Some Recent Contributions to Our Understanding of Corn Diseases

There is probably no other disease problem of greater significance economically than that of corn. Hence, the purpose of this paper is to sketch briefly the progress that has been made in this study and to point, in a general way, to some phases of the problem that are immediately before us. Because of its complexity and the misconception as to its significance, a beginning in this field was tardy. Our method of attack on the corn problem seems to be passing through the characteristic successive stages of investigation. These stages may be traced as beginning with observation of the significance of the disease, and the causal relationships, followed by intensive biological investigations and field studies. My discussion of the corn-disease situation will follow this order and I hope you will bear with me if I refer frequently to work done in our own laboratory

Plant research in the tropics: A symposium on growth and development of maize in the Latin Americas

The Tropical Research Center is an outpost of the Iowa State College located at Antigua, Guatemala, in tropical America. This outpost was organized for research and graduate study in agriculture and the natural sciences by The Iowa State College and approved by the State Board of Education in December, 1945. The Iowa State College believed that to improve the service which plants give to man, it would be desirable to study plants of other climates comprising areas known to be centers where nature and the primitive man cooperated to bring so many of our crops into existence. The College believed too that a station in the tropics would facilitate the solution of its problems in the natural sciences, which are basic to all technology. And lastly the Tropical Research Center was created in order that the College might broaden and liberalize the training and thereby increase the usefulness of its staff and graduate students by affording them an opportunity to work and study in the tropics where the plant, animal and human environment are very foreign to our own. All of this was made possible largely through a grant of money from a public. spirited citizen of Iowa, the late Earl E. May. The work of the Center was initiated in February, 1946, with headquarters in Antigua, Guatemala, where laboratories, offices and trial grounds have been established in sympathetic cooperation with public.spirited citizens of Guatemala engaged in private enterprise and with the Guatemalan Government

Cabbage Diseases

Cabbage diseases are the chief limiting factor In profitable commerclal cabbage growing In Iowa. The most destructive of these are black·leg, black-rot, and cabbage yellows. Any one may destroy the greater portion of a crop. The first two are known to be distributed with the seed and cause Infection of the young plants In the seed bed. Some of these naturally find their way Into the field and under favorable conditions become destructive. Cabbage yellows may also be distributed with the seed but Is probably more commonly spread with the plants by the soil adhering to the roots

An Improved Method of Potato Seed Treatment

Half of the seed potatoes that are planted each spring are infected with some plant disease. Black leg, Black scurf, Common scab, and Dry rots are the commonest of these diseases. They cut down the stand, injure the roots, mar the potatoes and reduce the yield. Illustration on cover shows the seed potatoes from a 2 1/2 bushel sack bought in the open market, sorted into two lots: those free from disease and those not free. Note that there are more diseased potatoes than healthy ones. \u27!\u27his is not an unusual case; in fact, it is somewhat better than the average. Such potatoes can be made into good seed by treating them, but seed treatment will not make good seed out of culls. The little potatoes and those badly diseased should be discarded for seed purposes

The Barberry Bush and Black Stem Rust of Small Grains

During the season of 1916 the cereal crop of the middle west suffered another severe epidemic of black stern rust {Pucclnla graminis). It is estimated that this disease caused a loss of $110,000,000 in the wheat growing districts of Minnesota, North and South Dakota, and Nebraska. In the four principal spring wheat growing provinces or Canada the damage was placed at$100,000,000. Altho Iowa did not suffer as severely as adjoining states on the north, yet the damage was probably not less than $5,000,000. Unquestionably, these severe losses are in a large measure responsible for the present high cost or food stuffs. The protection of the cereal crops from this rust Is or importance, not only to the farmer who grows the grain, but also to every bread consumer

The pathogenicity of Fusarium niveum (EFS.) and the development of wilt resistant strains of Citrullus vulgaris (Schrad.)

