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

**Physiological Determination of Oats Yield: Thoughts on Promissory
Traits for Further Genetic Gains**

Daniel Calderini

Department of Plant Production and Protection, Campus Isla Teja,
Universidad Ausral de Chile, Valdivia (CHILE)

PH: +56 63 22-1723; E-mail: danielcalderini@uach.cl

The World is facing a major challenge: to supply food for an increasing
population. In addition, biofuels are also increasing grain crops
demand. As no enlargements are expected in growing area, and little
opportunities exist for expanding irrigation, future yield levels of
most grain crops will depend on plant breeding and management techniques
to match the expected increases in demand. The most cost effective, and
environmentally safe, way to meet increased demand for grain crops
production is probably to improve genetic yield potential through plant
breeding, which has been shown effective in on-farm yield increase.

The importance of oat breeding aimed at increasing yield potential has
been noteworthy during the 20^th^ century. This impact has been
evaluated in different countries of the World (e.g., Finland, Italy, UK,
USA). These studies showed that grain yield was increased by a higher
harvest index; however, few evaluations reported changes in biomass
production. Regarding major grain yield components, grain number has
been found as the component determining grain yield. When the effect of
plant breeding has been analyzed in small grain cereals, most of them
showed that grain yield was associated with grain number per square
meter. Interestingly, in oat some evidences showed that grain weight has
also been a component associated with grain yield increase. In addition,
recurrent selection of grain weight had positive effect on grain yield.
Therefore, these findings support the idea that grain weight could be
useful to continue increasing grain yield potential. To identify
physiological bases of grain weight determination would be promissory
for further increases of gain yield potential in oat and other cereals.

Many efforts have been carried out to understand grain weight
determination in small grain cereals. Most of the research aimed at
studying grain weight was focused on the grain filling period; however,
the importance of the phase immediately previous to anthesis, in
addition to the post-anthesis period, has been shown. Recently, the
booting-anthesis period was identified as the most affecting
pre-anthesis phase for grain weight determination in wheat, barley and
triticale. Regulation of grain weight by the pre-anthesis period could
be ascribed to the carpels of florets which are growing fast between
booting and anthesis. Associations between final grain weight and carpel
weight at anthesis were found in barley and wheat. Therefore, it is
hypostatized that pericarp cells (developed when the carpels are
growing) are involved in grain weight determination. Pericarp growth is
the result of the number of pericarp cells and the enlargement of these
cells. Little is known about pericarp cell number in small grain
cereals, but more knowledge is available on plant cell enlargement. The
last process is controlled by a family of proteins called expansins,
which are involved in cell wall loosening. Recent experiments found
expansin expression in wheat grains. In addition, it was found that the
expression of expansin A6c mimics the enlargement of grains which occurs
early in the grain filling period. Manipulation of expansin expression
of growing grains could be a promising trait for increasing grain
weight, and grain yield, in oat and other small grain cereals.