Role of Multiple Awns in Determining Barley Yields 1

We developed barley ( Hordeum vulgare L.) lines differing in number of awns to learn if yield would be increased by the presence of additional awn tissue. Experimental procedures included field experiments conducted over several years, and structural characterization of awn tissue by light and scanning electron microscopy. In “multiple awn” lines the glumes are the size of lemmas and have an awn at their apex. These lines therefore contain three awns per spikelet, compared to one awn per spikelet in normal awned lines. Glume awns are structurally similar to normal awns and possess stomata which appear to be functional. The multiple awn lines had 46% more awn tissue by weight, and 76% more by length, than ‘Dickson’. The large glumes supporting the extra awns had six and‐a‐half times the surface area of normal glumes. The multiple awn lines produced lower grain yields than normal awn lines. Yields ranged from 50 to 88% of Dickson. At least three factors appeared to be involved in the yield decrease; the multiple awn lines were less robust, they had an average of 15 fewer kernels/head, and their kernels were 10% lighter (indicating the absence of component compensation). The reduced plant size suggests that the multiple awn gene affects overall plant growth. We postulate competition for substrate during floral initiation and development to explain the marked reduction in kernel number. The reduced kernel weight presumably means that the extra awns and large glumes had a net negative effect on photosynthate deposition in the kernel.