Dwarf Bunt Screening
 
                                       Blair Goates
                                  USDA-ARS, Aberdeen, ID
 
 
 The Western Regional Winter Wheat Nurseries were included in the dwarf bunt screening nursery at the
 dryland Green Canyon site near Logan, Utah.  The nursery was seeded October 8, 1997 into very moist
 soil.  Entries were seeded into two replicate 5 foot rows.  The cultivar "Cheyenne" was included every
 20 rows within the nursery as a susceptible check.  Plants emerged well and were in the ideal 1-3 leaf
 stage of growth going into winter.  There is considerable teliospore load in the soil from previous
 nurseries, and in addition the nursery was inoculated with a mixture of pathogenic races from
 throughout the Pacific Northwest.  Early and mid-winter was relatively warm and wet, and the nursery
 received a lot of "warm" snow.  These conditions produced an ideal environment for dwarf bunt.  As
 you can see from the data, the disease pressure this year was extreme!   Some of the best resistant lines
 and selections from National Small Grains Collection I test annually had low disease incidence, whereas
 others had no disease as in previous nurseries.  Most of the highly resistant cultivars, and some entries
 in the Regional Nurseries, had very low or no disease demonstrating the excellent performance of this
 material under such extreme pressure.  Disease incidence in some of the cultivars was the highest ever
 recorded.
 
 The following table presents dwarf bunt incidence of entries in the Regional Nurseries, the best resistant
 cultivars, and the bunt differential cultivars.  For purposes of comparison, the control cultivar
 Cheyenne is included in the table in the order it was placed in the nurseries.
 
 Of 1500 entries from the National Small Grains Collection, 3 had resistance, but these were lines that I
 was already aware of.  The most common rating for the Collection lines was 98 to 100%!
 
 Resistant cultivars and National Small Grains Collection accessions showing resistance to dwarf bunt are
 tested annually for resistance to various races common bunt to determine the resistance genes they
 contain.  It has always been assumed that our current highly resistant cultivars originating from crosses
 with PI 178383 have, at least, the resistance genes Bt-8, Bt-9, and Bt-10.  The Bt-8 resistance gene is
 particularly implied because field races of dwarf bunt that challenge these cultivars have strong virulence
 to Bt-9 and Bt-10.  However, experiments with common bunt races conducted over the past two years
 indicate that Bt-8 is not present in the highly resistant cultivars Hansel, Manning, and Promontory,
 which all derived their resistance from PI 178383.  These results show that dwarf bunt resistance in our
 commercial cultivars is more broadly based than previously thought.