In dry bean (Phaseolus vulgaris L.), growth form, i.e., determinate vs. indeterminate, and growth habit, i.e., upright/erect/bushy vs. viny/prostate, are among the most important characteristics for classifying cultivars from an agronomic viewpoint (Kelly, 2001; Laing et al., 1984; Singh, 1982). Dry bean is morphologically classified as determinate or indeterminate growth forms depending on whether the terminal meristem is reproductive (determinate) or vegetative (indeterminate) (Miklas and Singh, 2007). This characteristic is genetically controlled by the gene Finfin and unaffected by the environment (Koinange et al., 1996). Having a determinate terminal meristem was the result of FinFin or Finfin that is dominant over an indeterminate type (finfin) and this probably evolved through natural mutation of the wild-type Fin gene (Gepts, 1998). Indeterminate agronomic cultivars were classified into Type II and Type III based on vine growth extension and climbing ability. Determinate cultivars were classified as Type I and subdivided by their climbing ability. North American-grown commercial dry bean cultivars are described by Singh (1982) as:
Type I = determinate, erect (bushy). Further classified into Ia (no climbing ability) and Ib (some climbing ability);
Type II = indeterminate, erect (bushy). Further classified into IIa (no climbing ability) and IIb (some climbing ability = semiclimbing); and
Type III = indeterminate, prostrate (viny). Further classified into IIIa (some climbing ability = semiclimbing) and IIIb (strong climbing ability = climbing).
Vine length is highly affected by environment conditions, especially light (Kelly, 2001; Singh, 2001). The climbing phenotype of dry bean may be the result of a dominant gene, C1, whereas the nonclimbing types may be the result of a recessive gene, c1, that has evolved through natural mutation of C1 (Gepts, 1998; Kretchmer and Wallace, 1978).
Type II and III dry bean cultivars are the most common ones grown in the U.S. High Plains. The lower pods of common dry bean grown in the field are very close to the ground. Because of this, the conventional practice in dry bean production in the U.S. High Plains is to harvest by first undercutting plants, conventional harvest, to minimize yield loss (Smith, 2004). The alternate method of harvest is direct harvesting but the yield loss in the Nebraska Panhandle may be greater than 10% even with the addition of lifters (Smith, 2004). In the Red River Valley, the mean of nine cultivars grown in four North Dakota locations over 2 years, seed yield was reduced from 2240 for conventional harvest to 1410 kg·ha−1 for direct harvest or 27% (Eckert et al., 2011). Most of the yield reduction was the result of seed loss during harvest, 4.5% by conventional harvest vs. 23.2% by direct harvest (Eckert et al., 2011).
One possible method of reducing yield loss is to stimulate growth of lower internodes, those below the node with the first flower and pod, to raise lower pods higher off the ground and allow the cutting blades on a direct harvester to cut the stem below those pods. This may be accomplished by application of a growth-stimulating compound such as GA3.
The ability of gibberellins to promote stem growth was known since the 1930s when a rice disease was identified to be the result of a pathogenic fungus Gibberella fujikuroi (Takahashi et al., 1991). Since then, there have been more than 130 gibberellins identified. Gibberellic acid, a key gibberellin, is highly active and well known to stimulate stem elongation (Davies, 2010; Marth et al., 1956). A greenhouse bioassay for GA3 applied to fully opened unifoliate leaves of snap bean cultivars (P. vulgaris) was developed showing a dose–response for stimulating stem elongation and exposure between 2 and 10 μg GA3/plant for maximum effect (Knoche et al., 1998, 2000).
The objective of this study was to compare the GA3 dose–response of indeterminate dry bean cultivars with an erect, upright (Type II) growth or a prostate (Type III) growth habit and determinate cultivars (Type I).
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