io8 
Journal of Agricultural Research 
Vol. XXVII, No. 2 
EFFECT OF RUST ON WATER REQUIREMENT 
REVIEW OF LITERATURE DEALING WITH EFFECT OF PARASITIC INFECTION 
ON THE WATER REQUIREMENT OF PLANTS 
The literature of transpiration which relates to the effect of parasitic 
infection on the water use of the host is not extensive. Burgerstein (6) 2 
cites the work of Miiller-Thurgau ( ii ) who, using the cobalt-chloric! 
paper method, measured the alteration in transpiration rate induced by 
infection of pear and apple leaves by scab and mildew fungi. Leaves 
infected by Fusicladium showed, in the diseased areas, increased trans¬ 
piration as compared with adjacent healthy portions, especially if the 
upper leaf surface bore the lesion. Sphaerella, on the other hand, caused 
no marked change, while the lesions produced on grape leaves by Perono- 
spora viticola (sic) lost almost no water at all, due to stoppage of the 
stomata by the conidiophores. 
Blodgett ( 2) observed that a shoot of Rubus, heavily infected by Gym- 
noconia, took up nearly twice as much water as a comparable healthy 
branch, yet its leaves wilted while those of the latter remained turgid. 
Reed and Cooley (ij, 14) measured the water loss from healthy apple 
leaves as compared with those infected by Gymnosporangium, making 
the determinations on leaves in situ and using an apparatus in which the 
transpired water could be absorbed and weighed. Under all conditions 
the amount of water transpired by infected leaves was less than that by 
healthy ones, the reduction being about 25 per cent. This was attributed 
to hypertrophy of the spongy parenchyma, reduction of intercellular 
spaces and the filling of these by fungus hyphae, and to the absence of 
stomata on the aecial cushions. At an early stage of infection the trans¬ 
piration of affected leaves was not much less than that of sound ones. 
The reduction of transpiration was greatest at full development of the 
aecial cushions together with spore liberation. A rise in the rate of 
transpiration of rusted leaves occurred later when the lesions were sur¬ 
rounded by extensive areas of dead tissue. The possibility of an intoxi¬ 
cating effect on the host cells produced by fungous excretory products 
also was suggested. 
Rust infection of cereals was found by Humphrey 3 and by Weaver ( 22) 
to cause accelerated transpiration. Weaver grew wheat, rye, barley, 
oats, and com infected by stem and leaf rusts and compared the water 
loss under a variety of light and temperature conditions with that from 
uninfected controls. The amount of transpiration was determined by 
weighing the sealed pots at intervals and was expressed in grams per square 
centimeter of leaf surface. The rate was consistently higher in the rusted 
plants, the excess being greatest under environmental conditions favoring 
rapid water loss. A quantitative relation between acceleration of rate and 
area of the pustules was demonstrated. So slight an infection of oat 
leaves as involved only 0.5 per cent of the leaf area caused the trans¬ 
piration rate to rise by 37 per cent. On the other hand dicotyledonous 
plants such as Xanthium, Helianthus, and Dianthus, when attacked 
by rust, either lost less water by transpiration than uninfected ones, or 
showed a slight acceleration when the pustules appeared, followed by a 
reduction if infection remained restricted to the original leaves. 
2 Reference is made by number (italic) to “Literature cited,” pp. 117-118. 
* Humphrey, H. B. Unpublished data cited by J. E. Weaver (22). 
