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J. Erron Haggard and James R. Myers

White mold, caused by Sclerotinia sclerotiorum (Lib.) de Bary, causes major losses in dry and snap bean (Phaseolus vulgaris) production. With little genetic variation for white mold resistance in common bean, other potential sources for resistance must be investigated. Accessions of scarlet runner bean (P. coccineus) have been shown to have partial resistance exceeding any to be found in common bean. Resistance is quantitative with at least six QTL found in a P. coccineus intraspecific resistant × susceptible cross. Our goal is to transfer high levels of resistance from P. coccineus into commercially acceptable common bean lines. We developed interspecific advanced backcross populations for mapping and transfer of resistance QTL. 111 BC2F5 lines from a cross between OR91G and PI255956 have been tested in straw tests and oxalate tests, as well as in a field trial. The data show that the OR91G × PI255956 population carries a high level of resistance, but because of the quantitative nature of resistance, it may be necessary to intercross individuals to achieve higher levels. SSR, RAPD, and AFLP markers are being tested in the population to construct a linkage map for placement of QTL. QTL identified from each type of test (straw, oxalate, and field) may provide additional information about the genetic architecture of white mold resistance. Three other populations are from advanced backcrosses of the recurrent parents G122, OR91G, and MO162, with PI433251B as the donor parent in each. Analyses and advance of these populations will follow, the results of which should confirm QTL identified in the OR91G × PI255956 population, as well as possible additional resistance QTL from PI433251B.

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Paul Skroth, Jim Nienhuis, Geunhwa Jung, and Dermont Coyne

Knowledge of genetic relationships and genetic diversity among accessions is essential for the efficient construction, maintainance and utilization of large ex-situ germplasm collections. Furthermore, streamlining of large collections into care collections necessitates validation of germplasm sampling techniques. DNA molecular markers provide potentially unbiased estimators of genome diversity end may facilitate organization, maintainance, and sampling of plant genetic resources. Our data suggests that RAPD markers will be o good tool for testing tore collection concepts and organizing genetic diversity in common bean. However, the genomic distribution of markers is unknown. Currently we are using recombinant inbred (RI) populations to place RAPD markers in the context of the bean genetic map. We hove evaluated the the distribution of RAPD markers in three RI populations: Bat93 × Jalo EEP558, PC50 × Xan159, and BAC6 × HT7719. Cultivated P.vulgaris has two primary renters of diversity Mesoamerican and Andean, the RI populations used for mapping RAPD markers ore Meso × Andean, Andean × Andean, and Meso × Meso crosses respectively. In the Bat93 × Jalo EEP558 population 383 markers have been mapped for a map length of 735 cM. However, approximately 150 of these markers ore members of 9 dusters which span only 90 cM. This inter gone pool mop is being integrated with linkage mops constructed in the other two populations to compare within and between gene pool marker distributions and to evaluate clustering of markers on the different mops. Implications for the application of RAPD markers will be discussed.

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J.R. Baggett and D. Kean

Inheritance of a twisted pod characteristic, in which bean pods develop with a twist that sometimes exceeds 360°, was studied in crosses between round-podded green bean cultivars. In crosses between `Oregon 91G' (normal) or `Oregon 54' (normal) and OSU 5256-1 (twisted), the F1 was normal. Segregation in F2 populations, tested over a 4-year period and including 4,995 plants, clearly fit a 3 normal: 1 twisted ratio. All plants of backcrosses of the F, to the normal parent were normal and backcrosses of the F1 to the twisted parent segregated 1 normal: 1 twisted. The ratios observed indicated that twisted pods are conditioned by a single recessive gene for which the symbol tw is proposed.

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Agnes A. Flores-Nimedez, Paul H. Li, and Charles C. Shin

Protection mechanism of a new compound, coded as GLK-8903, from chilling injury in bean plants was assessed by measuring several physiological parameters. The decline in leaf water potential caused by the chilling exposure to 4°C (day/night) was minimized when GLK-8903 was applied to the plants as compared to the non-treated control. Chilling causes an increase in electrolyte leakage, an indication of chilling injury that occurs at the site of plasma membrane. An increased electrolyte leakage was reduced in the GLK-8903-treated plants during chilling. Data from plasmolysis and deplasmolysis studies of epidermal cells suggest that GLK-8903 is able to stabilize the plasma membrane under stress condition by determining the permeability coefficients plasmometrically (1.96 cm s-1 × 10-4 for GLK-8903-treated plants vs. 4.00 for the controls 3 d at 4°C) with less decreased activity of the plasma membrane ATPase (9.36 μmol chl-1·h-1 for GLK-8903-treated plants vs. 5.04 for the controls 3 d at 4°C). GLK-8903 appears to have high application potential in protecting bean plants from chilling injury with improved yield.

