Environmental responsiveness of flowering time in cassava genotypes and associated transcriptome changes

Cassava is an important food security crop in tropical regions of the world. Cassava improvement by breeding is limited by its delayed and poor production of flowers, such that cassava flowering under field conditions indirectly lengthens the breeding cycle. By studying genotype and environment interaction under two Nigerian field conditions (Ubiaja and Ibadan) and three controlled temperature conditions (22°C/18°C, 28/24°C and 34/30°C (day/night)), we found that while early flowering genotypes flowered at similar times and rates under all growing conditions (unfavorable and favorable field and controlled-temperature environments), late flowering genotypes were environmentally sensitive such that they were substantially delayed in unfavorable environments. Flowering times of late genotypes approached the flowering time of early flowering genotypes under relatively cool Ubiaja field conditions and in growth chambers at 22°C, whereas warmer temperatures elicited a delaying effect. Analysis of field and controlled temperature transcriptomes in leaves revealed that conditions that promote early flowering in cassava have low expression of the flowering repressor gene TEMPRANILLO 1 (TEM1), before and after flowering, among others. Field transcriptomes showed that the balance between flower promoting and inhibitory signaling, appeared to correlate with flowering time across the environments and genotypes.