Improvement of in vitro somatic embryogenesis in cashew (Anacardium occidentale L.)

Abstract

Studies were conducted for improving techniques for in vitro somatic embryogenesis in cashew during 1996-1999 in the Plant Tissue Culture Laboratory of the Department of Horticulture, College of Agriculture, Vellayani. Attempts were made to standardise the various stages of somatic embryogenesis, namely, induction, initiation, maturation and germination using nucellus and embryo mass as explants. Out of the two explants tried, nucellus responded better than embryo mass in initiating embryogenic callus/somatic embryoids. Induction of somatic embryogenesis from nucellus was found to occur at its maximum when cultured in darkness on MS basal medium having half strength major salts, supplemented with 2,4-D 1.0 mg/l, BA 1.0 mg/l, NAA 1.0 mg/l, sucrose 30.0 g/l, Activated charcoal 0.5 g/l and agar 6.0 g/l. The best treatment identified for the induction of embryogenic callus / somatic embryoids from embryo mass was MS basal medium supplemented with 2,4-D 4.0 mg/l, NAA 4.0 mg/l, kinetin 4.0 mg/l, adenine sulphate 40.0 mg/l, yeast extract 200.0 mg/l, PVP 250.0 mg/l, sucrose 30.0 g/l and agar 5.5 g/l, in dark culture condition at regulated temperature (26 ± 2°C).

2 Initiation of somatic embryoids from nucellus as well as embryo mass occurred at its best in darkness on MS basal medium supplemented with NAA 0.5 mg/l, kinetin 2.0 mg/l, adenine sulphate 40.0 mg/l, PVP 250.0 mg/l, yeast extract 200.0 mg/l, sucrose 30.0 g/l and agar 5.5 g/l. . Among the treatments tried for inducing proper maturation of the somatic embryoids, the maximum survival of embryoids was recorded on a combination of basal media with Bs major salts and MS minor salts supplemented with ABA 1.0 mg/l, coconut water 200.0 mlll, casein hydrolysate 100.0 mg/l, PVP 10.0 g/l, sucrose 40.'0 g/l and agar 5.0 g/l. Culture conditions did not influence the maturation process of the somatic embryoids. Maturation process was not found to be essential in inducing normal germination of the somatic embryoids. The cultures showed good response when subcultured from initiation media to germination media without a maturation phase. Germination of somatic embryoids occurred only in the presence of light, on a combination of basal media with Bs major salts and MS minor salts supplemented with BA 1.0 mg/l, PVP 10.0 g/l, coconut water 200.0 mlll, sodium chloride 0.1 per cent, cobalt chloride 10.0 g/l, sucrose 50.0 g/l and agar 6.0 g/l.