Читать книгу Biotechnology of Fruit and Nut Crops - Группа авторов - Страница 180

Protocol. Although pineapple is not generally considered to have an unstable genome, at least 30 variants of ‘Smooth Cayenne’ have been recorded (Collins and Kerns, 1938). Spiny leafed variants are the most common and occur during conventional propagation of ‘Smooth Cayenne’ and are frequently observed during micropropagation (Wakasa, 1979, 1989; Smith and Drew, 1990). Smith et al. (2002) showed that the percentage of plants showing spininess was similar for plants regenerated from callus cultures (0–12%) compared to plants that had been micropropagated (11%). Spiny variants have also been observed in micropropagated ‘Red Spanish’ (Liu et al., 1987).

A range of other somaclonal variants derived from callus has been described (Wakasa, 1989), and these include variants for leaf colour, leaf shape, waxiness, foliage density and abnormal phyllotaxy. In addition, Soneji et al. (2002) described albinos, white streaked shoots, anthocyanin-rich leaves and shoots with elongated internodes derived from proliferating shoots maintained in liquid medium.

Protocols exist to limit the extent of somaclonal variation during commercial pineapple micropropagation. These involve limiting the number of plants multiplied from each explant (some commercial laboratories limit multiplication to 300–1000 plants per explant) with regular initiation of new cultures (Smith et al., 2005). Using RAPD analysis, Roostika et al. (2015) showed that long-term pineapple cultures of up to 4 years also contributed to greater somaclonal variation. Roguing of undesirable variants is required, particularly during nursery establishment, and many of the variants lend themselves to easy identification and roguing while the plants are quite small. Other variants that involve increased vegetativeness and changes in fruit phenotype require that plants are grown to maturity in the field, which requires the establishment of nursery blocks so that vegetative material for production comes from true-to-type plants.

ACCOMPLISHMENTS. Although most of the variation that has resulted from shoot tip micropropagation or organogenesis is either of no benefit or of a deleterious nature for commercial production, one study has reported variants with useful attributes. Pérez et al. (2012) set out to examine the extent of genetic variation in ‘Red Spanish Pinar’ using NAA, BA and kinetin as ‘putative mutagenic agents’ during callus initiation and shoot proliferation, and IBA and gibberellic acid during plant regeneration. In other words, a standard tissue culture protocol was followed. One mutant, ‘P3R5’, had significantly fewer spiny leaves, while retaining the fruit characteristics of the donor plant, thereby facilitating easier and safer handling. A dwarf mutant was obtained which had ornamental value. Mujib (2005) used 0.01% colchicine as a mutagenic agent on ‘Queen’ callus cultures but only managed to obtain albino plants.