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.
Genetic and morphological characteristics of an architectural mutant in common beans were studied. The mutant had shiny, dark green leaves, overlapping leaflets, short petioles and a terminal reproductive bud even though the line did not carry the fin gene. Branching was nearly absent, resulting in a single stem vine. This is a new form of determinancy in common bean. Inheritance studies demonstrated that the mutant trait was controlled by a single recessive gene. Allelism tests were performed between the mutant and a previously reported similar mutants, which were overlapping leaflets mutant (ol), and dark green savoy leaf mutant (dgs). Results showed that the mutant trait was not allelic to ol and dgs. As a temporary designation, the name “”opiary” describing its compact and neat appearance is being used. Linkage was tested for growth habit (fin), shiny leaf, cross-sectional shape of pods, striped pod (prpst) and pod suture strings (st) with the topiary mutant. No linkages were detected between either the mutant and marker genes or among the marker genes. The topiary mutant has potential for improving common beans. Its single stem growth habit may allow closer row spacing leading to higher planting populations and may enhance the efficiency of mechanical harvest. Pod formation at higher nodes may escape disease. Currently, the thin stems cause lodging. Development of thick and upright forms will be the subject of future studies.