IMPROVED PLANTING STOCK THROUGH SYNTHETIC VARIETIES 5 : .- 



Schreiner, E.J. 1968. Forest tree breeding. Unasylva 22(-2^_: 3-9. 

 Snyder, E. B. 1968. Seed yield and nursery performance of self -pollinated 



slash pines. Forest Sci. 14: 68-"4. 

 Sprague, G. F. 196". Plant breeding. Annu. Rev. Genet. 1: 269-294. 

 Sprague, G. F., and Merle T. Jenkins. 1945. A comparison of synthetic 



varieties, multiple crosses, and double crosses in corn. J. Amer. 



Soc. Agron. 35: 137-147. 

 Stettler, Reinhard F. 1966. The potential role of haploid sporophytes 



in forest genetics research. Sexto Congreso Forestal Mundial , Madrid, 



June 1966. 6CFM/E/C. I . I ./21 . 7 p. 

 Suneson, Coit A. 1960. Genetic diversity--A protection against plant 



diseases and insects. Agron. J. 52: 319-321. 

 Theurer, J. C, and L. J. Elling. 1963. Comparative performance of 



diallel crosses and related second generation synthetics of alfalfa. 



I. Bacterial wilt resistance. Crop Sci. 3: 50-55. 

 Theurer, J. C, and L. J. Elling. 1964. Comparative performance of 



diallel crosses and related second-generation synthetics of alfalfa, 



Medicago sabiva L. III. Forage yield. Crop Sci. 4: 25-28. 

 Wakely, Philip C, 0. 0. Wells, and T. E. Campbell. 1966. Mass production 



of shortleaf x slash pine hybrids by pollinating unbagged female 



flowers. Joint Proc, Second Genet. Workshop, Soc. Amer. Forest, and 



"th Lake States Forest Tree Improv. Conf. U.S. Dep . Agr., Forest Serv. 



Res. Paper NC-6: ~8-~9. 

 Wernham, C. C. 1960. Maize synthetics for disease resistance. Plant 



Dis. Rep. 44: 498-500. 

 Williams, Watkin. 1964. Genetical principles and plant breeding. 



F. A. Davis Co., Philadelphia. 504 p. 

 Winton, Lawson L. 1968. Plantlets from aspen tissue cultures. Science 



160: 1234-1235. 

 Winton, Lawson, and Dean W. Einspahr. 1968. The use of heat-treated 



pollen for aspen haploid production. Forest Sci. 14: 406-407. 

 Wolter, Karl E. 1968. Root and shoot initiation in aspen callus 



cultures. Nature 219: 509-510. 



FLOOR DISCUSSION 



ZUFA: Dr. Borlaug, did you say that a newly produced rust resistant 

 multilineal wheat variety could be used for only 5 to 15 years? 



BORLAUG: For conventional varieties, the average life in winter 

 climates is 15 years. When you move them into the tropics where the rust 

 persists the year around, it's likely to be 5 or 6 years. 



ZUFA: Dr. Schreiner, how would that apply to our blister rust 

 resistant white pine varieties? 



SCHREINER: The answer to that question will have to wait until we 

 plant some improved varieties and find out how fast the fungus mutates. 



CAMP AN A: There is some recent evidence of air pollution damage to 

 eastern white pine (P. stvdbus) in the East (i.e., U.S.A.). Would you 

 care to speculate on the breeding situation in view of this new evidence? 



SCHREINER: Yes, I'm glad you asked that, because this may raise the 

 time required for creation of pest-resistant seed varieties , including 

 resistance to air pollution, to well over 100 years. But I predict that 

 we can get such resistance. We have observational evidence that we have 



