REPORT OF THE SOCIETY 9 



A REVIEW OF OUR KNOWLEDGE CONCERNING IMMUNITY AND 



RESISTANCE IN PLANTS 



J. E. Howitt, Professor of Botany, Ontario Agricultural College, Guelph, Ont. 



Imiuiinit}' and resistance in plants is a subject of great possibilities to 

 the Plant Pathologist. It appears to offer a solution for some of our most 

 out-standing and important pathological problems, such as the prevention of 

 loss from grain rusts; the control of citrus canker in the south; the re-establish- 

 ment of the American chestnut in the United States; the production of beans 

 free from anthracnose, mosaic and root rot; and the prevention of soil diseases, 

 such as cabbage yellows, flax wilt, cotton wilt, tobacco root rot, and stem and 

 root rot of canning peas. It offers to the man of scientific inclination a host 

 of intricate and fascinating problems in the fields of bio-chemistry, plant 

 physiology^ genetics and ecology. It is by no means a new subject. We find 

 it stated in "Diseases of Field and Garden Crops" by Worthington Smith, 

 published in 1884, that "Experiments are now being carried out under the 

 auspices of the Royal Agricultural Society to improve cjualities of the potato, 

 especially in its power of resisting attacks of the potato disease, by crossing 

 S. tuberosum L. with its allies, and among them S. Maglia, Sch." (1). 



Let us very briefly note some of the more important accomplishments in 

 the production of disease resistant plants. W. A. Orton by selection, succeeded 

 in producing a number of varieties of cotton resistant to wilt (Necomospora 

 vasinfectum) and by crossing the citron Avith the water-melon he produced 

 a commercial water-melon resistant to wilt caused by a soil Fusarium (2) . 

 It is interesting to know that this water-melon did not prove to be resistant 

 when grown on the Pacific coast. Bolley by selection has produced strains 

 of flax resistant to wilt (Fusarium lini). J. B. Norton by hybridization has 

 furnished asparagus growers with varieties resistant to rust, such as Martha 

 and Mary Washington (3). L. R. Jones has supphed Wisconsin cabbage 

 growers with commercial varieties of cabbages resistant to yellows, caused 

 by the fungus Fusarium conglutinans. Johnson has by hybridization and 

 selection produced strains of White Burley tobacco showing marked resistance 

 to root rot caused by Thielavia basicola. The immunity of many commercial 

 varieties of potatoes to canker or wart disease has been demonstrated in 

 Germany, Holland, England and America, and affords a striking instance of 

 practical control by substitution of immune for susceptible varieties. 



Time will not permit of any extended review of the progress that has been 

 made with the wheat rust problem in the production of resistant varieties. 



1. Smith Worthington G. Diseases of field & Garden Crops. 



2. Smith, Erwin F. Royal Hort. Soc. Kept. 1907. .^ ^ t^. 



3. Norton ,1. B. Washington Asparagus, U. S. Sept. of .-Vgr. (Office Cotton Truck & Forage Crop Disease 

 •Cir. 7, 1919. 



