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Virginia Pinillos and Julián Cuevas

fruits per panicle. Tagged shoots were hand-thinned before bloom at the same load of 12 panicles per shoot. Self-pollination was achieved by bagging shoots individually using tissue paper sacks before anthesis. Open-pollination consisted of the free

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Christopher S. Cramer

This research was funded by the NMSU Agricultural Experiment Station and the New Mexico Dry Onion Commission. Thanks to Petoseed Co., Rio Colorado Seed Co., and Shamrock Seed Co. for the contribution of open-pollinated and hybrid onion

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Suzanne Stone, George Boyhan and Cecilia McGregor

-maintained landraces are favorable sources of genetic variation because they are more adapted to agricultural production than wild relatives ( Villa et al., 2005 ). By their nature, open-pollinated (OP) cultivars maintain greater population-level genetic diversity than

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D.N. Maynard, G.W. Elmstrom, J.K. Brecht and L. Wessel-Beaver

Bush and short-vined calabazas [Cucurbita moschata (Duchesne) Poir.] derived from crosses of `Bush Butternut' with `La Primera' and `La Segunda' followed by several generations of selection and self pollination, are quite uniform in plant and fruit characteristics. Likewise, selfing and selection of vining cultigens has resulted in uniform vine and fruit characteristics. Hybrids between bush/short-vined and vining lines usually retain the plant habit of the bush/short-vined parent, and produce higher yields of fruit with thicker and better-colored flesh than open-pollinated cultigens. Hybrid bush/short-vined calabazas are earlier, have more concentrated fruit set, and utilize space better than open-pollinated cultigens. Commercial seed of hybrids is likely to be more readily available than seed of open pollinated cultigens.

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

Cold tolerance useful for sweet corn improvement may be present in open-pollinated (OP) cultivars. Cold tolerance in sweet corn is the ability to germinate, emerge, and grow under low temperatures. The cold tolerance of 35 open-pollinated sweet corn populations and controls was measured by growing the entries under 14 °C day/10 °C night in growth chambers. The same entries were grown under warm (24 ± 2 °C) conditions in a greenhouse. Traits measured included percent and time to emergence, seedling color, and seedling root and shoot dry mass. Respective repeatability estimates calculated from mean squares were 0.08, 0.33, 0.33, 0.50, and 0.60 for these traits. Entries were ranked separately in each environment based on their performance using a rank-summation index. Differences in cold tolerance existed among the entries. Emergence ranged from 75% to 100% among the entries, with a mean of 90.9%. Time to emergence ranged from 16.2 to 21.9 d, with a mean of 18.2 d. Root and shoot mass ranged from 0.07 to 0.27 g/plot and 0.07 to 0.24 g/plot, respectively. Correlations among the traits measured were favorable, permitting simultaneous improvement. The rankings between the warm and cold environments were significantly correlated (r = 0.67***), indicating that some entries that performed well under low temperatures also performed well under warm conditions.

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Pedro Revilla and W.F. Tracy

Heterotic patterns in sweet corn are weakly defined. Most sweet corn inbreds are descended from three open-pollinated cultivars: `Golden Bantam', Stowell's Evergreen', and `Country Gentleman'. Heterotic and phylogenetic relationships among these three cultivars and others are not clearly known. This investigation was designed to investigate the heterotic patterns among some historically important open-pollinated sweet corn cultivars: `Country Gentleman', `Golden Bantam', `Lindsey Meyer Blue', `Stowell's Evergreen', `Howling Mob', and `Pease Crosby'. The 15 possible hybrids from the diallel cross plus the 6 parents were grown in midspring and late summer plantings. Heterosis and combining ability effects were estimated for 13 traits. Hybrid × planting date interactions were significant for most of the main traits, hence, planting dates were analyzed separately. Average midparent heterosis for grain yield was 29.17% in the first planting date and 57.04% in the second planting. Midparent heterosis for yield and plant height were highest for hybrids with `Country Gentleman' as a parent. `Stowell's Evergreen' when crossed to `Pease Crosby', `Lindsey Meyer, and `Golden Bantam' exhibited high heterosis. The two late-maturity cultivars `Country Gentleman' and `Stowell's Evergreen' had higher general combining ability than the four early-maturity cultivars for most traits. Specific combining ability was seldom significant. Yield of `Country Gentleman' hybrids averaged over all crosses and planting dates was the highest. These data indicate a strong heterotic pattern—`Country Gentleman' × `Pease Crosby', `Golden Bantam', and `Lindsey Meyer Blue'—and a weaker one—`Stowell's Evergreen' × `Pease Crosby', `Golden Bantam', and `Lindsey Meyer Blue'.

