Virus-free Plants

Field-grown perennial crops are routinely infected by a wide range of pathogens - fungi, bacteria, mycoplasma and viruses - that cause significant economic losses, and while chemical treatments can usually control fungal and bacterial infections, they are generally ineffective against viruses. Shoot meristem tip culture solves this specific problem because the apical meristem of an infected plant is characteristically free of virus even when the rest of the plant is infected, most likely because the meristem's rapid cell division outpaces the rate at which the virus can spread into it. The protocol (Figures 5.13 and 5.14) starts by excising, under sterile conditions, an apical meristem tip carrying one or two leaf primordia to serve as the explant; this is cultured in vitro in about 10 ml of solid MS medium supplemented with growth hormones. Cultures are first maintained at 24 degC +/- 1 degC in the dark for three days, and only then moved to normal illumination of about 2400 lux. As the meristem tip develops plantlets through organogenesis …