Trench layering using indole-3-butyric acid and local organic substrate mixtures to enhance rooting and survival of apple rootstocks

Apples (Malus domestica) were introduced to enhance nutrition and improve livelihoods of famers in highlands of Uganda. However, adoption and commercialisation of apples is largely constrained by low quality rootstocks due to poor rooting and low survivability. This study determined the effect of organic substrate mixtures (OSM) and indole-3-butyric acid (IBA) on rooting, sprouting and survival characteristics of apple rootstocks propagated by trench layering. Four apple rootstock varieties (M106, M109, MM793 and bitten-felder) were planted in OSM (Site soil as control, TsaOm and TsdOm) then treated with IBA concentrations (IBA-0 ppm, IBA-4000 ppm and IBA-8000 ppm) in a factorial randomised block design with three replications. Results showed significant (P<0.001) variability among rootstocks for all characters. OSM significantly (P<0.01) increased rooting, root numbers and root length while IBA significantly (P<0.01) increased all traits, except rooting. The highest rooting (46.7%), root numbers (23.1) and root length (14.9cm), and sprout length (59.5cm) were obtained in bitten felder under TsaOm + IBA-4000ppm, TsaOm, and TsdOm, respectively. For M106, maximum rooting (28.1%) and root numbers (22.3) were obtained under TsaOm + IBA-8000ppm while root (14.3cm) and sprout (35.2cm) lengths under TsdOm. TsaOm gave the highest root numbers (14.2), root (12.8cm) and sprout (30.7cm) lengths in M109 likewise root (7.8cm) and sprout (38.3cm) lengths in MM793. Logistic regression revealed that rooting, sprout length, and IBA-4000ppm significantly (P<0.01) increased survival of apple rootstocks. The highest survival rates in bitten felder and M106 were 52.4% and 51.7% under TsdOm + IBA-4000 ppm and TsdOm + IBA-8000 ppm respectively; likewise 49.5% in M109 and 51.7% in MM793 both treated with IBA-8000 ppm. The results demonstrate that trench layering with OSM and IBA improves rooting and survival of apple rootstocks which might improve farmers’ access to quality apple planting material.