Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/1998
Publication Date: N/A
Interpretive Summary: In alfalfa, the crown is the connecting plant structure between the shoots and roots. The crown gives rise to new stems each spring and after each harvest and therefore influences overall plant productivity and long term survival. Lack of information about what factors influence crown size and vigor limits our ability to develop improved alfalfa varieties. We investigated genetic control and environmental responses for crown depth, crown width, crown stem width, number of crown stems, and number of crown buds. We found that the expression of all crown traits studied can change depending on the environmental conditions in which alfalfa plants are grown. Crown stem width was controlled mostly by the genetic make up of the alfalfa, so plant selection programs for increased crown stem width should be successful. Crown width, number of crown stems, and number of crown buds were controlled by genetic information but also were influenced by environmental conditions. Plant selection programs to improve these crown traits would be possible, but environmental conditions will affect the level of success. Crown depth was controlled mostly by environmental factors and selection programs to increase crown depth are not likely to be successful. Our results suggest that crown stem width, number of crown stems, and number of buds are the most promising crown traits for improvement through plant breeding. New alfalfa varieties with modified crown traits could provide alternative uses of alfalfa for farmers and farm communities. Increased crown stem and bud production would enhance long term survival under grazing or mowing stress and biomass types with increased stem yield could be used as a biofuel to produce electrical energy.
Technical Abstract: The crown is the transitional structure connecting the shoots and the roots and is associated with persistence and productivity in alfalfa. The objectives of this research were to determine the effect of geographic location and plant spacing on the expression of alfalfa crown traits and to determine the inheritance of five crown traits. Progenies from design II matings and diallels were planted during May 1991 at two locations in 30-cm rows with 2.5 cm between plants. During October 1991 plants were dug and evaluated for crown depth, crown width, number of crown stems, crown stem width, and number of crown buds. Border effects were determined by evaluating single plants at the ends of the plot separately from the plants in the middle of the plots. Progenies responded similarly to the extra growing space at the ends of the plots. Locations affected crown morphology but only number of crown buds showed a significant location x progeny interaction. Additive effects were important for determining heritability for crown stem width and number of crown buds while both additive and nonadditive effects were important for crown width and number of crown stems. These traits had moderate (0.38) to high (0.90) heritabilities. Few genetic effects were found for crown depth. Selection for crown stem width at one location with uniform plant spacing should be successful. Multiple location selection schemes would be more appropriate for number of crown buds. Selection programs for crown width, number of crown stems and buds may be feasible but selection of parental material could be critical for success. Selection programs for crown depth would not be effective.