In vivo pollen tube growth of pecan [Carya illinoinensis (Wangenh.) K. Koch] was estimated to be ≈ 150 μm·hour-1 from 3 to 8 hours postpollination. Pollen tubes averaged 47, 194, 405, and 946 μm after 2, 3, 4, and 8 hours postpollination, respectively. Pollen tube growth was strongly influenced by temperature, and in vitro studies demonstrated pollen germination and tube growth were optimal at 27C for `Cape Fear' pecan. In in vivo studies, tubes of cross-pollen did not grow significantly faster than tubes of self-pollen. Pollen tubes of water hickory [C. aquatica (Michx. f.) Nutt.] grew significantly faster than those of C. illinoinensis. Bitternut [C. cordiformis (Wangenh.) K. Koch] and mockernut hickory (C. tomentosa Nutt.) pollen tubes grew significantly slower on pecan stigmas than did pecan pollen. Pollen arriving first on the stigma has a decided advantage for fertilization success of pecan. The fertilization success rate of pecan pollen arriving 24 hours after first pollen arrival was <3%.
Six phosphoglucomutase phenotypes were observed in pecan [Carya illinoensis (Wangenh.) K. Koch] progeny after controlled pollinations. At least one locus (Pgm-1) is present that controls polymorphism of phosphoglucomutase (PGM) isozymes in pecan. The inheritance appears simple with three observed alleles. However, progeny produced from two crosses resulted in significant deviation from the expected segregation ratios. Out of 65 named cultivars, 61 were of a single phenotype, and two of six possible phenotypes were not observed. Only one region of PGM activity was consistently expressed by gel electrophoresis from pecan tissue.
Self-pollination was estimated in three Georgia pecan [Carya illinoinensis (Wangenh.) K. Koch] orchards. Selfing in two large orchards lacking an interplanted complementary pollinizer (one orchard being comprised of `Curtis' and the other `Moneymaker') was estimated to be at least 3% and 49%, respectively. A `Cheyenne' orchard containing `Stuart' as a complementary pollinizer at 5% density was estimated to have had at least 14% and 42% of ripened nuts derived from selfing in two consecutive years. These estimates suggest self-pollination may reduce yield in pecan orchards in the southeastern United States.
Strobili distribution on crowns of 8- and 9-year-old white spruce (Piceaglauca (Moench) Voss) was evaluated and modified by gibberellin A4/7 (GA4/7) applied as a foliar spray to branches in the transitional (female → male) zone and strictly male zone. Treatment with GA4/7 increased female strobili production 6.2-fold and male strobili production 2.4-fold on branches in the transitional zone. On male zone branches treated with GA4/7, female strobili were induced and male strobili production increased sixfold.
Treatment with the gibberellin mixture A4 and A7 (GA4/7) enhanced female flowering on mature white spruce (Piceaglauca (Moench) Voss). Time of treatment, crown position, and GA4/7 concentration influenced treatment success. GA4/7 treatment initiated before meristematic differentiation began (late June) enhanced female strobilus production, whereas those initiated after late June were ineffective. Shoots treated with 250 mg•L−1 GA4/7 bore significantly more female strobili than shoots that received 500 mg•L−1. Treatment did not affect female production on uppermost crown positions, male strobilus production, or seed yield per cone. Female strobili predominated from axillary buds centrally located on untreated shoots. GA4/7 treatments that enhanced female production shifted the distribution of strobili to more distal shoot positions.
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