Submitted to: Journal of New Seeds
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2007
Publication Date: 5/12/2008
Citation: Riday, H. 2008. Alfalfa subsp. sativa by falcata intersubspecific semi-hybrid seed production using alfalfa leafcutter bees. Journal of New Seeds. 9(1):19-31.
Interpretive Summary: Yellow flowered by purple flowered alfalfa hybrids have been shown to produce increased hay yields. The alfalfa leafcutter bee is an important pollinator species used to produce alfalfa seed. This study examined leafcutter bee preference for purple flowered alfalfa versus yellow flowered alfalfa. Higher amounts of yellow to purple flowered alfalfa plants in the seed production environment was shown to produce less hybrid seed than would be expected without pollinator preference. These results are important to seed producers trying to maximize production of purple by yellow flowered alfalfa hybrid seed using alfalfa leafcutter bees.
Technical Abstract: Intersubspecific sativa by falcata alfalfa (Medicago sativa L.) hybrids offer a means of improving alfalfa dry matter yields. The alfalfa leafcutter bee (Megachile rotundata F.) is a major pollinator used in alfalfa seed production in North America. Alfalfa leafcutter bees have a pollinator preference for purple-flowered subsp. sativa plants over the yellow-flowered subsp. falcata plants. This study was conducted to quantify the pollinator preference by observing the amount of hybrid seed produced using alfalfa leafcutter bees. Two pollination environments and three different proportions of falcata parents in pollination cages (50%, 75%, and 90%) were included to determine shifts in quantities of hybrid seed produced due to environment and/or pollinator subsp. falcata flower availability. Total and hybrid seed amounts and seed size differed between environments. Seed size differences were observed between subspecies. Hybrid seed yields were 57% of expected hybridity on an experiment mean basis. In crossing cages with higher subsp. falcata parent proportions, a decreased amount of observed percent hybridity compared with expected hybridity was observed (i.e., 50% subsp. falcata = 72%, 75% subsp. falcata = 59%, and 90% subsp. falcata = 39% of expectation). Seed yield per plant and seed size did not differ between cages with differing subsp. falcata parent proportions. Plant to plant variation for seed yield and seed weight was observed; however, no plant to plant variation for observed percent hybridity of expected hybridity was found. This study suggests using 50% subsp. falcata plants to 50% subsp. sativa plants will produce 36% hybrid seed (or 72% of expectation) in alfalfa seed production fields using alfalfa leafcutter bees as pollinators and suggests increasing percent subsp. falcata parentage will decrease the percent of hybrid seed observed compared with expectation.