Sterilisation of the seeds

Orchid seeds, especially when they have been allowed to come in contact with atmospheric air , is sure to carry on their surface spores of fungi and bacteria which they have collected from the atmosphere . Every single one of these spores should be killed before introducing the seeds into the medium. Hence the sterilisation of the seeds should be complete and thorough . Calcium hypochorite or the commercial bleaching powder is shaken with 140 ml of water in a small via!. The filtrate will contain 2 % chlorine which is the effective disinfectant . Redlinger (1961) is of opinion that 2. 6 % solution of Chlorox (sodium hypochlorite ) is a better sterilant than bleaching powder. According to him chlorox has better detergent qualities than bleaching powder . According to him chlorox has better detergent qualities than bleaching powder, even though the latter is less injurious to seeds . He also suggested using bleaching powder along wiht a detergent like hydrogen peroxide . One gram of bleaching powder may be used in 50 ml of water with 3 % hydrogen peroxide. Jessel (1962) also recommends 3 % hydrogen peroxide as an orchid seed sterilising agent.

Because of the covering of fluff over them , orchid seeds are very difficult to wet . To overcome this difficulty the seeds are placed in a small vial with 2-3 ml of the sterilant and shaken vigorously for 2-3 minutes. If the seeds have previously been exposed to the atmospheric air then shaking for a longer interval is necessary for through sterilisation . Several modifications to this procedure have been put forward for increasing efficiency of sterilisation . Graeves (1959) reported that placing the seeds overnight in distilled water helped to remove air bubbes which adhere to the seeds and protect the fungal and bacterial spores from the action of sterilant . Soaking of the seeds for too long a time in the disinfecting solution for this purpose will harm the orchid seeds . After overnight soaking in distilled water add sterilising solution (double strength) which is equal in quantity to the distilled water and let stand for 2-3 minutes as usual .

Thomasen (1964) suggested previous soaking of seeds for four hours in a mixture of 4 % honey in water at a temperature of 98 F. The honey stimulates the fungel and bacterial spores to germinate ,w hile the seeds remain intact. Decant off the solution and add calcium hypochlorite solution or hydrogen peroxide . In the germinated state the spores are killed quicker and that too with a weaker solution of the disinfectant than in the case of the ungerminated spores.

Karasawa and Boyd (1966) also suggest soaking of seeds in a week solution of sugar prior to sterilisation .

When the seeds are still contained within the pods the pod is either dipped in sterilising solution or dipped in alcohol and flamed before cutting open with a sterile knife.