Evolutionarily genetic dissection of flowering behavior in Asian wild and cultivated rice

Flowering behaviors (FBs) are important life-history and agronomical traits, and their genetic architecture and evolution are of great interest to crop breeders. Flowering behavior simply indicates days to the first-flowering time from germination (DFF) when considering only modern cultivars with small genetic variation, but flowering continuity as the result of asynchronous flowering can be relevant for the FB when an evolutionary variation is present. Evolutionary and genetic nature of asynchronous flowering has been unknown until now. Through daily observation, we recorded the first- and third-flowering date of a plant, and then calculated DFF and days to the third-flowering time from germination (DTF). Flowering asynchrony in a plant (FA) was defined as the equation, FA = DTF - DFF. Quantitative-trait locus (QTL) analyses were performed on DFF, DTF, and FA in each of two-density conditions in a paddy field by using 35 recombinant-inbred lines derived from an interspecific cross between domesticated rice (Oryza sativa L.) and an annual form of its wild relatives (O. rufipogon Griff.). The present results suggest the following points: (a) FA could have a genetic component that is independent of flowering genes; (b) genetic nature of FA might be polygenic and the majority of the QTLs associated with FA behaved in a complex density-dependent manner; and (c) FA might have been developed by feeding pressure of animals in their wild habitat.