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Stage of maturity at harvest and relative seed size can affect seed vigor. Greenhouse and field studies were conducted to determine the effect of seed maturity on seed vigor, storability, and subsequent plant growth of four cultivars of snap bean (Topcrop, Provider Black, Provider White, and Cherokee Wax). Seeds harvested between physiological maturity (PM) and harvest maturity (HM) showed the highest seed vigor and storability. At PM, seed moisture content was about 55%. A drop in seed fresh weight and a pod color change from green to yellow appear to signal the stage of PM. Delaying harvest past HM reduced seed vigor. The three cultivars with colored seed coats showed higher seed vigor than Provider White. Climatic and weathering effects on maturity, vigor, and yield of Topcrop and Cherokee Wax seed were evaluated at three locations (L-I, L-2, and L-3) in Sri Lanka having different agro-climatic conditions. Seeds that developed and matured under cooler conditions (L-l) produced higher yields and had larger size, better color, and higher vigor. Seeds developed and matured faster under warmer conditions (L-3); however, seed vigor and yields were lower and seed vigor dropped prior to HM. Cherokee Wax was the most tolerant to field weathering. Seeds of Topcrop and Cherokee Wax were separated by weight into three seed sizes (small, medium, and large) and evaluated for crop performance in two plantings (12/90 and 3/91). Field emergence was higher from larger seeds in the second planting, where the soil conditions were more stressful. Seedlings and plants at the flowering stage were larger and pod yields higher from larger seeds. The cultivar x seed size interaction was significant for pod yield per plant. Topcrop showed no differences, while with Cherokee Wax, pod yield per plant increased with increase in seed size during both plantings. Seeds produced from small seeds were similar or higher in vigor, indicating that small seeds could be used for seed production purposes. The data from these experiments indicate that vigor in snap bean seeds can be optimized by harvesting at an early stage after PM and by grading to remove small seeds. / Ph. D.

Two accessions of tepary (phaseolus acutifolius Gray var. latifolius) and navy (P. vulgaris L. 'Fleetwood') beans were studied for salt tolerance at several• developmental stages. Genotypes were germinated at 0.0 through -2.5 MPa NaCl at 25°C and 35°C for nine days. Tepary accessions had higher germination percentages and rates than navy for ≤ - 2.0 MPa at 250C and ≤ - 1.5 MPa at 35°C. Fresh weights of root plus hypocotyl decreased severely with the first increment of NaCl (-0.5 MPa) for all genotypes. Fresh weight of navy was reduced more at 35°C than at 25°C. Genotypes were stressed in vermiculite-filled trays with 0.0 through -1.5 MPa NaCl for 14 days. Final growth stage and rates of emergence were reduced at salinities ~ -0.6 MPa NaCl, and were higher in tepary than navy at -1.2 MPa. Tepary beans tended to maintain higher water and osmotic potentials, and at -0.9 MPa had less reduction in leaf area than navy beans. Fresh weights, dry weights and root:shoot ratios declined in all genotypes with increasing salinities. Plants grown hydroponically were stressed with -0.10, -0.25, and -0.50 MPa NaCl during either vegetative or reproductive stages. Navy had equal or greater fresh and dry weights of leaf, stem, and pods at -0.10 MPa, but tepary beans had equal or greater weights at the highest salinity relative to navy. Tepary had the greatest pod weight with -0.50 MPa NaCl applied during the reproductive stage. Carbon exchange rates (CER) were lower in navy than one or both tepary beans at some sampling times. Tepary beans tended to have higher leaf water and osmotic potentials than did navy. Transpiration and stomatal resistance values were similar in all genotypes, while leaf temperatures were different in white tepary versus navy. Tepary beans yielded higher than navy when grown in low and high salinity fields. Transpiration rates, leaf water and osmotic potentials, and CERs were similar or higher, while stomatal resistance and leaf temperatures were similar or lower in tepary than in navy. Plant height and stand count also were measured. Tepary was more salt tolerant than navy, exhibiting greater tolerance to NaCl at every growth stage.

Shoot and root fresh and dry weight, shoot length, leaf area, leaf area index and relative growth rate of 14 day old tepary bean (Phaseolus acutifolis Gray) and navy bean (Phaseolus vulgaris L.) seedlings were reduced following treatment with NaCl solution exhibiting osmotic potential of either -0.25, 0.50, and -0.75 MPa. Salinity reduced the growth of navy bean more than tepary bean. The physiological basis of the adaptive response of tepary bean seedlings to salt stress was explored by determining the water and osmotic potentials, relative water content, free amino acid and sugar concentrations, distribution and levels of inorganic ions within the seedlings and ATPase activity of the root plasma membrane. Salinity led to an osmotic adjustment in the leaves and the proximal part of the root of tepary bean. Turgor remained almost constant whereas osmotic and water potential and relative water content declined following the salt treatments. The osmotic adjustment of the leaves and proximal part of the roots was -1.7 MPa and -1.2 MPa, respectively, in seedlings treated with -0.75 MPa NaCl solution. Free amino acids and sugars increased under salinity stress in both species but they increased more in the tepary bean. Glucose was the most abundant free sugar. The nonstructural carbon solutes contributed -0.15 MPa to the seedling's osmotic adjustment whereas Na, Cl, K and Ca ion levels contributed -0.85 MPa. However, the levels of these solutes were not large enough to account for the total osmotic adjustment observed in the salt treated seedlings. This study shows that tepary bean has specific strategies to overcome the impact of salinity through osmotic adjustment and exclusion of Na and Cl ions from the stems and leaves by retaining these ions in the proximal part of root and stem base. (Abstract shortened with permission of author.)

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