Effects of Surface Sterilization Protocol and Haustorium Removal on Germination and Growth of Hybrid PB121 Coconut Palm (Cocos nucifera L.) Zygotic Embryos Cultured in vitro

Aims: This study aims to identify the best surface sterilization and evaluate the effect of haustorium suppression on in vitro germination of coconut palm (Cocos nucifera L.) zygotic embryos.

Study Design: Survival rate and contamination rate of zygotic embryos after different surface sterilization treatments, regeneration rate and organogenesis through the number of leaves and the length of shoots after haustorium suppression were determined. For data processing, the Analysis of Variance was used to compare the means which were separated according to Tukey test (P = 0.05).

Place and Duration of Study: Coconut fruits (hybrid PB121) were collected 12 to 14 months after controlled pollination from CRAPP (Centre de Recherches Agricoles Plantes Pérennes), station of Sèmè-kpodji in Benin. Experiments were done in Central Laboratory of Plant Biotechnology and Plant Improvement, University of Abomey-Calavi and conducted from june to december in 2019.

Methodology: For the zygotic embryos surface sterilization, four treatments combining three concentrations (3%, 6% and 15%) of commercial bleach (Javel la Croix© containing 12° active chlorine) and immersion durations (5 min, 10 min and 20 min) were tested and the survival rate were determined for each treatment after two months culture. The zygotic embryos were then divided in two sets (haustorium excised embryos set and the whole embryos set) and cultured in modified Y3 medium supplemented with 7 g L-1 agar, 2.5 g L-1 activated charcoal, 5% sucrose, 6.10-3 mM 2.4 D (2.4-dichlorophonoxyacetic acid), gibberellic acid and 0.3 mM BAP(6-benzylaminopurine). After five months culture, the regeneration rate, the number of leaves and the length of shouts were recorded.

Results: The high survival rate (80%) was obtained with 6% of bleach and 20 min for the immersion duration without pre-disinfection. The suppression of haustorium have significantly increased the number of leaves (4.3 ± 0.02) and the length of shoots (16.2 ±0.7cm) compared to the whole zygotic embryos.

Conclusion: This protocol can help to ensure better surface sterilization of zygotic embryos before their in vitro culture and the development of vigorous plantlets in order to improve the slow growth of plantlets, when transferred to the greenhouse or field.