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S. H. Hulbert and T. J. Orton

Abstract

Fourteen hybrid progenies from a diallel cross of 6 commercial broccoli (Brassica oleracea var. italica) inbreds were grown at 3 locations on 3 planting dates. The hybrids were compared for uniformity and for the average number of days to maturity. The earliness of the hybrids was predicted from the performance of the parents while their uniformity was not. Genotype × environment interactions accounted for 44.4% of the total variation in plot uniformity and indicated that replication over planting dates and locations is valuable when screening for stable and uniformly maturing hybrids.

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P. E. Hansche, C. O. Hesse, and V. Beres

Abstract

Estimates were obtained of the means, variances, and heritabilities of 10 commercially important traits from approx 200 parents and their more than 2,000 offspring observed over a period of 8 years. After adjustment of measurements for the effects of yearly variations in climate, heritabilities were found to be very high for ripe date; high for bloom date, amount of bloom, fruit length, suture, and cheek; modest for fruit firmness and acidity; and low for percent soluble solids and crop. The implications of these results on the design and execution of breeding programs in such crops are discussed.

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Helen Beaufort-Murphy

Yield and insect damage of 50 potato cultivars, representative of genetic variation found in CIP germplasm collection, were evaluated over two years in a wide range of environmental conditions throughout Peru, from 4°S to 17°S, including coastal desert, cool highland and humid jungle, at altitudes from 180m to 3280m. Storage root and foliage yields were related to maximum and minimum temperature, photoperiod, precipitation, soils, and insect damage. Genotypic yield varied considerably from one location to another. Jonathan (Peruvian cultivar) produced well in Cañete (coastal desert) but not in the jungle or highlands. Jewel (US cultivar) produced well in Yurimaguas (jungle) but not in coastal deserts. Pesticides were not used but several cultivars had little or no insect damage, others were badly damaged. Some cultivars produced a reasonable yield over a wider range than did others. Results suggest that a cultivar can be strongly adapted to a particular set of environmental conditions. Data provide valuable information for growers-breeders.

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E.W. Stover and D.W. Greene

Plant response to foliar application of plant growth regulators (PGRs) is often variable, in part due to environmental factors. Weather prior to application is thought to influence cuticle development and thus PGR uptake. For example, in growth chamber studies foliar uptake of 1-naphthaleneacetic acid (NAA) is sometimes increased when fruit trees are placed in low temperature and high humidity several weeks prior to application. Environmental conditions over an extended period of time after application may influence PGR conversion to active form (e.g., ethephon), PGR metabolism, or metabolic factors that affect PGR activity in the plant. The effects of environmental conditions on PGR uptake have been investigated extensively in laboratory studies. In many cases, uptake is clearly increased by high temperatures immediately after application. Laboratory studies report a linear positive correlation between temperature and uptake and greater temperature response above 25 °C (77.0 °F). High humidity and longer drying time often are also reported to increase PGR uptake in laboratory studies. These results are consistent with many grower observations on effects of weather on chemical thinning and have been incorporated into many product labels and extension recommendations. However, relatively few field experiments have been reported in which the relationship between PGR response and environmental conditions were assessed. Wash-off studies have demonstrated that rain shortly after application may reduce efficacy of NAA. Several studies demonstrate environmental interaction with metabolic activity involved in PGR action. For example, shading after thinner application is reported to increase fruitlet abscission and enhance effectiveness of some thinning agents. Chemical thinning of apples (Malus ×domestica) with ethephon is reported to correlate strongly with temperature in the days after application, while studies suggest that higher temperatures after aminoethoxyvinylglycine (AVG) application may reduce control of preharvest drop. However, the stage of fruitlet development at apple thinning often appears to be more important than environmental conditions at the time of PGR application. In addition, field experiments indicate that longer drying times at lower temperatures seem to largely compensate for greater uptake rates at higher temperatures. This paper discusses data from published and previously unpublished experiments in order to understand the effects of environment on PGR response variability.

