D. Avanzato, S. Cherubini
Direct rooting is a technique which can be taken into consideration as the connecting link between in vitro and in vivo propagation to reduce the cost of production.

The higher sensitivity of the microcuttings in regards to stress caused by water makes it necessary to seek out substrates suitable to direct rooting. In this trial the substrates were tested (fine perlite, rough perlite, river sand, peat, used singularly or in mixture) taking into consideration the relationship between their water retention capacity and rhizogenic response. Apple MM106 ex vitro cuttings, treated with 10 ppm IBA were rooted under tunnel for four weeks.

An analysis of the results shows that in the substrates with an elevated water retention capacity there is a reduced rhizogenic response and an increased mortality rate of the microcuttings. A particularly negative trend is evident if we proceed from an examination of the substrates made up of rough perlite (48.9% average rooting), to those made up of fine perlite (12.5% average rooting); on the other hand the average mortality ratio increases from 17.7% in the substrata made up of rough perlite to 61.4% in the mixtures containing fine perlite.

In direct rooting of ex vitro microcuttings, it is absolutely inadvisable to use fine perlite because of its capacity, with its minute particles, of insinuating itself into every interspace obstructing the aerobic capacity of the substrata and favouring an increase in its water retention capacity. Peat and sand used separately are also to be avoided, while, if mixed with rough perlite, the water retention capacity is decreases and, at the same time, a positive rhizogenic response is favoured rough perlite used by itself is to be taken into great consideration, because it is characterized by great equilibrium between aerobic and water retention capacity, but also because it has a positive influence on the development of the roots.

An additional advantage of rough perlite is that the original material with which it is composed is sterile and therefore, less likely to be attacked by pathogens defiling elements as testified in this trial by a total lack of mortality rate due to rotting.

Avanzato, D. and Cherubini, S. (1993). INFLUENCE OF THE SUBSTRATES ON THE DIRECT ROOTING OF EX VITRO, MM106 APPLE MICROCUTTINGS.. Acta Hortic. 342, 297-302
DOI: 10.17660/ActaHortic.1993.342.35

Acta Horticulturae