Development of a strong lateral root system is critical for establishing vigorous cotton seedlings. Trifluralin, a preplant dinitronailine herbicide, reduces lateral root development in the treated soil. Previous work has suggested variation among cotton cultivars for number of lateral roots developed both In the presence and absence of trifluralin. This study was conducted to determine the inheritance of lateral root development in trifluralin treated and untreated soil.

Six genotypes which represented a range of differences in production of lateral roots and expected tolerance to trifluralin were chosen and crossed in a diallel fashion without reciprocals. F₁ seed from each single cross were pregerminated on germination paper at 25C for 30 hours. Seed with uniform radicle extension were selected and planted in greenhouse flats filled with trifluralin treated (.56 kg a.i./ha rate) and untreated soil then placed in a growth chamber at 25 ± 1C. After 14 days incubation seedlings were evaluated for number of lateral roots produced.

Number of lateral roots was significantly reduced when grown in trifluralin treated soil as compared to untreated soil. Significant differences were found among the single crosses for number of lateral roots produced In both environments. A highly significant correlation coefficient (r = .92) between number of lateral roots produced in trifluralin treated and untreated soil indicated that the herbicide treated soil provided an adverse environment for lateral root development. Therefore, selection pressure for lateral root production may be intensified by screening seedlings In trifluralin treated soil.

The partitioning of sum of squares for single crosses into general combining ability (GCA) and specific combining ability (SCA) revealed that a larger portion of the genetic variation was due to GCA. The GCA variance estimates associated with the parents revealed that GCA was significantly more important than SCA In both environments. Therefore, the genetic variation for number of lateral roots with these particular parents was primarily additive. Heritability estimates, calculated by the standard unit method, were 91 and 88% for number of lateral roots in untreated and trifluralin treated soil, respectively. Progress through selection for increased number of lateral roots should be expected in the early generations from these crosses.