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Mark K. Ehlenfeldt, James J. Polashock, Allan W. Stretch, and Matthew Kramer

Mummy berry (Monilinia vaccinii-corymbosi) is an important disease of cultivated blueberry (Vaccinium spp.). The disease has two distinct phases: a blighting phase initiated by ascospores and a fruit infection stage initiated by conidia during bloom. In this study, we investigated, in a nursery setting, blueberry cultivar resistance to both phases of the disease and, using multiple “standards” with a range of susceptibilities, examined, over 9 to 12 years, factors affecting disease incidence in controlled inoculations. The analyses of our data show that a minimum of 8 years of testing is necessary to obtain stable rankings of cultivar susceptibility for the fruit infection phase of the disease. Insufficient years of data were available to estimate this for the blight phase. Eight years are necessary largely as a result of uncertainty arising from the large environment × genotype interaction, estimated to be more than double any other source of observed variation, other than that resulting from sampling/individual plants. For individual cultivars, temperature and the amount and frequency of precipitation in January to March (when neither plant nor pathogen were presumed active and when both were in cold frames somewhat protected from environmental conditions) were predictive of later disease incidence. For most cultivars, the same weather variables at the same time period were found to be predictive for independently modeled cultivars. Additional cultivars, with only a few years' data, were grouped with the standard with which they shared similar environmental (year) responses and possibly similar disease predictive models.

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Kevin A. Lombard, Emmanuel Geoffriau, and Ellen B. Peffley

Because of potential benefits on human health, the content of quercetin, the major flavonol found in onion (Allium cepa), could become a selection trait in breeding programs. Total flavonol concentration in onion was examined by spectrophotometric analysis at 374 nm in three long-day hybrid cultivars grown at three locations (Parma, Idaho; Grand Rapids, Mich; Elba, N.Y.), and in three shortday hybrid cultivars grown at one location in Georgia in three different fields. Mean total flavonol concentrations for long-day hybrids ranged from 176 to 232 mg·kg-1 (ppm) fresh weight and 110 to 173 mg·kg-1 fresh weight among short-day cultivars. No significant effect of location (state or field) was detected (P > 0.05). A significant (P > 0.05) cultivar by field interaction was detected in the short-day experiment, with the hybrid `Sweet Vidalia' showing significant differences among fields. Overall, our results suggest that quercetin content in onion, as expressed by the total flavonol content, does not vary depending on the growing origin, and therefore could be evaluated effectively in breeding or commercial material.

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Xin Zhao, C.B. Rajashekar, Edward E. Carey, and Weiqun Wang

Demand for organically grown produce is increasing, largely due to concerns of consumers about health and nutrition. Previous studies have not shown a consistent difference of essential nutrients, such as vitamins and minerals, between organic food crops and the conventional counterparts. However, to date, little consideration has been given to phytochemicals, secondary plant metabolites with potential health-promoting properties. We first discuss factors that can infl uence the levels of phytochemicals in crops, and then we critically review the results of published studies that have compared the effects of organic and conventional production systems on phytochemical contents of fruit and vegetables. The evidence overall seems in favor of enhancement of phytochemical content in organically grown produce, but there has been little systematic study of the factors that may contribute to increased phytochemical content in organic crops. It remains to be seen whether consistent differences will be found, and the extent to which biotic and abiotic stresses, and other factors such as soil biology, contribute to those differences. Problems associated with most studies tend to weaken the validity of comparisons. Given the limitations of most published studies, needs for future research are discussed.

