IN VITRO STUDIES OF DISEASE RESISTANCE IN LOBLOLLY PINE (FUSI-FORM RUST, PITCH CANKER, FOREST GENETICS)

Two studies investigating the potential of in vitro screening of loblolly pine for resistance to fusiform rust and pitch canker were conducted. Additionally, studies investigating aspects of growing the fusiform rust pathogen in vitro were performed.; In the first study, 12 loblolly pine embryos from each of 24 full-sib families (arranged in a 3 x 8 factorial mating design were inoculated in vitro with basidiospores of the fusiform rust pathogen. Histological assessment of two types of responses, rapid incompatible necrosis and the appearance of a red staining substance at the inoculation point were made. Combinations of the traits evaluated explained much of the variation in family field resistance ratings at age four. Also, some traits possessed moderate to high family heritability estimates so that development of a rapid in vitro resistance screening technique is promising.; In the second study, 20 loblolly pine embryos from each of 24 seedlots of loblolly pine were inoculated in vitro with microconidiospores of the pitch canker pathogen in each of two tests. Eight half-sib families were common to both tests while the remaining 16 seedlots differed between tests. Combinations of the traits evaluated explained much of the variation in family field resistance to pitch canker of seedlings and a lesser amount of the variation in family field resistance to fusiform rust at age four. The in vitro evaluations from one test were combined with means of the same families for symptom types assessed in a greenhouse screening at the U.S. Forest Service Resistance Screening Center following inoculation with basidiospores of the fusiform rust pathogen. Traits from the combined data explained much of the variation in family field resistance to fusiform rust at age four. Many of the in vitro traits evaluated had moderate half-sib family heritability estimates so that development of a rapid in vitro method of screening for field resistance to pitch canker that simultaneously provides information about fusiform rust field resistance appears feasible.; In studies of the in vitro culture of the fusiform rust pathogen, differences in the growth and development of colonies derived from basidiospores were found for four media. Additionally, the presence of loblolly pine embryos from a resistant half-sib family inhibited colony growth and development. Techniques for the establishment and growth of single genotype axenic cultures as well as techniques for inoculating with axenic cultures of this pathogen were described.