Texas Forestry Paper No. 24

Open-pollinated .seedlings from suspected loblolly x shortleaf pine hybrids did not differ significantly from shortleaf pine for six morphological characters. These seedlings were significantly different from loblolly pine seedlings in hypocotyl height, cotyledon number, number of needles per fascicle and percent basal crook. Hy brid indices were developed for parents and their respective openpollinated progeny using morphological characters. One suspected hybrid parent produced progeny which had hybrid index scores which were consistently intermediate to loblolly and shortleaf pines. This parent is probably a natural hybrid but the hybridity of other individuals is questionable. Natural hybridization between loblolly (Pinus taeda L.) and shortleaf (P. echinata Mill.) pines is widely recognized (BiJan, 1965a; Bilan, 1965b; Hare and Switzer, 1969; Mergen, Stairs and Snyder, 1965; Schroidtling, 1971). Trees which are morphologically intermediate between loblolly and shortleaf pine have been speculatively called hybrids (Zobel, 1953). To provide further evidence as to whether such intermediates actually are hybrids, and to investigate the reliability of morphological classification, open-polli.nated seedlings from parents classified morphologically as loblolly, shortleaf and suspected hybrid pines were grown under homogeneous conditions. Traits of these three progeny groups should reveal genetic differences, if any, resuJting from cross-breeding. Five trees from each group (loblolly, shortleaf and "hybrid" ' ) were selected in the field by subjective evaluation of gross morphology. Sample trees were from two predominantly pine stands approximately 10 miles west of Nacogdoches, Tex~ AMifitant Professor, Sc:hool of Forestry. Stephen F. Austin Sune University. 1 Although the genotype of these morphologically in1ermediaLt trees was unknown. 1)8.ronual plllnl-i and resulting (omiliett from this group will be referred to 8.1! "hybrids." This research was supported in SJart by fundB mnde uva:ilable under the Mclmira·Slonni~ Act . Johnn.y H. Wilson, Ernest 1-~rickson, and Ronald I)Qs:a.ar, students at the School of Porcstry, assisted in ttchnienl MIX!CUI of the. ~ttudy. as. The sites varied from stream bottom to upland. In each stand, approximately 75 percent of the pines were shortleaf and 25 percent loblolly. The trees were ranked by Anderson's (1949) hybrid index technique on the basis of needle length, number of needles per fascicle, fascicle sheath length, terminal bud width and cone length. These characters were used because of their low within-tree sampling variance and because their values differed significantly for loblolly and shortleaf pine (Hicks, 1973). Mean values for these characters were based on a sample of 10 structures per tree except for cone length and bud width where five structures per tree were measured. Tree character means were equally weighted by expressing them as scores on a 0 to 4 scale, and the hybrid index value for a tree was obtained by sum ming its character scores. A detailed description of the parental morphology is available (Hicks, 1973). Open-pollinated families from the above parents were propagated in the greenhouse and nursery bed. Five 6-month-old seedlings per family were transplanted into each of three blocks in a randomized complete block design in the nursery during January of 1972. At that time, seeds from the same families were planted in the greenhouse using the same design. Measurements of height to the cotyledonary whorl and cotyledon number were obtained from greenhouse-grown seedlings when the hypocotyls were fu lly extended. Measurements obtained from 1year-old seedlings were: number of seedlings with basal crook, first year height growth, number of needles per fascicle, and needle length. For the latter two traits, seedling means were based on a sample of 10 fascicles. RESULTS Means and standard deviations for the seedling traits are listed by families in Table 1, and the results of analysis of variance of these data are summarized in Table 2. In height to cotyledons, needle length and number of needles per fascicle, overall means of "hybrid" seedlings were intermediate between means for seedlings of loblolly and shortleaf parentage. For the other three traits, "hybrid" means fell slightly (not significantly) outside the span of the other parental group means. "Hybrid" means for cotyledon number, basal crook percentage and number of needles per fascicle were about equal to those of the shortleaf group and "hybrid" seed lings at one year of age averaged slightly taller than loblolly or shortleaf seedlings. Good growth of known loblolly x shortleaf pine hybrids has been reported previously (Sluder, 1970). Two hybrid indices were constructed from morphological data of the seedlings; one in which all six characters were considered and a second using only traits for which "hybrid" seedlings had intermediate values (Fig. 1). Index values for seedling fam ilies were developed in a similar manner to parental indices, except family means were used to calculate character scores. With the exception of families S-4 and H-5, the index ranking of seedling families closely approximated that of their respective parent. This consistency was especially noticeable when seedling families were ranked on the basis of the three intermediate traits. Hybrid index scores of hybrid family H-1 were obviously and consistently intermediate to the two species as was the hybrid index score of the parent tree. T his strongly suggests hybrid origin of parent H-1. Table 1. Means and standard deviations for morphological characters of seedlings, by open-pollinated family and parental group. Parental group Cotyledons and Family (number)