Adapting cutting and tissue culture techniques to clonal propagation of the shea tree (vitellaria paradoxa) in Uganda

Abstract

A study to adapt tissue culture and stem cutting techniques to vegetative propagation of Vitellaria paradoxa (Shea tree) was conducted between March and July, 2014. The specific objectives of the study were to: determine appropriate culture media composition for in vitro regeneration of V. paradoxa, evaluate the influence of cutting type on the rooting success of V. paradoxa stem cuttings, and assess the effects of mode of application of rooting hormones (IBA) on adventitious root formation of V. paradoxa stem cuttings. To achieve these objectives, four media compositions were evaluated for in vitro regeneration of V. paradoxa shoot tips; four modes of auxin (IBA) application at three different levels of concentration were evaluated with respect to adventitious root formation of Shea cuttings, and a third experiment was set to determine the effect(s) of cutting types on rooting success of V. paradoxa stem cuttings. A total of 2,556 Shea stem cuttings and 360 explants were evaluated in the study. Data were then entered in Ms Excel and analyzed using R-system software. Data on tissue culture regeneration were collected on survival rate, callus development, root and shoot formation. For the stem cutting experiments, data were collected on; number of rooted cuttings, quantity and length of developed roots including evidence of auxiliary bud break. Frequencies were derived to determine the extent, to which explants survived, rooted, callused or remained dormant. One way ANOVA was conducted to investigate the quality of rooting success between the four modes of auxin application. Where treatments were found to be significantly different, the Tukey‘s Honestly Significant Difference (HSD) was used to make pair wise comparisons. The linear relationship between rooting success and bud break was investigated using correlation and regression analysis. The highest level of callus formation was observed in media containing MS+BAP (27.3±1.00%) and lowest (16.7±0.58%) in the one composed of MS+BAP+GA3. Root formation (11.1±0.58%) was observed only for the treatment (MS+BAP + NAA). Basal cuttings dipped for 24hr at 80ppm showed the highest rooting percentage (69.0±3.61%) compared to the other application methods. The basal cuttings also recorded comparatively better rooting percentage (38.1±4.00 to 69.0±3.61%) than the tip cuttings (35.7±3.61 to 57.1±6.66%). Results also revealed that bud break was generally lower in basal cuttings and that bud break and root number were positively correlated (r=0.577). It was therefore recommended that further experimentation needs to be conducted on tissue culture using more media compositions and explants so as to enhance survival rate and generate V. paradoxa plantlets. Also, a thorough study should be carried out on the potential for foliar application of IBA, such that if adapted well, it can be incorporated for mass production of V. paradoxa subsp. nilotica. For now the 24hr long soak method at 80ppm is recommended for large scale