such is not the case in the perennial hosts having a peren- 

 nial infection disproportionately small when compared to 

 the biomass of the host. But as the blister rust cankers ap- 

 proach complete girdling of the stems (80 to 100 percent 

 of the circumference), death of the portions above the 

 cankers is evident; needle colors change from green to 

 yellow to reddish brown. Before their rapid decline, 

 however, all needles are of normal color and apparently 

 are capable of near normal metabolism as is indicated by 

 sugar concentrations found comparable to those in needles 

 of healthy trees. 



The impact by blister rust to soluble sugar pools in pine 

 bark was measurable in June (Welch and Martin 1975). 

 However, there were no apparent differences between 

 seasons in amounts of fructose, glucose, and sucrose in 

 bark located distally from the cankers compared to 

 similarly located bark of noncankered trees. Infection 

 depressed the canker levels of fructose and glucose 

 without significantly altering sucrose levels. Although 

 some differences are not significant, the implications 

 within the data are that infections have an area of in- 

 fluence extending a limited distance beyond canker 

 margins but does not include the foliage. These findings 

 help explain the absence of an impact by the rust upon 

 host growth (Buchanan 1938) until girdling of the bole is 

 complete. That this disease affects only locally the 

 amounts of certain sugars in certain tissues is also evident 

 in the raffinose and stachyose concentrations. The 

 seasonal concentrations of these sugars were unaffected 

 by the presence of blister rust in another location on the 

 bole. Regardless of blister rust, bark, like needles, showed 

 sugar concentrations were highest during host dormancy 

 and lowest during rapid growth. 



Sugar concentrations in proximally located bark ex- 

 hibited the same trends for each sugar as those found in 

 the distal bark samples. Samples of proximal bark had 

 smaller amounts of fructose, glucose, and sucrose, but 

 similar amounts of raffinose and stachyose to those found 

 in distal bark. The distal and proximal bark, although 

 separated physically, are physiologically similar in their 

 storage capacities for sugars as is evidenced in the 

 similarity of raffinose and stachyose concentrations. 

 Because the rust fungus is making its initial invasion into 

 these tissues (Ehrlich and Opie 1940), the implications are 

 that the lesser amounts of fructose, glucose, and sucrose 

 are due to the metabolic demands of the neighboring, 

 greater concentration of the fungus in the yellow margin. 



Bark tissues inhabited by the blister rust fungus— the 

 yellow margin of the cankers and the sporulating areas- 

 exhibited the same trends in sugar concentrations that 

 characterized the proximal bark locations. As the sample 

 locations progressed toward the canker centers, amounts 

 of soluble fructose and glucose were less. This may show 

 that small pools of these sugars reflect diminished needs 

 after sporulation or that glucose has been synthesized into 

 chitin, the glucosamine constituent of the fungal cell wall, 

 a compound known to be present in this rust (Martin 

 1967). 



The notable contrast in the low February levels of fruc- 

 tose, glucose, and sucrose in sporulating areas when com- 

 pared to relative levels of the same sugars in other bark 

 tissues in February also indicates that metabolism on the 



part of the blister rust fungus is greater than that of the 

 pine tissues. Apparently, soluble sugars are being assimi- 

 lated into aeciospores, which are subsequently dispersed 

 from April through early June. Synthesis of pycnial fluid, 

 which contains a high proportion of sugar alcohols and 

 fructose (Wicker and others 1976), and synthesis of sugar 

 alcohols in rust invaded bark (Welch and Martin 1975) 

 would also utilize fructose at a time when host reserves in 

 raffinose and stachyose are not available for maintaining a 

 constant reservoir. Deductively, February is a period of 

 late dormancy in the host and early spore development in 

 the fungus in which the metabolism of pathogen and host 

 are not synchronized in their rates of use of common pools 

 of metabolites. This period may be a point in the life cycle 

 of the pathogen at which it could be vulnerable to chemi- 

 cal attack while the host remains insensitive. This would 

 achieve target selectivity in chemical control and minimize 

 ecological impacts (Sbragia 1975). 



REFERENCES 



Allen, P. J. 1966. The role of the host in the development 

 of disease symptoms— a review. Phytopathology. 56(3): 

 255-260. 



Brown, W. 1936. The physiology of host/parasite relations. 

 Botanical Review. 2: 236-281. 



Buchanan, T. S. 1938. BHster rust damage to merchant- 

 able western white pine. Journal of Forestry. 36: 

 321-328. 



Daubenmire, R.; Daubenmire, J. B. 1968. Forest vegeta- 

 tion of eastern Washington and northern Idaho. Tech. 

 Bull. 60. Pullman, WA: Washington State University, 

 Washington Agricultural Experiment Station, College of 

 Agriculture. 104 p. 



Durbin, R. D. 1967. Obligate parasites: effect on the 

 movement of solutes and water. In: Mirocha, C. J.; 

 Uritani, I., eds. The dynamic role of molecular consti- 

 tuents in plant-parasite interaction. St. Paul, MN: 

 American Phytopathological Society: 80-99. 



Ehrlich, J.; Opie, R. L. 1940. Mycelial extent beyond 

 blister rust cankers on Pinus monticola. Phytopathology. 

 30: 611-620. 



Goodman, R. N.; Kiraly, Z.; Zaitlin, M. Vascular transport. 

 1967. In: The biochemistry and physiology of infectious 

 plant disease. Princeton, NJ: D. Van Nostrand Co.: 

 281-307. 



Grainger, J. 1956. Host nutrition and attack by fungal 



parasites. Phytopathology. 46: 445-456. 

 Horsfall, J. G.; Dimond, A. E. 1957. Interactions of tissue 



sugar, growth substances, and disease susceptiblity. Z. 



Pflanzenkr. Pflanzenpathol. Pflanzenschutz. 64: 415-421. 

 Huber, D. M.; Watson, R. D. 1974. Nitrogen form and 



plant disease. Annual Review of Phytopathology. 12: 



139-165. 



Kozlowski, T. T.; Keller, T. 1966. Food relations of woody 



plants. Botanical Review. 32: 293-382. 

 Little, C. H. A. 1970. Seasonal changes in carbohydrate 



and moisture content in needles of balsam fir {Abies 



balsamea). Canadian Journal of Botany. 48(1): 2021-2028. 

 Martin, N. E. 1967. Histochemical analysis of the blister 



rust fungus, Cronartium ribicola. Phytopathology. 57: 



820-821. Abstract. 



5 



