BACTERIAL WILT OF CUCURBITS. 31 
besides the many races or pure lines of the organism showing various 
degrees of relative virulence to any particular host there may be also 
distinct cucumber and squash strains. 
SOME HOST RELATIONS. 
On the other side of the host-parasite relation the species and 
varieties of cucurbits themselves differ in susceptibility to the wilt 
organism as a whole and to its various races. Thus cucumbers con- 
stitute the most susceptible host species so far tested, and most of 
the isolations have proved highly virulent to them. Some differences 
in varietal susceptibility have been observed, but none have shown 
marked resistance, and apparently little hope of control through 
resistant varieties is given here. 
At the other extreme are watermelons, the most resistant of our 
economic cucurbits. No authentic report of natural infection to this 
host has come to our notice, and our inoculations have given negative 
results or at most a very slight local wilt immediately around the 
points of inoculation. 
The squash group stands next to the watermelon in resistance. 
Unlike the cucumber, most isolations tested on squash have given no 
infection or only slight local wilting. The few remaining were highly 
virulent, but slower in developing the disease than when inoculated 
into cucumber. Much greater differences in varietal resistance were 
shown within the squash group than among cucumbers. 
Aside from the differences in resistance inherent in the species and 
varieties of cucurbits, a further cause of variability in the host reaction 
to the parasite appears to be directly connected in some way with the 
growth condition of the host at the time of inoculation. 
It has long been thought by many growers that the spread of wilt 
and the extent of damage done are in some way connected with 
weather conditions. In two different papers, W. G. Sackett 1 states 
that growers seem to think that wilt is worse during wet weather and 
just after a heavy rain, especially if the sun comes out hot. He says 
further that if this is true it is probably due to the fact that these con- 
ditions favor growth of the germs and bring about a more rapid dis- 
tribution of the bacteria through the plant. 
G. H. Coons 2 thought it probable that hot, dry summers, such as 
the summer of 1911, might do much to check the spread of the disease 
by drying out the wounds made by insects before the bacteria could 
obtain a foothold. He stated further that perhaps the temperature 
conditions alone are sufficient to check the growth of the disease. 
1 Sackett, W. G. Some bacterial diseases of plants prevalent in Michigan. Mich. Agr. Exp. Sta. Bull. 
230, p. 217. 1905. 
Some bacterial diseases of plants. Colo. Agr. Exp. Sta. Bui. 138, p. 22-23, 1909. 
* Coons, G. H. Cucumber and muskmelon wilt. In Mich. Farmer, v. 140, no. 1, p. l-2,illus. 1913. 
