CORTICIUM DISEASE OF POTATOES.

New Zealand Journal of Agriculture, Volume 43, Issue 3, 21 September 1931, Page 204

CORTICIUM DISEASE OF POTATOES.

I. PROPAGATION AND SPREAD OF THE DISEASE.

E. E. CHAMBERLAIN,

Mycological Laboratory, Plant Research Station, Palmerston North.

Corticium disease, caused by the fungus Corticium vagum Berk, et Curt., is one of the commonest potato-diseases in New Zealand. The symptoms of this disease have been described by Cunningham (1925) as follows :

“ When the crop is being lifted the disease may be seen in the form of small black sclerotia scattered over the surface of the tuber. These sclerotia are resting bodies of the causal organism capable of remaining in a quiescent condition for an indefinite period. They are firmly attached to the tuber by means of hyphae, and are not readily removed, consequently they accompany the tubers when the latter are planted. In the presence of moisture, such as is present in the soil, the sclerotia produce hyphae which ramify through the soil in the vicinity of the tubers, and spread to the potato-shoots as they develop. These hyphae would appear frequently to damage the growing points of the main shoots, with the result that secondary shoots are produced from below the injured portion. In this manner affected tubers may give rise to bunches of small and stunted plants ; these in turn produce few and small tubers. Thus infection, when severe, may tend greatly to reduce the yield.”

A Tuber-borne Disease.

On most potatoes will be found the black sclerotia of corticium (Fig. 1). When the tuber is planted the sclerotia germinate and produce hyphae which follow the shoots up through the soil and attack the growing tips (Fig. 2). While the plant is making its early growth the fungus forms cankers on the stems just below the ground-level and lives as a parasite on the growing plant. Later in the season when the new tubers are formed the fungus, generally but not always, spreads through the soil and produces sclerotia on some or all of them. That only partial infection may occur is shown by an experiment in which a line of one hundred infected tubers were planted in 1929, and in which the progeny of only seventy of the tubers became infected. In the 1930 experiments the progeny of seventy-three out of one hundred infected tubers showed the disease. Bisby, Higham, and. Groh (1923), using one line of potatoes, tested out the effect of different times of harvesting on the percentage infection of the tubers. They found that the longer the crop was left in the ground the higher was the percentage of infection, as follows : Date of digging, Ist September, 39 per cent. ; 10th September, 43 per cent. ; 4th October, 71 per cent. ; 13th Obtober, 83 per cent. From this it may be seen that although the fungus must have been present in the soil, and had possibly been living as a parasite on the parent plant, it had not up to the time of the earlier diggings had time to reach the new season’s tubers. This failure of the fungus to reach the progeny, or all the progeny, in every case, explains why it is rare for a line of potatoes to show 100 per cent, infection.

SOIL-EEBSISTENCE.

Corticium is a fungus which, according to the work of McAlpine (1911), Mueller (1924), Wellensiek (1925), Hurst (1926), Rayllo (1927), and Braun (1930)., has a wide host-range. Thus when introduced into the soil it is capable of attacking plants other than potatoes, and so remaining in the ground for a number of years. Mueller (1924) listed 160 different hosts on which the fungus is parasitic. These hosts include most of the common garden and crop plants. Braun (1930) has since compiled a more . complete list of some 230 hosts belonging to sixty-six families. Corticium has not so far been recorded in New Zealand as being parasitic on any plant other than the potato.

Several workersßisby, Higham, and Groh (1923), Dana (1925), and Clayton (1929) —have found that soil-infection occurs to such an extent in certain districts that it is quite useless to treat seed potatoes for corticium. Melhus and Gilman (1921), realizing the significance of soil-infection when conducting seed-treatment trials for the control of corticium, demonstrated the presence of the fungus in the soil and carried out experiments to estimate the degree of infection.

An experiment was laid down in 1928 at the Plant Research Station to test the persistence of the disease under various crop rotations. Details of the experiment and the results are given in the following diagram, the figures representing the percentage of plants bearing corticium-infected tubers :

1928-1929 : The area, which is 2| chains by | chain, was sown with. a line of corticium-infected potatoes. . The crop was inspected during the harvest, and the potatoes were found to be heavily infected with the disease.

1929-1930 : The same area was divided up into five |-chain-square plots, and each plot sown as indicated in the diagram. Potatoes from an infected line on which the sclerotia had been killed bv treatment

with acidulated corrosive sublimate* were sown in one of the plots. The crop was examined during harvesting, and the counts taken showed an Bi-per-cent. corticium infection. A control plot of 120 tubers of the same line of treated seed, planted in soil which had not grown potatoes before, showed an infection of 8 per cent, at digging-time.

1930-1931 : The whole area was again planted in potatoes, the seed tubers being hand-selected for freedom from sclerotia, and then treated by the standard acidulated corrosive sublimate method. Three hundred sets were sown in each of the small plots shown in the diagram, and the tubers of all the plants examined for sclerotia. The percentage of plants which yielded infected tubers at harvest-time are given in the diagram. A control plot of ninety plants grown from the selected seed showed 100 per cent, freedom from the disease when sown in soil where there had not been a previous crop of potatoes.

The results of this experiment show that in a one-year crop rotation grass is the only crop to bring about any apparent reduction in the amount of soil infection.

