Fruiting efficiency differences between cereal species

Abstract

Grain number (GN) is critical for yield determination, and understanding its physiology may be instrumental to further improving yield. Studying similarities and differences in yield physiology among cereals may highlight physiological traits that might become critical for understanding some constitutive differences between them. Recently it has been proposed that fruiting efficiency (FE, grains set per unit of inflorescence dry weight at anthesis IDWa) would be a relevant trait to further increase GN. In this research we report for the first time a comparison of GN determination due to IDWa and/or FE between five winter cereals crops (wheat, rye, barley, oats and triticale), analysing likely physiological bases for them and possible trade-offs. First, we performed a literature search and found a small number of papers on FE, mostly in wheat with limited data available for barley and triticale and nothing on oats and rye. Then, we conducted four experiments in which treatments consisted of the five small-grained cereal crops; in two of the experiments genotypes were combined with two levels of soil nitrogen availability. In triticale and barley the relationships between GN and either IDWa or FE were not significant implying that in these two cereals the environmental conditions affected in some cases one, while in other cases the other, physiological determinant of grain number. In wheat and rye, however, the relationships were clearer (and more significant) with FE than with SDWa, while for oats it was the other way around. Triticale and wheat showed the lowest FE values, rye exhibited the highest, and barley and oats were intermediate. When compared across cereals, FE was negatively related to the average spike- or panicle-DWa, indicating a trade-off in interspecific determination of GN. No relationship was found between FE and grain set percentage: differences in FE were mainly due to variation in the efficiency of setting fertile florets during pre-flowering inflorescence growth. The results also evidenced that this efficiency for setting fertile florets was related to the proportion of inflorescence resources partitioned to the growth of floret primordia. We observed no trade-off between FE and grain weight within each of the species, but an overall negative relationship when comparing across cereals (the latter likely explaining constitutive differences in grain weight among species). Therefore, it seemed that manipulations of FE within each of the species would not necessarily bring about compensations through reductions in grain weight and that to further increase fruiting efficiency cereal breeders may benefit from identifying prospect parents with an allocation of resources away from structural parts of the spikelets in favour of survival of labile florets.