The physiology of seasonal growth in tall fescue varieties (Festuca arundinacea Schreb.) Public Deposited


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  • The winter and summer growth of varieties of tall fescue (Festuca arundinacea Schreb.) that had originated from the Mediterranean region (Oregon 1000 and Tunisia) and northern Europe (Alta) were studied outdoors in the Mediterranean climate of western Oregon, and in greenhouses and controlled environment chambers. Treatments of temperature, photoperiod and gibberellic acid (GA) were imposed in order to establish the limitations to winter and summer forage production. Measurements of photosynthesis and the distribution of assimilates were made by growth analysis and the level and nature of reserve carbohydrates by the copper-iodometric method. In western Oregon, the varieties that had originated from the Mediterranean region made more foliar growth during the winter but less during the summer than Alta. These two different patterns of seasonal growth were interpreted as ecotypic variation that had enabled the species to survive seasons of stress in the regions of origin--freezing winters of northern Europe and summer droughts of the Mediterranean. Cubes of sod taken during the winter months from swards of Alta and Tunisia showed that Alta had a greater density of tillers and buds, and a higher level of reserve carbohydrates than Tunisia. This result suggested that Tunisia utilized photosynthate during the winter for the production of leaves rather than storing it as carbohydrates. During the winter of 1967 the foliar growth of both Alta and Oregon 1000 was increased by a temperature of 15 to 20C, a foliar spray of 0.1% GA, and possibly by a long photoperiod. The suggestion was that winter growth was limited more by the internal growth regulator balance than the external weather, and that relative rather than true dormancy was involved. Although the chlorophyll concentration in the foliage was reduced by GA the total chlorophyll was actually increased by 10 to 30% and, consequently, the chlorosis may not be deleterious to pasture production. The rate of regrowth of Tunisia was greater at 7/3C than Alta but this difference was eliminated by GA. Rate of regrowth may be an important determinant of winter growth of ecotypes of forages grasses and GA may promote the mobilization, or utilization, or both, of reserve carbohydrate--reserves that were found to be higher in Alta than Tunisia. At the end of a prolonged exposure of 18 weeks in a simulated winter environment of 7/3C and 19 ly/day (400 to 750 nm) the total weight of Tunisia was greater than Alta and proportionately more dry weight was present in the leaves than roots. The total available carbohydrates (TAG) extracted with 0.2N H₂SO₄ was similar for Alta and Tunisia; it was 20% of the dry weight of stems. Gibberellic acid increased the concentration of TAC 6% in Alta and 4% in Tunisia. The total water soluble carbohydrates (WSC) were 14 and 9% of the stems of Tunisia and Alta respectively, and 6% of the leaves and 5% of the roots of both varieties. Fructosans were the main component of WSC, and sucrose and reducing sugars were of lesser concentrations. The WSC were increased by GA in all parts of the plants and the increase was greatest in Alta; sucrose showed the greatest increase. Subtraction of WSC from TAG gave an estimation of starch; it was unexpectedly high with concentrations as high as fructosans and indicated that 0.2N H₂SO₄ may have extracted structural carbohydrates. The superior growth rate of Alta in the summer was established in June. At the end of June 1968 the relative growth rate of both Alta and Tunisia was increased by GA due to a stimulation of net assimilation rates. The WSC were highest in the stems and were 14 and 9% of the stems of Alta and Tunisia respectively. Fructosans were the main WSC and the higher level of WSC in Alta was due to a higher level of fructosans. Gibberellic acid increased the WSC by 1% of the dry weight during the treatment time of 8 days. The measurement of photosynthesis of leaf segments of tall fescue by manometry was unreliable. The activity of isolated chloroplasts was also unreliable although some improvement was obtained by isolating in the presence of polyvinylpyrrolidone. The concept developed in this thesis was that when an ecotype is introduced to a new environment, or used as a basis for a new variety, the production and utilization of photosynthate may be controlled by an internal growth regulator balance which is not well coordinated with the weather. In such a circumstance, the possibility exists that the growth regulator balance may be adjusted by a timely application of the appropriate growth regulators in order that the variety may grow to the limit of its genetic capacity during periods of favorable weather.
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