Seedling growth under osmotic stress and agronomic traits in Bulgarian semi-dwarf wheat: comparison of genotypes with Rht8 and/or Rht-B1 genes

Abstract

Early-season drought is an adverse environmental factor affecting seedling emergence and crop establishment in winter wheat grown in continental climates. The different semi-dwarfing (Rht, reduced height) genes exert various effects on seedling growth, plant height and productivity. The occurrence of the major Rht genes in 69 Bulgarian bread wheat cultivars was postulated by molecular markers. Cultivars carrying Rht-D1b+Rht8 (1), Rht-B1b/d (6), Rht-B1b/d+Rht8 (19), or Rht8 (43) were identified. The three latter groups were compared in respect to germination and seedling growth in response to polyethylene glycol-induced osmotic stress, plant height and main yield components. Cultivars carrying only Rht8 produced longer roots, coleoptiles and shoots, and had smaller root-to-shoot length ratio in non-stress and in osmotic stress conditions compared with those carrying Rht-B1b/d or Rht-B1b/d+Rht8. The same cultivars produced shorter culms, shorter spikes with fewer spikelets, reduced number and mass of grain in the main spike, and reduced 50-grain mass. The Rht genic effects were confirmed on Rht near-isogenic lines. The preferential semi-dwarfing allele selection aiming to combine the advantages of Rht8 and Rht-B1b/d alleles in specific eco-climatic conditions and to improve breeding efficiency in wheat is discussed.