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Pedro Revilla and W.F. Tracy

Sweet corn is one of the most important vegetable crops in the United States, however the morphology and phylogeny of open-pollinated sweet corn cultivars has not been studied. Fifty eight open-pollinated sweet corn cultivars were characterized with thirty-four descriptors to provide information for breeders interested in broadening the genetic base of sweet corn. Principal component analysis and cluster analysis were performed to classify sweet corn cultivars based on morphology. Also, relationships among morphological variables in this set of cultivars were determined. The general ordination of cultivars followed an axis representing earliness, and plant, leaf, and tassel size, while ear and kernel attributes were less variable. The morphological variability among all of the widely used sweet corn cultivars, except `Country Gentleman', was not greater than the variability found among the `Golden Bantam' strains. Based on morphology, 52 of the cultivars could be considered as one race, which we propose be called `Northeastern Sweets'. These may be a subset of the race `Northern Flint'. Five of the remaining cultivars are from the north-central or southwestern United States and may represent races from those areas. The sixth cultivar is `Country Gentleman', a commercially important sweet corn cultivar. Due to the importance of `Country Gentleman' and the introgression of nonsweet germplasm into modern sweet corn, we believe that sweet corn should be defined based on its use as a vegetable and on the presence of one or more genes that increase sugar levels in the endosperm.

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Ibrahim Duman, Eftal Düzyaman, Dursun Esiyok, Hüseyin Vural and Semih Erkan

In contrast to developed countries open-pollinated (OP) processing tomato cultivars still have a certain market value in Turkey. A total of 26 subpopulations of 6 different OP cultivars (9 of Rio Grande, 5 of Rio Fuego, and 3 of each of C-37, Interpeel, T2 Improved, and VF 6203) were evaluated in two experimental sites in Marmara Region and Aegean Region. A high degree of phenotypic variance for yield (kg/plant) was found for most subpopulations which revealed the variation for yield amongst individuals, and hence the possibility to select for superior plants. Eighteen populations were developed by two cycles of mass selection conducted within the initial populations in both regions. Most progeny populations significantly exceeded their source cultivars in yield. Heritability estimates occurred generally parallel to that of yield increases of the progenies, which were slightly higher in the Karacabey trial (Marmara Region) as compared to the Muradiye trial (Aegean Region). Results were discussed from the point of view of the resource-poor farmers conducting low-input agriculture.

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Christopher S. Cramer*

Heritability estimates of bolting percentage (BP), pink root (PR) and Fusarium basal rot (FBR) incidences, and percentage of single centered (PSC) bulbs were calculated for an intermediate-day, open-pollinated onion population using selection response and half-sib (HS) family analyses. BP was determined by counting the number of seedstalks per plot when the population was seeded at an earlier planting date to induce bolting. PR and FBR incidences were determined by rating 30 bulbs/plot for the severity of PR and FBR, and calculated an incidence rate from the number of infected bulbs out of 30 rated. The PSC bulbs was determined by cutting transversely 30 bulbs at the vertical center of the bulb and looking for the presence of a single growing point or multiple growing points within 1.3 cm from the center of the bulb. Families were also evaluated for bulb quality that consisted of shape, size, maturity, firmness, number of scale layers, and dry outer scale thickness, adherence, retention, and color. Families were selected based upon an index that equally weighted BP, PR and FBR incidences, PSC bulbs, and bulb quality. No progress was made for BP even though the narrow sense heritability (h2) estimate was 0.51. PR and FBR incidence was reduced by 18% and 12%, respectively, and realized heritability (RH) estimates of 0.65 and 0.60, respectively, were calculated. h2 estimates calculated through HS family analysis was 0.46 and 0.37, respectively, for these two traits. Very little progress was made for the PSC bulbs and this was reflected in a RH estimate of 0.17. However, the h2 estimate was 0.71, suggesting that progress should be possible.

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Michael J. Havey

selection of maintainer lines after crossing (i.e., at maximum linkage disequilibrium), they may not be in linkage disequilibrium with Ms among plants from open-pollinated (OP) populations ( Gökçe and Havey, 2002 ). Yang et al. (2012) identified two