Effect of pretreatments on seed viability during fruit development of two varieties of Irvingia gabonensis

Studies to identify the stage at which developing fruits of Irvingia gabonensis (var. excelsa and var. gabonensis), picked from standing trees and/or forest floors, attain maximum viability and germinability were conducted in two harvesting seasons in 2000 and 2001. Some pretreatment methods were used as a means of stimulating expression of maximum germinability as source of seeds for seedling production. The moisture contents of whole seeds decreased steadily and significantly (P = 0.05) throughout the developmental stages of both varieties and in both harvests. Seeds harvested from standing trees and forest floors, pretreated by steeping in water for 24 h at 26 oC and sown in sawdust and petri dishes on moist filter paper, gave 80% germination in variety gabonensis, 20 weeks after fruiting. Germination potentials of seeds in both harvests were enhanced significantly (P = 0.05) with seeds pretreated by steeping in water for 24 h at 26 oC, and sown in sawdust and petri dishes on moist filter paper by as much as 60% and 80% for var. excelsa and var. gabonensis, respectively, in the developmental stages, 14–20 weeks after fruiting with significant (P = 0.05) decrease in germination time to 21 and 15 days, respectively. There was also significant (P = 0.05) relationship between viability and germination in both harvests and in the two varieties throughout the developmental stages. Potassium nitrate (KNO3) significantly (P = 0.05) enhanced germination potentials of the seeds over the control when soaked in 1.5 g/l concentration in both varieties and in the two harvests (18–20 WAF) by 80%. Mannitol significantly (P = 0.05) reduced germination potential (40%) of the seeds with increased germination time in both harvests and in the two varieties throughout the developmental stages. There was a high significant (P = 0.05) increase in germination potential (60%) of seeds treated with polyethylene glycol (PEG) when soaked in concentration of 10 g/l for 48 and 72 h in both varieties and in the two harvests (18–20 WAF). The study shows that the fruits of I. gabonensis assume ripening characteristics (yellowing) and that the viable seeds can be obtained from standing trees and/or picked from forest floors from the 12th to 20th week after fruiting.