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Gary Thompson

Sales of organic foods at retail have grown at rates from 20% to 35% in many countries throughout Europe, Asia, and the Americas during the 1990s. Yet market shares of organic foods remain quite small, less than 5%of retail value in all countries throughout the world. As mainstream retail outlets have begun to carry and promote organic foods, lack of availability of organic foods has become less of an impediment to consumer demand. The major impediment to continued growth in organic food demand is high price premiums for organic foods over conventional food counterparts. Some of the highest price premiums at retail are displayed by fresh and frozen vegetables and fruit; premiums as high as 250% for frozen green peas in the United States have been recorded. Indirect evidence in the form willingness-to-pay studies and retail pricing experiments indicate that the majority of consumers will not pay such high price premiums for organic fruit and vegetables. Small market shares at retail tend to corroborate consumers' willingness to pay such high prices. How much prices of organic fruit and vegetables would have to be reduced relative to conventional produce in order to increase market shares of organic produce is not clear.

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Gary Thompson

Sales of organic foods at retail have grown at rates from 20 to 35% in many countries throughout Europe, Asia, and the Americas during the 1990s. Yet market shares of organic foods remain quite small, less than 3% of retail value in all countries throughout the world. As mainstream retail outlets have begun to carry and promote organic foods, lack of availability of organic foods has become less of an impediment to consumer demand. The major impediment to continued growth in organic food demand is high price premiums for organic foods over conventional food counterparts. Some of the highest price premiums at retail are displayed by fresh and frozen vegetables and fruit: premiums as high as 250% for frozen green peas (Pisum sativum L.) in the United States have been recorded. Indirect evidence in the form of willingness-to-pay studies and retail pricing experiments indicate that the majority of consumers will not pay such high price premiums for organic fruit and vegetables. Small market shares at retail tend to corroborate consumers' unwillingness to pay such high prices. How much prices of organic fruit and vegetables would have to be reduced relative to conventional produce in order to increase market shares of organic produce is not clear.

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Gary Thompson, Russel Tronstad, and Michael Kilby

During the last two decades, per capita consumption of fresh fruit has increased markedly. Although many believe that this increase has been caused by a heightened concern in health and diet, economic analyses indicates that changes in retail prices and increasing per capita incomes adequately explain the increased consumption of fresh fruit. Also, with more single households and women entering the labor force, the convenience factor of focal preparation has likely caused an increase in the consumption of fresh fruit. Substantial substitution between fresh fruit products has occurred: grapes and strawberries have increasingly substituted for citrus fruit, particularly grapefruit. These results suggest that relative prices for fresh fruits, increasing disposable income, and the changing demographic composition of households have prompted observed increases in the per capita consumption of fresh fruit.

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R. Mark Hurley, Paul G. Thompson, and Gary W. Lawrence

A factorial test was conducted to evaluate the potential of screening sweetpotato plants to three pathogens simultaneously. The pathogens were Meloidogyne incognita, Fusarium oxysporum, and Streptomyces ipomoea. The test also involved six sweetpotato cultivars and three evaluation times. Evaluation times were 3, 6, and 9 weeks post inoculation. The symptoms evaluated were vascular necrosis, fibrous root necrosis, and gall and egg mass production. For each of the three pathogens, the ability to separate cultivars with intermediate levels of resistance from those with low levels of resistance decreased as post Inoculation time increased. Simultaneous screening was practical if the goal was to select plants with resistance to all three pathogens. Resistances to individual pathogens could not be identified in plants inoculated with all three pathogens.

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Arthur M. Richwine, Jimmy L. Tipton, and Gary A. Thompson

Shoot cultures of Aloe, Gasteria, and Haworthia species were initiated directly from immature inflorescences. Explants placed on a modified MS medium containing 5.4 mm zeatin riboside initiated shoots within 8 to 12 weeks. Long-term shoot cultures were established and maintained on media containing either 5.4 μm zeatin riboside or 4 μm BA. Shoots easily rooted in vitro, and rooted plantlets were esablished in soil. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (BA); 6-[4-hydroxy-3-methyl-but-2-enylamino]purine riboside (zeatin riboside).

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Kittipat Ukoskit, Paul G. Thompson, Gary W. Lawrence, and Clarence E. Watson

The inheritance of root-knot nematode race 3 [Meloidogyne incognita (Kofoid & White) Chitwood] resistance was studied in 71 progenies of the F1 backcross population produced from the resistant parent `Regal' and the susceptible parent `Vardaman'. The distribution frequency of the progenies measured on total nematode number (eggs + juveniles) indicated a bimodal distribution with a ratio of 4 resistant: 1 susceptible. Based on this phenotypic ratio, the proposed genetic model was duplex polysomic inheritance (RRrrrr = resistant). Bulk segregant analysis in conjunction with the RAPD technique was employed to identify RAPD marker linked to the root knot nematode-resistant gene. Nine of 760 random decamer primers screened showed polymorphic bands. Primer OPI51500 produced a band in the resistant bulk, but not in the susceptible bulk. Estimated recombination frequency of 0.24 between the OPI51500 marker and the root-knot nematode-resistant gene indicated linkage.

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John Klingler, Irina Kovalski, Leah Silberstein, Gary A. Thompson, and Rafael Perl-Treves

Resistance to cotton-melon aphid (Aphis gossypii Glover) segregated as a single dominant gene in a melon (Cucumis melo L.) mapping population derived from the cross `Top Mark' × PI 414723. Sixty-four F2-derived F3 families were used to map the aphid resistance locus, Vat, with respect to randomly amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP) markers. RFLP markers NBS-2 and AC-39 flanked Vat at distances of 3.1 cM and 6.4 cM, respectively. NBS-2 is homologous to the nucleotide binding site-leucine-rich repeat (NBS-LRR) superfamily of plant resistance genes. Another homolog of this superfamily, NBS-5, was positioned ≈16.8 cM from Vat, raising the possibility that Vat resides in a cluster of NBS-LRR paralogs. RFLP marker AC-8, which has similarity to plant lipoxygenases, was positioned at ≈5.5 cM from Vat. Monogenic resistance to A. gossypii has been identified in two sources of melon germplasm, Indian accession PI 371795 (progenitor of PI 414723) and Korean accession PI 161375. To test for an allelic relation between the genes controlling aphid resistance in these two distinct germplasm sources, melon plants of a backcross population from a cross between two resistant lines having Indian- or Korean-derived resistance were infested with aphids. At least 90 out of 92 segregating progeny were aphid resistant, suggesting that the same resistance gene, Vat, is present in both sources of melon germplasm.