Читать книгу Biotechnology of Fruit and Nut Crops - Группа авторов - Страница 37

Micropropagation of cashew has been accomplished using 3–4-week-old seedling shoot tips and 1–3-year-old juvenile plants (D’Souza, 1988). Lievens et al. (1989) induced multiple shoots from microshoots of six 15-month-old seedlings on Lepoivre medium (Quoirin and Lepoivre, 1977) containing 9.84 μM N6-(2-Isopentenyl)adenine and 1.44 μM Gibberellic acid (GA₃). Multiple shoots were obtained from nodal segments of 15-day-old seedlings on basal Murashige and Skoog (1962) (MS) medium with 44 μM GA₃ (Lad et al., 1994). Multiple shoots from axillary buds of juvenile plants using a modified MS medium with 100 ml/l coconut water, 44.4 μM 6-benzylaminopurine (BA) and 22.2 μM kinetin were obtained by D’Silva and D’Souza (1992). Basa and Sardinha (1994) induced budding from nodal segments in half strength MS liquid medium supplemented with 4.44 μM BA and 2.86 μM indoleacetic acid (IAA). Farrant et al. (1990) observed multiple shoot formation from apical shoot explants from all genotypes tested on woody plant medium (WPM) (Lloyd and McCown, 1980) supplemented with BA. Thimmappaiah and Samuel (1999) obtained regenerated cashew by shoot tip and nodal culture from seedlings on MS medium with thidiazuron (TDZ) (0.45 μM) or with naphthaleneacetic acid (NAA) (2.68 μM) and indolebutyric acid (IBA) (1.46 μM). Munthali and Ford-Lloyd (1990) on the other hand, failed to obtain a growth response from shoot tips. Ananthakrishnan et al. (1999) described regeneration from the embryo axis.

Buds were initiated from the cotyledonary nodes of seedlings (Das et al., 1996; D’Souza et al., 1996) on MS medium supplemented with 14.61 mM sucrose and BA (D’Silva and D’Souza, 1992). According to Lievens et al. (1989), GA₃ in an agitated liquid medium stimulates elongation of the internodes of axillary shoots; however, D’Silva and D’Souza (1996) found that 4.44 μM BA and 146 mM sucrose stimulated elongation of microshoots. Rooting of shoots was successful in a mixture of sand, soil and powdered coconut husk. Young tree explants from repetitively grafted plantlets showed 50% bud break compared with 30% bud break in non-grafted explants (Thimmappaiah et al., 2002). Up to 80% rooting was obtained when shoots were subcultured for 4–8 days in ¼ strength liquid MS medium supplemented with IBA (4.92 μM) after a 2 min pulse with IBA (492 μM) and potted in sterile sand (Keshavachandran and Riji, 2007).

D’Souza et al. (1996) and Anuradha et al. (2005) have reviewed cashew micropropagation and its challenges. The most difficult challenge is the presence of phenolics which exude into the medium (Dhanaraj et al., 2002).

Regeneration of plants by embryo rescue following hybridization has been reported (Thimmappaiah, 2011). Three-week-old immature nuts of five different cultivars were cultured on modified B5 (Gamborg et al., 1968) medium with 0.5 mg/l NAA and 5 mg/l GA₃ in darkness. Immature embryo culture on defined media usually results in callus initiation or precocious germination (Das et al., 1999). Browning of the embryos was addressed with 0.3% (w/v) activated charcoal and 0.5% (w/v) polyvinylpyrrolidone (PVP) and culture in darkness during radicle emergence. BA (8.88 μM) and GA₃ (5.78 μM) enabled radicle emergence and seedling development.