Seedling Growth of Cicer Milkvetch as Affected by Seed Weight and Temperature Regime1

Abstract

Seedling vigor of cicer milkvetch (Astragalus cicer L.) has been improved by breeding for high seed weight, but it is not known how growth characteristics differ among seedlings derived from seed of different weight classes. Therefore, the objective of this study was to determine the effect of seed weight (3.2, 3.6, 4.0, 4.4, 4.8, 5.2, and 5.6 g/1,000 seeds) and temperature regime (20 C day/15 C night and 25 C day/20 C night) various seedling growth traits. When averaged over all sampling dates, temperature regime significantly affected area of upper leaves; dry weight of cotyledons, primary leaf, upper leaves, stems, and roots; height of seedlings; total dry weight of shoots; and total dry weight of seedlings. Values for all traits except weight of cotyledons and primary leaf were higher at 25/20 C than at 20/15 C. Cotyledon area and primary leaf area were not influenced by temperature. Within a temperature regime, seed weight also significantly affected all characters. For most seedling traits an increase in dry weight or area was associated with increased seed weight.In a growth analysis study, temperature treatments significantly affected initial seedling weight, initial leaf area, relative growth rate, relative leaf area expansion rate, relative leaf weight expansion rate, leaf area partitioning coefficient, leaf weight partitioning coefficient, and final seedling weight. Temperature regime did not affect initial leaf weight and net assimilation rate. Seed weight was positively and linearly associated with initial seedling weight, initial leaf area, and initial leaf weight at both temperatures and with final seedling weight at 20/15 C. The lack of association of seed weight with some important growth analysis traits suggests that certain seedling vigor characters are entirely independent of seed weight. The initial advantage of high seed weight progenies, however, tended to be maintained in the early phases of seedling development, as indicated by final seedling weight. Thus, with populations selected for high seed weight, additional progress in improving seedling vigor might be achieved through selection for relative leaf area expansion rate, net assimilation rate, or other traits.