THE CHANCE DISCOVERY of Kassoer, the supposedly natural hybrid between the wild cane of Java and the Noble Black Cheribon, which proved to be resistant to sereh, presented dramatically to the Dutch scientists the possibilities of obtaining disease-resistant varieties through the crossing of different parent stocks. The result has been the development in many cane-growing countries of breeding programs, a primary aim of which is the production of resistant varieties.

Observations of differences in reaction to disease among varieties of different species of sugarcane led to a search for resistant germ plasm by breeders and pathologists.

FORMS of S. officinarum, noble canes, were almost universally the world's commercial sugarcanes before the outbreaks of epiphytotics of disease. Because of disease susceptibility, few now remain in large-scale commercial cultivation. They are, however, important in breeding work as sources of many of the qualities required in a commercial cane other than disease resistance, such as large diameter of stalk, low fiber, and good quality of juice. With few exceptions, the noble varieties are susceptible to the major diseases, including mosaic, sereh, streak, red rot, root rot, and gummosis. As a group, their greatest resistance is to smut, although some varieties are also resistant to leaf scald.

Varieties of S. barberi are generally susceptible to red rot. They are susceptible to, though tolerant of, mosaic. They are intermediate in resistance to pythium root rot, moderately susceptible to smut, and resistant to sereh, streak, and gummosis.

The wild, grassy members of S. spontaneum are important sources of resistance to several diseases. They are resistant to sereh, pythium root rot, and gummosis; some of them are resistant to red rot and (with the exception of the forms from Turkestan) are resistant or immune to mosaic. On the other hand, they are susceptible to smut, Fiji disease, red stripe, downy mildew, and some of the leaf-spotting diseases.

Forms of S. sinense are resistant to sereh, pythium root rot, gummosis, and generally to mosaic. They are very susceptible to shut. Most forms for which there are records are susceptible to red rot and streak. This species has been used relatively little in breeding.

Relatively few forms of S. robustum have been tested for disease resistance. In the United States they have proved to be susceptible to mosaic, pythium root rot, and intermediate in resistance to red rot. Both resistance and susceptibility to gummosis have been recorded. Fiji disease and downy mildew have been observed on them in their native habitat in New Guinea.

COMPARED with the use of resistant varieties, other means of controlling sugarcane diseases are less important. Disease injury sometimes may be minimized by planting at such time as to escape severe infection or by avoiding the planting of varieties susceptible to certain diseases in soils where the effects of such diseases are most severe.

Progress has been made in the control of the seed-cane rot, pineapple disease, by the use of protective fungicides in South Africa, Hawaii, and Queensland. For several reasons, economical methods for the use of fungicidal seed treatments have not been developed in the southern United States. Certain leaf-spotting diseases could be controlled by the application of fungicides but the losses caused by them are not sufficient to justify the expense.

Considerable work has been done on the control of the diseases by treating the seed cuttings with hot water. The Pioneer experiments in this field were done by the Dutch in Java in an effort to control sereh, and it has since been tried there and elsewhere as a curative for other diseases that are transmitted in the seed cuttings. Various temperatures and time intervals have been used, as a result of which exposure at 125.6 F. for 20 minutes is generally considered the standard treatment. Mature buds of most sugarcane varieties can be subjected to the treatment without injury; in fact, it usually results in stimulation of germination. Lower temperatures or shorter periods of exposure may not be effective in killing the disease organisms, while higher temperatures or longer intervals of exposure frequently injure the cane buds.

The standard hot-water treatment eliminates infection by the virus diseases sereh and chlorotic streak and the bacterial disease gummosis. It is partly effective against leaf scald and is not effective against mosaic or streak. Spores of some leaf-spotting fungi that may be present on the cuttings are killed by the treatment. Although certain diseases can be controlled by the hot-water treatment and some increase in germination and yields of cane often results aside from any control of the diseases, the treatment has not been widely adopted in plantation planting. That is because the benefits derived generally have not been sufficient to justify the expense. A deterrent also is the fact that the very exact temperature control required is often difficult to maintain in large-scale handling of the bulky seed material. If the temperature falls below the required level, the purposes of the treatment will not be accomplished; if it goes much above, the cane buds may be injured. Hot-water treatment is widely used by quarantine authorities in the movement of planting material from one country to another.

E. V. ABBOTT is a pathologist in the division of sugar plant investigations of the Bureau of Plant Industry, Soils, and Agricultural Engineering. He is stationed at Houma, La.