Floret development and grain setting in near isogenic two- and six-rowed barley lines ( Hordeum vulgare L.)

Abstract

Although floret abortion is related to a shortage in assimilates acquisition by the spikes, differences in floret abortion and grain setting has been reported between two- and six-rowed barley types. However, the origin of those differences has not been studied until now. This study was designed to explore the dynamics of floret development and to analyze the coordination between floret primordia development and growth of vegetative and reproductive organs in near isogenic barley lines differing only in the lateral spikelet fertility gene ( Vrs1). Two field experiments using four near isogenic lines differing only in the spike type were carried out. Floret primordia development together with stem and spike growth were studied. In both barley types floret primordia mortality starts at the beginning of the spike active growth phase and continued when stem and spike growth were at their maximum rate. A reduced contribution of fertile florets in apical and basal spikelet positions explained the lower floret survival in six-rowed barleys. The chance to reach the fertile floret stage at heading was highly dependent on the floral development stage attained at the start of floret primordia mortality. Floret development stage at the beginning of active floret primordia mortality was higher for all spikelet positions in two- than six-rowed barleys. Grain setting was lower in six- than two-rowed genotypes associated to a lower grain setting in distal spikelet positions. Smaller carpels in six- than two-rowed genotypes in those positions could be associated with a reduce chance of those florets to set grains. The lower grain survival within the spike in six-rowed genotypes was caused by (i) a lower floret survival due to a lower degree of floret development in distal and lateral spikelet positions at the beginning of the floret primordia mortality stage and (ii) a reduced establishment of the fertile florets initially formed.