RESISTANCE BREAK OF HARTWIG CULTIVAR BY FIELD POPULATION OF THE SOYBEAN CYST-NEMATODE (HETERODERA-GLYCINES)

In February 1997, during a current evaluation of soybean cyst nematode (SCN) in Brazil, a field population collected at Sorriso county - Sta te of Mate Grosso - was identified in the greenhouse as race 4. This r ace was also found to infect soybean cv. Hartwig which had been until that time, resistant in all tests even with race 4. The present work a imed to confirm the race of the nematode, to investigate its multiplic ation in the cv. Hartwig and other breeding lines, and to compare the capacity of infection of Sorriso population with that one of another p opulation from Chapad (a) over tilde o do Ceu. It was found that nemat ode population from Sorriso, identified as race 4, could infect 'Hartw ig' and also three breeding lines from the cross 'Hartwig'(4) X BR92-3 1830 with the same reaction. The genotype PI 437654 remained resistan t in all tests. The two nematode populatios proved to be different in relation to parasitism in soybean cv. Hartwig. This is the first repor t of SCN population collected in the field infecting 'Hartwig'. It is suggested that 'Hartwig' be added to the four differential genotypes u sed for race identification in Brazil and that this specific populatio n of Sorriso be called race 4(+) (four-plus).