Production of disease-free plants

Abstract

Internal infections caused by viruses, mycoplasmas, bacteria and fungi, can be very difficult to combat. It is virtually impossible to eliminate the plant of these internal pathogens by the use of chemicals. It is sometimes possible to suppress the virus multiplication by the use of the relatively expensive compounds Virazole (ribavirine) and vidarabine (antimetabolites), in the nutrient medium (Walkey, 1980; Kartha, 1986; Long and Cassells, 1986). In a few cases, such as with lily (Cohen, 1986) and apple (Hansen and Lane, 1985), the use of Virazole has resulted in the production of virus-free plants. The addition of antibiotics to counter internal bacterial infections is equally ineffective. In a review article Bastiaens et al. (1983) state that bactericides are of no use for eliminating bacteria in in vitro cultures, since the necessary concentrations are phytotoxic; sometimes the micro-organisms do not react to the added antibiotics at all. The use of antibiotics can also result unwittingly in the selection of resistent strains.