X4S-12 MANUAL OF METHODS FOR PURE CULTURE STUDY 



RELATIVE EFFICIENCY IN TECHNIC 



The best methods of procedure for making inoculations and for 

 recording results have not always been worked out and are not obvi- 

 ous from inspection. If the question is of sufficient importance, the 

 answer may be secured statistically. There may be a question, with 

 a leaf-spot organism, for example, as to whether it is better when 

 making inoculations to spray or to make needle punctures. Likewise, 

 when infection is secured, the question may occur whether the results 

 should be recorded in terms of total number of lesions, of total tissue 

 involved, the effect of the disease on yield, or of some other criterion. 

 Such possibilities may be tested by means of the frequently described 

 "analysis of variance" (e. g., Goulden, 1939). Thus the best 

 method for making the trials and for recording the results may be 

 determined. In general, the method that gives the greatest value 

 for the variance ratio, "F", is the most desirable. This value indi- 

 cates a greater uniformity in readings from different trials with the 

 same technic, or a greater differentiation of the varieties used or 

 treatments employed without a proportional increase in error. 



ANTIBIOTICS 



A recent survey (Osborn, 1943) has shown that various plants 

 contain substances adversely affecting certain bacteria. Doubtless 

 many instances (cf.. Link and Walker, 1933; Ark and Hunt, 1941; 

 Trussel and Sarles, 1943) occur in w^hich various higher and lower 

 forms of plant life contain chemicals that inhibit successful plant 

 inoculations. 



Records 



Taking notes on plant inoculations presents various problems 

 depending upon the experiment in hand. To assist with such records 

 a tentative protocol (Table 1) has been prepared. For some lines of 

 work it is obviously too complex while for others it is clearly inade- 

 quate. 



A number of the items listed for records may be critical factors for 

 the success or failure of an experiment. Since each one cannot be 

 discussed, several examples are mentioned. (1) Infection may fail if 

 the incubation temperature is either too low or too high. Many plant 

 pathogens operate best between 18° and 30° C. (2) Plenty of moisture 

 is important for disease development, a deficiency of water often 

 being responsible for negative results. (3) The age of the plant or 

 of the part inoculated may influence the result. The relatively young 

 leaves are frequently more susceptible than old leaves to bacterial 

 leaf spots. (4) Some varieties of plants are highly resistant to patho- 

 gens which readily attack other varieties. Similarly, different strains 

 of bacteria often vary in pathogenicity. 



