Purdue University Ag* Exp. Station
CLARK SOYBEAN
AY 6D
October, 1953
A. H. Probst, U. S.  Regional Soybean Laboratory, U.S.D.A. and Agronomy Department, Purdue University
Clark is a new high yielding, high oil content, frog-eye leaf spot resistant soybean variety. It is about 7 days later in maturity than Lincoln and about 4 days earlier than Wabash. This new variety is adapted to the southern one-half of Indiana,
ORIGIN AND DEVELOPMENT Clark is a pureline selection from the backcross Lincoln X (Lincoln X Richland). The Lincoln.X Richland cross was made in 1941 by M. G. Weiss at the Iowa Agricultural Experiment Station. The backcross was made in 1942 in the greenhouse by L. F. Williams of the U.S. Regional Soybean Laboratory, Urbana, Illinois. Early generation selection and testing were done by L.F. Williams. This variety was developed cooperatively by the Midwestern Agricultural Experiment Stations of the North Central Region and the U.S. Regional Soybean Laboratory.
DESCRIPTION Clark has medium to large-sixed yellow seeds with a black hilum. The seed is rather similar in shape and color to Lincoln, But slightly larger, The pods are medium to large in size, mainly two-and three-seeded, brown in color, and are borne primarily on the central stem. The plants are medium to tall in height, indeterminate and usually rather erect in growth habit with purple flowers and brown pubescence. The plants are very similar to the Lincoln parent but slightly taller, about 7 days later in maturity, and they have purple flowers whereas Lincoln has white flowers.
PERFORMANCE This new variety has been grown in a number of tests at four locations in Indiana during the period of 1948-1952.
The average results of these tests are given in Tables 1 and 2.
ADAPTATION Clark is well suited as a full-season variety in Indiana mainly south of a line drawn across the state through Indianapolis and Richmond. In the upper two tiers of counties in this area this variety will be suited best only for early planting or in rotations where it will not be followed by wheat. Because of its higher yield and earlier maturity than Wabash and Perry it will be suited especially well in southern Indiana in rotations where wheat follows soybeans. In southwestern Indiana, south of Vincennes, Clark may be planted under most conditions as late as June 20 and usually mature sufficiently early to permit timely seeding of wheat, Clark generally will not produce as good quality seed as Wabash in southwestern Indiana, especially when planted in early May.
DISEASES Like Lincoln and Wabash, Clark also is resistant to frog-eye leaf spot. Clark has not been observed to be any more or less susceptible to the other soybean diseases occurring in the area of adaptation than recommended varieties now grown in that area.
Purdue University Agricultural Experiment Station, Lafayette, Indiana
in cooperation with
U.S, Regional Soybean Laboratory, Bureau of Plant Industry, Soils, and Agricultural Engineering, Agricultural Research Administration, U. S. Department of Agriculture, Washington, D. C.
(over)