Characterization of Topiary (Top) an Architectural Mutant of Common Bean
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J. AMER. SOC. HORT. SCI. 126(1):105–109. 2001. Characterization of Topiary (top) an Architectural Mutant of Common Bean N. Guner1 and J.R. Myers2 Department of Horticulture, Oregon State University, Corvallis, OR 97331 ADDITIONAL INDEX WORDS. plant breeding, growth habit, determinacy, genetic analysis ABSTRACT. Plant breeders are interested in developing upright common beans (Phaseolus vulgaris L.) to reduce diseases and permit mechanical harvest, and improve seed quality. Morphological and genetic characteristics of an architectural mutant in common beans were studied. The mutant had shiny, dark green leaves, overlapping leaflets, and short petioles. Branching was nearly absent, resulting in single stemmed plants. Although mutant plants carried Fin for indeterminacy, and plants progressed in flowering from lower to higher nodes, the terminal node was reproductive. This represents a new form of determinacy in common bean. Inheritance studies demonstrated that the mutant syndrome was controlled by a single recessive gene. Allelism tests between the mutant and overlapping leaflets (ol), and dark green savoy leaf (dgs) showed that the mutant was not allelic to either locus. The trait was designated as Topiary with the gene symbol top, describing its compact and neat appearance. Linkage was tested between top and growth habit (fin), shiny leaves, cross- sectional shape of pods, striped pod (C prpst), and pod suture strings. All genes segregated independently. The genetic merit of the Topiary mutant for improving common beans needs to be investigated, especially the value of single stem growth habit combined with an upright plant habit. Plant breeders have been interested in using architectural traits determinate or indeterminate habit, number of nodes, internode to avoid disease, and to improve grain quality, lodging resistance, length, climbing ability, and degree and type of branching. and yield (Coyne, 1980). Plant architecture may be critical to Growth habits are Type I, determinate bush; Type II, indetermi- success of dry bean cultivars (Phaseolus vulgaris L.) in various nate short vine; Type III, indeterminate prostrate nonclimbing cropping systems (Kelly and Adams, 1987). Varieties in the vine; and Type IV, indeterminate climbers (Fernandez, et al. kidney market class are determinate because growers require a 1986). Another growth habit category not included in this classi- bean that matures uniformly and quickly. The indeterminate vine fication is the determinate climber (Debouck et al., 1988). The architecture characteristic of small red, pinto, pink and great mutant trait described herein affects plant architecture. The northern market classes is associated with higher yields com- objectives of this study were to perform a genetic analysis of the pared to determinate types (Myers, 1992). Growers in the western mutant trait, including inheritance, linkage, and allelism studies, United States have used cultivars with a floppy vine (type III) and to characterize the morphology of the mutant. habit because these types produce the highest yields, and upright architecture is not needed to avoid foliar diseases. Midwestern Materials and Methods growers have greater foliar disease problems, and have preferred upright short vine cultivars that sacrifice some yield potential, but The mutant line used in this study was first observed and avoid disease. A prostrate growth habit creates considerably more selected in 1995 in the small red (dry bean) breeding line 611413 risk of harvest losses from white mold [Sclerotinia sclerotiorum from the cross ‘UI 35’//’NW 59'/92001 by J.R. Myers at the (Lib.) de Bary] (Kelly and Adams, 1987), and Coyne (1980) University of Idaho (UI) Kimberly Research and Extension suggested that severity of white mold could be reduced consider- Center, Kimberly, Idaho. UI 35 is a small red bean cultivar ably by developing dry edible beans that have an upright architec- released in 1959 by the UI (LeBaron, 1959). NW 59 is also a small ture with porous canopy. red cultivar developed by the USDA–ARS at Prosser, Wash. Upright plant architecture allows use of direct harvest systems (Burke, 1982). The breeding line 92001 was used in the UI with narrow row spacing, high plant populations, and a flat breeding program, and derived from the cross ‘UI 36’/6917 planting surface. Narrower rows and higher plant populations where UI 36 is another small red cultivar (Dean and LeBaron, cause pods to form higher on the plant and allow better competi- 1964) and 6917 is a large seeded purple mottled cranberry type tion with weeds. Compared to traditional production systems, breeding line of the Andean center of origin. Seeds from fertile less energy is used when direct harvest is incorporated (Smith, plants with strong expression of the mutant syndrome were 1996). harvested to initiate the line. In three generations of self-pollina- Four principal growth habits were identified by researchers at tion, the