Germplasm Supply, Propagation and Nursery Management of Miombo Fruit Trees - Indigenous Fruit Trees in the Tropics: Domestication, Utilization and Commercialization - page 353

indigenous fruit trees; (iv) it increases plant growth rate and reduces the times to
production and reproductive maturity, leading to earlier fruit production; and (v)
it enables the repair of damaged parts of trees (Hartmann et al. , 1997). Grafting
involves placing two similar or dissimilar plant organs (stem/stem, stem/root,
root/root) from genetically compatible plants in intimate contact, with sufficient
pressure and cambial alignment to induce the formation of an anatomically and
physiologically functional graft union between scion and stock (Mudge and
Brennan, 1999). It is the art of connecting two pieces of living plant tissue
together in such a manner that they will unite and subsequently grow into one
composite plant (Hartmann et al. , 1997). It is more expensive than cutting or air-
layering. However, the selection of scion and rootstock may affect the outcome of
grafting. The most common grafting method for miombo fruits is the whip and
tongue method. Others are the whip (splice graft), cleft graft, wedge graft, saddle
graft, four-flap graft, side stub, side tongue, side veneer graft, bark grafting
(detached scion), approach grafting and bridge grafting (Macdonald, 1986;
Hartmann et al. , 1997).
Until recently, limited success with vegetative propagation has been a
constraint to the domestication of miombo indigenous fruit trees in southern
Africa. For example, a graft take of less than 10% was earlier reported for
Uapaca kirkiana (Jaenicke et al. , 2001). However, this problem was overcome
once the conditions necessary for scion collection were properly understood
(Akinnifesi et al. , 2006). In Malawi, grafting success has been reported to be
100% in Vangueria infausta , 85-100% in Adansonia digitata , 80% in Uapaca
kirkiana , 40-79% in Strychnos cocculoides , 52-80% in Sclerocarya birrea , and
71% in Parinari curatellifolia (Mhango and Akinnifesi, 2001; Swai et al. , 2004)
and 74% for Strychnos cocculoides in Zambia (Mkonda et al. , 2004). In
Botswana and South Africa the best results have been obtained when scions of
Sclerocarya birrea are grafted in September-October (Taylor et al. , 1996).
Mature scions of Sclerocarya birrea grafted onto spring-sown seedling
rootstocks have developed into plants that yield first fruits in the fourth or fifth
year after grafting. Plants from seedlings not grafted have been observed to
take 8-10 years before the first signs of flowering (Taylor and Kwerepe, 1995).
Some of the major determinants of grafting success include the skill of the
person doing the grafting, the time of the year the scion is collected and the
interval between scion collection and grafting (Akinnifesi et al. , 2004;
Nkanaunea et al. , 2004). The best time for grafting or collecting the scion is
from August to December. In the field, growth rates of grafted trees improve
greatly with increased moisture availability. Other factors include proper
alignment of the vascular tissues between scion and rootstock, stock plant
nutrition, scion respiration rate, the disease status of scion and rootstock, and
the relative humidity of the propagation environment (Akinnifesi et al. , 2006).
Budding is a form of grafting, except that the scion is reduced in size to
contain only one bud. As done in oranges, budding has been found to be very
effective in propagating Ziziphus mauritiana . Budding can be done by T-
budding or shield budding or using the inverted T method (Macdonald, 1986).
There are two types of stock: seedling rootstocks and clonal rootstocks.
Seedling rootstocks have the advantage of being able to penetrate the soil and