Phenotyping primocane fruiting trait in raspberry (Rubus idaeus)

In raspberry (Rubus idaeus), two groups of cultivars are known: once fruiting, where fruit occurs annually on floricanes, and repeat fruiting (remontant), where a second fruit crop occurs on primocanes in the late summer or fall. Primocane fruiting extends the harvest, resulting in higher yields. The development of primocane fruiting cultivars is a primary objective of current raspberry breeding programs. The phenotypic identification of this trait is not easy because there is a strong interaction genotype/environment, influenced by temperature and photoperiod. In addition, there is a gradual expression of the character. The objective of this research was to generate descriptive data to make the selection of this character in segregating populations more efficient. A description of the degree of primocane fruiting was performed for five raspberry genotypes, ranging from high primocane fruiting to no primocane fruiting. The genotypes studied in order of increasing primocane fruiting were: ‘Meeker’, ‘Tulameen’, ‘Heritage’, ‘Autumn Bliss’, and UC103 (advanced selection). Plant height was measured, together with number of nodes, number and development of lateral shoots, and number of fruits per lateral shoot. Days from planting to first flower were also measured. With these values, a 1-5 scale was developed that identified the different degrees of primocane fruiting. Additionally, the effects of a chill treatment (2°C for 30 days) applied to plants in the early stages of development in the same genotypes were studied. This treatment was effective only in ‘Heritage’. These data have promoted progress in determining the type of inheritance of primocane fruiting in raspberry cultivars.