Watermelon wilt, caused by Fusarium niveum EFS., is a serious disease in Iowa as well as in many other sections of the United States. The present Iowa acreage is 90 percent less than it was before wilt became a factor. Infection may occur through the roots formed on a runner covered with infested soil. Injury induced by wind-blown sand seemed to favor wilt infection. Comparative physiologic tests were made with 18 cultures of Fusarium niveum obtained from widely separated localities. These cultures seemed to differ in: (a) rate of growth on artificial media, (b) type of pigmentation, (c) rate of starch digestion, (d) ability to change the pH of neutral media, (e) gross growth habit and (f) degree of sporulation. Seedling rot is more severe at a soil temperature of 16-18° C. than at 22-25° C. or 25-28° C. According to laboratory trials seedling rot may be partially prevented by treating the seed with certain organic mercury dust fungicides. Seedling wilt is more severe at a soil temperature of 25-28° C. than at a lower temperature. Relative resistance of the varieties Kleckley Sweet and Stock Citron remains unchanged when seedlings are transplanted from steamed soil into infested soil. The correlation between rate of wilting and degree of soil infestation appears to be positive. This applies whether or not the soil is naturally or artificially infested and whether or not seeds are planted in infested soil or seedlings are transplanted from steamed soil into infested soil. There is a tendency toward positive correlation of the rate of wilting in the field and the air temperature. In general, rapid wilting is accompanied by warm weather. The application of lime, manure and commercial fertilizer in various proportions to infested field soil failed to reduce infection of the variety Kleckley Sweet. Resistance to watermelon wilt among the varieties of Citrullus vulgaris is relative. In general, the edible varieties are susceptible, while the inedible varieties are resistant. Slight differences in the relative resistance of edible varieties exist, the variety designated as Japan No.7 being the most resistant of the edible varieties tested. The variety Conqueror, under Iowa conditions, is only slightly more resistant than Kleckley Sweet. Marked differences in the relative resistance of inedible varieties exist, the variety Preserving Citron being the least resistant, and the varieties White Seeded and Majorta being the most resistant of the varieties tested. A genotype was isolated from the variety Kleckley Sweet, a commercial type, whose progeny was approximately 50 percent resistant in 1928, while Kleckley Sweet was 100 percent susceptible. This selection is designated, temporarily, as K-S4. (Later K-S4 was distributed as the variety Pride of Muscatine). Five hybrids resulting from crosses of the variety Conqueror on the commercial varieties Kleckley Sweet, Tom Watson, Halbert Honey and Excel were more resistant than these varieties in 1928 and 1929. The relative resistance of these hybrids in 1928 was as follows: hybrid 30, 46 percent; 33, 59 percent; 43, 22 percent; 90, 35 percent and 137, 55 percent. The check variety Kleckley Sweet was 99 percent susceptible. Two hybrids, Q21 and Q23, apparently chance crosses with the variety Conqueror as one parent, were 68 and 64 percent resistant in 1928, when, under similar conditions, the varieties Kleckley Sweet, Tom Watson, Thurmond Grey, Excel, Dixie Belle and Halbert Honey were 99 percent susceptible. (Later Q21 and Q23 were distributed as varieties Iowa Belle and Iowa King, respectively). F2 hybrids of the variety Preserving Citron on Tom Watson were resistant to wilt, but highly susceptible to mosaic. F3 a hybrids resulting from crosses of the variety White Seeded on the variety Halbert Honey were resistant in 1927 and 1928. Type and flesh quality of the melons varied. The F3 of this cross produced 26.8 percent of red-fleshed melons. One family, namely 156-S2-S3, produced 44.2 percent red-fleshed melons. Technique is described for measuring the relative resistance of varieties, selections and hybrids in the seedIng stage grown in the greenhouse

Application of the Group Conference Method of Teaching to Beginning Classes in Plant Pathology

The teacher\u27s ability to stimulate and to work with each student largely determines the value derived from a course by the student. The contact of teacher with the individual student is more difficult to effect in large classes (50 students or more) than in small classes. In the large classes a restraint and formality may prevail that are lacking in groups of 20 students or fewer

A study of the control of crown gall on apple grafts in the nursery

Altho crown gall is one of the most serious diseases of apple trees in the nursery, effective control measures for root-grafted stock have not yet been found. This is doubtless due to previous lack of definite knowledge of the causal agent. Now, due to the excellent work of Erwin F. Smith and C. D. Townsend, Bacteriurn turnefaciens, Sm. and Tw., has been shown to cause this disease. Later, Smith, Brown and Townsend contributed many other important facts pertaining to the pathogenicity and biology of the organism. As a result of these studies, experiments on control measures have been made possible and their successful conclusion has been made probable

Study of Peronospora trifolioum Debary on Species of Leguminosae

The downy mildew, Peronospora trifoliorum deBy. of alfalfa, Medicago sativa L., is a widespread disease occurring in almost all countries of the world where alfalfa is grown. This disease assumes importance in the middle-west during wet seasons, particularly in the spring and fall. In Iowa it is most destructive on fall seedings and on the first cutting in the spring. The present studies were undertaken to throw light on the relation of moisture and temperature to spore germination and infection, the possible host range of the downy mildew, and its method of overwintering

Studies on the crown rust of oats

During some seasons crown rust of oats (Puccinia coronata Corda) becomes a serious limiting factor in successful oat production in Iowa. It is not uncommon to have this rust occur in epidemic form one year and the following year to have only a small amount of the disease present. Up to the present time the various factors which influence the growth, development and epidemiology of this rust have not been definitely studied