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Michael J. Havey and Christopher von Kohn

RFLPs and the Ms locus in open-pollinated onion populations J. Amer. Soc. Hort. Sci. 127 944 946 Gökçe, A.F. McCallum, J. Sato, Y. Havey, M.J. 2002 Molecular tagging of the Ms locus in onion J. Amer. Soc. Hort. Sci. 127 576 582 Goldman, I.L. Schroeck

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Ali Fuat Gökçe and Michael J. Havey

Cytoplasmic male sterility (CMS) in onion (Allium cepa L.) is conditioned by the interaction of the male-sterile (S) cytoplasm with recessive alleles at a single nuclear male-fertility restoration locus (Ms). In order to seed propagate male-sterile plants (S msms), onion breeders must identify maintainer lines possessing normal (N) male-fertile cytoplasm and homozygous recessive at the Ms locus (N msms). Molecular markers have been identified distinguishing N and S cytoplasms and closely linked to the nuclear Ms locus. In this study, we evaluated testcross progenies from randomly selected N-cytoplasmic plants from three open-pollinated populations for nuclear restoration of male fertility over at least three environments. The Ms locus and linked restriction fragment length polymorphisms (0.9 and 1.7 cM) were at linkage equilibrium in all three open-pollinated onion populations, indicating that these linked markers cannot be used to identify maintaining genotypes in open-pollinated onion populations. However, cytoplasmic evaluations were effective in reducing the number of testcrosses required to identify CMS-maintaining genotypes.

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M.J. Havey and O.H. Bark

Open-pollinated (OP) onion (Allium cepa L.) cultivars are primarily in normal (N) fertile cytoplasm; however, specific cultivars possess both N and sterile (S) cytoplasm or are exclusively in S cytoplasm. It is unclear whether the presence of S cytoplasm in OP cultivars is due to ancient or recent introduction or both. Restriction-enzyme analysis of the chloroplast DNA established that S cytoplasm has been introgressed into OP onion cultivars since its discovery in 1925. `Valencia Grano' (released in 1927), `New Mexico Early Grano' (1931), `Texas Early Grano (TEG) 502' (1947), and `Temprana' (1979) are in N cytoplasm; S cytoplasm was introduced into the population `TEG 502 PRR', and subsequent selections (`NuMex BR1' and `NuMex Sunlite') are in S cytoplasm. The inbred `TEG 951 C' and `Texas Grano 1015Y' possess a mixture of N and S cytoplasm and, because these two onions originated from self-pollinations of single plants, bulb or seed mixtures or both must have occurred.

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G. Yelenosky, D. Hutchison, and H. Barrett

Ten-month-old seedlings, grown from seed extracted from 22 individual pummelo [Citrus grandis (L.) Osbeck] × trifoliate orange [Poncirus trifoliata (L.) Raf.] citrus hybrid trees that survived -15C freezes near Monticello, Fla., were cold-acclimated in controlled-environment rooms and freeze-tested at -6.7C for 4 h. Freeze damage to open-pollinated progeny was ranked by the number of uninjured seedlings and percentage of leaves killed and wood dieback. Morphological segregation was not associated with differences in freeze survival, and the dominant trifoliate gene was readily evident. Progeny from one tree, identified as 98-71, are considered the most likely candidates for further study in developing cold-hardy citrus trees.

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Mark J. Henning, Henry M. Munger, and Molly M. Jahn

`PMR Delicious 51' is a new and improved version of the `Delicious 51' eastern type melon (Cucumis melo L.). It was developed in the Department of Plant Breeding at the Cornell University Agricultural Experiment Station in Ithaca, N.Y. It is well adapted for northeastern U.S. conditions and shows potential for good adaptation in the northwest. It is well suited for home gardeners, market gardeners, and commercial growers who want to grow an open-pollinated (OP) melon. `PMR Delicious 51' has excellent resistance to powdery mildew races 1 and 2 (Podosphaera xanthi) and resistance to fusarium wilt (Fusarium oxysporum f. sp. melonis) race 2.

