Fruit maturity, seed treatment and storage of Coffea liberica Hiern

Coffee seeds obtained through conventional methods performed poorly in the field with very slow and asynchronous germination. Harvesting at the right stage of maturity may result to improve the performance of seeds during the rootstock development. This study was carried out to determine the suitable fruit maturity stages for seeds to be used in seedling establishment, to determine the effect of various seed pretreatments to obtain a rapid germination rate and to establish an appropriate drying and storage method for Coffea liberica. The first part of study was conducted to assess the germination ability of seven different C. liberica clone seeds namely MKL 1, MKL 2, MKL 3, MKL 4, MKL 5, MKL 6 and MKL 7. The results revealed that seeds from MKL 5 had the highest germination percentage (GP) of 93%, germination index (GI) of 0.97 and mean germination time of 29 days, while seeds from MKL 3 had the lowest with 70% germination percentage (GP), 0.62 germination index (GI) and mean germination time (MGT) 35 days. The second part of the study determines the suitable fruit maturity stage for seedling establishment. From this part, the effect of maturity stages on germination and seedling establishment for C. liberica was studied using seeds from four stages of maturity. Seeds were extracted from fruits harvested at immature unripe [210 days after anthesis (DAA)], mature unripe (260 DAA), mature ripe (310 DAA), and overripe (360 DAA) stages. It was observed that the germination percentages between all the maturity stages were significantly different. Seeds of MKL 5, MKL 6 and MKL 7 were not able to germinate when harvested at immature unripe stage at stage 3. The highest germination percentage and germination index among all the three clones was obtained when seeds were collected at stage 3 (mature ripe). MKL 5 had the highest germination percentage with an average of 95%, MKL 6 gave 78% and MKL 7 was 84%. Fruits harvested at mature ripe stage showed better performance in all parameters evaluated. Therefore, harvesting of fruits at mature ripe stage is suggested to obtain faster and uniform growth of coffee seedlings. For the third part, the effect of seed treatment on the germination of C. liberica was studied. Seeds were grouped and treated with KN03 and GA3. The treatments included untreated seeds (control), seeds soaked with KN03 (0.2%, 0.4% and 0.6% for 12 and 24 hours) and GA3 (200 ppm, 400 ppm and 600 ppm for 12 and 24 hours). The effect of different growth condition (continuous light, continuous darkness and with 12h:12h light:dark) was also evaluated. The effect of growth condition tested as the third part of the study showed that C. liberica seeds germinated slowly when sown with continuous light (24 hrs light). It showed only 47.5% germination percentage, 0.25 germination index and required a mean germination time of 55.2 day. A significantly higher germination percentage was achieved at 25°C with 12- hour light and 12 hourr dark and 75% humidity. Seeds soaked in GA3 200 ppm for 12 hours and KNO3 0.4% for 24 hours did not significantly affected the germination percentage as compared to controls. However, they had significantly a higher germination index in comparison to control treatments. For the last part of this study, the seeds were then desiccated to determine the effect of seed moisture content on germinability of C. liberica. Germination percentage was reduced when the seeds were dried to the lowest moisture contents. Fruits from clone MKL 5 were dried out under the sunlight for three weeks until the moisture content reached 10%. The bag was sealed tightly to prevent moisture penetration, labelled and stored at 10°C, 15°C, 25°C and 29°C. Polyethylene bags stored at different temperatures were retrieved every month to test the germination rate. Germination percentage of seeds with 20% moisture content were higher with an average of 79%, 73% stored at 15°C in the second and fourth month. Seeds deterioration rate was higher at 29°C. The deterioration may be caused by the growth of fungi which is known to affect the seeds. Seeds containing 10% moisture content failed to germinate starting from the sixth month of storage. The germination percentage for this C. liberica seeds were higher as seed were dried to the lower moisture content irrespective of the temperature regimes. In conclusion, the most suitable seeds to be used for coffee seedling production are from the clone MKL 5 which were harvested at stage 3 (mature ripe) which has resulted with 93% germination rate. Chemical treatments did not increase germination percentages, but condition under 12-hour light and 12-hour dark played an important role of C. liberica growth by reducing mean germination time to 32.15 days compared to 55.22 days. For storage, seeds should be dried to 20% moisture content and stored at 15°C up to six months.

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