Screening for disease resistance is carried out under field and glasshouse conditions. The glasshouse tests are conducted under controlled conditions and, therefore, glasshouse screening is considered more reliable than field tests. However, field and glass house screening are equally important. The procedure of field inoculation differs for various types of diseases.
1. Soil borne diseases: For soil borne diseases like root rots, collar rots, wilts, etc., the screening is done in disease sick plots. Disease sick plots are developed in three ways: (1) by inoculum developed in the laboratory. mixing soil from other sick plots. (2) by adding remains of diseased plants, and (3) by adding The soil from disease sick plots can be used in pots for conducting tests in the glass house.
2. Air borne diseases: For air borne diseases such as rusts, smuts, mildews, blights, leaf spots, etc., the screening is done either by dusting the spores or by spraying the spore suspension on the healthy plants. Planting of highly susceptible varieties after few rows of test material is also used to develop the inoculum.
3. Seed borne diseases: In case of seed borne diseases like smuts and bunts, either dry spores are dusted on the seeds or the seeds are soaked in the spore suspension.
4. Insect transmitted diseases: In case of insect transmitted diseases, the insect from susceptible varieties are collected and released on healthy plants or juice of diseased plants is rubbed onto healthy plants after causing mechanical injury in healthy plants.
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