You should add lactic acid 2.5% 2 drops when you plated PDA in petridish. Also please make sure your laminar air flow clean and sterile it (the laminar) with ultra violet first. do Anything with sterile condition

Thank you. Lactic  acid is used for preserving fungal structures. i have to addd directly into prepared pda plate before transfering single spores

Dear,

Your question is somewhat unclear................ you are going to isolate the fungus by songle spore inoculation right? if so, then from where any environmental soil? if yes then you must be prepared serial dilution............... and made spread plate on a PDA or whatever other medium. Now you must pick spore developed from a separate single colony and transfer it in an new pda plate.............keeping properly sterile environment. i think no need to add any antibiotic of growth retardant on  PDA medium.

sorry sir iam isolating marine fungi from mangrove plants

thank u. but iam not interested in this type of isolation

Hi Devadatha,

As suggested by Monica, ensure you're working in a highly sterile environment (sterile laminar flow - clean with disinfectant and allow UV for about 15-30mins; sterilized apparatus - toothpicks, scapels, sterile water, etc). Lactic acid is nice to use but 2.5% may be too high and depending on the fungus, may affect growth - try 0.2% (2ml lactic acid per 1000ml of PDA). You may also try transferring the germinating spore onto a plate of water agar (15g or 20g agar powder per 1000ml of distilled water) and grow for just about 3-5 days before transferring unto PDA again. All these depends on the kind of fungus. Cheers!

thank u . i have to add laqctic acid  before the preparation of Pda or after  pouring into petripalate

Add just before autoclaving the medium.

thank u

Your problem can be resolved. Single spore isolation of fungi by using hand made glass needle from capillary tube. Also you have to do it in sterile conditions. See the link: http://www.fungaldiversity.org/fdp/sfdp/FD_2_47-63.pdf

thank u  i hd gone through this previously

use water agar with no antibiotica instead of PDA

Yeah i done it previously but encountered contamination with bacteria. so i started using Chloramphenicol  50microgram/ml eventhough iam encountering contamination with bacteria as well as Yeast and aspergillus n penicillium. So please suggest me how to overcome this problem