distal barks. For example, no seasonal trends were noted 

 in amounts of fructose and glucose. Again, sucrose peaked 

 in the June collection of proximal bark of cankered trees 

 (18.9 mg/g) and showed the least amount in November 

 (11.7 mg/g). Raffinose and stachyose were at their great- 

 est concentrations in November (10.8 mg/g, 7.7 mg/g) and 

 February (6.8 mg/g, 6.5 mg/g), with lesser amounts in 

 June (2.9 mg/g, 0.0 mg/g) and September (4.0 mg/g, 0.0 

 mg/g). 



Yellow margin bark (the yellowed bark that identifies 

 the advancing margin of the blister rust canker) had 

 significantly less fructose, glucose, and sucrose than either 

 distal or proximal bark locations, but had similar levels of 

 raffinose and stachyose (table 2). Seasonally associated 

 trends in amoimts of all sugars were found although pat- 

 terns among seasons differed (table 2). Fructose and 

 glucose were seasonally cycHc with alternating highs and 

 lows. For example, fructose concentrations were low in 

 November (9.2 mg/g), high in February (14.4 mg/g), lower 

 in June (11.3 mg/g), and higher in September (15.4 mg/g). 

 Seasonal values of sucrose concentrations were greatest in 

 Jime (15.7 mg/g) and smallest in November (9.1 mg/g). 

 Raffinose and stachyose were found in characteristically 

 greater amounts in November (10.8 mg/g, 7.7 mg/g) and 

 February (8.2 mg/g, 6.0 mg/g) rather than in June 

 (3.2 mg/g, 0.0 mg/g) and September (5.2 mg/g, 1.9 mg/g). 

 Contrary to the decreases shouTi by distal and proximal 

 samples, raffinose and stachyose each showed a slight in- 

 crease in September (5.2 mg/g, 1.9 mg/g) from the June 

 low (3.2 mg/g, 0.0 mg/g). 



The areas of the blister rust canker in which sporulation 

 of the rust fungus occurs generally had smaller concentra- 

 tions of each sugar than did other bark locations, and had 

 a seasonal pattern unlike that of other bark samples. 

 Table 2 illustrates that fructose and glucose concentrations 

 were relatively similar in November (10.2, 11.8), June 

 (10.3, 9.7), and September (12.0, 10.6) collections and at 

 least three times the amounts (3.1 to 3.3) found in the 

 February collections. Sucrose levels were consistent wath 

 those found in the other areas, except that the February 

 (4.8) rather than November (14.0) samples contained the 

 least amount. Amounts of raffinose in the sporulating 

 areas deviated from the patterns found in the yellow 

 margin samples, but stachyose showed no de\aation. Con- 

 centrations of raffinose were consistently high in the 

 November samples (10.6) but were depressed to lows 

 similar to those for stachyose in the February (3.6), June 

 (3.1), and September (4.7) collections. 



DISCUSSION 



The four sampling periods— November of one year, and 

 February, June, and September of the followng year- 

 were chosen to show that an obligate organism, the rust, 

 is at times physiologically out of phase with its perennial 

 host, the pine. For example, in our part of the temperate 

 zone, the Northern Rocky Mountains, western white pine 

 becomes dormant between September and November and 

 its growth has noticeably slowed or stopped. However, 

 blister rust growth such as canker enlargement and 

 yellowing of the bark continue at a rate responsive to bark 



temperatures. That is, the rate decreases as temperatures 

 decline and increases as bark temperatures increase. As 

 early as February, the 14-week to 16-week cold tempera- 

 ture requirements for resimiption of growi;h after dor- 

 mancy of western white pine have been fulfilled (Steinhoff 

 and Hoff 1972). Ambient temperatures of -12 to 2 °C 

 continue host dormancy, but cankers enlarge whenever in- 

 solation increases bark temperatures to a level suitable for 

 the blister rust fungus to grow. 



April and May sampling periods were avoided because 

 both organisms are metabolically very active at that time 

 as evidenced in rapid changes in morphology— for example, 

 current-year needle expansion, rapid leader growth, rapid 

 canker enlargement, profuse aeciospore liberation, and 

 pycniosori activity. These evident and dramatic changes 

 are probably accompanied by rapid turnover within 

 metabolic reservoirs of soluble sugars. By June, except for 

 some canker enlargement, these activities have subsided 

 and a balanced but dynamic equilibrium in sugar 

 metabolism is likely reached between host and parasite. 



Western white pines retain three generations of needles 

 during any year. Researchers have found quantitative 

 differences in starch, sugars, and nitrogen compounds 

 between each generation of needles (Kozlowski and Keller 

 1966). In the research reported here, sampling was timed 

 to minimize differences in amounts of soluble sugars 

 brought about by the demands of host growth as well as 

 the impact of immature or senescent needles. For exam- 

 ple, although current-year needles were sampled twice in 

 the year in which they were formed (June and September), 

 both sampling dates were after the needles were fully ex- 

 panded and are no longer juvenile but are considered as 

 physiologically matiire as 2- and 3-year-old needles. 

 Needles in their third growing season and sampled in 

 February of the following year are of comparable physio- 

 logical maturity because they have remained green and 

 free, of the evidence of senescence that will appear later in 

 April and May. These needles were not sampled in June 

 because the 3-year-old needles, now in their fourth grow- 

 ing season, were yellow to brown, indicating a probable 

 bias in the analysis due to senescence and death effects. 



Sugar concentrations in all needle age classes responded 

 to growth activities of the host. Concentrations of sugars 

 were greater during dormancy than active growth. Fruc- 

 tose and glucose concentrations, because of their direct in- 

 volvement in catabolic as well as anabolic metabolism, 

 were found to coincide closely vnth the demands of tree 

 growth. Raffinose and stachyose were noticeable only as 

 storage molecules in that they were measurable in dor- 

 mant periods and undetectable in periods of active growth. 

 In contrast, sucrose, a highly translocatable molecule, was 

 found in similar concentrations in all samples. This sug- 

 gests that, through translocation, pools of sucrose can 

 have high turnover rates but be maintained at similar 

 levels and therefore appear to be insensitive to host 

 physiological acti\aties. 



Amounts of sugars in needles of these western white 

 pines with bole cankers do not characterize the cankered 

 trees nor distinguish them from healthy trees. Intuitively, 

 stem infections could jeopardize the health of foliage as 

 exidenced in diseases of many cultivated annuals, a 

 phenomenon upon which aerial surveys rely. However, 



4 



