Single radicle emergence count for predicting vigour of marigold (Tagetes spp.) seed lots

This study was carried out to determine whether a single radicle emergence count (RE) during germination can be used for vigour assessment to estimate field emergence of marigold (Tagetes spp.) seed lots. Six marigold seed lots (Tagetes erecta and T. patula) with normal germination above 75% were germinated using the standard ISTA germination test and radicle emergence (production of 2 mm radicle) counted at regular intervals from 25 to 169 hours. The seed lots were also sown in the field with final seedling emergence assessed after 25 days. Seedling emergence was highly correlated with the radicle emergence count after 49 and 66 hours germination (r = 0.90 and r = 0.91, respectively; P < 0.01) but not with germination percentage (r = 0.26). Thus, the radicle emergence counts at 49 and 66 hours accounted for 81 or 83% of the variation in field emergence, respectively. The results indicate that a 49- or 66-hour count of RE during germination could be used as a vigour test to estimate field emergence for marigold seed lots.