**Session IV -- Physiology, Ecology and Production -- Talk: Rajala**

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# Floret Development and Grain Characteristics for Determining Yield Potential in Oat

\*Ari Rajala and Pirjo Peltonen-Sainio

MTT Agrifood Research Finland, FI-31600 Jokioinen, Finland

\* corresponding author ari.rajala@mtt.fi

In this presentation two basic processes that determine grain yield in
cereals, particularly in oat, are focused. Firstly, grain set is
approached by describing impacts of apical development rate and duration
of development phases. Secondly, the potential role of cell number in
developing grains is discussed regarding potential of grain to store
assimilates. Thirdly, the interplay between grain number and grain
weight in yield determination of oat is also discussed, based on
extensive field data.

Plant breeding has improved cereal grain yield by increasing harvest
index (HI) and number of grains per plant. Little information is
available on whether these breeding-induced changes in biomass
allocation pattern have resulted from concurrent changes in rate and/or
duration of apical development phases. In Finland, a set of oat
cultivars released over more than 60 years did not express marked
differences in duration of major apical development phases. Similarly,
in Argentina 50 years of barley breeding was not markedly or
systematically associated with apical floret development rate. These
studies indicate that breeding has not necessarily altered duration of
apical development phases. Nevertheless, altering duration of critical
developmental phases can be exploited to enhance floret and thereby
grain set to further increase grain yields. However, monitoring apical
development stages is laborious and not very attractive as a selection
criterion in breeding programmes.

Formation of fertile florets prior to pollination can be considered the
foundation of yield potential. The degree to which this potential is
realised as increased grain yield is determined principally by the
prevailing growing conditions and available resources during grain
filling. Before active grain filling occurs, there is a phase of
post-pollination cell division in grains. There is some evidence that
sink strength and potential weight of the grain can be determined by the
rate and duration of post-pollination cell division in developing
grains. Grain cell number and grain weight has been shown to correlate
positively in wheat and in oat. Generally, increase in grain number is
associated with decrease in grain weight. This is especially true at the
plant level, though the correlation is not necessarily as strong in oat
compared with other cereal species. According to extensive MTT Official
Variety Trial data single grain weight and grain number per square metre
did not correlate.

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# Conclusions: Despite the marked changes in dry mass allocation pattern, plant breeding has not markedly altered the duration of critical apical development phases. This seems to be an unexploited means for enhancing floret and grain set and thereby increasing grain yields. Post-pollination cell division (grain cell number) likely sets the limit for potential grain weight. The degree to which this potential is realised depends on growing conditions and available growth resources during the grain filling period. In contrast with the common trend in cereals, grain number and grain weight of oat grown at northern latitudes are not negatively correlated, thereby possibly emphasising the role of sink strength in yield determination.