Macro-and Micro-propagation of melia volkensii GÜrke (meliaceae) : an indigenous multipurpose drylands tree species
Abwao, Stephen Indieka
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Melia volkensii GÜrke (Meliaceae) is a popular indigenous multipurpose tree species endemic in the arid and semi arid lands (ASALs) of East Africa. It is a prolific seeder, though its mass-multiplication has been constrained by problems in propagation through seed and conventional stem cuttings. In this study, three vegetative propagation techniques were investigated: (i) macro-propagation using 3-month old rejuvenated leafy stem cuttings, (ii) direct in vitro shoot multiplication using shoot tip explants and (iii) direct somatic embryogenesis using mature zygotic embryo and cotyledonary explants. The effects of fungicide pretreatment, surface sterilization and PGRs (IAA, IBA and NAA) at 0, 2, 4, 6, 8, and 10 g 1-1 on rooting of leafy cuttings in a low cost mist propagator were evaluated. Up to 33 % rooting was achieved on cuttings treated with 8 g 1-1 IBA and 50 % of the rooted cuttings were successfully hardened. In vitro experiments were conducted using Murashige and Skoog (1962) basal medium (MS). The effect of MS supplemented with BAP, kinetin and zeatin (0.25-3.0 mg 1-1) alone and in combination with NAA or IAA (0.1 and 0.2 mg 1"1) on shoot multiplication was investigated. Generally, BAP: IAA combinations induced shoot multiplication and up to 5.4 shoots per explant were achieved in BAP: IAA (0.5: 0.2 mg 1-1) combination. Rooting of in vitro multiplied shoots was achieved only in IBA treatments and up to 40 % success was attained in MS supplemented with 2.0 mg 1-1 IBA. The effect of MS supplemented with BAP, NAA and 2,4-D (0.2-4.0 mg 1"1) alone and in combination on induction of direct somatic embryos was also investigated. Direct somatic embryos were initiated on 30-60 % of the cotyledonary explants from seeds stored for <3 months in BAP (0.5-4.0 mg 1-1) combined with 0.2 mg 1"12,4-D. Further development of somatic embryos into plantlets on MS and 1/2 MS (half macro-elements) without PGRs was unsuccessful but formed clusters of numerous shootlets. Nevertheless plantlets were successfully regenerated from shoot tips obtained from the shoot clusters formed. The results obtained in this study clearly demonstrated that M. volkensii is amenable to propagation by rejuvenated leafy stem cuttings, direct in vitro shoot multiplication and somatic embryogenesis. Optimization of the protocols developed in this study will open up opportunities for mass breeding, conservation and genetic manipulation of this species.