316 ALLAN KLINGSTROM 



Although P. pini is regarded as a classic subject in forest pathology, 

 the normal biology of the fungus is imperfectly known. Haack (1914) showed 

 that healthy branches of infected pines could be inoculated with aecio- 

 spores if the branches were wounded. Liese (1936) was able to demonstrate 

 that a progeny from a cross between two infected pines was easier to 

 inoculate than the progeny of a cross between two healthy trees. Even 

 these two early works contain suggestions of differences in resistance. 

 However, these tests showed that pines could be inoculated even though 

 they included few pines, made use of large amounts of inoculum, and left 

 the reader uncertain as to how the pines were wounded at the time of 

 inoculation. 



Several reports suggest that successful inoculations can be made 

 only on the annual shots of pine - not the needles - and that wounds are 

 necessary (Bolland, 1957; Murray, 1961; Klingstrtfm, 1967). On the other 

 hand, van der Kamp (1968) has successfully infected stem wounds and 

 needles. He concluded that infection can take place through stem wounds 

 but that most lesions arise from infection of wounded or unwounded 

 needles. It takes a long time to devise repeatable methods of inocula- 

 ting on a large scale in the field. Two years elapse between inoculation 

 and the development of aecidia. Current Swedish tests concerned with 

 inoculation methods are still unfinished. However, certain results are 

 available. 



PERIDEPMIVM PINI - CURRENT SWEDISH EXPERIMENTS ON INOCULATION 



Swedish tests have been made under nursery conditions an d concern 

 mostly plus tree progenies. Eventually they will entail the inoculation 

 of relatively large numbers of plants, which explains why the tests were 

 made in a nursery. In one test, dry aeciospores were used as inoculum 

 on 20 randomly selected progenies - approximately 4,000 pines between 

 3 and 5 years of age. Attacks resulted only when the annual shoots were 

 wounded with small punctures of a needle or small wounds with a knife in 

 conjunction with the inoculation. In no instance did a wound to older 

 stem parts or to needles of different ages lead to a successful attack. 

 These initial tests confirmed what was already known. The difficulty of 

 working with dry aeciospores in extensive field tests was quite obvious. 

 This was particularly noticeable where an attempt was made to keep 

 separate spore material from different sources, or to localize the 

 various inoculation sites on the plants. The attack frequency was low 

 in all cases, never exceeding 10 percent of the plant material. 



In another exploratory experiment involving 100 plants, an attempt 

 was made to utilize a water suspension of aeciospores dispensed by a 

 medical syringe. Small wounds were made on the surface of the shoot under 

 the drop of spore suspension. In this case inoculation led to the formula 

 tion of aeciospores in 10 percent of the inoculations. Brief mention has 

 already been made of this method (Klingstrtfm, 1967) . 



The above line of experimentation formed the starting point of the 

 next series of inoculation trials. Spores were obtained from different 

 geographical areas and kept separate by individual cankers from which 

 collected. The first step always involved inoculating Paeonia for the 

 purpose of eliminating the host-alternating Cronartium. The next step 

 was to check that the spores were able to germinate on 1% water agar 

 (KlingstrOm, 1963b) . This ensured that the spores had not been damaged 

 in transit. A check was also made on the viability of the spores in 



