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  • Author or Editor: L.S. Chang x
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Abstract

Respiration of sweet potato roots was significantly depressed by low oxygen concentrations from 5 to 15% compared to 20% O2, but respiration at 2.5% O2 was high. Total sugar accumulated with low oxygen (2.5 and 5.0%) storage. Protopectin was low in roots stored at low O2 concentrations but water soluble pectin was not significantly affected. Physical parameters Ew and δf the storage roots were high when stored at low O2 concentrations. Ey and Ef were not significantly affected. Ew was correlated with total sugar (r = 0.79).

Open Access

Abstract

Dormant, excised shoot segments from peach [Prunus persica (L.) Batsch.] seedlings previously identified as tolerant, intermediate, or susceptible to Leucostoma persoonii were evaluated for longitudinal canker necrotic length after incubation in contact with a culture of L. persoonii growing on clarified oatmeal agar. The differences in seedling canker necrotic lengths were significant and corresponded with field ratings of disease susceptibility. Seedling Yennoh 1-39 and NJ672017002 1-8 were the most tolerant, whereas Loring 14-20 and Elberta 8-25 were the most susceptible. The excised-shoot assay is sufficiently quick, reliable, and related to field disease reaction to be used as a screening procedure in the breeding of peach cultivars tolerant to L. persoonii.

Open Access

Abstract

Two sour cherry (Prunus cerasus L.) cultivars ‘Montmorency’ and ‘Meteor’ were evaluated over two seasons to determine the relative importance of different components of yield. A path coefficient analysis was performed to determine the direct and indirect effects of primary, secondary, and tertiary components on limb yield. Fruit number, fruit weight, the number of lateral buds and spurs, and fruit set were found to be the most important components affecting limb yield in both cultivars. However, the fruiting habits of the two cultivars were significantly different. ‘Montmorency’ produced 68% of its fruit on lateral buds on 1-year-old wood, while ‘Meteor’ had 70% of its fruit on 2-year-old spurs. When the data were standardized by dividing by limb cross-sectional area, ‘Meteor’ had a higher flower bud density (number of flowers/cm2) and yield efficiency (grams of fruits/cm2) than ‘Montmorency’. Although ‘Meteor’ had higher limb yields than ‘Montmorency’, the ‘Montmorency’ trees sampled had about four times more limbs than ‘Meteor’, and, therefore, higher tree yields.

Open Access

Abstract

Open-pollinated progeny from 15 peach (Prunus persica) cultivars, two peach × P. kansuensis hybrids, and one peach almond (P. amygdalus) hybrid were evaluated for their cold hardiness and for tolerance to Cytospora canker following artificial inoculation with Leucostoma persoonii. Winter hardiness was negatively correlated with canker necrotic length (r = −0.26**) and positively correlated with canker rating (r = 0.26**), as indicated by qualitative ratings. The half-sib families differed for canker necrotic length following fall inoculation, indicating that individuals with increased tolerance to L. persoonii canker could be selected from the population. Progeny from the cultivar Yennoh exhibited the shortest canker necrotic length following fall inoculation, and all the inoculated branches were visually healthy. ‘Yennoh’, a plant introduction from Russia, may have a higher tolerance to Leucostoma than has previously been found in U.S. germplasm.

Open Access

Eight open-pollinated peach families [Prunus persica (L.) Batsch] were selected from a germplasm collection that was screened for tolerance to Leucostoma persoonii (Nits.) Höhn. [imperfect state, .Leucocytospora leucostoma (Pers.) Höhn] following field inoculation. The eight peach families were either susceptible or tolerant to L. persoonii infection based on canker length measurements. Three open-pollinated seedlings per family were chosen for evaluation. Following artificial inoculation, measurements of hydraulic conductance per pressure gradient (Kh) were made on 2-year-old branch segments from the 24 seedlings, and safranin dye was used to mark the conductive xylem pathways. For the peach families tolerant to L. persoonii, the specific Kh of the canker branch segments was greater than that for the most susceptible peach families. The inoculated branch segments from the tolerant peach families maintained ≈15% to 30% of the water transport of control segments. Safranin dye movement indicated that the sapwood in inoculated branch segments of seedlings from the susceptible peach families was almost completely blocked. Isolation experiments indicated deeper penetration of the fungus into the xylem of seedlings of susceptible than tolerant families. Xylem dysfunction appears to be correlated with a reduction in Kh, and the seedlings in the tolerant peach families are better able to maintain water transport through the stem segment invaded by the fungus.

Free access

Shading has been used to produce high-quality lettuce (Lactuca sativa) in locations where production conditions are not optimal for this cool-season crop. To learn what additional benefits shading provides if heat-tolerant cultivars are used and to understand the effects of shading on growth, sensory quality, chemical content, and transcriptome profile on heat-tolerant lettuce, we grew two romaine lettuce cultivars with and without shading using 50% black shadecloth in 2018 and 2019. Shading reduced plant leaf temperatures, lettuce head fresh weights, glucose and total sugars content, and sweetness, but not bitterness, whereas it increased lettuce chlorophyll b content compared with unshaded controls. Transcriptome analyses identified genes predominantly involved in chlorophyll biosynthesis, photosynthesis, and carbohydrate metabolism as upregulated in unshaded controls compared with shaded treatments. For the tested cultivars, which were bred to withstand high growing temperatures, it may be preferable to grow them under unshaded conditions to avoid increased infrastructure costs and obtain lettuce deemed sweeter than if shaded.

Open Access

MN55 is an apple (Malus ×domestica Borkh.) cultivar recently released by the University of Minnesota apple breeding program, with fruit marketed in the U.S. as Rave®. When stored for 4 months at 0 to 4 °C, MN55 fruit can develop several storage disorders, including skin dimpling. Skin dimpling incidence was greater for fruit harvested 1 week later than those harvested earlier. Dimpling was not alleviated by prestorage treatments of 1-methylcyclopropene or diphenylamine or by holding fruit at room temperature for 1 day before long-term cold storage. However, dimpling incidence was very low when fruit were stored at 6 to 7 °C. Because viruses have been implicated in other fruit dimpling disorders, the presence of viruses in MN55 leaves and fruit was studied. Apple stem pitting virus (ASPV) was detected by microscopy, reverse transcriptase polymerase chain reaction (RT-PCR) methodology, and high throughput sequencing (HTS) in peel of fruit from MN55 trees that exhibited skin dimpling after 4 months of storage at 0 to 1 °C. ASPV was also detected in supermarket-purchased fruit of other cultivars with noticeable skin dimpling. Although ASPV was not conclusively demonstrated to cause skin dimpling in our work, its prevalence indicates that further investigations are warranted to determine the relationship between viruses and skin deformities in stored apples.

Open Access