Carnegie Institution of Washington Publication, 2: 198-201 (1911)
Bacteria in Relation to Plant Diseases
Erwin F. Smith

Many experiments have been made with grains to free them from smut fungi and in this way considerable knowledge has been gained respecting the toleration of seed wheat, oats, etc., for hot water, copper salts and various other disinfectants. Some of the leading papers are mentioned under Literature. Only a few of the results will be cited here.

Jensen who discovered the hot-water treatment for stinking smut (1888) advised temperatures between 127°and 133°F., and exposures of seed wheat and oats for not over 5 minutes. He did not, however, determine accurately the thing we are here specially interested in bringing out, namely, the killing temperature for the grains.

In 1890, Arthur determined the effect of hot water on the germination of wheat. Wheat seeds immersed 5 minutes in water at 135°F. (57°C.) are not injured. Six hundred seeds exposed to 130°F. (54°C.) for 10 minutes also gave excellent results on germination— 12.5 per cent in 24 hours and 93 per cent in 5 days. The injury to those treated 10 minutes at 135°F., and 5 minutes at 140°F. (60°C.) equaled about 20 per cent. The limit of germination is 150°F. for 5 minutes (33 per cent). No germinations were obtained when wheat seeds were exposed to higher temperatures, e. g., 155°F. for 5 minutes, or to 150°F. for 10 minutes.

In 1891 Arthur tested the effect of hot water on oats, with especial reference to the prevention of loose smut. He states that the hot-water treatment—10 minutes in water at 135°F., or 5 minutes in water at 135°F. to 140°F. (57°C. to 60°C.) entirely destroys the smut while at the same time it improves the growth and increases the yield of oats. The water may be even as hot as 145°F. when the oats are first put into it without much injuring the germination. Arthur made the exposures in cheese-cloth bags.

Latta found 5 minutes' exposure of oats in copper sulphate water (1 pound to 1 gallon) destroyed the smut but the germination was slower and the yield per acre was reduced. The comparative yields were: Hot water, 33 bushels; untreated, 28 bushels; coppered, 24 bushels. Arthur, who reports this, tested the effect of copper sulphate on germination on lots of 200 seeds and obtained in the germinating chamber the following per cents: Hot water, 99; untreated, 98; copper sulphate, 67. Even in the soil where 98 per cent of the oats treated with copper sulphate finally germinated, they did so very slowly, the primary roots were often killed, and often they pushed out the plumule in advance of the roots.

Kellerman & Swingle (1890) found that exposure of wheat at 139° to 140°F. for 15 minutes destroyed nearly all of the kernels, i.e., on a plot that should have yielded 3,000 or more heads there were only 9. Copper sulphate 8 per cent, 24 hours, limed or unlimed, reduced the germinations about one-fourth. Copper sulphate 5 per cent 24 hours, unlimed, reduced the yield nearly one-third. Bordeaux mixture reduced the yield over one-fourth. Eau celeste, 24 hours (on another page the time is said to have been 36 hours) destroyed all. Carbolic acid 5 and 10 per cent for 20 hours destroyed all. Mercuric chloride 1 per cent for 20 hours destroyed all. Potassium bichromate 5 per cent for 20 hours destroyed about half.

According to Kellerman & Swingle (1891) oats which were treated at 141.8°F. (61°C.) for 5 minutes gave a good crop. The same result was obtained by exposing at 138.2°F. (59°C.) for 10 and for 15 minutes, i.e., there was no destruction of the seed. Potassium sulphide 0.75 per cent and 0.5 per cent for 24 hours reduced the number of stalks about one-fourth. Copper sulphate 0.1 per cent for 24 hours reduced the number of heads about one-fourth. Copper sulphate 0.5 per cent for 24 hours reduced the number of heads nearly half. Copper nitrate in 5 per cent solution for 24 hours, limed or unlimed, destroyed most of the seeds. Even 2.5 per cent or 1 per cent greatly reduced the crop. Corrosive sublimate 0.1 per cent for 24 hours reduced the yield three-fourths. Potassium bichromate 10 per cent for 23 hours killed all; same, 1 per cent for 9 hours, reduced the crop one-half or more.

They recommend treating oats for smut by (1) hot water: temp. 132.5°F., time 15 minutes; or, (2) potassium sulphide: 1 pound to 20 gallons of water, time 24 hours.

In 1891, Kellerman Sr., recommended hot water over all other fungicides for great efficiency without injury to seeds. His experiments were with wheat kernels for the prevention of stinking smut. As a result of many experiments (about 70) he recommends exposure for 15 minutes to a temperature of 131°F. (55°C.). Hot water for 5 minutes at 137°F. and at 138°F. (seeds previously soaked 10 hours) destroyed all the grains. The following treatments greatly injured or nearly or quite destroyed the grains: Bordeaux, 24 hours; same, half strength; 1 per cent copper sulphate, 24 hours; 1 per cent copper acetate, 24 hours; 1 per cent copper chloride, 24 hours; 1 per cent potassium bichromate, 24 hours. The following treatments gave reasonably good yields, i. e., better than the checks, but not as good as the hot water: Copper sulphate 0.5 per cent, 24 hours, limed; copper sulphate 0.5 per cent, 12 hours, limed; copper acetate 0.5 per cent, 24 hours; copper nitrate 1.0 per cent, 24 hours; copper nitrate o. 5 per cent, 24 hours; mercuric chloride 0.05 per cent, 24 hours. The following gave a yield nearly equal to the checks: Eau celeste, 24 hours; mercuric chloride, 0.1 per cent, 24 hours. Ratio of grain to volume of fluid not given. Hot water at 136°F. (57.7°C.) for 5 minutes, then quickly cooled, appears to be the severest exposure compatible with a good crop.

