Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/1999
Publication Date: N/A
Interpretive Summary: The effects root disease and root feeding insects on red clover seed production systems are not well defined. Thirty-one red clover seed fields were used to determine the relationships of plant genetic background, Fusarium root rot disease, and the root borer insect on root healthy, plant-water uptake, and seed yield. Rapid plant regrowth after herbage removal in spring is needed to have high seed production and was affect by the ability of the plants to utilize available soil-water depletion. The capacity of plants to take up water was due more to amount of root borer infestation than root disease. Genetic selection for improved root borer rather than root rot resistance may be a useful strategy for increasing red clover seed yields and should be used in conjunction with high flower density to improve western U.S. seed production of cultivars grown for forage in the midwestern states.
Technical Abstract: Red clover (Trifolium pratense L.) an important forage legume grown in the USA, Canada, & northern & eastern Europe is primarily grown for seed in western OR. Thirty-one seed fields were selected in spring 1992 & their cultivar identity, age of stand, & seed genetic source groupings determined by grower interviews & DNA analyses. Two herbage removal time treatments were applied & the number of flowers & soil-water content measured during the period of flowering & seed production. Root rot & root borer [Hylastinus obscurus (Marsham)] infestation was measured at early herbage removal time & seed harvest. The primary causal agent of root disease was Fusarium solani (Kuhn). However, the percentage of plants infested with root borers was the greatest root health determinate of seed yield, regardless of early or late herbage removal time. Seed yield was also correlated with the ability of plants to regrow & produce flowers following herbage removal. For both herbage removal time, the ability of plants to regrow after removal was affected by their capacity to deplete soil-water. The season-end root borer infestation & soil-water depletion amount were inversely related, indicating that root integrity was required for water utilization. Second-year seed crops had greater disease & root borer damage than first-year crops. Late herbage removal time treatments had reduced flower density, seed yield, & season-end phytomass compared with early removal. Genetic selection for improved root borer rather than root rot resistance may be a useful strategy for increasing red clover seed yields.