BP Singh

Detection Procedures for Fungal Plant Pathogens and Salvaging 145Potato dextrose agar (PDA) is the most commonly used agarmedium; other media used are: malt extract agar (MEA), oat mealagar (OMA) etc. Antibiotics are often added to limit the growthof bacteria. Usually 5 to 10 seeds per plate are placed andincubated for 7 days at 20 to 25°C. The method is used for thedetection of Drechslera teres and D. graminea in barley; D. avena inoats, Colletotrichll7n lini in linseed; Ascochyta spp. in legumes, etc.However, the method is unsuitable for slow growing pathogensbecause they are overgrown by other pathogens or saprophytes,e.g. Pyricularia oYljzae is readily overgrown by Trichaniella padwickii.4. Examination of symptoms developed on seedlings grown insoil or sand : Sowing the seeds in sterilized soil, sand, or gravel,etc. provides more natural conditions and under such conditionsinfected seeds and seedlings may develop symptoms comparableto those developed under field conditions.(a) Sand method: The seeds are sown at the depth of 3-4 em incoarse grained sand. For small seeds, the depth js of 1 em only.The method is used for cereals in Germany. It is also applied fordetection of Drechslera, Septaria and Fusarium infections in wheat,oats and barley. In Israel, a combined routine method is used fordetection of Colletotrichum gossypii (Neergaard, 1969). The methodis time consuming but provides information comparable to fieldperformance.(b) Soil method : A uniform soil mixture composed of 4 partsof clay and 6 parts of peat with fertilizers is used for sowing. Themethod is used in Sweden where the soil is sold in plastic bags.The medium for the test is prepared by mixing 3 parts of abovesoil mixture, 1 part of sterilized sand and 0.6 parts of water for5 minutes to get uniformity and filled in plastic multipot trays.Plates after sowing of seeds are covered with plastic bags to avoidwater loss throughout the incubation. Cereals are kept at 10 D C forSeptaria and Drechslera. The symptoms are then recorded and thepercentage of attacked seedlings is calculated.5. Grow out test: Certain seed-borne diseases need' longerperiods for their expression than provided in the normal incubl1 t It mtests; specially some bacterial and viral diseases. In plantquarantine system, growing on tests have gre?-t importance, asexemplified from Portuguese quarantine import inspection of seed