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Jonathan P. Lynch and Stephen E. Beebe

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Zhanyuan Zhang, A. Mitra, and D.P. Coyne

Optimization of parameters influencing biolistic transformation is a crucial stage towards repeatable transformation of common beans. However, there has been no published study on such optimization of this crop species in a helium particle delivery system (BioRad). Using an intron-containing β-glucuronidase (GUS) gene as a reporter, we optimized several critical parameters of biolistic PDS-1000/He delivery system for common bean transformation. The target explant tissues included cotyledons, zygotic embryos, and meristemic shoot tips suitable for organogenesis. Thus, pretreatment of target tissues with osmotic medium containing 0.15–0.25 m mannitol and 0.15–0.25 m sorbitol, positioning of target tissues in 4 cm microcarrier flying distance, the use of 1.6-μm gold particle and high concentration of coating DNA, and bombardment of young immature tissues twice at 2000 psi, etc., significantly increased transformation rate and achieved the best coverage and penetration of the meristemic areas involved in direct shoot organogenesis.

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R. A. Hoyos and G. L. Hosfield

Opaque globules formed on bean callus induced on primary leaf explants cultured on induction media (IM) containing 10 to 30 mg/l 2,4-D. Calli with globules produce structures reminiscent of somatic embryos (embryoids) after subculture in a liquid challenge medium (LCM). Calli maintained on IM for 2, 3, 4, and 5 weeks produced significantly more (26 to 34/callus) embryoids in LCM than calli maintained on IM for one week (12/callus). Well developed embryoids only occurred after calli were subculture in liquid B5 with 0.1 to 1.0 mg/l IBA. Calli subculture in LCM with > 10 mg/l IBA turned necrotic and died. Embryoids produced in B5 with 2,4-D and NAA (0.1 to 1.0 mg/l) proliferated roots and formed “frosty” appearing structures, respectively. No differences were detected in number or quality of embryoids produced in LCM from callus maintained on IM in continuous light or darkness regardless of the induction time. Ethylene accumulation in IM cultures inhibited globule formation.

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Juan M. Quintana, Helen C. Harrison, and James Nienhuis

Calcium is an essential element for human nutrition. The lack of it causes various problems, such as osteoporosis. Snap beans rank as good sources of calcium among vegetables and are well-liked by most teenagers. In this study, pod yield and Ca concentration were analyzed for 64 genotypes of snap beans, plus four checks. The experimental design was a 8 x 8 double lattice, repeated at two locations (Arlington and Hancock, Wis.). Snap beans were planted in June 1993 and machine-harvested 67 days later, in Aug. 1993. Calcium analyses were made using an Atomic Absorption Spectometer. Results indicated significant differences for pod Ca concentration and yield. Pod size and Ca concentration showed a strong negative correlation (R = 89.5). Clear differences among the locations were also observed. Results were consistent—high-Ca genotypes remained high regardless of location or pod size. Selected genotypes appeared to have the ability to absorb Ca easier than others, but this factor was not related to yield.

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Karl J. Sauter, David W. Davis, and James S. Beaver

184 random F2 plants from a high temperature (HT) sensitive X HT tolerant snap bean cross were advanced to the F5 by single seed descent. At anthesis and after HT pre-treatment, all plants in each generation were evaluated in the laboratory for leaf ethylene evolution (EE), % viable pollen (VP), and leaf cell membrane thermostability (CMT). Population means among generations differed significantly for VP and CMT in a paired t-test, while EE means in the F3, F4, and F5 were similar. Correlations among traits were very low (≤.25) with a consistent negative correlation between VP and the others (high VP is a positive trait while low EE and CMT are considered positive). VP and total pollen were highly correlated (r≤.81). To determine if the 3 traits might predict HT tolerance in the field, F5-derived F6 lines were grown at Becker, MN (control), and Isabella, PR (HT environment). Yield component data were collected at both locations. Tolerance may be computed as % yield of the lines in the HT vs. the control environment for any or all of the yield components. Regression analysis showed a very low r2 (≤.16) when EE, VT, and CMT were used to predict tolerance as estimated by pod production. However, as expected, the F5 best predicted F6 performance. Further results from Minnesota field and greenhouse and from Puerto Rico field data will be discussed.

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Maria Fisher, David Eissenstat, and Jonathan Lynch

In annual plant species, root death has been assumed to be closely correlated with shoot senescence. However, in a preliminary study with common bean grown in sand culture beyond physiological maturity (114 days), no root death occurred. We investigated whether the incidence of bean root death was higher under field conditions than in sand culture. Root death was defined as root disappearance. The sand culture consisted of silica sand and P-loaded alumina. Plants in this system were fertigated twice daily with complete nutrients supplied in adequate amounts. The field planting was on a Hagerstown silt loam in central Pennsylvania. Roots were observed using minirhizotrons every 1 to 3 weeks after planting. In sand culture, incidence of root death was monitored on a population of 170 roots from three plants between 25 and 88 days (shoot senescence) after planting Root death was 10%. In the field study, 55% of the 53 roots examined died between 32 and 93 days (shoot senescence) after planting. Biological factors present in the field and not present in sand culture appeared to contribute to root death. The persistence of roots in sand culture suggests a lack of programmed root senescence in contrast to shoot senescence. This has interesting implications for resource allocation during reproduction and in face of belowground herbivores and pathogens.