A method for evaluating bolting-resistance in Brassica species

Kale (Brassica oleracea var. acephala), Chinese cabbage (B. campestris ssp. pekinensis), chikale (B. campestris ssp. pekinensis × B. oleracea var. acephala hybrid) and turnip (B. campestris spp. rapifera) were studied. The proper plant size (number of true leaves) for the beginning of vernalization treatment was determined. All vernalization experiments commenced when the plants were 4 weeks old, with 5–7 true leaves. Plants were classified as bolters either through the visible appearance of flower buds at the apex, or by making longitudinal cuts through the apex if the flower buds were not visible. Cut plants with a pointed apex were classified as bolters. A definite relationship between the number of true leaves and bolting was observed for kale, the more difficult biennial species.