Vegetative Propagation methods - theory

Transcription

1 Vegetative Propagation methods - theory Ebenezar Asaah ICRAF-WCA/HT BP Yaounde, Cameroon Tel: (+237) Fax: (+237) e.asaah@cgiar.org 1

2 Topics for discussion Definition of vegetative propagation Vegetative propagation methods Rationale for vegetative propagation Application of vegetative propagation in the domestication of Agroforestry trees: case of Allanblackia 2

3 Definition of Propagation What is propagation? Propagation is the natural mechanism by which plants regenerate. Propagation is most often by seeds produced by a plant or by plant parts like vines, roots, tubers, stem cuttings etc.. 3

4 Vegetative Propagation Asexual propagation (vegetative propagation) = reproduction of plant material from vegetative organs (leaf, stem, root, bud) so that the offspring will contain the exact characteristics of the parent plant with regards to genotypes and health status. 4

5 Vegetative Propagation method 1 Cuttings: severed uninodal leafy shoot or root fragments usually place into a suitable rooting substrate and kept under high humidity in propagators until adventitious roots and shoots are formed respectively. 5

6 Allanblackia propagation by cuttings Coppice shoots Cuttings in propagator Weaned cuttings CS of propagator 6

7 Vegetative Propagation method 2 Grafting is a technique used to untie parts of different plants by bring the cambium of each into contact and then creating a situation under which the cut surfaces can unite and grow away together. Field grafted AB wilding Yaounde, Cameroon 7

8 Grafting terminologies Scion -The part of the graft that will provide the new system. The scion maybe united either at the apex or side of the rootstock. Rootstock the lower part of the graft. It normally posses a root system that will support the subsequent shoot development from the scion 8

9 Grafting of Allanblackia 9

10 Grafting of Allanblackia % survival side tongue whip and tongue side veneer graft Time (weeks) Grafting experiments registered 80 % survival rate in A. gabonensis and flowering while still in the nursery. Effect of grafting techniques on survival of A. floribunda grafts 10

11 Grafting of Allanblackia Shade Light % survival Time (week) Effect of shade & light on survival of A. floribunda in situ grafts In situ grafting of A. floribunda wildings and coppiced shoots under shade open light registered 45% vs 35% survival rate respectively. 11

12 Vegetative Propagation method 3 Air layering (marcotting) technique is similar to cuttings with the advantage that the propagule is detached from the parent tree only after development of roots. Its multiplication rate is lower than that of cuttings Used in capturing the attributes of elite trees within genetically diverse wild populations, so avoiding the long, slow process of tree breeding. Rooted Marcot 12

13 Air layering Allanblackia trees 13

14 Capture of traits by air layering Noel cultivar 14

15 Vegetative Propagation method 5 Micropropagation specialized propagation with small pieces of plant tissues on artificial media under sterile conditions. It embraces the regeneration from: shoot & root tips, callus tissue, leaves, seed embryo, anthers and even single cells. 15

16 When is it appropriate to use vegetative propagation When the species in question: is an out breeder; is dioecious; has recalcitrant seeds; has low germination rates; flowers and fruits erratically and; to capture their genetic diversity. 16

17 Rationale for vegetative propagation. 1 Maintaining superior genotypes Most tropical tree species are outbreeders implying that through the recombination of genes during sexual reproduction, many important characteristics might disappear. If a superior individual tree has been identified by farmers or researchers, its genetic information can be 'fixed' through vegetative propagation, thus allowing the reproduction of the same superior individual in the next generation 17

18 Variation in Allanblackia fruits Creation of a cultivar Anticipated earlier fruiting, smaller trees and uniform quality Allanblackia fruits 18

19 Rationale for vegetative propagation. 2 Problematic seed germination and storage Some tree species produce seedless fruits (e.g. off-season Dacryodes edulis,) and need to be propagated vegetatively, others bear fruit very scarcely or erratically (Prunus africana) or seeds difficult to gereminate (Allanblackia spp). In these cases, vegetative propagation might be a suitable and cheaper alternative to seedling production. 19

20 Rationale for vegetative propagation. 3 Shortening time to flower and fruit Most vegetative progaules originate from scions or cuttings from mature trees, and maintain the characteristics of maturity after grafting or rooting. Flowering Allanblackia graft 20

21 Rationale for vegetative propagation. 4 Combining more than one genotype in one plant Grafting is a unique way of combining desired characteristics from two or more plants into a single one. Graft scions with particular fruit characteristics onto rootstocks with other desirable characteristics: disease resistance and adaptability to environmental constraints. Another possibility is the grafting of more than one cultivar or species onto the same stem, for example Irvingia gabonensis (sweet fruits) grafted to an Irvingia wombolu (bitter fruits) rootstocks and a male AB pollinator branch grafted to a female tree. 21

22 Rationale for vegetative propagation. 5 Uniformity of plantations For many commercially grown species, Irvingia spp, Dacryodes edulis, Cola spp, Allanblackia spp. etc. uniformity of growth form or fruiting season is important economically. 22

23 Application of vegetative propagation in Tree domestication Selection and Capture of desirable traits Suitable techniques include layering (marcotting) and grafting Mass propagation Suitable techniques include propagation by cuttings and to a lesser extent grafting. Micropropagation is most suitable but expensive and skill demanding. Tree Improvement Vegetative propagation techniques can provide an exact copy of the mother tree from which the seed was harvested and retain the desired fruit quality in the following generation if the traits are heritable 23