Inheritance of angled spikelet arrangement in Triticum durum Desf.

Abstract

The genus Triticum includes diploid (2n=2x=14), tetraploid (2n=4x=28) and hexaploid (2n=6x=42) species. The phylogenetic relationships among different Triticum species has been largely clarified [1]. The spike or head size in wheat varies from 2-8 inches or more. The number of spikelets in each spike usually varies from 10-30 and are arranged at nodes on the rachis of spike. The shape of spike varies within as well as between the species. Normally, the shape of spike is tapering, parallel, clubbed or fusiform. The spikes of common wheat, T. aestivum are long, slender and somewhat flattened, whereas T. durum has somewhat shorter and flattened spikes. T. aestivum ssp. compactum possesses short spikes, about 2-3 inches in length, very compact and flattened. The density of spikelet also varies in different species as well as in the varieties of the same species, depending on the relative length of internode on the rachis. In dense spikes, the internode or the rachis segments are relatively short resulting in the dense arrangement of spikelets on the spike. In lax or very lax spikes, the internode length is more. Compact spike has not been reported in tetraploid wheat [2] and only compactoid spike is found. However, even the compactoid spikes of tetraploid wheat are not so dense. There are a few reports of dense spike in Ae. squarrosa (syn. T. tauschii) and T. sinskajae [3]. Besides the normal spikes, several other non-standard morphological forms of spikes are known [4]. In this paper, we report a nonstandard morphological form of spike in tetraploid wheat Triticum durum which to the best of the knowledge of authors has not been reported earlier. Normally arrangement of the spikelets on the spike is such that when seen from side, it appears smooth, may be parallel, tapering or fusiform. However, we came across two genotypes of T. durum where the arrangement of spikelets in the spike were irregular, as some spikelets tilted towards one side whereas others get angled in opposite direction. The present paper describes the inheritance of this peculiar morphology of spike.