CONIFERS VS. CROP PLANTS AS BREEDING MATERIAL 21 



exhibit wide variations in reproductive activity. As a consequence, tree 

 breeders making selectionsin wild populations often find that otherwise 

 valuable phenotypes are sub-normal seed producers. Bergman (1968), using 

 data on flowering of 15 clones in a seed orchard of Pinus taeda. L. , reports 

 that the two heaviest cone-producing clones will be parents of at least 

 50 percent of the progeny from the orchard. 



Conifers are rather special trees. Historically, except for living 

 fossils like Gingko and second-rate imitation trees like cycads, conifers 

 are the oldest trees. Moreover, the best-attested records of longevity 

 of trees belong to conifers. Conifers, with the exception of Sequoia, 

 Juniperus and Pseudotsuga s have shown little tendency toward cytogenetic 

 adventures. The diploid number of 24 chromosomes is very widespread--in 

 fact almost universal in the family Pinaceae, except for Douglas -fir. 

 The pines have proven rather successful in their resistance to induced 

 polyploidy; most polyploid and aneuploid pines are phenotypically sub- 

 normal and of reduced viability. 



Conifers are predominantly cross-pollinated by wind. They produce 

 pollen abundantly in catkins which are easy to collect. The pollen is 

 easily extracted and may be used successfully in artificial pollinations, 

 five years or more after collection, provided it has been properly 

 extracted and stored. The flowering of most conifers is usually compressed 

 into a very short period each year, except for some of the so-called multi- 

 nodal pines that produce megasporangiate strobili over a period of several 

 weeks. This compression of flowering, and the meiotic processes preceding 

 it, into a short period each year keeps the conifer cytologist alert and 

 the conifer breeder intensely busy for short periods. 



Most conifers are monoecious, although some do not become so until 

 rather late in life. Selfing does occur naturally, and some individuals 

 produce selfed progenies which are not markedly inferior in vigor to out- 

 crossed progenies. Possibilities for development of inbreds , with subse- 

 quent hybridization of inbreds, exist and are being explored, especially 

 in Pseudotsuga. 



Most conifers require one season from pollination to seed maturity, 

 but Cupressus and most pines require two seasons . A few pines require 

 three. The longevity of the male gametophyte in these cases fascinates 

 speculative botanists, and the technical problems of keeping legible tags 

 attached to exposed portions of tall trees in wind-swept terrain are con- 

 siderable, to say nothing of wear and tear on the patience of the tree 

 breeder. Seed of most conifers retains viability well for at least five 

 years; for some pines, more than 30. This is an advantage conifer breeders 

 have ever those who work with some of the angiosperm trees . Seed dormancy 

 in conifers and particularly in some of the white pines requires strati- 

 fication treatments lasting as long as 90 or more days. As a result, the 

 white pine breeder's planning flexibility is restricted. The first 

 season's growth of most conifer seedlings is slow. This is particularly 

 true of the white pines, which do not really enter the rapid growth phase 

 for several years (Bingham, Hoff , and Steinhoff , in press) . Corresponding 

 to this slow tempo, the development of rust symptoms and resistance- 

 reactions, even by seedlings infected early in life, is relatively slow. 

 This poses problems in testing as well as in planting practice with the 

 southern pines. The facts that rust mycelium may persist in pine tissues 

 for several years before aeciospores are produced and that aeciospore 

 production resulting from a single pine infection may continue for many 

 years have important implications for the spread and control of these 