During the 1929-30 season a corticium control and yield trial was carried out at Belfast, North Canterbury, in co-operation with the Fields Division. A line of corticium-infected potatoes was secured, and one-half of them were treated with the standard acidulated corrosive sublimate method, while the other half was left untreated as a control.

From these figures it is evident that the soil must have been heavily infected, and that under market-gardening conditions corticium is capable of remaining in the soil for several -years.

Spread of Corticium from one Plot to another.

Corticium is not dependent on previous soil-infection for its spread to healthy plants and tubers, but spreads readily from plant to plant during the season. To test the extent of this spread from plant to plant in the row clean treated tubers and corticium-infected tubers were planted alternately. ' The trial was carried out in two sections, (1) in which the tubers were planted 11 in. apart, and (2) in which the tubers were planted 16 in. apart. In all seventy-eight tubers, each of clean seed and infected-seed, were planted. A control of ninety sets of

the clean seed was planted in soil on which potatoes had not been grown before, and the progeny of these showed roo-per-cent. freedom from disease. The results at digging were —

Under field conditions the normal distance between sets is about 14 in., so that the spread in the field may be expected to be between 23 per cent, and 62 per cent. This spread from plant to plant explains the natural increase of corticium infection within a line of potatoes.

Spread during Storage.

Observations have shown that under certain conditions corticium

may spread from infected to healthy tubers in the sacks. When potatoes are piled up in sacks and allowed to remain undisturbed the potatoes in the lower sacks sweat and become damp. It has been found at the Plant Research Station that under these conditions the

fungus spreads rapidly and sclerotia are formed on the tubers and the sprouts. (Figs. 3 and 4.)

An inspection after storage of one sack of potatoes in which the original infection was known to be 9 per cent, showed that of 428 tubers examined 275, or 64 per cent., were carrying sclerotia. Since it is not unusual for potatoes to become damp in the sacks, either through sweating or other agency, this manner of spread may on occasions be of definite importance.

Literature cited.

Bisby, G. R., Higham, J. H., and Groh, H., 1923. Potato Seed Treatment, Manitoba. Scient. Agric., Vol. 3, pp. 219-221. V ■' Braun, H., 1930. Der Wurzeltaeter der Kartoffel Rhizoctonia Solani K. Monogr. zum Pflanzenschutz. 136 pp. . : Clayton, E. E., 1929. Potato Seed Treatment Experiments on Long Island, with special Reference to Organic Mercury Instant Dips. New York (Geneva) Agric. Exper. Stat. Bull. 564. .32 pp. Cunningham, G. H., 1925. Corticium-disease of Potatoes. N.Z. Jour, of Agric., Vol. 30, pp. 14-21. Dana, F. 8., 1925. The Rhizoctonia Disease of Potatoes. Washington Agric. Exper. Stat. Bull, 191 (Tech. Paper). 78 pp. Hurst, R. R., 1926. Report of the Dominion Field Laboratory of Plant Pathology, Charlottetown. P. E. T .—Report Dominion Botanist for Year igsg, Div. of Botany, Canada, Dept, of Agric. pp. 20-29. McAlpine, D., 1911. Rhizoctonia Rot, or Potato Collar Fungus. Potato Diseases in Australia. p. 60. Melhus, I. E., and Gilman, J. C., 1921. Measuring certain variable Factors in Potato Seed Treatment Experiments. Phytopath., Vol. 11, pp. 6-17. Mueller, K. 0., . 1924. Untersuchungen zur Entwicklungsgeschichte und Biologic von Hypochnus Solani P. et D. (Rhizoctonia Solani K.). Arb. Biol. Reichsanst Land-und Forstwirtsch,.Yo\. 8, pp. 198-262. Rayllo, A. 1., 1927. Experiments and Observations on Hypochnus Solani Disease of Potatoes. Abstr. in Ann. State Inst, of Exper. Agric., Leningrad, Vol. 5, p. 203. Wellensiek, S. J., 1925. Infektieproeven mi'z Rhizoctonia en Moniliopsis op Tomaat en Aardappel. Tydschr. over Plantenrickter , Vol. 31, pp. 236-250.

* The treatment used in this instance and referred to throughout this article as the standard acidulated corrosive sublimate treatment is as follows ; The potatoes are soaked for i| hours in a solution of 1 part corrosive sublimate, 6-6 parts concentrated hydrochloric acid, and 1,000 parts water. ' This treatment has been recommended by the Mycological Laboratory and used in New Zealand for several years, although the method has not been published.

Planted with a severely infected line of potatoes. , 1929-30. Grass. . Swedes. Peas.' . Cereals. Potatoes. ' 8

1928-29.

Planted with corticium-free treated potatoes. . . 73 93 • 91 9i 90

1930-31.

— . .. 1 Number of Tubers inspected. Number of Corticiuminfected Tubers. Percentage of Infection. Untreated . ■ ■ . . • • 1 509 5°9 ' 407 407 80 80 Treated . . . . 54 490 85 •

An examination of the potatoes before planting showed 93 per cent, to be infected with sclerotia. The potatoes were sown in 1-chain rows, and at harvest one bucketful of table tubers was selected from each row. All tubers were examined, and the results were as follow:

— Distance apart of Plants. Number of Clean Tubers planted. Number of Plants clean at Harvest. Percentage of Spread. Section i ii in. 48 18 62 Section. 2 16 in. 3° 23 23