Effect of Fruit Harvest Time and Fermentation Methods on Seed Viability and Seedling Vigour in Oleaginous Citrullus lanatus

Aims: In an attempt to improve the yields of Citrullus lanatus’s wlêwlê oilseed cultivar, generally low due to the lack of good germination seeds, the effect of fruit age at harvest and fermentation methods were studied. The present study is a contribution to the improvement the African oleaginous Cucurbits seed production system by optimizing the date of harvest combined to seed fermentation methods through enhancement of seed germination and seedling vigor. Study Design: Seedling vigor was evaluated on farm trial using five completely randomized blocks represented by seedbeds constituting each, one replication. Place and Duration of Study: The trials were carried out from July to December 2020, at the experimental farm of the Nangui Abrogoua University in the district of Abidjan, southern of Côte d'Ivoire between 5°17' and 5°31' North latitude and between 3°45' and 4°31' West longitude. Methodology: Fruits from grown plants were harvested at five different times  20, 25, 30, 35 and 40 days after anthesis (DAA)] and seeds fermented following four methods  fermentation at ambient air (SFA); fermentation in a plastic bag exposed at ambient air (SFB); fermentation in plastic bag buried in 30 cm depth (SFD) and control or non-fermented (NF)]. Seeds from these 20 treatments (5 harvest time × 4 fermentation methods) were sown for viability tests in laboratory and seedling vigor in the field. Results: Analysis of variance (ANOVA) showed that delaying harvest time (from 20 to 40 DAA) significantly (P < .001) improved fruit weight (from 512.20 to 760.50 g) and its seed content (from 71.75 to 230.70 seeds/fruit), seed size (length: 10.69 to 11.42 mm and width: 5.31 to 5.90 mm) and weight (5.16 to 6.37 g) as well as their viability (from 67.75 to 89.50 %). Moreover, in spite of facilitating seed extraction, all three fermentation methods (SFA, SFB and SFD) significantly improved seed viability and seedling vigor compared to control (NF) seeds. The highest agronomic performance (seed viability and produced seedling vigor), was obtained with fermentation under closed and deep confinement (SFD), followed by the closed confinement (SFB) and then by the open environment (SFA). Positive interaction (harvest time × fermentation method) revealed that the best performance was achieved with later harvested seeds (40 DAA) and closed fermented seeds (SFD) which could provide a better seed quality. Conclusion: Agronomic performances (viability and vigor) are influenced by both harvest date and fermentation method. Late harvesting of the fruit (40 DAA) and fermentation in a very confined deep soil condition (SFD) ensures the production of high germination quality seeds.