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Heritability of Seedling Disease Characteristics in Flax¹

Resistance to seedling disease in the field (two locations) and resistance to two specific isolates of Rhizoctonia solani Kühn were studied using unselected progenies of F₂ plants in the F₃ and F₄ generations of the flax cross ‘DeOro’ x ‘Dillman.’ There was a high level of dominance deviations towards resistance before and after germination. From 28.1 to 59.8% of the plants were susceptible before emergence and about 20% more after emergence. Heritability estimates in the broad sense ranged from .53 to .88 for preemergence resistance, and from .20 to .87 for postemergence resistance. In the narrow sense, heritability estimates ranged from .10 to .54 for preemergence resistance, and from .07 to .49 for postemergence resistance. Regression of F₄ on F₃ gave heritability estimates of .01 in the field, but .51 and .54 for the laboratory isolates for preemergence resistance. For postemergence resistance the regression was .05 in the field, while it was .08 and .27 in the laboratory. Genetic gains by selection were expected (and actually observed) in the laboratory tests, but no gain was expected or observed from the field tests. Genetic correlations existed between field and laboratory reactions, suggesting that it is possible to effectively select in the controlled environment of the laboratory for field improvement. Yellow-seeded families were much more susceptible than brown-seeded ones. Genetic gain for resistance to the less virulent isolate was greater than was gain for resistance to the more virulent one.

Key Words: Disease Resistance • Rhizoctania Solani • Linum Usitatissimum • Damping-off

² Respectively: Graduate Student, Department of Soil and Crop Sciences (Now Research Agronomist, Department of Agriculture, Giza, United Arab Republic); Assistant Professor, Department of Plant Sciences; and Professor, Department of Soil and Crop Sciences, Texas A&M University.

Received for publication May 4, 1968.