A. R. da SILVA e E. T. COELHO
Escola Agronomia Eliseu Maciel, Pelotas, Rio Grande do Sul, Brasil
Using the isogenec lines obtained by Dr. D. R. KNott from Canada through. backcrossing to Marquis, resistant varieties, with the genes Sr 6, Sr 7, Sr 8, Sr 9 and Sr 10; and the lines of the variety Chinese with the following chomosome substituted: Thatcher XIX (carries the gene Sr 5), Red Egyptian (carries the gene Sr 6), Red Egyptian VI (carries the gene Sr 8), Red Egyptian XIII (carries the gene Sr 9), Timstein X (carries the gene Sr 11), Hope III.VIII.XVII and Thatcher III and XIII obtained by Dr. E. R. Sears from United states, it was possible to recognize physiologic races of stem rust with information more usefull for breeding for resistance than by the use of the international set.
There is published the pedigree of a large number of wheat varieties descendent from Kenya varieties and from Reliance, Thatcher, Newthatch, Frontana and others and Dr. KNOTT has identified the genes that condition resistance to stem rust races 15 B and 56 in these varieties.
With such information available, the race identification through the use of genes, provides very usefull information to breeding for rust resistance because the breeder. will know the possible sources of resistance and can choose the one which is more similar to its own material well adapted to its local conditions, can organize the crosses to have the more wide basis of resistance and is able, by the inoculation of races, to know which lines after a cross have different genes for resistance.