B Phytochromes (PHYB1 AND PHYB2) and the CONTROL of EARLY Established PLANT-to-PLANT Variability of Maize Growth.

In maize canopies, plant hierarchies are established from early developmental stages. This effect can be determined by genetic or environmental factors. Among the latter, changes in light quality (red /far red) perceived by plants can produce early desuniformity in population growth. The aim of this work is to explain the role of phytochromes B1 and B2 on plant growth and plant growth variability along the cycle. A field experiment was conducted in blocks without water and nutritional limitations. Maize lines with mutations of PHYB1 (phyB1-PHYB2), PHYB2 (PHYB1-phyB2) and without mutation (wild type, WT) were cultivated at two plant densities (low and high), in plots pure (only one genotype) and mixed with equal proportion of its components (WT + phyB1-PHYB2; WT + PHYB1-phyB2; WT + phyB1-PHYB2 + PHYB1-phyB2; phyB1-PHYB2 + PHYB1-phyB2). From early vegetative stages, plants of WT and those of PHYB1-phyB2 in monocultures reduced their biomass in response to increased plant density. Unlike plants phyB1-PHYB2 did not respond to increased plant density and always had a lower biomass than those of the other genotypes. In polycultures, at the lowest plant density, plant biomass order was: WT> phyB1-PHYB2; PHYB1-phyB2> phyB1-PHYB2; WT = PHYB1-phyB2; WT = PHYB1-phyB2> phyB1-PHYB2. At high plant density: WT = phyB1-PHYB2; PHYB1-phyB2 = phyB1-PHYB2; WT = PHYB1-phyB2; WT> PHYB1-phyB2 = phyB1-PHYB2. These results highlight the role of PHYB1 in the response of maize plant growth to increased planting density.