The active accumulation of solutes by osmotically stressed plants is thought to be an adaptive response that increases the ability of drought-or salt-stressed plants to maintain leaf water content, turgor, and possibly growth. In an earlier study we developed two barley (Hordeum vulgate L.) isopopulations differing in solute potential (~q), and these isopopulations were characterized for their response to salt stress in the growth chamber. At each stress level tested, the low-q,~ population had about 0.1 MPa lower q,,. In the present study we used these isopopulations to test the effect of genetic differences in ~ on growth in well-watered and drought-stressed conditions in the greenhouse and field. When grown in the greenhouse, the lowq,, population had a slower rate of leaf production and accumulated significantly less total aboveground dry matter by midanthesis than did the high-q's population. This difference (up to 35%) was greatest in optimal environmental conditions (adequate water, high irradiance, warm temperatures) and decreased in less favorable environments. The growth differences were not associated with differences in partitioning of dry matter to the leaves or differences in water use efficiency. The growth disadvantage of the low-q,~ population was also observed for grain yield (11-44%) and total aboveground biomass production (10-25%) under dryland and irrigated conditions in multisite field trials. Thus the development of a barley isopopulation with constitutively lower q's resulted in a reduction in yield potential.
Five cultivars of flax (Linum usitatissimum L.) were each seeded at four rates to determine the influence of seeding rate on seed and oil yields, their components, and other plant and seed characteristics. A path coefficient analysis technique was employed to partition yield components into direct and indirect effects to assess the usefulness of yield components as selection criteria in a flax breeding program. Rates of seeding that were used in the study gave 0.8, 1.6, 2.8, and 3.9 viable seeds per cm of row.Seed yield, oil yield, oil content, iodine value, seed size, seeds per boll, bolls per area, and test weight were not significantly affected by variations in seeding rate. Bolls per plant and height were decreased and maturity was hastened by increased seeding rate. Approximately 85% of the variation in oil yield could be attributed to variation in bolls per area, seeds per boll, seed size, and percent oil. Stand accounted for only an additional 1% of the variation in oil yield.Path coefficient analysis showed bolls per unit area to be the most important component determining seed and oil yields, both directly and indirectly. Seeds per boll, seed size, and percent oil showed nonsignificant and negative correlations with oil yield, because the positive direct effects they exerted on yield were canceled by negative indirect effects through other components.
Protein percentage and its relationship with 15 other agronomic characteristics were studied in F5 generation progenies of F4 plants from crosses between Avena sterilis L. Var. Maxima Perez Lara and five A. sativa L. cultivars in an attempt to determine the relationships among factors involved in the improvement of oat quality. Mean percent protein of the progenies was intermediate between their parents. Transgressive segregation was present for both percent protein and yield in four crosses. The possibility of simultaneous improvement of these characteristics is suggested.Simple correlation coefficients indicated percent protein was positively associated (P<.01) with characters typical of A. sterilis. Regression analysis indicated yield had the most influence on percent protein of the characters studied.
The relationship between tillering in space‐planted early generation populations and in close‐planted commercial‐type stands of wheat (Triticum aestivum L.) was investigated over a 5‐year period. The primary objective was to determine if this relationship is strong enough to justify selection for tillering type in spaced populations. Secondary objectives were to examine tillering‐ yield relationships and possible differences in tiller survival among wheat genotypes. Four winter and two spring wheat cultivars with known tillering differences in densely‐seeded stands maintained their relative rankings when grown in spaced plantings. However, when F5 plants selected for high or low tillering in spaced populations were subsequently grown in densely‐sown F6 plant‐rows, little relationship was observed between tillering characteristics in the two planting densities. In attempting to explain the divergent results it is theorized that tillering differences among the cultivars, which had exhibited these differences over many years and environments, were largely genetic and would, therefore, likely persist regardless of planting density. Conversely, we suspect that much of the tillering variation observed among the spaced F5 plants was non genetic and would lack consistency under dense seeding. The relationship between tillering in spaced and close plantings appears to be further complicated by the differential ability of genotypes to mature spike‐bearing tillers, as a percentage of total tillers initiated. The cultivars we studied veried widely in the efficiency with which they matured fertile tillers in dense plantings. In only two of eight crosses did we observe a significant association between degree of tillering in space‐planted F5's and in their densely‐seeded F6 plant‐rows. Consequently, tillering differences in space‐planted early generation wheat populations do not appear to provide a reliable selection criterion. We observed no consistency between grain yield and degree of tillering. Other yield components largely compensated for variation in tiller number, with kernels per spike having a greater effect than kernel weight.
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