BREEDING FOR DISEASE RESISTANCE IN PLANTS 28 1 
The American gooseberry mildew, Sphaerotheca mors-uvae, is now 
repeating this history on the gooseberries of Europe. The late blight 
of potato and hollyhock rust are from South America, chestnut blight 
and citrus canker from Asia, white pine blister rust from Europe. In 
each case it is to be expected that resistant forms will be found to 
occur where the disease is native. This has in fact already been 
shown to be true, a recent and notable instance being that of the 
Chinese and Japanese chestnuts, which Dr. Van Fleet is using to cross 
with the American chestnut to produce a better and resistant tree. 
The disease-resistance factor is important in all breeding. In some 
cases we may select directly for resistance from races of established 
quality. The wilt disease of cotton, due to the vascular parasite, 
Fusarium vasinfectum, occurs very commonly in the sandy soils of our 
cotton belt, from North Carolina to Texas, rendering cotton culture 
impossible on millions of acres. This disease has been overcome by 
the selection of resistant plants from fields where the disease had 
eliminated all others. 
The cowpea suffers in the same area from a related parasite, 
Fusarium tracheiphilum, to which all varieties are subject except the 
iron and its derivatives, Brabham and Monetta. That these cowpeas 
are also resistant to root-knot is most remarkable, considering that 
the nematode, Heterodera radicicola, has several hundred hosts, and 
that cowpeas, as a class, are very susceptible. 
To produce a wilt-resistant watermelon it was necessary to hybri- 
dize with the hard-fleshed citron, and while good melons have been 
secured a fully satisfactory combination of resistance with quality and 
a rough rind for shipping has not yet been obtained (2). 
Working to combat a related disease of cabbage, due to Fusarium 
conglutinans, Professor L. R. Jones has employed the same method of 
selection with great success. Cabbage yellows will no longer be 
feared when these new varieties are disseminated (3). 
The Fusarium wilt of tomato, Fusarium lycopersici, a destructive 
disease in our central and southern states, is yielding rapidly before 
the plant breeder. The recent tests of F. J. Pritchard, of the Bureau 
of Plant Industry, show that a resistant late tomato has already been 
secured and that satisfactory early varieties are in sight. 
The strains of flax resistant to Fusarium lini, bred by BoUey (4) 
and others make possible the continued culture of this important 
crop in regions where it was being abandoned because all the land was 
infested with the wilt parasite. 
