INOCULATION WITH PINE TWISTING AND SCOTS PINE BLISTER RUST 317 



water suspensions. If dry spores are scattered on water agar they 

 usually germinate after about 5 hours at 20 to 25°C. But spores that 

 were stored in water in a medical syringe for up to 24 hours did not 

 show any sign of germinating in the syringe. If these spores were 

 transferred to an agar surface after 24 hours in the syringe, germina- 

 tion started in the normal way. The mechanism that inhibits germination 

 in water has not been studied. Pine shoots in nurseries were also inocu- 

 lated with spores that had been stored in the inoculating syringe for 

 various lengths of time. Spores stored for 5 minutes, 1, 3 and 5 hours 

 were used as inoculum to the same pine material simultaneously, and in 

 all cases aecia developed 2 years later on a low percentage of the pines. 



Tests were started on pine material consisting of plus tree progenies 

 The material has been described more thoroughly elsewhere (KlingstrCm, 

 1967) . Only a low percentage of the inoculations resulted in the develop- 

 ment of aecia. Had not some individual progenies (and clones) given 

 values of over 10% infection, the tests would have been discontinued. As 

 it was, another series of tests was made using individual host plants 

 that had proved to be susceptible in earlier tests. Unfortunately far 

 too many of these pines died as a result of the first inoculation before 

 the result of the second could be recorded. Another series of tests 

 using susceptible clonal material has been started. 



In one test, inoculation was carried out on 159 5-year-old pines 

 selected at random from 53 plus tree progenies. Inoculations were made 

 in three places on each pine, i.e., on three shoots surrounding the 

 terminal leader, near the top of a shoot, in the middle and at the base. 

 The attack frequency was low but did indicate greater success with 

 apical inoculation of shoots. 



In another experiment, inoculation was performed on 106 pines from 

 the same progenies. Inoculations were made on shoots of the first whorl 

 by applying a drop of spore solution without making a wound, by applying 

 a drop of spore solution and making one puncture with the injection 

 needle, and by the same procedure plus making 5 and 10 punctures. 

 Aecidia developed only in two cases, both from the treatment involving a 

 single puncture. The only conclusion that can be drawn from this is that 

 the wound as such is necessary, but it can be a very minor one. 



At the time of infection in the spring the shoots are still imper- 

 fectly lignified and are easily broken off. Damage of this sort is often 

 caused by birds. In an attempt to emulate this some first whorls were 

 broken off and a drop of spore suspension was applied to the fracture. 

 Compared with a puncture made by an injection needle, this is a massive 

 injury. Spore solution placed on 106 such fractures resulted in produc- 

 tion of aecia in only three cases. 



In another experiment 25 6-year-old pines that were known to be 

 susceptible were used in a second inoculation with the same type of 

 spore suspension used previously (i.e., the spores that formed on the 

 pines were collected and used again to inoculate the same pines) . The 

 intention was to discover how long the pines remained susceptible to 

 inoculation. The tests covered the period June 15 to July 27. Pairs 

 of shoots on 1-year-old branches were inoculated, 1 pair each week as 

 long as these shoots were available. The temperature and type of 

 weather were recorded for each inoculation. The result of this test 

 (Table 1) indicates that the pines are susceptible for a considerable 

 time, and that cool weather probably gives lower values for the formation 



