DIGITALIS PURPUREA is the main source of the drug digitalis in the United States, and it is the principal species collected and cultivated. There has been interest in other species, however, as sources of compounds of medicinal value. In 1946, a small acreage of D. lanata developed in Pennsylvania, but plantings were nearly a complete loss in 1948 because of anthracnose.

Anthracnose of digitalis is caused by a fungus, Colletotrichum fuscum, which produces tiny, purplish-brown, circular or angular spots on the leaf surfaces and sunken, fusiform lesions on veins and petioles. The organism is carried on the seed. It causes a damping-off disease of seedlings. It fruits on affected seedlings and is easily spread in the seedbed to healthy plants. Infection becomes severe by late summer. Affected plants are killed or stunted before the herb is ready to be harvested. The disease is favored by warm, wet weather. In the field it is spread mainly by splashing rain drops.

All species of Digitalis tested are susceptible. D. lanata is the most susceptible. D. purpurea is fairly resistant.

Observations over a period of years showed that plantings of Digitalis species made with disease-free seed remained free of the disease throughout the season. It thus appeared that if the organism on the D. lanata seed could be completely killed it would be possible to produce a disease-free crop. A hot-water treatment 031 F. for 15 minutes) of the seed gave complete control of the organism. Isolated plantings of D. lanata made with seed treated with hot water remained free of the disease. Commercial production of this drug crop is again possible.

The control of the disease through the use of disease-free seed is possible because the acreage is small and the plantings can be isolated from other plantings of Digitalis that might be affected with the disease. Although the organism may persist for a year or two on debris, it is easy to find land on which Digitalis has never been grown. The spores of the fungus are not carried for long distances by the wind. The organism is apparently not common on weeds or other farm crops.

CASTOR OIL, obtained from the seed of the castor bean plant, Ricinus communis, has a variety of uses as a medicinal compound, lubricant, drying oil in paints, lacquers, and varnishes, and for hydraulic fluids, linoleum, oilcloth, soap, printing ink, leather, and textiles. Cultivation of castor beans has been attempted several times in the United States. Before 1900 some production occurred in the Midwest. During both the World Wars, attempts were made to produce beans in this country.

Improvements in varieties, methods, and machinery for harvesting the beans and a renewed demand for a local supply caused growers to devote approximately 80,000 acres to castor beans in 1951. It is estimated that several hundred thousand acres will be needed to meet our industrial requirements.

Castor beans are susceptible to a number of diseases. More than 150 different organisms are known to be pathogenic on the plant. Most occur in areas of high rainfall, such as the Southeast. There, the leaf spots and capsule molds can cause such severe losses that production may not be profitable. In the more and sections of the Southwest the damage caused by these troubles is usually negligible. That is one of the factors responsible for locating the present plantings of castor beans in Oklahoma and Texas and the irrigated valleys of Arizona and southern California.

Castor beans are not entirely free of diseases there, however. Seedling diseases and troubles caused by soil-borne organisms are present. Research workers have undertaken studies of their prevalence, losses, effect of environmental conditions and cultural practices, and possible controls.

SAFFLOWER, Carthamus tinctorius, is a member of the thistle family. It has been grown since ancient times in Europe, Africa, and Asia, where the seed is used for poultry feed and as a source of oil for food and soap. The development of safflower as an oilseed crop in the United States since 1940 has been mainly for a source of drying oil for paint.

Safflower was first introduced and tested in the United States in the 1920's by the Department of Agriculture. The varieties tested then were not particularly suitable for production here because of their low yield and low oil content. Some 20 years later workers at the University of Nebraska began a program for improvement of varieties. The outcome of their work was the development of high-yielding, high-oil types. About 100,000 acres of safflower were grown in 1950 in the western part of the Great Plains and California.

Leaf and bud diseases are so serious in areas of high rainfall and high humidity that production of the crop is unprofitable. Although diseases are less serious in more and sections, where the crop is better adapted, certain ones are nevertheless troublesome.

Root rot, caused by Phytophthora drechsleri, has caused considerable damage to safflower in every State where the crop has been grown. Most of the plantings in the Imperial Valley of California were severely damaged in 1950. The organism is soil-borne and widely distributed. High soil moisture favors the disease. Some varieties of safflower are very susceptible, but others are resistant. Root rot has been most damaging where susceptible varieties have been grown under irrigation and in poorly drained dry-land fields. The use of resistant varieties promises to give satisfactory control.

Rust, caused by Puccinia carthami, is another serious disease of safflower. The organism is unique among the rusts in that it is seed-borne. This fact probably accounts for the presence of the disease in the United States. Rust has been known to occur on safflower in Europe and Asia for many years. It undoubtedly was introduced into this country on seed. Rust has become widely distributed in the Great Plains and California since 1950.

Safflower rust is important both as a seedling disease and a leaf trouble. Rust spores carried on the seed or present in the soil may germinate and infect the cotyledons and hypocotyl of seedlings. Hypocotyl infections usually girdle and kill the seedling with a resulting loss in stand. Treatment of seed with fungicides helps improve stands by killing the rust spores.

Rust and some other leaf diseases of safflower might be controlled by applications of fungicides to the foliage. The low dollar return per acre for the crop, however, would make such a practice economically questionable. Many of the leaf and bud diseases are not serious in and sections.

Troubles like rust and root rot are best controlled by the use of resistant varieties. Sources of resistance to each of the diseases are available to plant breeders among selections of present varieties or foreign introductions.

SESAME, Sesamum indicum, has been cultivated in foreign countries for many centuries. The seeds of the plant contain one of the finest edible oils known. Commercial production has not developed in the United States chiefly because the available varieties shatter their seed when ripe. Hand harvest therefore is necessary. Plant breeders are hopeful of developing nonshattering types. If their goal is accomplished, we undoubtedly shall see production started in this country.

Sesame is known to be susceptible to several diseases. One bacterial and two fungus leaf spot diseases, as well as wilts, root rots and stem rots, and virus diseases are present in experimental plantings. Some of the troubles are seed-borne.

Sesame is a warm-weather crop. It seems best adapted to the southern part of the country. When and if the crop is cultivated there, the net return in dollars per acre may not be high. It thus will be a profitable crop only for growers who can obtain the highest yields with the minimum expense and who are located in areas where diseases are least troublesome. It may be possible to control some of the diseases through exclusion of the causal organisms by special seed treatments or by using seed only from disease-free fields. Other troubles will have to be controlled by such other means as the use of resistant varieties, which may be developed.

The first objectives of the plant pathologist in studying a crop like sesame are the same as for any new crop. He must determine what the diseases are, their relative importance in terms of both direct and indirect losses, the identity of the causal agents, means of distribution, sources of inoculum, effect of environmental conditions on disease development, and sources of disease resistance. Only after a knowledge of these is obtained can he proceed to formulate programs aimed at control.

C. A. THOMAS, a pathologist in the division of tobacco, medicinal, and special crops at the Plant Industry Station, Beltsville, Md., joined the Department of Agriculture in 1948.