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Screening Cotton for Tolerance to Hoplolaimus columbus . D. T. BOWMAN, Crop Science Department, North Carolina State University, Raleigh 27695. D. P. SCHMITT, Crop Science Department, North Carolina State University, Raleigh 27695. Plant.Dis. 78:695-697. Accepted for publication 30 March 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0695.

In order to adequately plan experiments to measure tolerance of cotton to Hoplolaimus columbus, coefficients of variation (CVs) and error variances of yield were examined to determine the minimum number of replicates and environments needed to measure specified differences for tolerance index (TI) and field tolerance. In two greenhouse trials with 84 genotypes, the error variance was 1,423 and would have required 231 replicates to ensure detecting a 10% genotypic difference in TI. In the 3-yr, one-location field study reported, CVs ranged from 10.0 to 25.4%, while error variances for TI ranged from 68 to 512. The pooled error variance (243) was used in calculating the minimum number of replicates and environments. There was no genotype x environment interaction for TI. To detect a 20% difference in TI, a minimum of 14 replicates in one environment or six replicates in two environments was required. Field tolerance, on the other hand, revealed a highly significant genotype x environment interaction and required as many as 23 environments with four replicates per environment to detect a 10% difference at 0.05. Choosing an α level of 0.20 instead of 0.05 would reduce the minimum number of replicates and/or environments by over one-half. This information should be useful in planning experiments to screen cotton germ plasm for tolerance to Hoplolaimus columbus in the future

Keyword(s): Gossypium hirsutum, lance nematode