XIII Genetic Transformation of Pinus palustris

Longleaf pine (Pinus palustris Mill.) is an important softwood species in the southeast United States. In presettlement times, this species occupied extensive, pure stands throughout the Atlantic and Gulf Coastal Plains from southeastern Virginia to eastern Texas, as well as south throughout the northern two-thirds of Florida. Its range also includes the Piedmont Ridge and Valley, and Mountain Provinces of Alabama and Georgia (Burns and Honkala 1990). Historically, longleaf pine was the premier timber and naval stores tree, a fact which resulted in its virtual disappearance from extensive regions. Its value as a timber species remains high; it shows excellent form and good wood qualities, as well as resistance to fusiform rust, the most damaging disease of southern US three-needle pines. An aspect of longleaf pine which negatively affects its relative reforestation value is its grass stage, during which its first 5 years of growth remains essentially limited to root development. This stage is also characteristically expressed for several years by adventitious micropropagules generated in vitro, although a few genotypes have shown precocious and rapid shoot elongation (AM. Diner, unpubl.). Notwithstanding the obstacles to seedling growth presented by the grass stage, however, the value of this tree has compelled widespread reforestation efforts. Current perspectives for value-added longleaf pine genetic transformants relate to both disease resistance and early shoot growth. The major microbial disease of this species is brown-spot needle blight (Scirrhia acicolu), which causes severe defoliation and death to grass-stalge seedlings. Other commercially important microbial diseases include pitch canker (Fusarium moniliforme var. sub&tans), annosus root rot (Heterobasidion unnosum), and cone rust (Cronartium strobilinum). Longleaf pine s,uffers attack by a variety of defoliating insects, including both adult (Coluspis pini Barber) and larval [(Neodiprion lecontei (Fitch); Dendroctonus terebruns (Oliv.); Hylobius pales (Hbst.); Puchylobius picivorus (Germar); Dioryctriu spp.; Laspeyresia spp.)] insect forms. Because vector systems exist for plant transformation to such as chitinase and BT toxin syntheses, opportunities for transformation of longleaf