Fruit quality of 24 selected strawberry cultivars and selections were evaluated. There were great variations in the contents of soluble solids, titratable acidity, carbohydrates, organic acids, and ascorbic acid among different cultivars, reflecting primary genetic differences. Fructose, glucose, and sucrose were found to be the three major sugars, comprising >65% of the total soluble solids in strawberry. Fruit contained lower sucrose compared to fructose and glucose, whereas leaves contained comparable amounts of fructose, glucose, and sucrose. Citric acid was the major organic acid in strawberries. Strawberries were also rich in ascorbic acid. Leaves were much higher in ascorbic acid than fruit. There appeared to be no correlation between fruit and leaves on carbohydrate, organic acid, and ascorbic acid contents.
Shiow Y. Wang, Gene J. Galletta, and John L. Maas
Shiow Y. Wang, Dean Der-Syh Tzeng, and Gene J. Galletta
Foliar application of a mixture of methionine and riboflavin was effective in reducing the severity of powdery mildew [Sphaerotheca macularia (Wallr. ex Fr.) Jacz. F. sp. Fragariae] infection in 72 strawberry progenies and over 110 clonal genotypes. This biocidal activity was enhanced by supplement of copper, iron, and surfactants [such as sodium dodecyl sulfate (SDS), Triton X-100, or Tween-20]. Compounds free radical scavengers (n-propyl gallate, thiourea), or antioxidants (α-tocopherol, -carotene) reduced its biocidal activity. Plants treated with the MR formulation (26.6 μM riboflavin, 1 mM D,L-methionine, 1 mM copper sulfate pentahydrate and 1 mg·ml–1 SDS) or 29% SP formulation of MR (Technical Division of the American Cyanamid Corporation, Taiwan Subsidiary at Taipei) not only showed decreased powdery mildew infection but also showed increased chlorophyll content and leaf area and improved fruit quality. Results in this study suggest that treatment with mixture of methionine and riboflavin is beneficial to strawberry plants and may serve as an alternative to fungicides for controlling powdery mildew.
Shiow Y. Wang, Gene J. Galletta, Mary J. Camp, and Michael J. Kasperbauer
The influence of mulch types (black polyethylene, red polyethylene, and straw-vetch in raised bed hill culture) on the chemical composition of `Northeaster' and `Primetime' strawberry (Fragaria ×ananassa Duch.) fruit and plant parts was evaluated. Ascorbic acid (AA), malic acid, citric acid, and ellagic acid levels were higher in `Primetime' than in `Northeaster' fruits, while `Northeaster' had a higher soluble solids content (SSC). Fruit grown on straw-vetch had lower SSC than did those grown on the polyethylene mulches. The AA content in the fruit of either cultivar was not affected by the mulch treatment. Fruit grown on the straw-vetch mulch had less red surface and flesh color but higher pigment intensity than fruit grown on the polyethylene mulches. Strawberry plants grown on straw-vetch mulch had the largest leaf area and the highest chlorophyll content, while plants grown on red polyethylene mulch had the smallest leaf area and lowest chlorophyll content. There were significant mulch × cultivar interactions in fruit titratable acid (TA) and AA levels, sugars, citric and ellagic acid contents, leaf area and chlorophyll levels, and soluble carbohydrate and starch contents in leaves, petioles, crowns, crown-roots, and roots. TA was highest in `Northeaster' fruit when grown on red polyethylene, whereas TA was highest in `Primetime' fruit when grown on straw-vetch. The highest fruit citric acid levels were found in straw-vetch mulched plots of `Northeaster', and in black polyethylene mulched plots of `Primetime'. Ellagic acid accumulation was highest in `Northeaster' fruit grown on black polyethylene, and in `Primetime' fruit grown on red polyethylene or straw-vetch mulches. Fruit glucose content was highest in `Northeaster', but lowest in `Primetime', when grown on the straw-vetch mulch. There was a general tendency for soluble carbohydrate and starch levels in plant tissues to be lowest when the plants were grown in red polyethylene mulch and highest when grown in black polyethylene mulch. `Primetime' contained higher total carbohydrate levels than did `Northeaster' in all tissues tested.