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Jose Lopez-Medina, James N. Moore, and Ronald W. McNew

Inheritance of the primocane-fruiting (PF) characteristic was studied in seedling populations of tetraploid (4x) blackberries (Rubus subgenus Rubus). Four selections (A-1836, A-593, A-830, and A-1680) and two cultivars (`Arapaho' and `Shawnee') were used as parents in a full diallel crossing scheme. Selection A-593 was used as the main source for PF due to its origin (`Brazos' × `Hillquist,' the latter an old PF cultivar). All parents except `Shawnee' have A-593 in their parentage; among the parents, only A-1836 fully expresses PF. Selfing of A-1836 resulted in 100% PF offspring, indicating that A-1836 is homozygous for this trait. Selfing of A-593, A-830, and `Arapaho' produced either a 35:1 or a 20.8:1 FF (floricane or summer-fruiting):PF segregation ratio, fitting a tetrasomic inheritance model under either random chromosome assortment (RCSA) or random chromatid assortment (RCTA), respectively, also suggesting that PF is controlled by a single recessive gene and that the parents are duplex (AAaa) for this trait. Selection A-1680 and `Shawnee' selfed did not produce PF progeny, but when crossed with the nulliplex A-1836, gave a 27:1 FF:PF ratio, indicating RCTA and that they are triplex (AAAa) for PF. According to these research, both gametic outputs (RCSA and RCTA) seem to operate in 4x blackberry. The intensity in expression of PF had a negative relationship with time to harvest, with those seedlings showing the highest PF scores producing a crop in early to mid-August. This knowledge will be helpful in implementing breeding strategies to produce PF blackberry cultivars.

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Maurus V. Brown, James N. Moore, Patrick Fenn, and Ronald W. McNew

This research was conducted to compare an in vitro leaf disk technique with greenhouse and field evaluations for screening large populations of grape (Vitis sp.) seedlings for downy mildew (Plasmopara viticola Berk. & Curt. Berl. & de Toni) resistance. Seedlings produced by crossing resistant × resistant, resistant × susceptible, and susceptible × susceptible parents were rated for sporulation, chlorosis, and necrosis. Leaf disk sporulation ratings at the first and second rating were highly correlated with the second sporulation rating in the field. Necrosis ratings from the leaf disk evaluations were significantly correlated with field necrosis ratings, but leaf disk chlorosis ratings were not correlated with field ratings. Some correlations, including evaluations of chlorosis, between the greenhouse and field ratings were highly significant. Seedling ratings of 0 or 1 for sporulation, chlorosis, and necrosis in the leaf disk assay agreed with field evaluations 85.6% of the time vs. 80.3% agreement between greenhouse and field ratings. Sporulation was the parameter most highly correlated between leaf disk or greenhouse and field evaluation of resistance. The leaf disk procedure appeared to be a good predictor of field resistance, and is more practical than the greenhouse method for screening large populations.

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Richelle A. Sink, Alfred E. Einert, Gerald L. Klingaman, and Ronald W. McNew

Euonymous fortunei `Coloratus' (Turcz.) Hand.-Mazz. (purpleleaf wintercreeper euonymus) is a groundcover species commonly grown in the landscape and known for its characteristic purplish-red color in the fall. This species is dimorphic, having both juvenile and adult forms present in established plants. Young plants, planted from 5.7-cm containers, were grown under full sun and 60% shade and evaluated for 1 year from May 1998. Four fertilizer treatments, up to four applications, were applied over the year. Data collected included the percent of adult and juvenile plants per plot, percent canopy cover, plant quality, and fresh and dry weights of pruned plant material and whole plants. Results showed that 73% of Euonymus planted in the shade were “adult-like” in form, while only 44% of Euonymus planted in the sun were “adult-like” in form. These results were analyzed with the percentage canopy cover determined for March, April, and May 1999 and showed no interaction of the two variables. By the end of the study, the mean percent of canopy cover was 77% under the shade and 74% under the sun. These values were not significantly different. While it appeared that the maturity of the plant did not effect the percent of groundcover coverage in a plot, the more mature or “adult-like” plants were visually undesirable within a plot of juvenile plants, and vice versa due to morphological differences.

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Brian A. Kahn, Phillip G. Shilling, Gerald H. Brusewitz, and Ronald W. McNew

Broccoli [Brassica oleracea L. (Italica Group)] crops may be rejected by wholesale buyers due to unacceptably tough stalks. Four experiments were conducted to examine the effects of various N levels and two within-row spacings (15 and 30 cm) on force to shear the stalk, stalk diameter, and yield of transplanted `Premium Crop' broccoli. Shear was not affected by within-row spacing, and average stalk diameter was decreased only 3 mm by reducing spacing from 30 to 15 cm. Although the 15-cm spacing sometimes produced the greatest total number of marketable, heads, this spacing resulted in higher cull head production, lower average marketable head weight, delayed maturity, and a lower percentage of field-planted transplants producing marketable heads than the 30-cm spacing. Increasing N fertilization decreased force to shear the stalk in only one experiment, when plants were exposed to water deficits and high temperatures. Nitrogen affected stalk diameter only when very low rates (37 and 74 kg·ha-1) were included. Yield of marketable-quality heads often showed no significant response to rates of applied N >112 kg·ha-1, particularly at the 30-cm spacing. Hollow stem was negligible in all experiments.

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Maurus V. Brown, James N. Moore, Ronald W. McNew, and Patrick Fenn

A study was conducted to determine how resistance to downy mildew [Plasmopara viticola (Bert. & Curt.) Berl. & de Toni] is inherited in germplasm (Vitis vinifera L., V. labrusca L., V. rupestris Scheele, and V. riparia Michx.) used for breeding table grapes. Crosses, including reciprocals, among parents possessing different levels of downy mildew resistance were evaluated in 1994 and 1995. The proportion of foliar tissue with sporulation, chlorosis, or necrosis was used to measure resistance. All genotypes were rated for these characters on two separate dates in 1994 and 1995. Hypersensitive flecking was also evaluated in the 1995 seedlings to determine its relationship with downy mildew resistance. Crosses with at least one resistant parent had a larger number of resistant offspring than crosses between two susceptible parents. General combining ability (GCA) effects were highly significant for 1994 and 1995. Specific combining ability effects were significant, but were relatively small compared to GCA, suggesting additive gene action was a primary influence on downy mildew resistance. Heritability estimates for sporulation, chlorosis, and necrosis were the highest at the second rating in 1994 (0.88, 0.74, and 0.57, respectively) and 1995 (0.50, 0.60, and 0.60, respectively). Reciprocal crosses indicated that maternal inheritance did not influence downy mildew resistance. A small percentage of progeny with hypersensitive flecking were identified from the germplasm. Seedlings with the flecking characteristic tended to have lower sporulation, chlorosis, and necrosis ratings earlier in the growing season.