Effect of Water Stress Induced by Polyethylene Glycol 6000 on Somatic Embryogenesis in Cocoa (&amp;lt;i&amp;gt;Theobroma cacao&amp;lt;/i&amp;gt; L.)

Manlé Tokpapon Eliane,Kouassi Kan Modeste,Koffi Kouablan Edmond,Koné Mongomaké,Soumahoro Brahima André

doi:10.4236/as.2019.109092

Abstract

Climate change, coupled with insufficient and irregular rains, led to a decline in the productivity of Ivorian cocoa production. The present study aimed to screen three cocoa (Theobroma cacao L.) genotypes in order to evaluate their response to water stress at callus and somatic embryos induction and proliferation stages. Staminode and petal explants of the genotypes C1, C14 and C16 from the collection of National Center of Agronomic Research (CNRA) of Ivory Coast, were placed on medium DKW (Driver & Kuniyuki Walnut) in the presence of different concentrations of Polyethylene glycol (PEG) 6000 (0, 25, 50, 75, 100 and 125 g/l). This polymer was used as osmoticum to stimulate water stress. Data were recorded for callus induction frequency, callus fresh weight, embryogenic callus percentage and average number of somatic embryos. The results obtained showed that intensity of callus proliferation decreased with increasing concentration of PEG 6000. In all genotypes tested, only the petal explants underwent somatic embryogenesis. The induction rates and average number of somatic embryos per explant were reduced with the increase in the concentration of PEG 6000. Among the tested genotypes, C1 produced somatic embryos with all concentrations of PEG 6000 and expressed highest frequencies of induction (62%) and average number of somatic embryos per explant (6.22). This genotype would be the most tolerant to water stress. Somatic embryos obtained with high concentrations of PEG 6000 in this study provide an important basis for the selection and further production of water stress-tolerant varieties of cocoa.

Highlights

Cocoa (Theobroma cacao L.) is a crucial crop for the confectionary business, as it provides the key raw material for chocolate-based products [1]
Somatic embryos obtained with high concentrations of Polyethylene glycol (PEG) 6000 in this study provide an important basis for the selection and further production of water stress-tolerant varieties of cocoa
Regardless of the PEG concentrations used, the callus induction frequencies from both types of explants were similar in genotype C14 (90% to 99%)

Summary

Introduction

Cocoa (Theobroma cacao L.) is a crucial crop for the confectionary business, as it provides the key raw material for chocolate-based products [1]. It is a cash crop for producing countries and a potential source of income for farmers. World Cocoa production is ensured to 73% by Africa. Ivory Coast is the largest world producer and accounts for 41% of global supply [2]. The crop requires a temperature between 24 ̊C and 28 ̊C and high humidity. In recent decades, the cocoa sector in Ivory Coast suffered enormous production losses due to climate change, which is characterized by irregular and insufficient rains. A continuous shortfall in precipitation (meteorological drought) coupled with higher evapotranspiration demand leads to agricultural drought [4]

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