PhD

Investigations on “Induction of variation in vitro and field evaluation of somaclones in ginger (Zingiber officinale Rosc.)” were carried out at the Department of Plantation Crops and Spices and Centre for Plant Biotechnology and Molecular Biology, College of Horticulture, Vellanikkara, Thrissur during April 2002 to October 2005. The objectives of the study were to induce variability in ginger through in vitro techniques, to evaluate somaclones of ginger for morphological, yield and quality parameters and for reaction to rhizome rot and bacterial wilt diseases and to characterise the selected superior somaclones using RAPD markers. The studies were carried out in two cultivars of ginger viz., Maran and Rio-de-Janeiro.
Protocol for indirect organogenesis was developed in ginger using shoot tip explants. Half MS medium supplemented with 2,4-D at 1.00 mg l-1 exhibited higher callusing and callus growth. For shoot morphogenesis and rooting, half MS medium supplemented with BAP at 3.00 mg l-1 was found ideal.
The protocol for indirect embryogenesis was developed in ginger using rhizome bud explants. The explants produced embryogenic calli in half MS medium supplemented with 2,4-D (0.50-1.00 mg l-1) and BAP (0.50-1.00 mg l-1). Dark incubation of cultures favoured production of embryogenic calli. Basal half MS medium was found good for proliferation and maturation of somatic embryoids. Inclusion of BAP (3.00 mg l-1) in the basal half MS medium was found to enhance germination of somatic embryoids.
Dose of  irradiation for in vitro mutagenesis of organogenic / embryogenic cultures of ginger was standardized. Plantlets were produced from irradiated calli of the two cultivars.
Growth analysis in regenerants produced through various routes showed that regenerants produced through indirect organogenesis exhibited better root characters and plantlet establishment. Regenerants produced through in vitro mutagenesis exhibited better tillering characters.
Evaluation of somaclones (first set) for three seasons viz. 2002, 2003 and 2004 revealed the superiority of somaclones over conventionally propagated (CP) plants in yield and quality attributes. Of the somaclones of two cultivars studied, somaclones of cultivar Maran recorded higher yield, recovery of dry ginger and low fibre content.
Screening procedures were standardised for rhizome rot and bacterial wilt diseases in ginger. The toxic metabolites of pathogens were found to accumulate in vitro. The symptoms produced by the toxic metabolites were similar to that of inoculation by the pathogens. The toxic metabolites induced quick electrolyte leakage from leaves of ginger. Detailed screening done in first set somaclones could locate two somaclones (M VI and 364 R) showing tolerance to rhizome rot and bacterial wilt diseases. Preliminary screening done in second set somaclones by electrolyte leakage method revealed that 24 per cent clones exhibited low leakage of electrolytes showing their tolerance to diseases.
Analyses of various morphological and yield parameters and reaction to diseases revealed the occurrence of high amount of somaclonal variation in ginger. The extent of somaclonal variation observed was high in somaclones of cultivar Maran for morphological, yield and quality attributes. Somaclones of cultivar Rio-de-Janeiro exhibited higher variation for reaction to diseases.
Documentation of selected superior somaclones of first set was done using RAPD markers. The RAPD analysis done in selected clones revealed the occurrence of genetic variation in ginger somaclones. The genetic variability was high in somaclones of cultivar Maran (16.8 %) as compared to cultivar Rio-de-Janeiro (10.8 %).
The regeneration and screening protocols developed in the present study could be utilised in further investigations. The superior somaclones identified in the study could be advanced to further evaluation programmes.