INTRODUCTION 



Over the last few years, attempts have been made to establish single aeciospores lines 

 of Cronartium ribicola to facilitate the investigation of the genetics of this important 

 conifer rust. A principal objective was to complete the life cycle in isolation so that 

 known homozygous aeciospores could be produced. A modified version (McDonald 1978) of Clinton 

 and McCormick's (1924) Petri dish method has worked well for the ribes portion of the life 

 cycle. But lack of consistent and profuse production of teliosgores has been an unexpected 

 problem. Past greenhouse studies show that a constant 61 F (16 C) from inoculation to spore 

 production led to abundant telia (Riker and others 1947 and Van Arsdel and others 1956) . 

 Also, telia would not form if the day and night temperature was above 68°F (20°C) (Van 

 Arsdel and others 1956) . 



Our first problem arose when a group of single aeciospore lines isolated at a constant 

 70°F (21°C) were transferred to a constant 55°F (13°C) . One culture out of 69 produced telia 

 within 60 days (author's unpublished data). On the other hand, other single aeciospore cultures 

 held at 70°F+2 (21°C+_1) produced teliospores that would germinate as they formed (McDonald and 

 Andrews, in preparation). So, a reliable supply of ungerminated teliospores to use for inocula- 

 tion back to Pinus monticola proved difficult to obtain. A series of experiments were initiated 

 to determine the best procedure for producing teliospores on the detached leaf cultures. 



Two pieces of information were used to formulate a liypothesis. First, we observed that 

 when inoculations were made with urediospores instead of aeciospores, we could obtain teliospores 

 in as little as 14 days at 70 F (21 C) and 16 hr days (author's unpublished data). Whereas, 

 aeciospore inoculations would nearly always require 28 to 30 days for earliest appearance of 

 telia, regardless of temperature and day length. Second, Spaulding (1922) reported that 

 Pennington and Snell followed generations of urediospore production in the field. Teliospores 

 were not produced with the first generation but were found with all later generations. We 

 hypothesized that aeciosnore and urediospore infections differed in their ability to produce 

 teliospores and that a temperature of less than 68 F (20 C) was needed to stimulate teliospore 

 production by infection resulting from urediospores. The objective of this paper is to report 

 the results of initial experiments designed to test the above hypothesis by growing both 

 urediospore and aeciospore stages of identical genetic background on one clone of ribes in one 

 growth chamber (urediospore lines compared to the aeciospore line from which they decended) . 

 Thus, as near as is currently possible, only spore stage varied. 



MATERIALS AND METHODS 



We used two sets of materials, one isolated in 1976 and the other in 1979. Both consisted 

 of single aeciospore lines isolated according to McDonald and Andrews (in preparation) . Upon 

 production of urediospores, subcultures were established. All cultures of both spore types 

 were grown on Ribes hudsonianum var. petiolare clone lNT-1, The 1976 material has already 

 been described (McDonald and Andrews, in preparation) and was included in this paper to provide 

 some comparisons with other sources of aeciospores. The 1979 material was produced and the 

 experiment conducted as outlined in fig. 1. Two cankered P. monticola seedlings growing in 

 the greenhouse were producing aeciospores. Spores from one blister on each tree were used as 

 follows: About half of the 1,058 attempted isolations were made from each blister, and isolated 

 spores were randomly placed in a cool 55 F+^2 (13 C+_l), and a warm 70 F+^2 (21 C + l) , chamber as 

 they were isolated (16 hr day 8 hr night) , 



The aeciospore cultures were inspected every 7 days for 65 days, and presence of uredio- 

 spores and teliospores was recorded. Six subcultures were attempted from all the single 

 aeciospore cultures that had produced sufficient urediospores by 21 days. These cultures are 

 a random selection of possible cultures. One-half of these subcultures were placed in the 

 warm chamber and one-half in the cool chamber from each of the warm and cool cultures from 

 which they were isolated (fig. 1). These cultures were then inspected every 7 days for 49 

 days and presence of urediospores and teliospores was recorded. 



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