Relationships of certain pollen and pistil characteristics to different measures of self-fertility in alfalfa

Alfalfa (Medicago sativa L.) is one of the most important forage plants grown in the United States and many other countries. Many varieties of alfalfa have been developed which differ in adaptation, disease resistance, and other characteristics. Most of these varieties were developed by mass selection or by polycross progeny testing and maintained as synthetic varieties; therefore, such varieties do not make maximum use of heterosis. Hybrid varieties have resulted in yield increases of 20 per cent in corn and several other crops. It has not been feasible to produce inbred lines for production of hybrid varieties in alfalfa because inbreeding results in severe decreases in both reproductive and vegetative vigor. The mechanisms responsible for the low seIf-fertility in alfalfa are complex and poorly understood. An understanding of the relationships of various pollen and pistil characteristics to different methods of estimating self-fertility would help elucidate self-sterility in alfalfa. The first objective of this study was to compare three methods of selfed flowers that produced pods, seeds per flower selfed and seeds per pod produced. The second objective was to determine the relationships of pollen viability, pollen tube length, pistil length, style length and number of ovules per ovary to the three previously mentioned estimates of self-fertility in alfalfa.