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P. Revilla, J.R. Hotchkiss, and W.F. Tracy

Many sweet corn hybrids germinate poorly and have low seedling vigor in cold soils. Sources of cold tolerance and an understanding of its inheritance would benefit sweet corn production. Our objective was to determine the genetics of cold tolerance among open-pollinated progenitors of modern sweet corn. Six open-pollinated sweet corn cultivars were used as parents of a diallel. The 15 crosses plus reciprocals, parents, and checks were evaluated in cold chambers. Growing conditions were 14 hours with light at 14 °C, and 10 hours without light at 10 °C. Days to emergence, percent emergence, shoot dry weight, and root dry weight were recorded. The experiment was repeated in the greenhouse under warm conditions. Variation for cold tolerance was present among the crosses and cultivars. The variation was primarily due to general combining ability (GCA) effects, with specific combining ability (SCA) effects and reciprocal effects being significant for seedling dry mater. `Howling Mob' had significant favorable GCAs for all cold tolerance traits and resulted in the most cold-tolerant hybrids. `Country Gentleman' and `Stowell's Evergreen' were the slowest emerging parents. Days to emergence under cold conditions was not correlated to days to emergence under warm conditions. The correlations between root weight (cold) and root weight (warm) and shoot weight (cold) and shoot weight (warm) were significant, positive, and relatively large. In this material it appears that seedling vigor under warm conditions could be used to predict seedling size under cold conditions.

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S.L. Clark and S.E. Schlarbaum

Progeny from two open-pollinated mother trees were grown for 1 year in a commercial tree nursery in Murphy, N.C. Shade cloths were applied to one half of the seed plots from each mother tree and the other half were exposed to full sunlight. Seedlings were fertilized throughout the growing season to increase growth performance for better discernment of progeny and shade effects. Seedlings in shaded plots were significantly taller and had larger root collar diameters (RCD) than unshaded seedlings. An interaction between progeny and shade effects on first-order lateral root number indicates that genetic or other unknown factors were affecting the seedlings' response to changes in light. Results indicate that the use of shade cloths in nurseries may improve seedling quality of 1-0 sugar maple in the southern portion of the species range.

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Michael J. Havey and William M. Randle

A factorial mating design, using three male-sterile F1 lines in testcrosses with a sample of open-pollinated (OP) onion populations, was used to estimate combining abilities and heterosis for bulb yield, size, storage ability, pungency, soluble solids content (SSC), and water loss after 3 months in storage. Samples of testcross bulbs were flowered and scored for fertility to estimate frequencies of the nuclear allele maintaining cytoplasmic male sterility. General combining ability (GCA) estimates for OP populations (males) were significant (P < 0.05) for yield, SSC, and proportion of bulbs with diameters >7.5 cm. GCA estimates for female testers were significant for storage ability and proportion of bulbs with diameters <5.0 cm. Male × female interactions (specific combining ability estimates) were significant for SSC and storage ability. Our analyses did not reveal any storage population from which inbreds would likely yield significantly better with the male-sterile tester lines. Spanish OP populations tended to produce testcrosses with larger bulbs, lower pungency and SSC, and poorer storage ability. Heterosis estimates were most often significant for yield and SSC; less often for pungency, storage ability, and bulb size; and not significant for water loss in storage. Overall, significant GCA estimates indicate that superior onion inbreds and populations may be developed using recurrent-selection strategies that increase the frequency of desirable alleles with additive effects.

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T.E. Dickert and W.F. Tracy

Heterosis in corn (Zea mays L.) usually results in earlier flowering, larger plants, and increased yield. In extremely early sweet corn the effect of heterosis on flowering time may be reduced or eliminated due to developmental and physiological requirements for vegetative growth before the transition to reproductive phase. The objective of this study was to determine the level of heterosis and the combining ability for flowering time and other agronomic traits in a diallel cross of six very early open-pollinated sweet corn cultivars. The diallel was grown in 1995 and 1996. Hybrids and parents averaged over hybrids differed for silk date, plant height, ear height, 10-ear weight, ear length, and 100-kernel weight but did not differ for row number and ear width. Heterosis for silk date was significant, but the difference between parents and hybrids was very small, 0.5 day. No hybrids were earlier than the earliest parent, and average midparent heterosis was -0.8%. In contrast midparent heterosis was significant and relatively high for 100-kernel weight (10.0%), ear length (12.9%), ear height (8.6%), plant height (9.0%), and 10-ear weight (28.2%). The traits with low heterosis had very high general combining ability/specific combining ability ratios while these ratios were much smaller in traits with high heterosis. Heterosis for many of the traits, including 10-ear weight, was higher than published values. Conversely, heterosis for flowering time was small, compared to other traits in this study and to published values for silk date, indicating that this extremely early germplasm may be at or near the limit for flowering time under the photoperiod and temperatures typical of summer in Madison, Wis. (43.05°N, 89.31°W).

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George E. Boyhan, Suzzanne Tate, Ryan McNeill, and Jeffrey McConnaughey

production may be possible. Breeding vegetables for organic production systems has been limited. Although there are many open-pollinated vegetable varieties, most commercial varieties have been developed for conventional production with an emphasis on F 1