Multiplication, collection and storage of stem rust races

The races are multiplied to store in the -80°C refrigerator for future use and to supply inoculum for screening advanced lines at seedling and adult plant growth stages. A set of stem rust differentials, as well as the susceptible check McNair, should be planted and inoculated by the same race during multiplication. The set is planted together to confirm the race we are working with is the one we need (Fig. 21).

Equipment needed for collection and storage of the pathogen are petri dish, watch glass, cryovial, capsule, desiccator, marker, freezer and registering book.

Collect rust spores from infected leaves on aluminum foil and then to petri dish, watch glass or cryovials (Fig. 22a, b, c, d.); or collect with the vacuum pump directly into capsules and dry them in a desiccator with silica gel for 5-7 days. Then store in clean, dry, clearly labeled cryovials in a deep freezer (-80°C). For large amount of spores, disperse spores evenly in the bottom of a petri dish and leave it to dry in desiccator. After drying, move the spores to a cryovial, close cap tight and place in the -80°C freezer (Fig. 23).

Before using stem rust spores from the -80°C freezer, the rust must be “heat shocked.” Make sure the cryovial is tightly closed and then place it in a water bath at 48°C. Leave the vial in the water for 6 minutes. Heat shocked spores can be used as inoculum as usual.

To know whether the varieties/advanced lines are resistant in particular, they have to be tested with the dominant and virulent races at seedling and adult plant stages. During the testing, there should be positive and negative controls for the races (Fig. 24a, b.)

Race analysis requires organized human resources as well as materials. The activities involved in race analysis and the collection and storage of stem rust are intensive and demand excellent techniques and precautions. Following the steps outlined in this document will ensure that you can conduct safe and successful research to identify the pathogens that affect the wheat crop.