PHENOTYPIC VARIATION, ELITE TREES SELECTION AND NURSERY INVESTIGATION OF SOME INDIGENOUS FOREST FOOD TREE SPECIES

Abstract

Tropical forests have provided food and shelter to man for ages. Forest fruit trees have become of great nutritional, socio-economic, medicinal and traditional importance to rural communities in developing countries. These resources are in the danger of going into extinction, being endangered without much effort at domestication. To this effect, phenotypic variation, elite tree selection and nursery investigations of Chrysophyllum albidum, Irvingia gabonensis and Garcinia kola were investigated in this study. The field survey aspect of the study was conducted in rainforest and derived savanna ecosystems of Ondo State, Nigeria. In each ecosystem, 5 villages with good population of trees of the three fruit tree species were purposively selected. Ten trees of each species from each village were then selected for field enumeration. The silvicultural history of the selected trees, their growth characteristics and fruit phenology were examined. Fruits from the selected trees were harvested and the effects of light intensities on the germination and early growth of their seeds and seedlings were investigated in three screen houses that allowed the penetration of 40%, 60% and 100% Photosynthetic Active Radiation (PAR) (i.e. light intensities) as well as two controls (under natural forest canopy and open sky). Seed germination was monitored from the first day of sowing until no further seed germination was observed while early growth characteristics were monitored for 12 months for C. albidum and I. gabonensis seedlings and for 6 months for G. kola seedlings. Results of field investigation revealed that that only 6% C. albidum trees in the rainforest ecosystem were planted while 36% of trees of the species in derived savanna were planted, for I. gabonensis, 2% and 88% of the trees in rainforest and derived savanna ecosystems, respectively were planted while all the sampled G. kola trees were naturally regenerated. Mean tree age varied from 50 – 55 years and 30 – 50 years for C. albidum trees in the rainforest derived savanna, respectively; for I. gabonensis, mean tree age ranged from 43 – 47 years and 6 – 16 years in rainforest and derived ecosystems, respectively while for G. kola, tree age was not determined. Chrysophyllum albidum and I. gabonensis trees in rainforest ecosystem were significantly older (50-55 years), taller (17.3-20.7 m) and larger (dbh) (43.0-93.6 cm) and deeper crowns (11.4- 14.4 m) than those in derived savanna (30-50 years), (12.4-16.6 m), (25.7-67.6 cm), (8.0-11.8 m). The old ages of most trees of the three species and their lower level of domestication (i.e. planting by farmers) underscore the necessity for domestication, which should be farmer driven. Depending on ecosystem, C. albidum fruit and seed morphology were fruit length 4.2- 5.9 cm; fruit width 3.8- 6.1 cm; fruit weight 36.0- 97.7 g; seed length 2.0- 2.9 cm; seed width 0.5- 2.2 cm and pulp weight 32.5- 89.4 g. For I. gabonensis the morphology of the fruits and seeds from rainforest and derived savanna ecosystem were: fruit length, 2.7- 7.2 cm; fruit width, 2.6- 7.4 cm; fruit weight, 32.4- 202g; seed length, 2.0- 5.0cm; seed width, 1.8- 4.0 cm and pulp weight, 22.3- 177.7g. Fruit and seed parameters for G. kola were: fruit length, 5.2-7.4 cm; fruit width, 5.0- 7.6 cm; fruit weight, 65.4- 213.0 g; seed length, 2.4- 4.0 cm; seed width, 1.4- 2.1 cm and pulp weight, 60.3- 202.90g. Generally, the morphology of the fruits and seeds of each species from the rainforest and derived savanna ecosystems differed significantly. Many C. albidum and I. gabonensis trees did not meet the criteria for selection of elite trees. Fruits were harvested from the few selected elite trees and their seeds used for nursery investigation. Light intensity significantly affected the germination of C. albidum seeds from the rainforest and derived savanna ecosystems, but light intensity did not significantly affect the germination of I. gabonensis and G. kola seeds regardless of the ecosystem from which their fruits were harvested. Early growth rate of the seedlings of all the species were significantly affected by light intensity. At the end of 12 months, seedlings total height and collar diameter ranged from 16.27 cm- 44.27cm and 0.29- 0.57 cm for C. albidum seedlings from rainforest and from 17.92- 46.43 cm and 0.32- 0.62 cm for C. albidum seedlings from derived savanna. For I. gabonensis seedlings, the total height and collar diameter at the end 12 months were 38.67cm- 76.12 cm and 0.33- 1.06 cm for seedlings from rainforest ecosystem while they were and 35.01 cm- 74.99 cm and 0.46- 0.76 cm for the seedlings from derived savanna. For G. kola, seedlings total height ranged from 19.24- 23. 89 cm while the collar diameter ranged from 0.52- 0.69 cm. Chrysophyllum albidum seedlings placed under 100% light intensity and open sky died shortly after emergence. Though C. albidum seedlings from the rainforest and derived savanna ecosystem raised under 40% and 60% light intensities had significantly comparable early growth parameters, the best growth was obtained under 40%light intensity. For I. gabonensis from both ecosystems, the seedlings performed well under all the light intensities, but in rainforest open sky seedlings performed better than others whereas in derived savanna, 40% gave the best results. G. kola seedlings performed well under all the light intensities used, but 60% light intensity gave a better result compared to the results from the other light intensities used for the experiment