Nov. 29, 1915 
Varietal Resistance of Plums to Brown-Rot 
367 
PHYSIOLOGICAL REVIEW 
A considerable amount of literature has appeared, especially in recent 
years, on the subject of resistance and immunity to disease. The cereal 
crops have perhaps received the most attention. Bolley (1889) and 
Anderson (1890) attempted to correlate resistance with certain morpho¬ 
logical characters. Cobb (1892, p. 181-212) advanced the theory of 
mechanical resistance due to morphological characters, such as thick 
cuticle, waxy coating, and small stomata. Freeman (1911) showed that 
barley might escape rust owing to variation in amount of bloom produced 
on the leaves, which could be varied by growing in soils of different 
degrees of alkalinity. This escape from rust is not true resistance, but 
is due to the inability of the water to wet the surface of the leaves so that 
the drops containing the spores roll off. When these plants were infected, 
however, they “exhibited large and vigorous growths of the rust.” 
Marryat (1907) showed in the case of Puccinia glumarum grown on a 
semi-immune host that it killed small areas of the host tissue and formed 
only small or abortive pustules, while in the case of the susceptible forms 
the host cells, though containing haustoria, were apparently normal. 
Comes (1912) reported that Rieti wheat, which is very resistant to 
rust, contained a higher percentage of acid than other more susceptible 
forms and also that the acid content increases with the altitude at which 
wheats are grown, as does also the ability to resist rust. 
Jones (1905) showed that some varieties of potatoes are much more 
resistant to certain potato diseases than others. He based resistance 
more on chemical composition than on morphological differences in the 
host. 
Kinney (1897) noted that “ fruit of different varieties of plums varies 
in susceptibility to injury by rot fungus ” and attributed the difference in 
resistance to variations in texture of the skin. He also stated that early 
varieties are usually injured more than those which ripen their fruit later. 
Muller-Thurgau (1900) noticed that varieties of apples in Switzerland 
showed different degrees of susceptibility to a wilt or blight caused by 
M. fructigena . 
Quaintance (1900) observed a marked variation among varieties of 
drupaceous fruits in their resistance to attacks of the brown-rot fungus. 
Among the peaches the varieties densely covered with down were the most 
susceptible. Of the plums some varieties of the Miner group were prac¬ 
tically free, those of the Wild Goose rotted about 10 per cent, while the 
varieties of Prunus americana, P. triflpra , and P. pumila were very sus¬ 
ceptible. He suggested that the firmness and thickness of the skin of 
the Miner plums might have something to do with their resistance. The 
relative resistance of some varieties of P. domestica to brown-rot is given 
by Alwood and Price (1903). 
