| Summary: | Alfalfa (Medicago sativa L.) forage yield may be reduced by moderate levels of salinity. Increasing forage yield in saline environments through plant breeding could ameliorate this problem. Selection for increased salt tolerance in alfalfa in cell culture, at germination, or during seedling growth with high NaCl levels has not resulted in agronomically relevant levels of salt tolerance. Different selection schemes were examined to identify alfalfa plants with the ability to germinate, establish, and regrow at salinity levels common in agricultural areas. Data from 'Sonora' and its parental ecotype African grown in a greenhouse and irrigated with 0, 30, 60, or 80 mM NaCl were used to simulate selection for increased forage yield in each NaCl environment through five harvests. Predicted gains in forage yield were highest in non-saline conditions and gains decreased as the NaCl level increased in the selection environment. Selection based on plant yield from regrowth harvests was predicted to be more efficient than that based on seedling harvest. Genetic and phenotypic relationships between plant performance at seed germination, seedling development, and post-harvest regrowth at 0 or 80 mM NaCl were also determined. The effect of NaCl on forage yield of alfalfa regenerated from non-saline callus cultures was examined. This research showed that selection for increased forage yield can be made at moderate NaCl levels in germplasm with ample variation for yield when grown in saline environments. Selection for increased forage yield in non-saline conditions may eliminate potentially salt tolerant plants from a population. Selection for increased alfalfa forage yield in saline environments at early stages of development is not necessarily optimum. Selection methods that include each critical growth stage may be required to develop alfalfa cultivars with increased forage yield in saline environments. (Abstract shortened with permission of author.)
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