Strawberry Receptacle Growth and Endogenous IAA Content as Affected by Growth Regulator Application and Achene Removal

Abstract

Abstract Parthenocarpy was induced in emasculated strawberry (Fragaria × ananassa Duch.) flowers with aqueous solutions of 10−3M NAA, GA3 or GA4+7 in 2% DMSO plus 0.1% Tween 80. All fruit except those treated with NAA stopped growing within 12 days of treatment. Repeat application with NAA or GA4+7 20 days after initial treatment stimulated continued growth of NAA-induced fruit, but had little or no effect on growth of GA4+7-induced fruit. The diameters of mature parthenocarpic fruit ranged from 70% to 90% of that of pollinated fruit. Achene removal 12 days after pollination greatly reduced subsequent growth of receptacle tissue, complete removal being more effective than partial removal. Following achene removal 16 days after pollination, treatment with aqueous solutions of NAA in 2% DMSO and 0.1% Tween 80 produced receptacles 75% the size of controls with intact achenes, but neither GA3 nor GA4+7 stimulated growth. Achene removal 24 days after pollination did not influence further receptacle enlargement. Concentration of free indoleacetic acid (IAA) in NAA-treated fruit was 5-times that in controls and 3-times that in GA4+7-treated fruit 6 days after treatment. By 14 days after treatment, the levels had declined in all treated fruit. Free IAA concentration in the receptacle tissue of intact fruit was nearly equal to or greater than that in achenes 14 days after pollination. The growth rates of receptacles were positively correlated with numbers of intact achenes and free IAA content of the receptacle. Chemical names used: naphthaleneacetic acid (NAA); gibberellins (GA3 or GA4+7); dimethylsulfoxide (DMSO)