Ravi Koppolu, Guojing Jiang, Sara G. Milner, Quddoos H. Muqaddasi, Twan Rutten, Axel Himmelbach, Yu Guo, Nils Stein, Martin Mascher & Thorsten Schnurbusch

Theoretical and Applied Genetics; February 2022; vol. 135: 571–590

Key message

Spikelet indeterminacy and supernumerary spikelet phenotypes in barley multiflorus2.b mutant show polygenic inheritance. Genetic analysis of multiflorus2.b revealed major QTLs for spikelet determinacy and supernumerary spikelet phenotypes on 2H and 6H chromosomes.

Abstract

Understanding the genetic basis of yield forming factors in small grain cereals is of extreme importance, especially in the wake of stagnation of further yield gains in these crops. One such yield forming factor in these cereals is the number of grain-bearing florets produced per spikelet. Wild-type barley (Hordeum vulgare L.) spikelets are determinate structures, and the spikelet axis (rachilla) degenerates after producing single floret. In contrast, the rachilla of wheat (Triticum ssp.) spikelets, which are indeterminate, 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 rachillae 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, and two minor QTLs on 3H for the LS-IN phenotype. For, the CS-SS phenotype, we identified one major QTL on 6H, and a minor QTL on 5H chromosomes. 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 the way for cloning the genes underlying these QTLs in the future.

See: https://link.springer.com/article/10.1007/s00122-021-03986-w

Fig. 3: Phenotype classification for lateral spikelet indeterminacy. a Representative spikelet triplet showing wild-type rachilla of lateral and central spikelets. b–e elongated lateral spikelet rachilla developing class-I (b, c) and class-II additional florets (d, e). f–g Class-III rachilla elongating into a thin and long filament-like structure. (H-I) Class-IV phenotype showing a bifurcated (h) or wedge-shaped rachilla in lateral spikelets (i). Rachilla/additional florets/rachilla malformations in lateral spikelets are indicated with white arrowheads. Yellow arrowheads in Fig. 3d and e indicate a pedicel below the extra floret in lateral spikelets