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- Author or Editor: Joseph C. Scheerens x
Six strawberry cultivars (`Earliglow', `Honeoye', `Idea', `Jewel', `Northeaster', and `Seneca') were grown organically on three different composts (yard waste, dairy barn waste, and vermicompost). Organic treatments were contrasted against a synthetic fertilizer standard, a conventional pesticide standard and an untreated control. Plots were rated for tarnished plant bug (Lygus lineolaris) damage during the growing season. At harvest, berries were examined for their ascorbic acid levels and total anthocyanin and phenolic contents. Ascorbic acid content of berries in different cultivars and treatments were similar. As expected, fruit anthocyanin and phenolic contents were significantly different among the cultivars, and ranged between 160–230 μg·gfw-1 and 1039–1333 μg·gfw-1, respectively. Among treatments, anthocyanin contents of strawberries were not significantly different, but berries grown on the conventional pesticide standard had 8% to 12% lower total phenolic content than the other treatments. In organic treatments, production of phenolic compounds may have been induced in response to increased tarnished plant bug feeding. This putative biotic stress defense mechanism was seen most dramatically on tarnished plant bugsusceptible cultivars. However, as differences in phenolic levels were greater among cultivars than among treatments, cultivar choice may be a more important consideration than growing system for optimizing antioxidant levels in commercially available fruit.
Identical trials were conducted in a multibay high tunnel and an adjacent open field in southwestern Michigan to compare primocane-fruiting cultivars (Autumn Britten, Caroline, Chinook, Heritage) and floricane-fruiting cultivars (Canby, Encore, Heritage, Nova) of red raspberry (Rubus idaeus). Floricane-fruiting plots of ‘Heritage’ were pruned to produce fruit on floricanes and primocanes (double cropping). The most productive cultivars in both environments were ‘Nova’ and ‘Canby’ (floricane) and ‘Caroline’ and ‘Heritage’ (primocane). These cultivars produced annual yields of 5.5 kg·m−1 row in the tunnel and 2.5 kg·m−1 row in the field. The order of primocane harvest (earliest to latest) was the same in the tunnel and field: ‘Autumn Britten’, ‘Caroline’, ‘Chinook’, and ‘Heritage’. Cultivars with the greatest average berry weight in the tunnel and field were Encore and Nova (floricane) and Autumn Britten and Caroline (primocane). ‘Chinook’ and ‘Autumn Britten’ tended to have the highest incidence of gray mold (Botrytis cinerea) of primocane-fruiting cultivars, but incidence was similar in floricane cultivars. Overall mold incidence was 1% in the tunnel and 13% in the field. Leaf spot (Sphaerulina rubi), cane anthracnose (Elsinoe veneta), spur blight (Didymella applanata), and botrytis cane blight (B. cinerea) were common in the field but absent in tunnel. Phytonutritional analyses of primocane fruit indicated that genotype differences were not consistent across the two environments. Relative cultivar characteristics (harvest season, yield, berry quality) were similar in the field and tunnels, but the tunnel environment tended to increase plant vigor, yield, and fruit quality and suppress several diseases.
We investigated the response of staminate and pistillate floral components of Prime-Jan™ and Prime-Jim™ primocane-fruiting blackberry (Rubus L. subgenus Rubus Watson) to three different growth chamber temperature regimes, 35.0/23.9 °C (HT), 29.4/18.3 °C (MT), and 23.9/12.8 °C (LT). Temperature was negatively related to flower size and morphological abnormalities in floral structures were evident in 41% and 98% of the MT- and HT-grown plants, respectively. The viability (stainability) of pollen from LT- and MT-grown Prime-Jan™ flowers exceeded 70%; that of Prime-Jim™ pollen was significantly reduced (<40%) by the MT regime. Pollen in-vitro germinability was negatively influenced by temperature but was unaffected by cultivar. LT-grown pollen held at 23.9 °C retained 63% of its original germinability over a 32-hour period; the germinability of LT-grown pollen held at 35.0 °C was decreased by 97% from its original level after 16 hours. Virtually all flowers cultured under HT conditions were male-sterile, exhibiting structural and/or sporogenous class abnormalities including petaloidy, malformation of tapetal cells, and microspores or failure of dehiscence. The duration of stigma receptivity, pistil density, and drupelet set were also negatively influenced by increasing temperature; values for these parameters of floral competency among control plants were reduced by 51%, 39%, and 76%, respectively, in flowers cultured under HT conditions. Herein, flowering and fruiting parameters and presumably the yield potential of Prime-Jan™ and Prime-Jim™ were adversely affected by increased temperature. However, assessment of their adaptative response to heat stress under field conditions awaits experimentation.
