Resistance break of Hartwig cultivar by field population of the soybean cyst nematode (Heterodera glycines)

Abstract

In February 1997, during a current evaluation of soybean cyst nematode (SCN) in Brazil, a field population collected at Sorriso county – State of Mato Grosso – was identified in the greenhouse as race 4. This race 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 aimed to confirm the race of the nematode, to investigate its multiplication in the cv. Hartwig and other breeding lines, and to compare the capacity of infection of Sorriso population with that one of another population from Chapadão do Céu. It was found that nematode population from Sorriso, identified as race 4, could infect 'Hartwig' and also three breeding lines from the cross 'Hartwig'⁴ X BR92-31830 with the same reaction. The genotype PI 437654 remained resistant in all tests. The two nematode populatios proved to be different in relation to parasitism in soybean cv. Hartwig. This is the first report of SCN population collected in the field infecting 'Hartwig'. It is suggested that 'Hartwig' be added to the four differential genotypes used for race identification in Brazil and that this specific population of Sorriso be called race 4⁺ (four-plus).