Methods and Evaluation of Soybean Genotypes for Resistance to Colletotrichum truncatum.

Anthracnose of soybean (Glycine max) occurs throughout the soybean production areas of the world. There is little information on evaluating inoculation techniques or evaluating soybean germplasm for resistance. The objectives of this study were to develop a reliable inoculation technique for evaluating soybean for resistance to Colletotrichum truncatum and to evaluate soybean genotypes for resistance. Inoculated plants incubated in a dew chamber for 48 or 72 h had higher (P = 0.05) area under disease progress curve (AUDPC) values than when incubated for 24 h. Three experiments evaluated soybean genotypes for resistance to C. truncatum. In the first experiment using 15 soybean genotypes, 'Mandarin' had lower (P = 0.05) AUDPC values than all the other genotypes except for 'Mandarin 507', 'Mandarin (Ottawa)', and 'Boone'. In the second experiment using 28 soybean genotypes, Mandarin 507 had lower (P = 0.05) AUDPC values compared with all other soybean genotypes except 'Early White Eyebrow', 'Mandarin Yowa', Boone, and 'Manchuria'. In the third experiment, Mandarin 507 had lower (P = 0.05) AUDPC values compared with 23 other soybean genotypes except 'Spry', Mandarin, and 'Iroquois'. Plants of Mandarin 507 and 'Williams 82' were inoculated at the vegetative and reproductive growth stages; Mandarin 507 had lower (P = 0.05) AUDPC values compared with Williams 82 for both growth stages evaluated, and Mandarin 507 had less (P = 0.05) pod area covered by lesions compared with the pods of Williams 82. This study provided a descriptive method to inoculate soybean plants with C. truncatum and identified soybean genotypes with resistance to anthracnose.