A notable instance of progress was the discovery at the North Carolina Agricultural Experiment Station in 1943 that the variety CNS is highly resistant to bacterial pustule. The variety lacks some of the better agronomic characters, but its resistance to pustule makes it a valuable parent for hybridization with other varieties. Lines derived from hybridizing it with superior varieties, such as Roanoke and Ogden, at the North Carolina Station have yielded strains having the same high type of resistance as CNS. The same has been done at the Illinois Station, using Lincoln in the cross with CNS. Those strains give excellent promise of future varieties that combine the pustule resistance of CNS with more desirable agronomic characters, such as a high content of oil, resistance to lodging, and high yields.

About 1,100 plant introductions of soybeans were tested for resistance to bacterial blight at the Illinois Agricultural Experiment Station in 1947. Two that had high resistance to the disease were selected and used in crosses with locally adapted strains. Even in the preliminary stages of testing, strains resulting from the coatings showed a high degree of resistance to bacterial blight. The hope was to develop from them varieties that have blight resistance plus high yield and oil content. None of the varieties used in the Midwest in 1953 is highly resistant to bacterial blight, but there is considerable varietal difference in susceptibility. Illini, Lincoln, Black-hawk, and Monroe are highly susceptible. Richland and Hawkeye are intermediate. Flambeau and Patoka appear to have some resistance, but develop the disease to some extent.

Workers in the Wisconsin Agricultural Experiment Station reported in 1946 that Mandarin 7, Ottawa Mandarin, Habaro, Dunfield, Mukden, Flambeau, Kabott, Pridesoy, and several Manchu selections were resistant to downy mildew and that Richland and Illini were highly susceptible. Further work at the station, reported in 1950, showed that there were three physiologic races of the causal fungus. The variety Illini was found to be highly susceptible to all three races; Richland susceptible to two; while Chief, Manchu 3, Mukden, and Dun-field were resistant to all three races.

Most, if not all, of the existing varieties are susceptible to rhizoctonia root rot. Work at the Minnesota Agricultural Experiment Station, however, points to the development of future varieties incorporating resistance to this trouble. Reselection from Ottawa Mandarin, Flambeau, and the progenies of certain hybrids yielded 12 lines with a high degree of resistance to rhizoctonia root rot.

The severity of frogeye on certain varieties was observed in southern Indiana and studies of varietal resistance were undertaken at the Indiana Agricultural Experiment Station. The varieties Capital, Flambeau, Hokien, Mandarin (Ott.), Blackhawk, Earlyana, Habaro, Monroe, Richland, Harosoy, Cypress No. 1, Dunfield, Illini, Gibson, Patoka, Hawkeye, and Chief were found to be susceptible. Adams, Lincoln, Anderson, and Wabash were resistant.

Resistance is still unknown for some of our most serious diseases, such as brown stem rot, stem canker, and bud blight. At the Iowa Agricultural Experiment Station, various strains, varieties, and selections have been tested for resistance to stem canker. At the Illinois station, similar tests with introductions, strains, and varieties have been under way for 5 years in a search for resistance to bud blight and brown stem rot. Nothing with high resistance had been found in 1953.

Until such disease-resistant varieties are available, the following practices are recommended to soybean growers as disease control measures: crop rotation, plowing under of crop residues in the fall, the selection of seed for planting from fields relatively free from diseases, and seed treatment in some areas.

Tests of ways to treat the soybean seed have been conducted in various places since 1925. They have usually shown that the emergence of soybean seedlings can be increased 10 to 15 percent by treating the seed with a suitable chemical disinfectant before planting. Only a few reports, however, have said that an increased yield of soybeans resulted from the increased stand obtained by seed treatment. This failure to increase yields has been due apparently to the fact that the recommended seeding rate of 1 bushel or more to the acre provides sufficient plants for a maximum yield, even though 10 to 15 percent of the potential stand is lost through seed decay and damping-off of seedlings. Consequently treatment of soybean seed has not been recommended as a general practice in the major producing States of the Corn Belt.

In the southern areas, on the other hand, the combination of poorer seed and a cold, wet spring sometimes results in the loss of 20 to 25 percent of the potential stand if the seed is not treated before planting. Under such conditions, yield increases due to seed treatment can be demonstrated, and the practice has been recommended in the South as a disease control measure. A somewhat similar situation exists apparently as one approaches the northern limits of soybean cultivation.

Of the numerous seed-treating chemicals tested on soybeans, Arasan and Spergon dusts at the rate of 2 ounces to the bushel have consistently given good results. The slurry formulations of these materials are apparently just as satisfactory as the dusts and are somewhat more convenient to use. Tests conducted at the Delta Branch Experiment Station, Stoneville, Miss., show that the treatments may be applied in the fall or early winter and, when so applied, will aid in maintaining the germinability of the planting seed during its storage period.

Observations at many places are that seed treatment with those materials will have no serious effects on root nodulation in soils that have grown nodulated soybeans previously. When planting in such fields, therefore, a grower need have no apprehensions regarding the effect of seed treatment on nodulation.

When soybeans are being planted on land for the first time, the situation is somewhat different. Then the seed should always be inoculated with a culture of the root-nodule-forming bacteria just before planting. The presence of a seed-treating disinfectant on the soybean seed at the time of inoculation impairs the efficiency of the inoculation process to a greater or lesser extent, depending on the treatment used. For example, mercurial compounds are generally more injurious to the inoculation than are the nonmercurial seed treatments. For that reason seed treatment is not recommended for the first soybean crop on a field.

Should a grower wish to practice both seed treatment and seed inoculation, the procedures should be in that order. Treating can be done at any time before planting, even in the preceding fall. Inoculating should be done just before planting, whether the seed is treated or nontreated.

HOWARD W. JOHNSON, a graduate of Ohio State University, obtained his doctorate in plant pathology at the University Of Minnesota. He has been engaged in research on forage crop diseases since 1930. He is employed jointly by the division of forage crops and diseases of the Bureau of Plant Industry, Soils, and Agricultural Engineering and the Mississippi Agricultural Experiment Station, with headquarters at the Delta Branch Experiment Station, Stoneville, Miss.

DONALD W. CHAMBERLAIN is a graduate of St. Norbert College. He obtained his doctorate in plant pathology at the University of Wisconsin. He has been engaged in research on soybean diseases since 1946. He is employed by the division of forage crops and diseases, and is stationed at the United States Regional Soybean Laboratory Headquarters, Urbana, Ill.

Frogeye, bacterial blight, and purple seed stain of soybean are illustrated in the section of color photographs.

Fungus fruiting body.