BREEDING RUST RESISTANT TREES: MODERATOR'S SUMMARY 627 



Since parental breeding materials of pine can be propagated vegeta- 

 tively either through grafts or rooted cuttings, this type of world-wide 

 information could be developed much more easily and effectively than with 

 a crop such as maize. 



All that is needed to achieve this vital background information with 

 which to guide the breeding programs is the imagination, vision, determi- 

 nation, and cooperation of a group of forest geneticists, pathologists, 

 and breeders (such as are represented here today) , dedicated to combining 

 their efforts to fight for the development of several sites for 

 International Cooperative Testing in the areas of the world where white 

 pine is important or could become important and where the pathogen exists 



PROGRESS ACHIEVED IN BREEDING RUST -RESISTANT PINES 



IMPROVEMENTS IN SOUTHERN PINES 



Cronartium fusiforme , the pathogen causing southern fusiforme rust, 

 is endemic on a number of southern pine species, including the important 

 loblolly (Pinus taeda) and slash (P. elliottii) pines. Presumably in 

 the undisturbed southern forest a balanced host-parasite relationship 

 existed, as it does today in the little-disturbed western forests of 

 lodgepole pine, Pinus contorta Dougl., and the western gall rust pathogen 

 Peridermium harknessii Moore, where little damage is done to the host. 



The equilibrium between host and pathogen - between loblolly and 

 slash pines and C. fusiforme was undoubtedly first seriously disturbed 

 when logging operations 50 to 100 years ago removed all the merchantable 

 trees and left standing young non -merchantable trees. Unfortunately the 

 logging operation also left many large cull trees, including many 

 seriously galled or cankered by the rust fungus. The cull trees often 

 constituted much of the pollen source for the younger trees, and this 

 resulted in an increased rust problem on seedlings grown from such seed. 

 The problem was further aggravated during the economic depression years 

 and the war years (1930 's - 1945) when much abandoned agricultural land 

 was converted to slash and loblolly pine plantations. Seed was in great 

 demand and sources were not controlled. Much of the seed was probably 

 obtained from rust-susceptible trees of bad form. As a result, by the 

 end of the war many of the young plantations of loblolly and slash trees 

 were of bad form and/or seriously rusted. 



Aggressive forest tree improvement programs were organized in the 

 mid 1940' s, through the cooperation of universities, state governments, 

 the federal government and forest product -utilizing industries. The 

 results have been spectacular. Improved control of the seed sources of 

 both loblolly and slash pine are already paying big dividends by increasing 

 both the level of rust resistance and improving the growth rate and the 

 tree form. Perhaps the regeneration - both natural and plantation - 

 originating from improved seed sources has already achieved a level of 

 rust resistance considerably over what it was 25 years ago. Moreover, 

 seed from progeny-tested seed orchard trees is now rapidly becoming 

 available. This seed will give another increment in rust resistance 

 probably raising it to an average level that will be higher than that 

 which was present in the undisturbed virgin forests, and will also 

 simultaneously contribute to further improvements in growth rate and 

 tree form. 



