Embryogenic callus and suspension cultures of eastern white pine (Pinus strobus) have been obtained. The whole female gametophyte was plated on a medium containing 50 mg/l glutamine, 500 mg/l casein hydrolysate, 3% sucrose, 2 mg/1 2,4-D, 1 mg/1 BA and 0.2% Gelrite as a solidifying agent. Embryogenic calli could be seen as early as 5 days following culture. Histological studies indicate proliferation of pre-existing embryogenic tissue in the corrosion cavity followed by extrusion of embryogenic callus through the micropylar end of the gametophyte. Embryogenic suspension cultures were obtained by placing embryogenic callus into liquid medium. Embryogenic suspension cultures were subcultured weekly and proliferated as early-stage embryos with attached suspensors. Embryo development was obtained following transfer of the embryogenic tissue to an auxin-free medium containing 50 mM glutamine, 38 μM abscisic acid, and 6% sucrose. Although embryo development could be consistently obtained, whole plants have not yet been recovered from these somatic embryos.

The nuclear DNA of Pinusstrobus L. was characterized by whole-genome hydroxyapatite reassociation kinetics. The genome, which is very large, is not well described by partition into three, four, or five major kinetic components. Instead, it consists of a large array of sequence components with kinetics suggesting a more or less continuous range of frequencies from very large to a single copy. The single-copy fraction, which is estimated to be about 24% of the total, appears to fit the general hypothesis for large genomes, i.e., most of it probably consists of ancient diverged repeated sequences. Under standard conditions of DNA reassociation kinetics, these sequences are not completely diverged but react with kinetics indicating that there is an average of about three repeats for the fraction. It is estimated that only about 0.1% of white pine nuclear DNA is expressed as mRNAs.

No abstract

A grafted seed orchard of Acersaccharum Marsh, was established in Ohio in 1957 as part of a program of genetic improvement of sugar yield. During the 3rd decade, the orchard trees averaged 4.2% sap sugar. Although environmental sources of variance in sugar concentration were large, clonal differences were evident and generally consistent over the years; the clone × year interaction was negligible. Sap sugar concentration varied from year to year, but after an increase coinciding with early crown development in the 1st decade, there was no upward or downward trend with age. Inclusion of one seedling family in the orchard made it possible to obtain an approximation of within-family variance by comparison with within-clone variance. It was estimated to be about one-third of total family variance. The clone–family comparison also suggested that about 11% of total clonal variance was a rootstock effect. Sap tests over 3 years in a plantation of seed-orchard offspring showed that an initial thinning to an average 6.3 × 6.3 m spacing would leave trees with an average 4% sap sugar concentration. At final spacing the concentration would be higher. Only a few clones in the orchard produced medium or heavy crops of male or female flowers prior to age 27, but those from which seed was collected in early years averaged at least 4% sap sugar. All clones and the seedling family flowered by age 27.

Sap sugar data taken in four progeny plantations of sugar maple (Acersaccharum Marsh.) were analyzed to evaluate breeding methods for high sap sugar concentration. Two of the plantations included progeny from open pollination of mass-selected trees, one included progeny from a clonal seed orchard, and one included progeny from a breeding experiment. The plantations differed in proportions of maternal selection and biparental selection employed. Maternal selection was ineffective as a means of achieving gain for high sugar bush productivity, whereas biparental selection was clearly effective. Gain in rogued progeny plantations from maternal selection was no greater than would be expected from roguing progenies of unselected parents. Low female parent – offspring correlations were attributed to nonrandom mating resulting from insect pollination, rather than low heritability. The use of lower testing "standard" trees in mass selection favors low or mediocre performance of progenies, because of the probability that standards will contribute to the progeny gene pool. Biparental selection was effective through (i) open intercrossing of high-performing seed orchard clones and (ii) controlled pollination of selected superior trees. Seed orchard progeny could be selected by age 13 years and subsequently rogued to final sugar bush spacing. Long-term data support a prediction that the mature sugar bush will average about 4.5% sap sugar concentration. One gallon (1 gal = 3.79 L) of maple syrup of that concentration requires 18.4 gal of sap, compared with an average of 43 gal required from Ohio sugar bushes. The gain from biparental selection and intensive roguing of progeny is estimated to be about 40% greater than similar roguing of plantations from unselected or maternally selected parents.