Abstract
Propagation of cocoa trees with high yield and disease resistance is envisioned for the renewal of the cocoa orchard. The dissemination of these elite varieties by orthotropic cuttings is strongly recommended to achieve quantitative and qualitative objectives. Some experiments reported that some Theobroma cacao clones produced by orthotropic cuttings do not root easily and the rate is very low, around 30 to 50% results. In this work, the impact of earthworms and chemical hormonal growth promoters on cocoa cuttings acclimatization were studied to increase the survival rate of cocoa stems during acclimatization step. The presence of earthworms identified as Millsonia anomala in acclimatization substrates allowed to convert more than 65% of stems into plantlets and exceeds 83% when the section of stems was a softwood part of branch. In the same profile, growth promoters as chemical hormonal solutions, regularly used in the process, are converting around 49.5% of stems into plantlets. In this study, a variability on the presence of taproots number across various parts of the branch were shown. Indeed, 69.2% of stems from hardwood, 64.3% stems from semi-hardwood and 56.4% of stems from softwood have developed at least two main roots. Indeed, this fact corroborates the capacity of these trees to able supporting the probable weight of cocoa pods and resists on wind which could appear on areas with bad weather. Key words: Orthotropic cuttings, earthworms, somatic embryogenesis, hormones, cocoa crop.
Highlights
Cacao (Theobroma cacao) belongs to the genus Theobroma classified under the subfamily Sterculioidea of the mallow family Malvaceae
The stems from cocoa branches were better converted into plantlets when the substrate contained a humic soil with earthworms than other chemical growth hormones and than results shown by Gehlot et al (2014) on cuttings treated with auxins
The measurement of shoots dry weights rate showed that it is higher (62.3%) for substrates which contained earthworms than other ones. These results showed that earthworms could be involved in enriching substrates on nutrients and does not probably implicate in root systems development during the acclimatization of stems
Summary
Cacao (Theobroma cacao) belongs to the genus Theobroma classified under the subfamily Sterculioidea of the mallow family Malvaceae. Despite its importance in the country’s economy, cocoa cropping is facing different challenges in Côte d’Ivoire among which climate change, deforestation (Kouadio and Desdoigts, 2012), disease and pests pressure (Despréaux et al, 1987; Babin, 2009), aging of farmers and plantations, and low access to inputs as fertilizers and pesticides and good quality planting materials. This results in low yields per hectare (300 to 450 kg/ha/year) with a negative impact on farmers’ revenue (IITA, 2009)
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