We investigated the responses of staminate and pistillate floral components of Prime-Jan and Prime-Jim primocane-fruiting blackberry (Rubus L. subgenus Rubus Watson) to three different growth chamber temperature regimens, 35.0/23.9 °C (HT), 29.4/18.3 °C (MT), and 23.9/12.8 °C (LT). Temperature was negatively related to flower size, and morphologically abnormal floral structures were evident in 41% and 98% of the MT- and HT-grown plants, respectively. Anthers of LT- and MT-grown plants dehisced. The viability of pollen (as deduced through staining) from Prime-Jan grown at LT or MT exceeded 70%, whereas that of Prime-Jim pollen was significantly reduced (<40%) by the MT regimen. In vitro pollen germinability (typically <50%) was negatively influenced by temperature but was unaffected by cultivar. Pollen useful life was diminished under HT conditions; LT-grown pollen held at 23.9 °C retained 63% of its original germinability over a 32-h period, while the germinability of that held at 35.0 °C for 16 hours decreased by 97%. Virtually all flowers cultured under HT conditions were male sterile, exhibiting structural or sporogenous class abnormalities including petaloidy and malformation of tapetal cells or microspores; HT anthers that were present, failed to dehisce. Stigma receptivity, pistil density, and drupelet set were also negatively influenced by increased temperature; values for these parameters of floral competency among control plants were reduced by 51%, 39%, and 76%, respectively, in flowers cultured under HT conditions. In this study, flowering and fruiting parameters, and presumably the yield potential of Prime-Jan and Prime-Jim, were adversely affected by increased temperature. However, their adaptive response to heat stress under field conditions awaits assessment.
In addition to their physiological and metabolic roles, anthocyanin (Antho) levels in lettuce contribute to visual and nutritional value-based assessments of crop quality. Although 7 genes are now thought to help regulate Antho synthesis, deposition and/or degradation in lettuce, the genetic and abiotic controls of Antho levels remain less well characterized in lettuce than other plants. Previous greenhouse studies demonstrated that Antho levels in diverse lettuce varieties are a function of temperature and lighting regimen. Here, three strongly related Lolla Rossa-type varieties (`Lotto', `Valeria', and `Impuls') varying in the number of genes controlling intensity of anthocyanins were subjected to differential temperature conditions in growth chambers to better discern the independent and interactive effects of temperature (T) and variety (V) on Antho levels. Fifteen day-old seedlings were placed into one of three chambers maintained at 20 °C day/night (D/N), 30 °C/20 °C D/N or 30 °C D/N. Antho levels were measured in leaf tissue collected 30 d after transplanting. The entire experiment was replicated twice. Although significant, the T x V interaction resulted from differences in the magnitude, not direction, of the change in Antho concentrations among varieties with changes in T. This suggests that T was a main driver of Antho levels in this study. Regardless of V, Antho concentrations were highest, moderate and lowest after growth at 20 °C D/N, 30 °C/20 °C D/N and 30 °C D/N, respectively. Likewise, regardless of T, Antho levels followed the pattern `Impuls' (three genes) > `Valeria' (two genes) > `Lotto' (one gene). Correlations among instrumented and human eye-based evaluations of color are also being tested in samples from both studies.
Anthocyanins (Antho) are the source of red color in plants and the intensity of redness is an important quality parameter in red leaf lettuce. Despite the importance of Antho in leaf lettuce, little information is available regarding the effects of major production-related factors, such as planting date, on their levels. To address this issue, field studies were conducted in 2002 and 2003 in which Antho levels were measured in nine lettuce varieties planted in early and late summer (ES and LS, respectively) using a RCB design. Leaf tissue was sampled 30 d after transplanting. Data for three strongly related Lolla Rossa-type varieties (`Lotto', `Valeria', `Impuls') are reported here. The planting date × variety interaction was significant; however, Antho concentrations were higher following planting in LS than ES, regardless of variety. Planting date effects were more pronounced in 2002, when differences in average daily temperature between ES and LS plantings tended to be larger. Regardless of planting date and year, Antho levels followed the pattern `Impuls' (three genes) > `Valeria' (two genes) > `Lotto' (one gene). Correlations between human visual and two types of instrumented assessments of color are being tested in samples from the same study.
