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Abstract
The control of fruit set and development in strawberries (Fragaria X ananassa Duch.) was investigated by exogenous application of auxins to unpollinated flowers or receptacles from which achenes had been removed. Addition of 2% dimethylsulfoxide (DMSO) to aqueous naphthaleneacetic acid (NAA) sprays or dips increased fruit set from ca. 50% to 100%, thus providing a simple and dependable method to induce parthenocarpic fruit set in strawberries. Strawberry fruits were found to be less sensitive to auxin than coleoptiles when auxin-induced strawberry receptacle growth was compared with corn or oat coleoptile elongation. Suboptimal NAA concentrations induced parthenocarpic fruit set with limited fruit growth. Such fruits remained auxin-responsive and viable for 30-45 days when a second NAA treatment resumed their normal growth and development, thus doubling the life span of strawberry fruit from 30 to 60 days. In contrast, unpollinated flowers treated with optimal NAA concentrations in DMSO behaved like pollinated flowers and ripened within 25-30 days. Fifteen auxin analogs and structurally related non-auxins were tested for their ability to stimulate growth of strawberry receptacles following achene removal. The relative effectiveness of these compounds in inducing receptacle growth was very similar, with a few exceptions, to their relative effectiveness in stimulating corn coleoptile elongation.