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Genetics of Resistance in Soybean to "Race X" of Soybean Cyst Nematode¹

The soybean cyst nematode (SCN), (Heterodera glycines Ichinohe), is a major pest of soybean [Glycine max (L.) Merr.) and new biotypes have been identified in recent years. A new biotype that reproduces on the ‘Bedford’ cultivar has been identified in Arkansas and is designated as "race X". The objectives of this research were to study genetics of resistance to race X and measure heritability. Crosses and reciprocals were made between PI 90763, a genotype resistant to race X, and three susceptible genotypes, PI 88788, R74-1001, and PI 209332. Data from F₁, F₂, and backcross populations indicate that a single recessive gene conditions resistance in these genotypes. There was no evidence of maternal or cytoplasmic inheritance in any of the crosses. Ninety-four F₃ lines were evaluated for reaction to race X and race 4. Lines that are resistant to race X were susceptible to race 4, and the lines resistant to race 4 were susceptible to race X with correlation coefficients of –0.53 and –0.59, respectively. No F₃ lines from these crosses were identified as either highly resistant or susceptible to both race 4 and race X of SCN. Narrow sense heritability estimates based on regression of F₃ family means on parental plant values ranged from 61 to 64% for the three crosses. The data indicate that the screening techniques used to determine reaction of individual plants were relatively effective for determining resistance.

Key Words: Glycine max (L.) Merr. • Heterodera glycines Ichinohe • Heritability • Phenotypic correlations • Screening technique

² Former graduate student (now, agronomist, CR Seeds, Bay, AR 72411); graduate student; and professor, Dep. of Agronomy; and professor, Dep. of Plant Pathology, Univ. of Arkansas, Fayetteville, AR 72701.

Received for publication August 4, 1986.