PATHOLOGY AND GENETICS OF EUROPEAN PINE RUSTS 415 



first whorls equally. Scoring the percentage of healthy - or diseased - 

 pines per progeny fails to separate pines with isolated attacks from 

 pines that may have sustained very serious attacks. From the practical 

 aspect it would be more useful to know the percentage of pines with 

 permanent damage caused by Melampsora during, say, a 5-year period. The 

 attack frequency is higher for terminal leaders than for first whorls, 

 and damage to terminal leaders is of course of greater practical interest. 

 Thus attacks per cm of terminal leader is a reasonable scoring method for 

 M. pinitorqua on somewhat older pines. 



When making routine progeny tests one consideration is whether 

 exposure to Melampsora should be limited to the pines' second year in 

 nurseries, or in plastic greenhouses under controlled conditions, Finns 

 silvestris L. has no branches at this stage and Melampsora damage on the 

 pine stems is frequently serious. At this stage the percentage of 

 infected plants per progeny is an acceptable way of scoring M. pinitorqua 

 attack. 



Sometimes, however, the number of attacks per progeny is not neces- 

 sarily in proportion to permanent damage. One investigation (Klingstro'm, 

 1969) suggests that the ratio is low. Thus the ability to recover from 

 damage may be subject to variation. 



A study of the occurrence of Melampsora on progenies of ?. silvestris 

 shows that, with few exceptions, the attacked pines have longer terminal 

 shoots than healthy pines of the same progeny (Klingstro'm, 1969) . Damage 

 to terminal leaders is also much more common than damage to first whorls. 

 This indicates that there can be a relationship between growth regulating 

 substances and the occurrence of Melampsora. 



Initial tests have shown that uninfected pine clones of varying 

 susceptibility to pine twist rust can contain greatly differing quanti- 

 ties of preformed inhibitors in the annual shoots. Several acid sub- 

 stances that are soluble in ether have a strong inhibitng effect on 

 Melampsora basidiospore germination. The substances in the extracts 

 have been separated by gel filtration combined with thin layer chromato- 

 graphy (Klingstro'm, 1969) . In addition there are probably resistance 

 reactions which are triggered by the combination of parasite and host, 

 but no reports on this have been published in the case of M. pinitorqua 

 on pine. 



FIFFZFFMFIM FFFF 



BIOLOGY OF AUTOECIOUS AND HETEROECIOUS RACES 



The blister rust of P. silvestris in Europe can be described as a 

 Cronartiur. complex - C. flaooidum (Alb. £ Schw.) Wint. (= C. asolepiadeum 

 (Killd.) Fries). In this complex there are at least three races: C. 

 flaooidum with a great number of alternate hosts, among others Cynanchum 

 vincetoxi&jr: (L.) Pers. and Faeonia spp.; C. gentianeum Thum. with 

 Geritiana asolepiadea L. and Faeonia spp. as alternate hosts; and F. pini 

 (Willd.) Kleb. (= ?. pini (Pers.) Le"v.) as an autoecious race. 



This is not the place to discuss final scientific naming, but some 

 further reports on F. pini will be quoted. There are no obvious morpho- 

 logical differences between host-alternating and pine-to-pine races. 

 Since full-scale inoculation tests are extremely time consuming and are 