line was stable and true breeding. The four parental lines Centro Internacional de Agricultura Tropical (CIAT) based on were chosen to represent different bean types and were crossed to the mutant to study its inheritance. ‘Oregon 91G’ is a Type I bush Received for publication 11 Aug. 1999. Accepted for publication 30 June 2000. blue lake green bean developed at Oregon State University Oregon Agricultural Experiment Station technical paper 11537. This research is (Baggett et al., 1981). ‘Minuette’ is a Type I small sieve green a contribution to the W-150 regional project. From a MS thesis submitted by the bean obtained from Harris Moran Seed Company, Modesto Calif. senior author, who was supported by a scholarship from the Turkish Ministry of Genetic stock 5-593, obtained from Mark Bassett, University of Education. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby Florida, Gainesville, also has a Type I growth habit. ‘UI 906’ is marked advertisement solely to indicate this fact. a Type II upright, early maturing black bean developed in the UI 1Present address: Department of Horticultural Science, Box 7609, North Carolina dry bean breeding program (Myers et al., 1991). Table 1 summa- State University, Raleigh, NC 27695-7609. rizes phenotypic characteristics of the parents used in this study. 2 To whom reprint requests should be addressed. Mutant plants were crossed, using standard emasculation J. AMER. SOC. HORT. SCI. 126(1):105–109. 2001. 105 Table 1. Characteristics of the parents used in a genetic analysis of a mutant in common bean. Growth Allele at Flower Pod cross- Seed Seed Fiber in Line habitz Fin locus Market class color section luster color pod suture Oregon 91-G Type I fin fin Green bean White Round Dull White Absent Minuette Type I fin fin Green bean White Round Dull White Absent 5-593 Type I fin fin Genetic stock Purple Flat Shiny Black Present UI-906 Type II Fin Fin Black bean Purple Flat Dull Black Present zType I = determinate bush, type II = indeterminate upright short vine. procedures (Bliss, 1980), with the four parent lines to produce type III indeterminate growth habit, white flowers, medium-sized crosses and reciprocals in Spring 1997. F1 progeny were grown in shiny red seeds, and flat, fibrous, stringy pods. Traits associated the field and greenhouse to produce F2 populations. A total of 576 with the mutant phenotype include a single stem, dark green F2 seeds were planted in a greenhouse in Fall 1997, representing leaves that are thicker, smaller, and more brittle than normal 144 plants per cross, including reciprocals. Data on normal or leaflets, and determinate growth habit with long internodes. Long mutant type and growth habit type were evaluated in these F2 internodes and weak stems contribute to a floppy habit. populations. The F2 plants were harvested individually when the pods and seeds were dry. All F3 seeds taken from F2 populations were field planted as 576 plots (families) in Summer 1998. In Fig. 1. The Topiary architectural mutant of common bean. (A) Growth habit of addition, 250 remnant F2 seeds from each of eight crosses were Topiary plants; (B) comparison of Topiary (above) and ‘Minuette’ (below) planted. Data were collected for normal or mutant type from F leaves showing differences in rachis, petiolule, and petiole lengths (leaflets have 2 been separated from petiole); (C) leaf of the Topiary mutant showing reflexed and F3 populations. terminal leaflet compared to the lateral leaflets; and (D) terminal node from a Allelism tests were conducted to determine whether the new Topiary plant showing inflorescence development, and demonstrating that mutant was allelic to ol (overlapping leaflets), (Nagata and Topiary is determinate. Bassett, 1984) and dgs (dark green savoy leaves), (Frazier and Davis, 1966). Seeds of genetic stocks PI 583648 carrying ol and PI 583622 with dgs were obtained from the Western Regional Plant Introduction Sta- tion, Pullman, Wash. The new mutant was crossed to the ol and dgs stocks in the greenhouse in Spring 1998. Eighteen F1 plants of each cross combination and recip- rocal were grown in the greenhouse in Sum- mer 1998. Fifty F2 plants of each cross combination and reciprocal were planted in the greenhouse in Winter 1999. The F1 and F2 populations were evaluated for traits as- sociated with the three mutants, as well as other traits segregating in these crosses. Chi-square tests for goodness of fit and homogeneity were used to examine segre- gation ratios in F2 and F3 populations (Mather, 1951; Ramsey and Schafer, 1997). Contin- gency chi-square test for independence (Everitt, 1977) was used to test for linkage in two point segregation data. The contingency chi-square test of independence makes no prior assumptions about segregation ratios and was the preferred method because in- heritance of some traits was not known and/ or some segregation ratios deviated from expected segregation ratios. Results MORPHOLOGICAL DESCRIPTION. We chose Topiary as the designation for the trait be- cause of the resemblance of the mutant to shrubbery from a topiary garden (Fig.