The barley mutant multiflorus2.b reveals quantitative genetic variation for new spikelet architecture

Understanding the genetic basis of yield forming factors is of utmost importance especially in the wake of stagnation of further yield gains in small grain cereals. One such yield forming factor in these cereals is the number of grain-bearing florets produced per spikelet. Generally, the spikelet axis (rachilla) of determinate barley (Hordeum vulgare L.) spikelets degenerates after producing one floret. In contrast, the rachilla of indeterminate wheat (Triticum ssp.) spikelets elongates to produce up to 12 florets. In our study, we characterized the barley spikelet determinacy mutant multiflorus2.b (mul2.b) that produced up to three fertile florets on elongated rachilla of lateral spikelets. Apart from the lateral spikelet indeterminacy (LS-IN), we also characterized the supernumerary spikelet phenotype in the central spikelets (CS-SS) of mul2.b. Through our phenotypic and genetic analyses, we identified two major QTLs on chromosomes 2H and 6H, along with two minor QTLs on 3H for the LS-IN phenotype. For, the CS-SS phenotype we identified a major QTL on 6H, along with one minor QTL on 5H. Notably, the 6H QTLs for CS-SS and LS-IN phenotypes co-located with each other, potentially indicating that a single genetic factor might regulate both phenotypes. Thus, our in-depth phenotyping combined with genetic analyses revealed the quantitative nature of the LS-IN and CS-SS phenotypes in mul2.b, paving way for cloning the genes underlying these QTLs in the future.