AN INOCULATION SYSTEM FOR CRONABTIUM FUSIFORME 



L. D. Dwinell 

 Southeastern Forest Experiment Station s 

 Forest Service, U.S. Department of Agriculture 3 

 Athens, Georgia, U.S.A. 



ABSTRACT 



Standardized techniques for inoculations with Cronartium 

 fusiforme are lacking. A technique is outlined permitting 

 inoculation of up to 1,000 pine seedlings at a uniform, 

 reproducible, and controllable basidiospore density. Basidio- 

 spores of C. fusiforme , naturally abjected from telial columns 

 on oak leaves, are carried into an inoculation chamber in a 

 stream of air maintained at near spore temperature and moisture 

 optima. Densities of 100,000 spores/cu ft have been attained. 

 Relation of density to infection is being studied to deter- 

 mine density optima for future work utilizing the technique. 



Research studies on fusiform rust of southern pines are frequently 

 handicapped because the standard inoculation procedure of suspending 

 telia-bearing oak leaves over young pine seedlings gives highly variable 

 results. This is due primarily to fluctuations in inoculum density. The 

 inoculation technique outlined here was designed to overcome this limita- 

 tion. It allows for the inoculation of large groups of pine seedlings 

 with a uniform, reproducible, and closely controlled sporidia density. 



The basic principle utilized is that Cronartium fusiforme Hedge, and 

 Hunt ex Cumm. , as well as other rust fungi, naturally abject their basidio- 

 spores. By passing temperature-controlled, water-saturated air beneath 

 the telial columns of C. fusiforme, the sporidia are swept into an inocula- 

 tion chamber and uniformly deposited on pine seedlings in much the same 

 manner as in nature. Recently Snow (1968b) utilized this principle and 

 reported on an apparatus that inoculates tufts of primary needles of 

 individual pine seedlings with sporidia of C. fusiforme. 



Temperature, relative humidity, and rate of airflow are the most impor- 

 tant environmental factors to consider. The design specifications, there- 

 fore, called for construction of a system that controlled these factors 

 close to the environmental optimum for C. fusiforme. 



The inoculation system is shown in Figure 1. Compressed air is 

 bubbled through distilled water in 4-liter Erlenmeyer flasks held at 34 C 

 in a constant temperature water bath to provide maximum humidity. The 

 airflow meter for each of the three lines (0.95 cm ID Tygon tubing) to 

 these humidification flasks is normally adjusted to 70 liters per minute 

 (LPM) . Another airstream, similarily adjusted, is bubbled through distilled 

 water in a 4-liter Erlenmeyer flask held in a cold water bath (5 to 10 C) . 



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