The bulb is a storage organ of the plant, the parameters of which are key varietal traits when assessing crop marketability. The main morphological characteristics include bulb mass, its shape, defined as the ratio of height to diameter, as well as the color of dry and succulent scales and neck thickness. Important biological indicators are the number of bulbs per cluster, which characterizes the ability to form several bulbs from a single basal plate, and the number of growing points, which reflects the number of buds.
Evaluation of these traits during variety testing is carried out through biometric analysis, laboratory determination of sugar and dry matter content, and the study of keeping quality and taste. Bulb mass and shape depend directly on agronomic conditions: planting density, cultivation method, and availability of mineral nutrients. Bulb uniformity in size is an important advantage, as it facilitates the mechanization of harvesting and pre-sale preparation processes.
Cultivar resistance and productivity are predetermined by genetically fixed features of the number of growing points and the number of bulbs per cluster. For bulb onion varieties, a low number of bulbs per cluster is preferred, which allows for obtaining large marketable produce, whereas a high number of bulbs per cluster is characteristic of certain species, for example, shallots. Bulb quality also includes its ability to retain commercial appearance during storage, which is assessed during special tests for resistance to rot and general keeping quality.