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David W. Ramming

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David W. Ramming

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David W. Ramming

'Galaxy' is being released by United States Department of Agriculture, Agriculture Research Service to provide a fresh market, mid-season peento shaped peach that is larger, firmer and more attractive than 'Stark Saturn'. It ripens in late June in the Parlier area of the San Joaquin Valley of California. It has white flesh that is low-acid, sweet, melting and clingstone.

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David W. Ramming

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David W. Ramming and Owen Tanner

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David W. Ramming and Ronald Tarailo

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Frederick J. Ryan and David W. Ramming

The development of grapevines with berries with small seed traces, so-called seedless grapes, is a costly process. Marker assisted selection would save time and money. Adam-Blondin et al. (Vitis 40:147. 2001) demonstrated that a sequence characterized amplified region, SCC8, could identify seedless grapevine cultivars in European accessions of Vitisvinifera L. We have applied this marker to two populations of grapevines in a breeding program in California. One population consisted of 100 individuals while the second had 109. The two crosses had a common female parent, derived from `Flame Seedless'. Fruit were evaluated over several seasons for parameters including total weight of seeds or traces. DNA was isolated from leaves during the spring. Amplification was carried out with SCC8 primers, followed by digestion with Bgl II, and agarose gel electrophoresis. Individuals were scored as homozygous SCC8+ (small seeded), heterozygous SCC8+/scc8-(intermediate sized seeds), or homozygous scc8-(large seeded) and mean total seed weight per berry was calculated for each genetic class. In the first population, the number of individuals in the inferred genotypes fit an expected 1:2:1 distribution (χ2 = 0.480, P> 0.787) and seed weights for each genetic class were reasonable. For the second population, it was necessary to postulate a null allele in one parent, with a 1:1:1:1 expected distribution for genotypes SCC8+/SCC8+, SCC8+/null, SCC8+/scc8-, and scc8-/null. The actual distribution was in agreement with this model (χ2 = 4.379, P> 0.223). The genotype SCC8+/null had the SCC8+ marker and total seed weight >10 mg per berry. Large seeded individuals and heterozygotes could be reliably identified with this marker.

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David W. Ramming, Richard L. Emershad and Carol Foster

Various in vitro conditions for culture of ovules prior to extraction and culture of immature embryos of peach [Prunus persica (L.) Batsch] and nectarine [Prunus persica (L.) Batsch var. nucipersica Schneid.] were investigated. Culture vessels consisting of test tubes, petri dishes, and polycarbonate jars were tested along with various types of support and nutrient media. Agar support was superior to liquid media with filter paper supports. Agar produced the largest embryos with 90% to 93% being converted into plants compared to liquid with only 1% to 12% embryo conversion. The best ovule orientation and support was with the micropyle down and pushed halfway into an agar-gelled medium. In experiments two and three, test tubes with vertical ovule orientation (micropyle end of ovule pushed into agar) produced larger embryos, the largest plants and the greatest percentage of embryos that converted into plants (60% and 91%). Petri dish treatments were less successful in embryo conversion than test tubes and polycarbonate jars. The addition of activated charcoal (AC) to an agar-gelled medium produced significantly larger embryos with a similar conversion rate. The addition of an agar-gelled medium to culture vessels reduces preparation time compared to filter paper supports, and placing each ovule within a test tube eliminates cross contamination, making immature embryo culture more successful.

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David W. Ramming, Richard L. Emershad and Ronald Tarailo

Hybridizations between seedless Vitis vinifera L. genotypes and V. rotundifolia (Michx.) were made specifically to introgress the seedless trait into the disease-resistant background of V. rotundifolia. The seedless, gynoecious P79-101 was hybridized with three V. rotundifolia parents, producing a total of 102 ovules. From these ovules, 44 embryos developed, producing 20 plants. Isozyme analyses and morphological traits confirmed that 19 of the plants were hybrids. Sixteen were planted in an experimental vineyard at California State Univ. Fresno. One seedling, C41-5, produced seedless fruit that appeared to be stenospermocarpic based on fruit and aborted seed size. Fruit weight was slightly less than that of `Thompson Seedless' (stenospermocarpic) and at least twice that of parthenocarpic fruit of `Black Corinth' and C41-7, a seeded hybrid with many parthenocarpic fruit. Aborted seeds of C41-5 were larger than, but not significantly different from, those of `Thompson Seedless', while parthenocarpic fruit from `Black Corinth' and C41-7 had aborted seeds that were smaller than those of C41-5. Seed weight of C41-7 averaged almost 10 times that of aborted C41-5 seeds. This is the first report of a stenospermocarpic, seedless hybrid of V. vinifera × V. rotundifolia.

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David W. Ramming, Ronald Tarailo and Sayed A. Badr