The soybean cyst nematode (SCN) (Heterodera glycines Ichinohe,
1952) is considered to be the most important problem for soybeans
(Noel, 1992). Losses can reach 100%, depending on the pathogen density
in the soil. In Brazil there is not much information about the damage
caused by the SCN since it was first detected in 1992, in the counties
of Nova Ponte, Iraí de Minas and Romaria, Minas Gerais State. Four
years later, SCN was found in 62 counties distributed in seven states,
race 3 being predominant (EMBRAPA, 1996).
use of resistant cultivars in rotation with susceptible ones and
non-host species is the most economic and reliable method for
controlling SCN (Wrather et al., 1984). The resistance
mechanism is hypersensitivity, which determines the death of infected
cells and blocks the nematode cycle (Schmidt and Noel, 1984). The
genetics of soybean resistance to SCN, race 3, is complex and studies
carried out by several authors (Caldwell, 1960; Rao-Arelli and Anand,
1988; Rao-Arelli et al., 1992), with North-American soybean
genotypes, found that two or three recessive and one dominant gene were
involved in resistance.
soybean cultivar resistant to SCN it is necessary the knowledge of
number of genes related to resistance, as well as the type of gene
action and the heritability of this character. This knowledge will
allow the breeder to use more efficient selection procedures and a
better use of the variability in the segregating population.