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Y.-K. Chen, J.P. Palta and J.B. Bamberg

Wild potato species provide a valuable source of genetic variability for the improvement of freezing tolerance in cultivated potato, Solanum tuberosum (tbr). However, breeding for freezing tolerance by using wild genetic resources has been hampered by contradictory results regarding the genetic control of this trait. Both dominance and recessiveness for this trait have been reported. To explore the genetic control of freezing tolerance, the expression of freezing tolerance was investigated in various interspecific F1 and somatic hybrids between hardy and sensitive species. In addition to 2 years of field evaluation, freezing tolerance before and after acclimation was characterized separately under controlled environments to dissect the two independent genetic components of freezing tolerance, namely nonacclimated freezing tolerance (NA) and acclimation capacity (ACC). The expression of freezing tolerance, including NA and ACC, was closer to that of hardy parent, sensitive parent, or approximate parental mean, depending on species combination. However, the expression of freezing tolerance tended to be greater when the hybrids contained more sets of chromosomes from the hardy parent than from the sensitive parent. The significance of hardy: sensitive genomic ratio was further supported by using sexual and somatic hybrids between tbr and S. commersonii (cmm) to achieve different genomic ratios without the confounding effect of species. Therefore, we propose that the hardy: sensitive genomic ratio is an important determinant for the expression level of freezing tolerance before and after cold acclimation.

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J. Angel Saavedra, Elden J. Stang and Jiwan P. Palta

Uniconazole (UCZ) can control tree size by suppressing tree growth. Growth control of one year-old `Haralred' on MAC 9 `MARK' (dwarf) and EMLA 7 (semidwarf) rootstock was evaluated in the greenhouse. Uniconazole (65 or 130 mg/L) was sprayed 0, 1, 2 or 3 times at 3 week intervals. Total shoot growth was inhibited 31% and 24% on `MARK' and EMLA 7 rootstock, respectively, with 130 mg/L. Rootstock and scion diameter and number of leaves per tree were not affected by UCZ. Total leaf area on `MARK' rootstock increased when UCZ was applied once at 65 or 130 mg/L. On EMLA 7 two 130 mg/L sprays resulted in 22% less total leaf area compared to the control. UCZ applied three times reduced specific leaf weight on EMLA 7 trees 12% compared to the control. Branch angle was increased proportional to UCZ applications on semidwarf rootstock from 40° to 47°, and decreased on dwarf rootstock from 47° to 39°. Stomatal conductance increased 43% on `MARK' with 130 mg/L UCZ applied two times. Net photosynthesis of attached leaves did not differ. All UCZ treatments produced 18 to 56% fewer total flower clusters per tree than the control. UCZ appeared to delay bloom significantly.

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R.A. Teutonico, T.C. Osborn and J.P. Palta

Identification of the genes involved in low temperature responses in oilseed Brassica could lead to genetic improvement of this crop and other species. We developed a genetic linkage map for B. rapa using restriction fragment length polymorphisms (RFLPs) and identified molecular markers which are linked to genes controlling vernalization requirement and freezing tolerance. We mapped the location of a group of cold-regulated (`cor') genes from Arabidopsis thaliana in this population and determined their association with these cold responses. We developed genetically fixed, recombinant inbred lines of B. rapa to assay the physiological processes involved in these cold responses. Specifically, we measured the differences in lipid composition of the plasma membranes of acclimated and nonacclimated plants of a subset of this population. We will determine if the genes involved in the physiological responses to low temperature are also associated with the acquisition of freezing tolerance.

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Karim M. Farag, Jiwan P. Palta and Elden J. Stang

The application of ethanol for enhancing effectiveness of ethephon under field conditions on cranberry (Vaccinium macrocarpon Ait.) fruit was tested during three seasons (1986 to 1988). The formulation containing ethephon plus the surfactant Tergitol (0.3% or 0.5%, v/v) and ethanol (2.5%, 5%, or 10%) consistently increased anthocyanin content in the fruit by 28% to 54% over the control. In general, fruit size was not affected by the ethephon treatment containing ethanol and Tergitol. The application of ethephon plus surfactant did not increase the anthocyanin content in the fruit. The presence of ethanol in the ethephon and surfactant mixture, however, consistently enhanced the fruit anthocyanin content by 21% to 40% as compared to ethephon plus surfactant. No adverse effect of various treatments on vine growth or appearance was noticed over the three seasons. Chemical name used: (2-chloroethyl) phosphonic acid (ethephon).

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J.M. Quintana, H.C. Harrison, J.P. Palta, J. Nienhuis and K. Kmiecik

To measure the effect of added Ca fertilizer on the Ca concentration of snap bean pods, four snap bean cultivars were grown during Summer 1996 and 1997 at Hancock, Wis. Fertilizer treatments consisted of 80 kg of Ca per hectare applied as Ca sulfate (CaSO4·2H2O) or Ca nitrate [Ca(NO3)2], and the control (no Ca applied. The experimental design was a randomized complete block with a factorial set of treatments (4 × 3). Calcium sulfate was applied at planting, whereas Ca nitrate was split applied four times at weekly intervals starting 1 week before flowering. Yield and Ca concentration in pods were determined. The statistical analysis showed no significant effect of Ca fertilizers on pod Ca concentration or yield. A strong cultivar effect was detected for both parameters measured. `Evergreen' (5.47 mg Ca per gram dry weight) had the highest pod Ca concentration and `Labrador' (4.10 mg Ca per gram dry weight) the lowest. No significant fertilizer × cultivar interactions were observed. Results for pod Ca concentration remained consistent, even when significant year effects were found for both parameters.