In preliminary studies, we found that relative and absolute antioxidant (AO) levels varied within and among small fruit types. AO levels were affected by assay method used, time of reaction, volume of sample, and the ratio of reactants to total AO activity. To identify the physicochemical parameters that affect accuracy and reproducibility, a series of experiments were conducted to test the roles of AO assay, different AOs, and AO concentration on measured AO content and reaction kinetics. Three assays (DPPH, FRAP, ABTS) were used to evaluate AO capacity of seven fruit types (black and red raspberry, blackberry, strawberry, grape, elderberry, and cranberry) and nine purified AOs (ascorbic, caffeic, chlorogenic, gallic, and ellagic acids, α-tocopherol, trolox, cyanidin-3-glucoside, and quercetin). Ascorbic acid, trolox, caffeic acid, chlorogenic acid, and α-tocopherol exhibited simple reaction kinetics and reached endpoints quickly, regardless of assay. Gallic and ellagic acids, quercetin, cyanidin-3-glucoside, and all fruit extracts exhibited more complex kinetics and long reaction times (>70 min) to reach an endpoint. Moreover, the latter four AOs had the highest AO capacity among the compounds tested. We observed differences in reactivity between assays, compounds and fruit extracts, but relative AO activity was comparable, although the absolute values differed. Since AO capacity of fruit extracts is a composite of the individual AOs present, it is important that reactions progress to near steady state, assay reactants are in excess of (30–50×) the AO capacity being measured, more than one assay is used to describe the total AO activity of fruit samples. Thus, there may not be a single AO assay method that completely defines the AO activity of a given fruit.
Leaf samples collected from field plots of nine lettuce cultivars established in the early (ES) and late (LS) summer of 2002 and 2003 in Celeryville, Ohio, were subjected to spectrophotometric measurement of anthocyanin concentrations or color analysis based on colorimeter and spectroradiometer readings and human panelist ratings. Interactions among year (Y), transplanting date (TD), and cultivar (C) main effects for anthocyanin concentration were significant as a result of shifts in response magnitude but not direction. Anthocyanin levels were higher after LS than ES transplanting regardless of Y and C. The effects of TD were pronounced in 2002, when differences in average daily temperature between ES and LS transplantings tended to be larger. Also, regardless of Y and TD, anthocyanin levels followed the pattern ‘Impuls’ > ‘OOC 1441’ > ‘Valeria’ > ‘OOC1426’ > ‘Lotto’ > ‘SVR 9634’ > ‘OOC 1434’ = ‘OOC 1310’ > ‘Cireo’. Treatment-based color differences were also evident in colorimeter and spectroradiometer readings. Also, panelists differentiated samples grown in 2003 based on red color intensity. Correlations between analytic and instrumented and human panelist-based measures suggest instrumented assessments of red coloration may serve as proxies for direct measures of anthocyanin levels or human panelist ratings, particularly if the aim is to establish color differences between major experimental groups and assign quantitative, repeatable values to red color intensity.
Shading effects on chlorophyll a (ChlA), chlorophyll b (ChlB) and anthocyanin (Antho) concentrations were examined at three developmental stages in four varieties of lettuce (Lactuca sativa) grown under contrasting temperature regimens in the greenhouse. Seedlings were transplanted to pots and grown at 30 °C (86.0 °F) day/night (D/N) (Study 1) or 30/18 °C (86.0/64.4 °F) D/N (Study 2). One-half of all plants in each study were positioned under bottomless shade boxes which reduced incoming light intensity by 50%. Pigment concentrations were measured in leaf tissue 9, 16, and 23 days after transplanting. Each study was repeated twice. Regardless of temperature regimen, variety influenced all pigment concentrations, while shading affected, primarily, Antho concentrations. ChlA and ChlB concentrations were influenced by growth stage. In Study 1, chlorophyll concentrations were significantly greater in `Green Vision' than `New Red Fire' or `Rolina', but not `Galactic'. Also, Antho concentrations were significantly greater in `Galactic' than the other varieties. In Study 2, chlorophyll concentrations were greatest in `Green Vision', with similar concentrations among the remaining varieties. Antho concentrations were greatest in `Galactic', intermediate in `New Red Fire' and `Rolina', and lowest in `Green Vision'. Shading significantly reduced Antho concentrations in `Galactic' and `Rolina' under both temperature regimens and `New Red Fire' at 30/18 °C D/N, but increased Antho concentrations in `Green Vision'. Chlorophyll concentrations tended to decrease with plant age. Pigment concentration data clarified what was apparent to the unaided eye—namely, that the amount and intensity of green and red color varied among plants subjected to different shading and temperature treatments. Therefore, these data may aid in developing strategies to achieve targeted levels of pigmentation (especially red) in lettuce, an important criterion of crop quality and potential market value.