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J. R. Baggett and D. Kean

An abnormal pod condition, in which bean pods are twisted, sometimes as much as 360°, was discovered in a selection of OSU 5256, a Bush Lake breeding line. The amount of twisting of affected pods and the number of affected pods/plant are both variable. F2 progenies from crosses between twisted pod line 5256-1 and two normal bush Blue Lake cultivars segregate 3 normal:1 twisted, showing that the twisted mutant is controlled by a single recessive gene.

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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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Feishi Luan and Zhanyong Sun

The purpose of this study was to analyze the genetic relationship by using morphological, biochemical, and molecular markers. Sixty accessions of green bean [Phaseolusvulgaris (L.)], including 43 from North China, 13 from the International Center for Tropic Agriculture, and four from Poland, were collected and divided into three groups: cultivated determinate (35), cultivated indeterminate (12), and semi-wild determinate (13). Dendrograms were constructed based on the genetic similarity and distance analysis of these 60 accessions by using biological characters, allozyme, and random amplified polymorphic DNA (RAPD) markers. The 60 accessions were classified into two groups based on the genetic relationship examined in their biological characters. The cultivated indeterminate formed one group, and cultivated determinate and semi-wild determinate belonged to another group. Ten allozymes with 25 polymorphic loci divided the 60 accessions into nine groups, i.e., five groups for cultivated determinate, two groups for cultivated indeterminate, and two groups for semi-wild determinate. Twenty-nine RAPD markers with 314 polymorphic loci divided the 60 accessions into 13 groups, i.e., nine groups for cultivated determinate, three groups for cultivated indeterminate, and one group for semi-wild determinate. The average genetic similarities and genetic distance of intra-group and inter-groups were 0.81 and 0.75, and 0.19 and 0.24, respectively. Ten bands were characterized as specifically associated with cultivated determinate, one band specific for cultivated indeterminate, and one band for semi-wild. These biochemical and molecular markers provided more information than morphological markers. Allozyme and RAPD markers can be used as an available tool to exploit green bean germplasm in the future.

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

Factors influencing Agrobacterium–mediated DNA transfer of P. vulgaris were examined using an intron-containing β-glucuronidase (GUS) gene as a reporter system. Tissue culture procedures used were based on direct shoot organogenesis. Two A. tumefaciens strains, A2760 and EHA105, were used with more emphasis on the former due to its overall higher transformation rate. Ten bean entries including breeding lines and cultivars from both Meso-American and Andean origins were compared for compatibility with the two bacterial strains under different pre- and coculture conditions. Pinto `Othello' was extensively used in testing different transformation conditions. Factors found to have significant effects on transformation rate included Agrobacterium-host interactions, explant maturity, preculture and cocultivation conditions, as well as selection schemes, based on transient expression. Some factors, such as the effect of explant maturity and dark preconditioning of explants on gene transfer, have not been reported before. The best transformation conditions included the use of susceptible genotypes and mature explants, preconditioning of explants in darkness, followed by a maximum cocultivation period in the presence of cytokinin, and the use of high selection pressure.

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Geunhwa Jung, Paul W. Skroch, Dermot P. Coyne, James Nienhuis, and E. Arnaud-Santana

Common bacterial blight (CBB) incited by the bacterial pathogen Xanthomonas campestris pv. phaseoli (Smith) Dye is an important disease of common bean. In a previous study, QTL associated with CBB resistance were described based on RAPD marker analysis of a recombinant inbred population derived from the common bean cross BAC-6 (R) × HT-7719 (S) (resistant × susceptible). The objective of this research is to confirm these previously described candidate marker locus-QTL associations using an inbred backcross PC-50 (S) × BAC-6 (R) and a recombinant inbred Venezuela 44 (S) × BAC-6 (R) population. Two markers previously found to be associated with QTL for CBB resistance in the BAC-6 × HT-7719 population were found to account for 30% of the phenotypic variation for CBB resistance in the PC-50 × BAC-6 inbred backcross population. The three most resistant BC2F3 lines based on marker locus genotypes were ranked 1, 3, and 7 (out of 64) based on phenotypic evaluation. These results provide important confirmation of marker locus-QTL associations and indicate that RAPD markers linked to loci controlling the expression of CBB resistance in common bean may be used to transfer resistance genes into susceptible breeding material.

