Browning of Medium - In many species, phenolics leach into the medium from the cut surfaces of explants. These phenolics turn dark brown on oxidation and are detrimental to the cultures. This is very common in case of woody species, particularly when explants are taken from mature trees.

The problem can be overcome in one of the following ways; in some species like mango, control of phenolics is the chief problem.

1. Frequent (every 3-7 days) subculture of explants on agar medium may be sufficient to overcome this problem in many species.
2. A brief period (usually 3-10 days1 of culture in liquid medium is effective in many species, e.g., apples, Rubes, Eucalyptus, etc.; this may remove from the explants not only polyphenols but other possibly inhibitory substances.