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J. Pieters, B. Van Assche, and A. Buekens

The solid waste streams specific to soilless horticulture (substrate slabs, propagation cubes, and plastic films to cover the soil and to wrap the substrate slabs) were determined quantitatively and qualitatively, while methods to reduce these waste streams without yield loss were evaluated in a case study applied to the Flanders region of Belgium and based on an explorative inquiry among horticulturists. Rockwool used for substrate slabs and propagation cubes was found to be by far the most important waste stream. The use of long-lived, polyurethane (PUR) slabs could reduce the total slab waste stream by ≈90%. Moreover, if substrate blocks are used instead of slabs, this reduction could even increase to 95%. The introduction of new cultivation techniques could further reduce the required volume of substrate slabs. Rockwool propagation cubes could be successfully replaced with peat pots that can be composted after 1 year of use. The reuse of plastic films to cover the soil or to wrap the substrate slabs cannot be considered because of the danger of plant diseases. Due to the susceptibility of these films to contamination, they cannot yet be recycled on a large scale. The use of thinner films and the cultivation on profiled concrete floors were found to allow drastic reductions (of up to 80%) of the quantity of plastics used.

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Richard L. Hassell, Jonathan R. Schultheis, Wilfred (Bill) R. Jester, Stephen M. Olson, Donald N. Maynard, and Gilbert A. Miller

The goal of this study was to evaluate miniwatermelon (Citrullus lanatus) cultivars/experimental hybrids (cultigens) for yield, quality, and adaptability in various growing environments. Eighteen cultigens were evaluated in field locations at southern Florida (Bradenton), northern Florida (Quincy), central South Carolina (Blackville), coastal South Carolina (Charleston), and eastern North Carolina (Kinston). Fruit at each site were harvested when watermelons in several plots were at market maturity. Fruit were categorized as marketable if they weighed between 3.0 and 9.0 lb. Fruit were categorized by size as follows: ≤3.0 lb (cull), 3.1–5.0 lb, 5.1–7.0 lb, 7.1–9.0 lb, and ≥9.1 lb (cull). Fruit were graded according to U.S. Department of Agriculture (USDA) grading standards for all watermelon fruit. We found that eight cultigens (Meilhart, Petite Perfection, Precious Petite, Little Deuce Coupe, RWT 8162, Master, Bibo, and Vanessa) were consistently among the top yielding and four cultigens (HA 5138, HA 5117, Petite Treat, and Valdoria) were consistently among the lowest yielding. These had a consistent yield response regardless of location. Within the small marketable melon category (3.1–5.0 lb), ‘Bibo’, ‘Precious Petite’, and RWT 8162 produced a uniform fruit over the five locations. Within the medium marketable melon category (5.1–7.0 lb) ‘Meilhart’, ‘Little Deuce Coupe’, HA 5109, ‘Xite’, ‘Mohican’, SR 8101, and ‘Vanessa’ produced uniform fruit size over the five locations. HA 5117, HA 5109, ‘Extazy’, ‘Mohican’, ‘Petite Treat’, and ‘Valdoria’ produced more fruit in the larger category. Those cultigens that produced melons that were consistently >9.0 lb were HA 5138, HA 5117, Bobbie, and Valdoria. The larger USDA marketable class (7.1–9.0 lb) was considered too large to be in the miniwatermelon market. We found five cultigens that provided consistently high soluble solids readings at each location: Master, RWT 8162, Betsy, Bobbie, and Bibo. We sampled only five fruit at each location for internal quality, and found dark seeds in all of the cultigens in at least one of the locations. Rind thickness and fruit shape did not appear to be influenced by test site location.

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Oved Shifriss

Abstract

Squash (Cucurbita pepo L.) cultivars are monoecious. A phenotypically sensitive gynoecious line, NJ34, was developed through crosses of 3 monoecious inbreds and selection for increasing number of pistillate flowers in plants of several filial generations. NJ34 consists of female and predominantly-female plants under conditions favoring strong male expression. Predominantly-female plants differentiate sporadically 1–3 staminate flowers. The proportion of females is estimated at over 50% with a potential increase of up to 100% under conditions favoring strong female expression. The data show: 1) that NJ34 is later in time of flowering than its monoecious parents, 2) that its females can be converted into monoecism by spraying with an aqueous solution of 250 ppm GA3, and 3) that this line carries gene B for precocious fruit pigmentation.