Inheritance of coumarin in sweet clover

A study was made of the manner of inheritance of coumarin content of sweet clover in a cross between inbred lines that differed in coumarin content. Inheritance of the dwarf branching habit also was studied in the same cross. The analytical method used to determine coumarin content does not separate coumarin, coumaric acid, melilotic acid, and other phenolic bodies from one another so the term coumarin as used in this study includes these substances and is reported on a green weight basis. In the cross studied the mean coumarin content of the F1 generation approached closely the mean coumarin content of the low coumarin parent and it appeared that in this cross relatively low coumarin was dominant over high coumarin. Approximately 77% of the F2 population fell in the range of the low coumarin parent and 23% in the range of the high coumarin parent when all the material was grown the same year. Therefore, it seems probable that a single major factor pair is involved in the inheritance of coumarin content. The distribution of the F2 population was not bimodal. F3 lines from selfed plants of the Alpha type were grown in two different fields at University Farm and also at Waseca in southern Minnesota. The mean coumarin values for field E were significantly higher than the mean coumarin values in the other field or location. The degree of association of coumarin content between the different fields and locations as indicated by r exceeds or closely approaches the 5% point of significance. A highly significant correlation coefficient of +.2358 indicates that it was not possible within the range of coumarin content studied to determine accurately the coumarin content of second year growth by measuring the coumarin content during July of the first year's growth. Growth habit and coumarin content do not appear to be associated with each other on the basis of a study by the X2 test for independence.