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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.

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Cheng-lie Zhang, Paul H. Li, and Charles C. Shin

Twenty-day-old `Bush Blue Lake 47' common bean plants grown in a growth chamber at 25 days/22C night and a 12-hour photoperiod regime were foliar sprayed with 0.5% GLK-8903 including 0.05% Tween-20. After 24 hours of treatment, plants were chilled in a cold room (4C day/night, 12 hours of light). After 3 days of chilling, leaves of untreated controls were injured, as visually characterized by leaf wilting, whereas leaves of the GLK-8903-treated plants still retained turgor. During chilling, the activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) decreased. GLK-8903 treatment had no effect on SOD and POD activities; however, the CAT activity was reduced significantly after GLK-8903 treatment either at 25 or at 4C. During chilling, the content of malondialdehyde, a decomposition product of phospholipid peroxidation, increased in treated plants and untreated controls, with increased content significantly lower in the former compared with the latter. The GLK-8903 per se and total lipid extracted from GLK-8903-treated plants were able to reduce the linoleic acid oxidation in vitro. The mechanism by which GLK-8903 alleviates chilling injury in bean plants is discussed.

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Katy M. Rainey and Phillip D. Griffiths

The genetic basis for heat tolerance during reproductive development in snap bean was investigated in a heat-tolerant × heat-sensitive common bean cross. Parental, F1, F2, and backcross generations of a cross between the heat-tolerant snap bean breeding line `Cornell 503' and the heat-sensitive wax bean cultivar Majestic were grown in a high-temperature controlled environment (32 °C day/28 °C night), initiated prior to anthesis and continued through plant senescence. During flowering, individual plants of all generations were visually rated and scored for extent of abscission of reproductive organs. The distribution of abscission scores in segregating generations (F2 and backcrosses) indicated that a high rate of abscission in response to heat stress was controlled by a single recessive gene from `Majestic'. Abscission of reproductive organs is the primary determinant of yield under heat stress in many annual grain legumes; this is the first known report of single gene control of this reaction in common bean or similar legumes. Generation means analysis indicated that genetic variation among generations for pod number under heat stress was best explained by a six-parameter model that includes nonallelic interaction terms, perhaps the result of the hypothetical abscission gene interacting with other genes for pod number in the populations. A simple additive/dominance model accounted for genetic variance for seeds per pod. Dominance [h] and epistatic dominance × dominance [l] genetic parameters for yield components under high temperatures were the largest in magnitude. Results suggest `Cornell 503' can improve heat tolerance in sensitive cultivars, and heat tolerance in common bean may be influenced by major genes.

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Mohamed F. Mohamed, Dermot P. Coyne, and Paul E. Read

Plant regeneration has been achieved in two common bean lines from pedicel-derived callus that was separated from the explant and maintained through successive subcultures. Callus was induced either on B5 or MS medium containing 2% sucrose and enriched with 0.5 or 1.0 mg thidiaznron/liter alone or plus various concentrations of indoleacetic acid. The presence of 0.07 or 0.14 g ascorbic acid/liter in the maintenance media prolonged the maintenance time. Up to 40 shoot primordia were observed in 4-week-old cultures obtained from 40 to 50 mg callus tissues on shoot-induction medium containing 1-mg benzyladenine/liter. These shoot primordia developed two to five excisable shoots (>0.5 cm) on medium with 0.1-mg BA/liter. A histological study confirmed the organogenic nature of regeneration from the callus tissues. The R2 line from a selected variant plant showed stable expression of increased plant height and earlier maturity. Chemical names used: ascorbic acid, N- (phenylmethyl)-1H-pnrin-6-amine [benzyl-adenine, BA], 1H-indole-3-acetic acid (IAA), N- phenyl-N'-1,2,3-thiadiazol-5-ylurea [thidiazuron, TDZ].