Limbs & Needles 25(3):8-9.

Control pollination is a technique used in tree improvement to produce offspring which receive genes from each of two known parent trees. It consists of transferring pollen from one tree to receptive female strobili (cones) of another tree while excluding all other pollen. The steps involved in control-pollination of Fraser fir have previously been described (Limbs & Needles 24(2): 10,12-15).

During the spring of 1998, numerous Fraser fir control-pollinated crosses were performed at the North Carolina Division of Forest Resources’ (NC DFR) Lodge Seed Orchard located at the Linville River Nursery near Crossnore. Two groups of crosses were made to produce:

• high value seed for commercial marketing and

• pedigreed seed for research into the genetic control of resistance to Phytophthora root rot.

The schedule of these pollination activities are presented in Table 1. The control-pollination work associated with these crosses is discussed below in separate sections.

High Value Seed for Commercial Marketing

The NC DFR Lodge Orchard originally contained 312 trees when established in 1969-1971. Information from two or more progeny tests is available for 50 of the 200+ trees currently surviving. Height and USDA grades were measured on all progeny trees in these tests at ages 6, 7 or 8 and economic values calculated. The orchard trees were then ranked for genetic quality based on their progeny performance.

Control-pollinations among the top three ranked orchard trees were completed. Unfortunately, the second ranked tree (16-288) had only a few strobili (5) and was therefore, not used as a female parent. Table 2 presents the number of isolation bags installed and the number of female strobili pollinated for each of the three crosses made.

In total, over 1700 female strobili were pollinated. These cones will be harvested and the seeds extracted this fall. A strategy to market seedlings grown from these and future control-pollinated seeds to North Carolina Christmas tree growers will be developed.

Seed for Researching the Genetic Control of Phytophthora Resistance

One of the 20 progeny tests of the NC DFR Lodge Seed Orchard inadvertently became infested with Phytophthora root rot. Each tree in this Alleghany County test which was established in 1991 was assessed a disease score in fall of 1996. In areas of that test classified as highly infested, open-pollinated families ranged from 0 to 42 percent healthy trees indicating that Phytophthora resistance is under some degree of genetic control. Parents of the three most resistant and the three most susceptible families were selected for breeding (Table 3). (Unfortunately, the third most resistant parent tree was dead and the fourth most resistant parent tree became receptive prior to bagging. Thus, the fifth most resistant parent tree was substituted.)

These six trees were bred in a complete diallel mating design. In this mating design, all parent trees are mated in all possible combinations. Thus, every tree is mated to every other tree both as a male and a female and also mated to itself (selfed). A complete diallel with six parent trees results in 36 unique full-sib crosses. (Seed from the same full-sib cross have the same mother and father parents.)

The number of isolation bags installed and strobili pollinated for each of these crosses are shown in Table 4. The crosses along the diagonal in the matrix in Table 4 represent selfed crosses. Pairs of crosses that are symmetrical with respect to the diagonal in the matrix are reciprocal crosses. Reciprocal crosses involve the same parent trees with opposite sexual roles.

The number of strobili pollinated varied from 8 to 45 per cross. Sufficient seeds for research will be obtained if theses cones average 50-100 viable seeds each. Additional crosses may be repeated next year if additional seeds are needed for some crosses.

Seedlings grown from these seeds will be inoculated with Phytophthora cinnamomi under controlled greenhouse conditions. Data collected and analyzed will be studied to better understand the nature of genetic control of Phytophthora resistance in Fraser fir. This understanding is critical to effectively plan strategies to develop Phytophthora resistant Fraser fir.

Reprinted from Limbs & Needles with permission.