Association Between Root‐Knot Resistance and Economic Characters of Flue‐cured Tobacco After Seven Backcrosses1

The effect of the root‐knot nematode resistance factor on agronomic characteristics and chemical constituents of flue‐cured tobacco (Nicotiana tabacumL.) was studied. Within each of four cultivars efforts were made to isolate lines that were genetically identical with their respective parental cultivars in all attributes except root‐knot resistance. ‘PD 611’ was used as the source of root‐knot resistance and the following four cultivars were used as recurrent parents: ‘Coker 316,’ ‘Coker 187,’ ‘402,’ and ‘Hicks Broadleaf.’ Each cultivar, a root‐knot susceptible selection, and two resistant selections were compared for days to flower, number of harvestable leaves per plant, plant height, yield, value per 45.4 kg, leaf senescence, percent total alkaloids, and sugars. Estimates were made of the degree to which the genotypes of the recurrent parents were recovered. The recovery of the recurrent parent genotype was sufficient in at least one family to study each of the traits. The root‐knot resistance factor was associated with slower leaf senescence in every family, and in the Hicks Broadleaf family with a lower value per 45.4 kg. There was no other significant effect attributed to the root‐knot resistance factor for any of the other traits studied.