Genetic variation in the flowering and yield formation of timothy (Phleum pratense L.) accessions after different photoperiod and vernalization treatments.

Venla Jokela,Ben Trevaskis,Mervi M Seppänen

doi:10.3389/fpls.2015.00465

Abstract

Timothy is a perennial forage grass grown commonly in Boreal regions. This study explored the effect of vernalization and photoperiod (PP) on flowering and growth characteristics and how this related to changes in expression of three flowering related genes in accessions from different geographic origin. Large variation was found in accessions in their vernalization and PP responses. In southern accessions vernalization response or requirement was not observed, the heading date remained unchanged, and plants flowered without vernalization. On the contrary, northern types had obligatory requirement for vernalization and long PP, but the tiller elongation did not require vernalization at 16-h PP. Longer vernalization or PP treatments reduced the genotypical differences in flowering. Moreover, the vernalization saturation progressed stepwise from main tiller to lateral tillers, and this process was more synchronized in southern accessions. The expression of PpVRN1 was associated with vernalization while PpVRN3 accumulated at long PP. A crucial role for PpVRN3 in the transition to flowering was supported as in southern accession the transcript accumulated in non-vernalized plants after transfer to 16-h PP, and the apices transformed to generative stage. Differences in vernalization requirements were associated with variation in expression levels of PpVRN1 and PpVRN3, with higher expression levels in southern type. Most divergent transcript accumulation of PpMADS10 was found under different vernalization conditions. These differences between accessions can be translated into agronomic traits, such as the tiller composition of canopy, which affects the forage yield. The southern types, with minimal vernalization response, have fast re-growth ability and rapidly decreasing nutritive value, whereas northern types grow slowly and have better quality. This information can be utilized in breeding for new cultivars for longer growing seasons at high latitudes.

Highlights

Timothy (Phleum pratense L.) belongs to Poaceae family, which includes some of the world’s most important cereal and pasture grasses (Stewart et al, 2011)
This study explored the effect of vernalization and photoperiod (PP) on flowering and growth characteristics and how this related to changes in expression of three flowering related genes in accessions from different geographic origin
After 15 weeks of vernalization the genotypic differences in heading time (HD) were diminished (HD ca. 35 days) with exception of breeding lines of northern (BOR N) for which no flowering tillers were observed when plants were vernalized for 15 weeks and grown in 16-h PP (Figure 1)

Summary

Introduction

Timothy (Phleum pratense L.) belongs to Poaceae family, which includes some of the world’s most important cereal and pasture grasses (Stewart et al, 2011) It is a perennial cool-season forage grass that is commonly used in grass leys in temperate regions. When tested at natural Danish day length conditions (15–18 h), Fiil et al (2011) identified considerable variation in vernalization response for timothy accessions of different origins, collected from latitudes between 35◦ N and 70◦N. Vernalization accelerated flowering and development of timothy in all tested cultivars and accessions (Seppänen et al, 2010; Fiil et al, 2011; Jokela et al, 2014). The length of vernalization was chosen based on previous studies of the effects of 0–15 weeks vernalization on flowering of timothy (Seppänen et al, 2010; Fiil et al, 2011; Jokela et al, 2014)

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