In general, the larger the meristem explant, the greater the chances of its survival and shoot development. But the risk of infection by the virus also increases with explant size. Therefore, a compromise has to be reached between these two opposing forces in deciding about the explant size.

It may be emphasized that many viruses have been shown to be present within the apical meristem, e.g., carnation mottle virus, chrysanthemum stunt virus, etc. Further, all the plants derived from meristem culture are not necessarily virus free; many of them may even contain latent bacterial and or fungal infections.

Therefore, it is essential that each tissue culture raised plant must be tested, using specific tests, for the presence of a given virus or pathogen before it is claimed that the plant is free from the concerned virus/pathogen. Further, freedom must be claimed only from the specific virus/ pathogen for which it has been shown to be free.