit development in day-neutral strawberries
Author: Cook, Sandra M.
Advisors: James R. Ballington, Committee Chair
Judith F. Thomas, Committee Member
Gina E. Fernandez, Committee Member
Abstract: The development of an economical system for the production of disease-free nursery plants of day-neutral strawberry cultivars is vital for large-scale production in the southeastern United States. This study investigated the effects of plastic mulches, runner harvest method, and deblossoming on runner formation in day-neutral strawberry cultivars at three locations in North Carolina (Laurel Springs, Kinston, and Reidsville) chosen to represent the three major climatic regions. The day-neutral cultivars 'Aromas', 'Diamante', and 'Seascape' were used along with the junebearing cultivar 'Chandler' for comparison. Each cultivar was established in single rows in 20-plant plots with four replications per mulch treatment (black plastic, white-on-black plastic, or bare ground). The experiment was a split-split-split plot design with mulch treatment at a particular location representing the main plot while cultivar, runner harvest method, and flower removal represented the sub plot, sub-sub plot, and sub-sub-sub plot treatments, respectively. Harvest method was runner removal at three-week intervals versus a once-over final harvest. Flower removal was initial flower removal only versus periodic removal. Soil, canopy, and air temperatures along with nutrient status were recorded for comparison. Results showed runner plant yields were similar and higher for Laurel Springs and Kinston than Reidsville. At Laurel Springs the black plastic treatment yielded the most runner plants, while the white-on-black plastic produced the most at Kinston. The day-neutral cultivar 'Aromas' produced runner plants almost exclusively. 'Diamante' produced runner plants as well as fruit, while 'Seascape' produced fruit with little runner plant production. The once-over harvest method resulted in nearly double the amount of runner plants as the intermittent harvest method, and flower removal was impractical. Temperature data revealed that in warmer climates the black plastic was limiting to runner plant production, whereas it increased production in the cooler climate. Conversely, the white-on-black plastic moderated the temperatures in the warmer locations increasing runner plant yields. Petiole analysis indicated locations with the highest runner plant yields also maintained the highest levels of nitrogen. Based on the results, the use of an appropriate plastic mulch chosen according to area climate combined with sufficient nutrient levels can produce acceptable runner plant yields regardless of location. A moderate day-neutral such as 'Diamante' can provide both the runner plant and fruit yields required to support a day-neutral industry in the southeast. The fruit of day-neutral cultivars that develops following dormancy from flowers initiated prior to dormancy are often substandard, while the fruit from flowers initiated following dormancy are of suitable quality. The second study examined the effects of light intensity on floral initiation prior to dormancy and flower and fruit development following dormancy. The experiment was a randomized complete block design with two replications. The day-neutral cultivars 'Seascape' and 'Everest' were potted and grown in one of two chambers receiving 12-hour light (180 or 360 μmol•m-²•s-¹ irradiance) and dark periods. Temperatures were lowered to induce dormancy and later raised to simulate spring growth. Emerging flowers were hand pollinated and resulting fruit was counted and weighed. Misshapen fruit and dead flowers were also counted. The results suggested that the light intensity following dormancy during which the flowers emerged and fruit developed was important in determining both total yield in weight and number of fruit produced. The higher intensity treatment (360 μmol•m-²•s-¹) resulted in significantly higher yields for weight and number of fruit. The number of misshapen fruit was minimal. 'Everest' produced more fruit than 'Seascape' regardless of light treatment. Mature anthers were absent in the first flowers to emerge which may provide an explanation for low quality and misshapen fruit from the first flowers in the spring. Viable pollen was eventually produced suggesting a possible temperature effect.
Date: 2002-09-17
Degree: MS
Discipline: Horticultural Science

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