Biological aspects of seed production by Pinus caribaea morelet variety hondurensis barret and golfari in Nigeria

Procurement of seeds of Pinus caribaea Morelet variety hondurensis Barret and Golfari for afforestation programme in Nigeria has been by importation even though the species has been grown in the country for 20 years. The flowering and seeding problems across the planting range in Nigeria were therefore investigated through a survey of cone and seed production including cone and seed quality, a survey of flowering and pollen dispersal and viability, pollination efficiency, initiation and development of reproductive structures in relation to vegetation growth. Attempt was made at flower induction by means of fertilizer (NPK(5:15:5) and K) and hormone (GA4/7 and NAA) application with girdling as an adjunct treatment. Ripeness-to-flower was attained earliest, at age three in southern lowland locations. Conelet production increased with increasing age up to 10 years before declining on certain sites especially the impoverished derived savanna sites and in densely stocked stands. Cone production was most affected by altitude being highest at 393 m followed by 227, 600 and then 1,300m. The Mount Pine Ridge provenance produced best. Cones ripened for collection earliest in the derived savanna (starting from July) followed by the northern guinea savanna, the highland and the lowland rain forest. In Ibadan ripe cones could still be seen in March of the following year. A harvest of ripe cones contained a higher percentage of unproductive cones than a harvest of green cones. Seed content increased with increasing tree age up to 10 years. Various cone and seed characteristics although varying from one vegetation zone to another did not influence the filled seed percentage. Flowers of both sexes occurred in the upper crown within the stand and while production of pollen cones were more restricted in time, conelets were not. Synchronization between conelet receptivity and anthesis occurred sometimes and was most frequent at 393m, 6026’N where also pollen catch was highest. The initials of reproductive structures were laid down in the terminal long shoot bud (TLSB) stage and only differentiated after elongation of the TLSB. Conelet production was associated with earlier flushes in the growing season while pollen from bud scales in 3 – 138 days and were receptive right from the time of emergence. Receptivity lasted 18.3 ± 3.9 days and cone maturation 33 months. Pollen cone reached anthesis in 107 ± 12 days and lasted 18 ± 6 days. A pollen cluster was about 30.5 ± 8mm long and consisted of 15 ± 4 pollen cones with average length of 30.72 ± 5.7 mm and width of 4 ± 1 mm, producing 21.5 ± 12.6 mg pollen per cone. Pollen grain viability was 83%. Flower induction treatments with NPK improved growth in younger stands (6 – 8 year old) while increasing percentage branches flowering in the older stand (16-year-old). Potassium improve girth growth and conelet production and possibly pollen cone production. High NAA concentrations (60 –80 ug/100ul) were injurious to plant growth and sometimes in combination with GA4/7 induced pollen cone production. High GA4/7 level tended to induce conelet production. Girdling as an adjunct treatment increasing pollen production. Girdling as an adjunct treatment increased pollen production.