ARE THERE COMMON SYSTEMS FOR FLOWER BUD INITIATION IN THE GENUS RUBUS?

In Rubus ideaus L. our research indicates that flower bud initiation is controlled by three systems: 1) temperature and daylength; 2) a period of chilling; and 3) juvenility. We postulate that in the first system, flower bud initiation is primarily controlled by the maximum temperature at which flower buds will initiate and that this temperature becomes higher in longer daylengths. Within the species there appears to be continuous variation for the maximum temperature - being highest in primocane-fruiting genotypes, progressively lower in tip-fruiting, and early floricane-fruiting genotypes, and lowest in late floricane-fruiting genotypes. A period of chilling appears to irreversibly condition the primocane to initiate flower buds when grown below the maximum temperature at which initiation will occur, once the juvenile period is over. Hence, chilling is epistatic over juvenility, and juvenility is epistatic over temperature and daylength. Similar systems appear to exist in Rubus subgen. Rubus, so it seems reasonable to suggest that these systems may be common throughout the genus.