Rooting Response of Air-Layered Shea (<i>Vitellaria paradoxa</i>) Trees to Media and Hormonal Application under Two Different Climatic Conditions

Abstract

Shea tree ( Vitellaria paradoxa Gaertn. Family; Sapotaceae) indigenous to the Sudano-sahelian zone of Africa has great economic and ecological potential and attributes. Commercial cultivation of the tree is however, hampered by the poor rooting success of its planting material with adverse consequences on field establishment and total fruit yield. A 3 × 2 factorial experiment arranged in a randomized complete block design was carried out in 2012 at Bole in the Interior Savanna agro-ecological zone. The objective was to assess the rooting success of Shea shoots by the air-layering technique using two media types (palm fibre and Sphagnum moss) and three IBA hormone concentrations (0, 5000 and 10,000 ppm) under contrasting climatic (wet and dry) conditions. Layered shoots which were sprayed with 10,000 ppm IBA and wrapped with Sphagnum moss gave significantly (P < 0.05) higher rooting success in terms of more roots per cutting (73.3%) and longer roots per cutting (9.0 cm) than palm fibre at both 5000 ppm (30.0%; 3.7 cm) and 10,000 ppm (46.7%;7.9 cm) concentrations. Higher rooting success was significantly achieved in the wet season than in the dry season. Sphagnum moss treated with 10,000 ppm IBA facilitated the translocation of higher levels of sugar and total free phenol (TFP) to the base of the layered shoots which resulted in significantly (P < 0.05) higher number of roots and better roots protection from fungal infection than the other treatments. Rooting of layered shoots was affected to a greater extent by low temperatures (Rooting = 836 – 34.2 Temp (low); R 2 = 82%, p < 0.001) than by high temperatures (Rooting = 5250 – 175.0 Temp (high); R 2 = 64.5%, p < 0.009). Rooting of layered shoots was also significantly and negatively affected by the spread of the canopy of the selected tree such that closed canopy trees resulted in higher and better rooting that open canopy trees (Rooting = 113.87-23.697(Canopy spread); R 2 = 89%, p = 0.002; n = 9). Furthermore, significant and positive correlations were found between IBA concentration level and simple sugars (r = 0.99; P < 0.0001; n = 9) and also between IBA concentration level and total free phenols (r = 0.98; P < 0.0002; n = 9). The study concluded that to achieve high rooting success in the propagation of Shea nut tree by the air-layering technique, a combination of Sphagnum moss treated with 10,000 ppm of IBA hormone should be used and the whole set up carried out in the wet season.