Off-season flowering and expression of flowering-related genes during floral bud differentiation of rabbiteye blueberry in a subtropical climate

Abstract

Rabbiteye blueberries (Vaccinium virgatum Aiton) cultivated in subtropical climates often display autumn flowering on shoot apices, which offers a potential for off-season berry production. The aim of this study was to elucidate the mechanism of off-season flowering through field observation and gene expression analysis. Field trials from 2018-2020 indicated that apical blooming occurred mainly in non-terminated shoot tips, suggesting that vegetative growing status was necessary for the development of apical flowers. Microstructure of apical buds showed that vegetative growth on shoot tip and apical inflorescence developed simultaneously. To understand the molecular basis of off-season flowering, expression of flowering-related genes, i.e., VcFT, VcCEN, and VcCOL5, in rabbiteye blueberry ‘NTU031’ and ‘Austin’ were analyzed. Although most shoots of the two cultivars continued vegetative growth in October, ‘NTU031’ showed intensive off-season apical flowering from late November while most shoots of ‘Austin’ terminated with apical growth cessation. In ‘NTU031’, VcFT expression increased in mid-October with floral meristem development whereas VcCEN and VcCOL5 expression decreased. On the other hand, ‘Austin’ did not show any significant fluctuation in the expression of these genes. The results suggested that autumn apical flowering in rabbiteye blueberries was positively correlated with the transcription of VcFT but negatively correlated with the expression of VcCEN and VcCOL5.