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J.M. Quintana, H.C. Harrison, J. Nienhuis, J.P. Palta and K. Kmiecik

This study was designed to compare snap and dry beans (Phaseolus vulgaris L.) for pod Ca concentration, and to identify genetic resources that might be useful in breeding programs directed to increase Ca concentration in bean pods. Pods from eight snap bean and eight dry bean cultivars were evaluated for Ca concentration during 1995 and 1996 at Hancock, Wis. A randomized complete-block design was utilized with three replications in 1995 and six in 1996. Beans were planted in June and hand-harvested in August for both experiments. Soil Ca at planting time was 580 mg·kg–1 in 1995 and 500 mg·kg–1 in 1996. No additional Ca was added. Plots consisted of 10 plants each. At harvest, a pooled sample of 10 to 15 size no. 4 pods was collected from each plot. Atomic absorption spectrophotometry was used to determine Ca content. Significant differences (P ≤ 0.01) were detected among and within bean types (dry and snap). Although bean type × year interaction was nonsignificant, a strong year effect was observed (P ≤ 0.01). Snap beans (4.6 ± 0.7 mg·g–1 dry weight) had significantly higher pod Ca concentration than did dry beans (4.2 ± 0.6 mg·g–1 dry weight). Within snap beans, `Checkmate' had the highest pod Ca concentration (5.5 ± 0.3 mg·g–1 dry weight) and `Nelson' the lowest (3.8 ± 0.3 mg·g–1 dry weight). Within dry beans, `GO122' had the highest (5.1 ± 0.4 mg·g–1 dry weight) and `Porrillo 70' the lowest pod Ca concentration (3.6 ± 0.3 mg·g–1 dry weight). Six cultivars had pod Ca concentrations significantly (P ≤ 0.01) higher than the overall mean (4.4 ± 0.3 mg·g–1 dry weight).

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J.M. Quintana, H.C. Harrison, J. Nienhuis, J.P. Palta, K. Kmiecik and E. Miglioranza

To understand the genetics that control pod Ca concentration in snap beans, two snap bean (Phaseolus vulgaris L.) populations consisting of 60 genotypes, plus 4 commercial cultivars used as checks, were evaluated during Summers 1995 and 1996 at Hancock, Wis. These populations were CA2 (`Evergreen' × `Top Crop') and CA3 (`Evergreen' × `Slimgreen'). The experimental design was an 8×8 double lattice repeated each year. No Ca was added to the plants grown in a sandy loam soil with 1% organic matter and an average of 540 ppm Ca. To ensure proper comparison for pod Ca concentration among cultivars, only commercial sieve size no. 4 pods (a premium grade, 8.3 to 9.5 mm in diameter) were sampled and used for Ca extractions. After Ca was extracted, readings for Ca concentration were done via atomic absorption spectrophotometry. In both populations, genotypes and years differed for pod Ca concentration (P = 0.001). Several snap bean genotypes showed pod Ca concentrations higher than the best of the checks. Overall mean pod Ca concentration ranged from a low of 3.82 to a high of 6.80 mg·g-1 dry weight. No differences were detected between the populations. Significant year×genotype interaction was observed in CA2 (P = 0.1), but was not present in CA3. Population variances proved to be homogeneous. Heritability for pod Ca concentration ranged from 0.48 (CA2) to 0.50 (CA3). Evidently enhancement of pod Ca concentration in beans can successfully be accomplished through plant breeding.

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J.M. Quintana, H.C. Harrison, J.P. Palta, J. Nienhuis, K. Kmiecik and E. Miglioranza

Two commercial snap bean (Phaseolus vulgaris L.) cultivars (Hystyle and Labrador) that differ in pod Ca concentration were grown aeroponically to assess physiological factors associated with these differences. Xylem flow rate, Ca absorbed, and Ca concentration in sieve sap and pods (all and commercial size no. 4) were measured. Flow rate, Ca absorption and pod Ca concentration, but not sap Ca concentration, differed between cultivars, and this suggests that genetic variability in pod Ca concentration is caused mainly by differences in flow rate, rather than differences in sap Ca concentration. `Hystyle' showed 1.6 times greater flow rate, 1.5 times greater pod Ca concentration, and 1.7 times greater Ca absorbed than `Labrador'. Flow rate correlated positively with Ca absorbed (R = 0.90), Ca concentration in pods of size no. 4 (R = 0.55), and total pods (R = 0.65). Plant maturity influenced sap Ca concentration and Ca translocated increased as plant matured. These results provide evidence that flow rate differences may cause variability for pod Ca concentration in snap beans.

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J.M. Quintana, H.C. Harrison, J.P. Palta, J. Nienhuis, K. Kmiecik and E. Miglioranza

Stomatal density of pods and leaves were determined for six commercial snap bean cultivars (Phaseolus vulgaris L. `Evergreen', `Hystyle', Labrador', `Tenderlake', `Top Crop', and `Venture') grown at three planting dates, in an attempt to find morphological traits that could be related to cultivar differences in pod Ca concentration. Snap beans were planted three times at ≈1-week intervals beginning 15 June 1995, and harvested 59 to 62 days after planting. Stomatal counts were performed using a microscope linked to a video camera, and Ca concentration determinations were made using atomic absorption spectrophotometry. Calcium concentration and stomatal density of leaf tissue was higher than that of pods. Cultivar differences for pod Ca concentration (P = 0.001) and stomatal density (P = 0.001) were observed although cultivars with higher pod stomatal density did not necessarily result in higher pod Ca concentration. Calcium concentration and stomatal density for leaves did not differ among cultivars. Stomatal density and Ca concentration of pods were positively correlated (R 2 = 0.37), while pod maturity was negatively associated to both pod Ca concentration (R 2 = 0.93), and pod stomatal density (R 2 = 0.99). The effect of planting dates was absent in pod Ca concentration and significant in pod stomatal density.