In 1893, Hitchcock and Carleton published the results of their experiments with maize. They tested the effect on germination of 82 chemicals in various strengths, making a total of 400 experiments.

They obtained in moist sand a germination of 80 to 100 per cent (retarded) after exposure to the following strengths of mercuric chloride water: 0.1 per cent for 1, 3, 5, 8, hours; 1.0 per cent for 1 hour. One per cent mercuric chloride for 24 hours or 3 per cent for 1 hour killed all. Chromic acid 1 per cent for 48 hours gave 75 per cent retarded germinations. Copper chloride 10 per cent for 2.4 hours gave 100 per cent retarded germinations. Copper nitrate 10 per cent for 24 hours gave about 80 per cent retarded germinations. Potassium permanganate 2.5 per cent for 24 hours gave 100 per cent germinations. Hyposulphite of soda 10 per cent for 24 hours gave full germinations. From 80 to 100 per cent of retarded germinations were obtained after exposure to potassium cyanide as follows: 1 per cent, 1 hour; 5 per cent, 1 and 3 hours; 10 per cent, 1 hour. The same, 0.5 per cent for 1 hour scarcely affected germination.

In 1897, Bolley published studies on the fungicidal treatment of wheat, oats and barley which he had carried on for a period of 5 years. The following are some of his conclusions respecting resistance of the dry grain. He states that if the wheat grain is dried at once germination is not retarded by applying corrosive sublimate solutions in strengths up to 4 parts in 1,000 parts of water: Of selected seed of Scotch Fife wheat exposed 2 minutes, 95 per cent germinated; exposed 3 minutes, 82 per cent germinated; 4 minutes, 72 per cent; 5 minutes, 78 per cent; 6 minutes, 67 per cent; 7 minutes, 45 per cent; 20 minutes, 17 per cent; 25 minutes, 0. As little as 0.1 per cent corrosive sublimate weakened the first growth in a rapidly increasing degree in exposures longer than 3 minutes, but even from too strong treatments the final after-growth is stronger than from untreated grain. Mixed samples of oats treated with 0.3 per cent corrosive sublimate water for 30 minutes gave good first growth (94 to 100 per cent germinations) and a good yield per acre. Barley after 15 minutes exposure to 0.3 per cent mercuric chloride gave 94 per cent germinations.

Seed wheat treated 10 minutes or less with 1 to 2 per cent solution of formalin gave a normal number of germinations or better, but soaking over 10 minutes decreased slightly the per cent of germinating seeds. Exposure for 10 minutes to 10 per cent killed all, and merely dipping into 5 per cent reduced the germinations to 34 per cent. Subsequent experiments showed that wheat or oats would germinate perfectly after soaking in 0.4 per cent formalin 1 to 3 hours.

Seed wheat will stand an exposure of 1 minute at 150°F. (655°C.) and give 80 to 90 per cent of germinations. Oats exposed to hot water at 140°to 143°F. for 5 minutes gave 98 per cent germinations and exposure for 5 minutes in water at 140°F. (60°C.) or below may be recommended as not injurious to wheat.

Barley dipped for 30 minutes in copper sulphate water (1 pound to 4 gallons) gave 86 per cent of weak germinations; and when exposed for 1 hour, 47 per cent.

Wheat exposed to potassium sulphide (1 ounce to 1 gallon for 75 minutes gave 100 per cent germinations. Barley treated in the same way for 75 minutes gave 90 per cent germinations. Oats treated in same way gave 96 per cent germinations; but exposed for 19 hours gave 42 per cent weak germinations.

According to Cranefield (1901), formalin used as weak as 2.5: 1,000 (1 pound [pint] to 50 gallons of water) for 20 minutes may injure oats used for seed. The experiments cover 20 varieties of oats and the germination of over 25,000 seeds. The amount of injury varied greatly in different varieties, and was more noticeable in planted seeds than in those used in the germinating chamber.

Longer exposures than 20 minutes at the standard strength (1 pint to 50 gallons) did not much increase the injury. The early growth from the treated seed was retarded and at no time did the treated quite equal the untreated in height.

When more concentrated solutions of formalin were used the injury was progressively greater, e.g., 1 pint to 50 gallons of water, 91 per cent germination (check 94.5); 1 pint to 25 gallons of water, 74 per cent; 1 pint to 20 gallons, 73 per cent; 1 pint to 10 gallons, 31 per cent; 1 pint to 5 gallons, 12 per cent.

In 1901, Windisch published many experiments on lupins, peas, horse beans, soy beans, corn, flax, rape, lucern, and clover, showing the effect of formaldehyde on germination. Each of these was in duplicate. The following are some of his conclusions:

  No. of
seeds each
Formaldehyd (Per cent in Water)
0.02 0.05 0.10 0.20 0.40
White lupins 50 100 100 99 89 4 4
Victoria peas 50 84 80 56 19 6 12
Horse beans 50 100 97 100 98 94 26
Soy beans 100 99 98 97 92 40 6
Flax 200 97.75 94.25 11.75      
Maize 100 100 100 100 99.5 100 94
Summer rape 200 98.25 80.25 4 2    
Lucerne 200 90.50 88.75 27 7.75 7 7.5
Clover 200 95.00 89.50 34 7.5 8 4.5