Calorimetric assessment of pod disease in peanuts: comparison with visual methods and efficacy of use in selection.
GB Parker; OD Smith; WJ Grichar
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Abstract: Colorimetry was evaluated as a method to assess pod disease caused primarily by Pythium myriotylum, Sclerotium [Corticium] rolfsii and Rhizoctonia solani. Data analysed were from 19 replicated tests conducted from 1982 to 1987, exclusive of 1985, in 3 South Texas locations. Each plot was scored for pod disease colorimetrically and visually. A negative linear relationship (R2>96%) was found between Hunter colour values (L and b) and percentage infection measured visually for samples hand selected to approximate 11 disease levels varying from 0 to 100%. Variability among readings was less at extremes of infection. Correlation both between visual ratings and between visual and colorimetric ratings was affected by soil differences, pathogens infecting the pods, pod genotype, and level of infection present. Correlation among visual raters was Generally higher than between colour value ratings. Two-thirds of the lines in these tests classified visually as being in the best 50% f! or pod disease were also in the best 50% according to colorimetric scores. Use of colorimetry in conjunction with a single visual rating was estimated to increase efficiency and reduce costs of evaluation compared with multiple visual ratings.