Morphological and phenotypic variations in Irvingia gabonensis. – E. A. Edu, P.J. Nya, A. E. Nkang, D. N. Omokaro, A.A.J. Mofunanya and J.K. Ebigwai
Studies were conducted to assess the range of phenotypic variation in morphological characters and seed germination potentials within the natural populations of bush mango (Irvingia gabonensis) collected from different ecological zones. Results show that fruit colour in Akamkpa and Ikom zones were recorded as greenish yellow, Yakurr (Green), Etung (Brownish) and Boki (Bright reddish yellow). The fruit shape in Akamkpa and Yakurr were observed to be oblique and Ikom and Boki to be spheroid while that of Etung zone was ovoid. The best average fruit and seed sizes (length and width) were obtained from Ikom ecological zone (10.61 cm and 6.80 cm) and (7.20cm and 4.76cm) respectively while the least were obtained from Akamkpa zone (6.71 cm and 3.69 cm) and (4. 60 cm and 2.22 cm) respectively. This study has also shown that the highest fruit and seed weights were obtained from fruits sourced from Ikom ecological zone (80.3g and 23.4g) respectively. Germination time (25 days) decrease significantly (P < 0.05) with a corresponding increase in germinability (50%) with seeds obtained from Ikom ecological zone. A highly significant (P < 0.05) variation in germination value among the seeds collected from the different ecological zones were recorded. Results show that Ikom had 7.92 Etung (4.74) while Akamkpa (18). There was a positive relationship between the amount of rainfall, germinability and morphological parameters with seeds sourced from the five ecological zones. The best relationship was recorded with fruits/seeds sourced from Ikom ecological zone between rainfall and fruit weight (r = 0.93: p < 0.05) seeds length (r = 0.88: p< 0.05), seed weight (r = 0.71:P<0.001), thickness of seed coat (r = 0.74:P<0.00) and thickness of mesocarp (r = 0.89:P<0.05) while fruits/seeds from Boki Zone also recorded positive relationship between rainfall and mesocarp thickness (r = 0.76:P<0.001). A strong relationship was also recorded between germinability and seed weight (r = 0.70:p < 0.001) with seeds sourced from Ikom while Etung recorded (r = 0.76: p< 0.001), hence these traits can be taken into consideration while selecting superior seed material for better germination vigour. The occurrence of higher seed weights with low germination percentage in moderately wet zones is evident from the study. It is recommended that knowledge of such differences may be important in breeding programmes.