Cotyledonal- or transverse-cracking (TVC) in certain cultivars of snapbeans, Phaseolus vulgaris ~. seeds, clearly evident during germination, seriously places affected seedlings at a competitive disadvantage. TVC is an inherited trait and occurs across cell walls of cotyledons rather than along cell walls. Thus, it might be hypothesized that internal pressure resulting from swelling of storage proteins during imbibition might account for cellular rupture. To further elucidate this possibility, experiments were designed to compare electrophoretic patterns of storage proteins from seeds of snapbeans resistant and susceptible to TVC, and to correlate the different patterns of polyacrylamide gel el ectrophoretograrns of these proteins to TVC. One hundred seeds were selected randomly from a bulk sample of 225 g from each of 17 seed lots representing 15 cultivars, seed coats removed and cotyledons finely ground (60 mesh). Seed flours were defatted twi ce with hexane (50 ml / g) at 4°C and defatted flours reground with a mortar and pestle. Seed proteins were extracted in 0.5 M NaCl (solvent to four ratio of 10:1) at pH 7.5 for 1 h at 4oc with centrifugation at 10,000 g for 30 min. Separated proteins were subjected to electrophoresis under denaturing and non-denaturing conditions and molecular weight of different protein brands determined. Different protein banding patterns were identified and correlated to the TVC phenomenon. The data showed visual differences between banding patterns of resistant and susceptible cultivars. While the electrophoretic technique shows observable differences in cultivars expressing differential TVC, it is not clear which protein bands are associated with the TVC phenomenon. For plant breeders to employ this tool in screening for TVC resistant snapbean cultivars, further requirements are needed.

Certain varieties of snap bean, Phaseolus vulgaris L. , seeds are very susceptible to cracks that develop naturally across the cotyledons during pre-harvest, storage, or germination. This phenomenon is commonly known as cotyledonal cracking and may cause serious yield reductions on plants developing from affected seeds. Cotyledonal cracking susceptibility of six white and six colored seeded varieties of snap beans were compared. Considerable differences were found in cracking susceptibility, but there was little or no relationship between seed coat color and cracking susceptibility. An experiment was conducted to determine if a metabolic stress of the plant during the time of pod set could be involved in cotyledonal cracking. Blossoms were tagged on individual plants beginning with the day of first blossom, and tagging was continued for 21 days as blossoms emerged . Individual pods were harvested at maturity and maintained under controlled conditions throughout a simulated weathering treatment to follow. Seeds of each pod were classified according to the amount of cotyledonal cracking sustained. It was concluded that if a stress were involved, it apparently affected the seed several days after pod initiation and that an increase in cotyledonal cracking was negatively correlated to an increase in the number of pods set during one day. Simulated weathering tests were made of seeds remaining in the pod and seeds from the same varieties that were shelled. The results indicated that the pod provides about equal cotyledonal cracking protection for all varieties tested. Apparently the pod is not an important cause of cracking resistance in certain varieties of snap beans. Seed coat permeability was measured and compared for the 12 varieties . A technique was employed by which the bean seed coat served as a semipermeable membrane between a distilled water and a sucrose solution. Sucrose dilution was measured refractometrically and the rate of water penetration calculated. There was little relationship between seed coat permeability and cracking susceptibility among the varieties. The rate of imbibition and drying for seeds of six varieties having varying degrees of cracking susceptibility was tested. Imbibition and drying conditions were closely controlled and weight changes were recorded at regular intervals during imbibition and drying. Results indicated that some of the varieties expressing the most rapid moisture changes were also the most resistant to cracking. It was concluded that the rate of change of seed moisture was not the primary factor controlling cotyledonal cracking susceptibility. Rate of imbibition was tested for two susceptible and two resistant varieties. When the pre-imbibition seed moisture was above 10 percent, a ll varieties imbibed water freely. When pre-imbibition moisture was below 10 percent, several seeds of resistant varieties became slowly permeable while nearly all seeds of the susceptible varieties imbibed freely. This suggested the possibility that a hard seed tendency of the resistant varieties may be one source of protection against cotyledonal cracking. Preliminary data suggested that the seed coats of susceptible varieties remain permeable even at moisture levels below 10 percent, while many seed coats of the resistant varieties become rather impermeable at low moisture levels. Microscopic examination of cotyledonal cracks from four different varieties indicated that the splitting occurred across cotyledonal cell walls more rapidly than between cell walls. This suggested that a weakness of the intercellular middle lamella is not responsible for cotyledonal cracking susceptibility. Further microscopic examination and comparison of the cotyledonal cell structure of two susceptible and two resistant varieties failed to show any structural differences between varieties that could account for differences in cotyledonal cracking susceptibility.