ENVIRONMENT, PHYSIOLOGICAL AND BIOCHEMICAL EFFECTS ON SEED GERMINATION CHARACTERISTICS OF AFRICAN EGGPLANT (Solanum aethiopicum L.)

Abstract

The Gilo group of the African eggplant (Solanum aethiopicum L.) is one of the most important vegetable crops cultivated by smallholder farmers in Ghana and other West African countries. In the absence of a formal quality seed production and supply system for the African eggplant, over 90% of farmers rely on farmer-saved and other informal sources for seed. Seeds from these sources show no or low (0 – 25 %) germination, which affects seedling emergence and field establishment. The seeds are also known to possess short longevity. The quality of seed and its viability is affected by environmental, physiological and biochemical factors independently or interactively. The objectives of this study were to determine the effect of temperature and light on germination of two cultivars of African eggplant, evaluate the influence of fruit harvesting maturity stage on the physical and physiological quality of African eggplant, determine the effect of seed maturity stage on biochemical characteristics of African eggplant, evaluate the effect of harvest time and after-ripening on seed physiological characteristics of African eggplant and lastly to evaluate the effect of fermentation and drying methods on seed physiological characteristics of two cultivars of African eggplant. Field experiments were conducted under tropical monsoon (Bungoma, Kenya) and temperate oceanic climates (Chepkoliel, Eldoret, Kenya) between April, 2019 and January, 2021. Laboratory experiments were conducted at Seed physiology laboratory of University of Eldoret and International Livestock Research Institute (ILRI, Kenya). Field experiments were laid out in a randomized complete block design with factorial arrangements depending on the specific objective. Results showed that the environment, temperature, light, harvesting maturity stage, after-ripening, fermination and drying methods independently and interactively (p ≤ 0.01) affected seed physical, physiological and biochemical characteristics of two cultivars of African eggplant (Solanum aethiopicum L.). Temperature and light interactively improved seed germination of African eggplant. The maximum seed germination (76 and 95%) was obtained when seeds were germinated at alternating temperatures of 30/20 °C under alternating 8/16 hours light/dark periods. This condition also gave the shortest time (4-5 days) required to complete the germination process. The results established that seeds harvested precociously (20 and 34 days after anthesis), did not germinate or recorded very low percentage germination (≤ 15%). The suitable maturity stage to harvest fruits for maximum seed quality was 76 days after anthesis. Fruit characteristics such as weight, size and colour have shown to be suitable indicators of seed physiological quality with a strong positive correlation. Seed sugars and crude protein were not strongly associated with seed quality characteristics of African eggplant. The results showed that tannin content positively influenced physiological quality in terms of germination and vigour of African eggplant seeds. Further, after-ripening of fruits for 10 to 15 days improved seed vigour and germination quality when fruits were harvested 40 or 50 days after anthesis. It was however, confirmed that after-ripening is inconsequential and not necessary when seeds are harvested at physiological maturity, which coincides with maximum germination at 70-76 days after anthesis for cv. Kpando. Lastly, results from the study suggest that African eggplant seeds do not require fermentation prior to extraction for enhanced seed germination percentage, although, fermentation up to 12 hours can improve and maintain seed vigour. All drying methods used in this study were able to reduce seed moisture content to an ideal level (< 10 %) for safe storage and maintained seed physiological quality. For the purpose of seed production of African egpplant, it is recommended that seeds should be extracted from fruits harvested between 60 and 76 DAA for maximum seed quality. Oven drying at 30 °C for 24 hours or 48 hours of shade drying can maintain seed quality.