**9. Conclusion**

252 Fungicides for Plant and Animal Diseases

Application of fungicides to the mother plants in the field before collection of explants (preconditioning of the ortet plants) greatly contributes to aseptic cultures. This could reduce the need to use stronger disinfectants such as HgCl2. Furthermore, it may also improve decontamination efficacy. For instance, the use of HgCl2 alone was less effective on field collected *U. kirkiana* (Mng'omba et al., 2007). Thus, preconditioning of grafted *U. kirkiana* stock plants using Benomyl contributed to achieving culture asepsis. Therefore,

The problem with the use of concentrated disinfectants and fungicides is that there is always a lengthy washing of stock plants in running tap water and distilled water to remove pathogens and, especially excess residues that may be lethal to the explants in the culture media. Our experience has indicated a possibility that there are some reactions between HgCl2 and aluminum foil. This suggests a possible affinity for chloride (Cl-) in that Al 3+ could be replacing Hg 2+. We observed that the foil was completely eaten up as a result of this reaction. Since stock plants were covered with aluminum foil throughout the disinfection, rinsing and culture excision processes which also took time, this could mean accumulation of aluminum deposits in the cultures, and hence possible aluminum toxicity

There are several studies undertaken and illustrate the deleterious effect of heavy metals such as aluminum and mercury on plant growth in the fields. However, such studies have not been accomplished in plant culture laboratories. It is possible that the poor performance of some plant cultures or explants might be attributed to the presence of residues of the strong disinfectants and fungicides used during decontamination process and toxicity of the heavy metals. However, research studies are needed to confirm or establish whether the use of such disinfectants and heavy metals *in vitro* culture contributes to plant culture toxicity or

Fungicides, surface sterilants and disinfectants are obviously harmful to human beings, and hence proper handing and storage are always good and important practices in plant tissue culture laboratories. Poor storage of fungicides/disinfectants could lead to their fast deterioration. This can make them less efficient in decontaminating plant cultures. Poor storage can also accelerate the expiry of the fungicides and disinfectants as they may be exposed to moisture. Long exposure to moisture due to the poor storage could alter the chemical composition of the fungicides or disinfectants, and hence making them less efficient. Proper storage of fungicides should include observing its ideal storage

Proper disposal of fungicides and other disinfectants must be adhered to. In many plant culture laboratories, disinfectants, surface sterilants and fungicides are decanted through

temperature and good containers to avoid any possible damage or leakage.

**6.2 Preconditioning mother plants** 

**6.3 Fungicide toxicity** 

to plantlets.

mortality.

**7. Storage and disposal of fungicides** 

**7.1 Storage of fungicides** 

**7.2 Disposal of used fungicides** 

preconditioning reduces the fungal loads on the stock plants.

This chapter has outlined the significant roles that fungicides and other disinfectants play in plant culture laboratories in achieving aseptic *in vitro* plant cultures. This is a vital process for the success of *in vitro* plant culture protocols. However, selection of an appropriate fungicide or disinfectant is important since endogenous or endophytic pathogens require the use of systemic and strong fungicides to effectively disinfect stock plants. Proper handling of fungicides and disinfectants and also proper disposal of the used disinfectants in the plant culture laboratory are equally important as they may become corrosive to the water drainage systems, and hence dangerous to the environment. Many research studies are needed in order to increase our understanding with respect to various disinfectants used in the plant culture laboratories.
