Effects of double encapsulation and coating on synthetic seed conversion in M.26 apple rootstock.

Encapsulated vitro-derived apical buds of M.26 apple rootstock (Malus pumila Mill) can be employed for the formation of the synthetic seed. Satisfactory levels of conversion (plantlets from synthetic seed) can be achieved if there are adequate (i) rooting induction treatment, (ii) protocol of encapsulation, and (iii) nutritive and environmental conditions. For capsule manufacturing, sodium alginate is largely used; however, this is excessively permeable with loss of the nutritive substances (artificial endosperm) and/or dehydration risks during conservation and transport causing detrimental effects on the synthetic seed conversion and on the plantlet's growth. In order to overcome these problems, two experiments were carried out comparing simple encapsulation in alginate with double encapsulation, and with encapsulation-coating procedures. The presence of a second layer of alginate (double encapsulation) and of a thin external coating layer over the alginate (encapsulation-coating) did not show any detrimental effects on viability, sprouting and regrowth of the encapsulated microcuttings. Satisfactory conversion (70%) was reached with the encapsulation-coating procedure, whereas the double and simple encapsulation converted less than 40% of the synthetic seed. The effect of the addition to the capsule of an anti-microbial substance (Plant Preservative Mixture - PPM) was examined: it did not compromise the conversion of the encapsulated microcuttings sown in ex-vitro non-aseptic conditions.

Effect of bead nutrient composition on regrowth of stored vitro-derived encapsulated microcuttings of different woody species.

Aseptic encapsulation in a sodium-alginate bead containing different nutritive solutions of microcuttings (uninodal explants excised from micropropagated shoots) of 10 different genotypes from four different woody species (Actinidia deliciosa, kiwifruit, cv Hayward and Tomuri; Malus spp,, apple, rootstock M. 26 and cv Starkspur Red and Wellspur; Olea europea, olive, cv Canino, Moraiolo, Ascolana tenera and Dolce Agogia; Rubus Idaeus, raspberry, Selection 1401) was investigated. The aim of the study was to evaluate the best nutritive formulation of the bead among seven different solutions, made of inorganic and organic compounds, growth regulators and sucrose, alone and combined, in order to maintain viability throughout 30 days of storage at 4 degrees C and subsequent regrowth ability of the encapsulated microcuttings on agarized medium, in view also of the possibility of inserting this storage phase in micropropagation cycles of these species. Olea plants gave interesting viability rates from 47.6 to 100% (according to cultivar and nutritive solution of the bead) immediately after storage, but the least satisfactory results in terms of regrowth, because of probable inadequacy of the culture medium. Actinidia, Malus and Rubus, instead, gave maximum rates in regrowth of 90.6% ('Hayward'), 83.3% ('M.26') and 83.4% ('Sel.1401'), respectively, and in sprouting of 62.5% ('Tomuri'), 75.0% ('M.26') and 77.2% ('Sel.1401'), respectively. Furthermore, encapsulated Rubus microcuttings proved usable also as synthetic seeds, with a maximum rooting (and conversion) rate of 60.7%.