Is flowering a signal for stem lignification and decreased digestibility of the biomass?

It is thought that flowering causes a rapid decrease in digestibility and nutritive value of harvested forage biomass due to lignification of the stem.

We followed the development of apices and stem elongation in field conditions and studied it's relationship to development of lignified schlerenchyma ring. Our studies showed that transition to generative stage is not necessary for the initiation of extensive stem lignification but rather the height of the stem was important. Together with our colleques in Luke Maaninka we identified a third tiller type in timothy so called elongating tiller, where stem elongation had initiated without flowering stimulus. These elongating tillers contribute significantly to summer and autumn yields and their digestibility decreases as the stem elongation proceeds.

Decreased digestibility is, however, strongly related to the developmental rate of the genotype. Boreal Plant Breeding Ltd. has a long experience in breeding timothy cultivars with good nutritive value and digestibility. Two timothy lines selected for high or low digestibility in breeding program were studied for lignin amount and subunit composition. The results obtain in collaborative work with lignin experts at University of Helsinki and former Finnish Forest Research Institute revealed that the decrease in digestibility was associated with increased amount of S units in stem and leaf sheaths.

Seppänen, M.M., Pakarinen, K., Jokela, V., Andersen, J., Pedersen, A., Virkajärvi, P. 2010. Vernalization response of Phleum pratense L. and its relationship to canopy architecture, stem morphology and expression of VRN1 and VRN2 genes. Annals of Botany 106:697-707.

Virkajärvi, P., Pakarinen, K., Hyrkäs, M., Seppänen, M., Belanger, G. 2012. Tiller characteristics of timothy and tall fescue in relation to herbage mass accumulation. Crop Science 52:970-980.

Kärkönen, A., Tapanila, T., Laakso, T., Seppänen, M., Isolahti, M., Hyrkäs, M., Virkajärvi, P., Saarenpää, P. 2014. Effect of lignin content and subunit compostion on digestibility in clones of timothy (Phleum pratense L.) Journal of Agricultural and Food Chemistry 62:6091-6099.

Lemettinen, J. 2011.Genetic variance in digestibility of timothy and its crop-fysiological backround MSc thesis, 49 p.