342 ROBERT A. SCHMIDT 



susceptible tissue, (3) germination of sporidia, (4) penetration of the 

 suscept by the germinating sporidia, and (5) subsequent colonization. , 

 Therefore, many factors other than inoculation per se are involved and 

 the term "successful inoculation", as used herein, implies the development 

 of at least foliar symptoms. Table 1 lists some of the requirements for 

 successful inoculation. Little is known about factors affecting deposition 

 penetration, or post penetration phenomena. 



INOCULATION TECHNIQUES 



INOCULATION OF PINE 



The techniques dealing with the inoculation of pine are arbitrarily 

 divided into those involving relatively large numbers of trees (mass 

 inoculations) and those made on one tree (individual tree inoculations) . 

 Mass inoculations are used extensively in screening trials for the 

 identification of rust resistant pines while individual tree inoculation 

 techniques are useful for studies of fungus taxonomy, the host range of 

 the pathogen, the mode of resistance, etc. Both techniques are used in 

 investigations of the epidemiology of fusiform rust. A summary of each 

 technique, including literature citations, purposes, results, advantages 

 and disadvantages, is provided in Table 2. The number and name of the 

 technique in the table corresponds with that in the text where only a 

 brief resume* is given. Techniques presently being developed are included 

 as unpublished reports. 



A. Mass Inoculations 



trees are exposed to inoculum under natural field conditions, are of two 

 kinds. These are (1) experimental plantings that are established to 

 evaluate factors such as rust resistance, survival, or growth rate, and 

 (2) natural stands and plantations established for production of wood. 

 The latter, although not established to provide data, yield useful informa- 

 tion on the incidence of fusiform rust in relation to cultivation, ferti- 

 lization, year of planting, age of tree, stand density, etc. 



Problems associated with natural inoculations center around the 

 difficulty of controlling inoculum density, time of inoculation, and 

 temperature and relative humidity at the infection court. The resulting 

 variability in the intensity of disease from year to year and among sites 

 makes the identification of resistant genotypes a slow and sometimes 



Mass inoculations can accommodate relatively large numbers of 

 seedlings and involve the deposition of sporidia onto the surface of test 

 plants. Mass inoculations differ from one another with respect to the 

 control of (1) inoculum density (the number of sporidia deposited per unit 

 area of the test plant) , (2) the timing of inoculation (when spores are 

 deposited in relation to when pine tissues are susceptible) , (3) the age 

 of suscept tissue, (4) the temperature and/or relative humidity at the 

 infection court, and (5) the geographic interaction. Geographic inter- 

 action is used here to identify that interaction among suscept, pathogen, 

 and environment that can condition differential susceptibility of a given 

 genotype planted in different geographic locations. It is of prime impor- 

 tance to consider geographic interaction when climate or racial variation 

 of the pathogen differs among sites. 



1. Natural inoculations. --Natural inoculations, i.e., those in which 



