Wheat reduced height (Rht) genes encode modified DELLA proteins, which are gibberellin insensitive, accumulate under stress, restrain growth and affect plant stress response. The seedling reaction to soil water deficit regarding leaf gas exchange and chlorophyll fluorescence was compared in near-isogenic lines carrying the alleles Rht-B1a (tall), Rht-B1b (semi-dwarfing) and Rht-B1c (dwarfing) and was related to leaf water content and anatomy. Under drought, Rht-B1c line was characterized by less decreased CO 2 assimilation, delayed non-stomatal limitation of photosynthesis and higher instantaneous water use efficiency. The functional state of its photosynthetic apparatus was better preserved as evidenced by the less decreased actual quantum yield (Φ PSII ) and potential maximum quantum yield (F v /F m ) of PSII, and the less increased quantum yield of non-regulated energy dissipation (Φ NO ). Rht-B1b line also tended to perform better than RhtB1a, but differences were less pronounced. Although the leaves of both dwarf lines were smaller, thicker and more pubescent, their water content was not higher in comparison with the tall line. Nevertheless, in Rht-B1c, leaf thickness was less decreased and mesophyll cells were less shrunk under drought. The more effective performance of the photosynthetic machinery of dwarf lines under water deficit could be explained by a combination of morpho-anatomical and metabolic characteristics.

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) (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.

We investigated the effect of genotype and culture medium on the in vitro germination and development of plantlets from seeds of 6 different Paulownia genotypes (P. tomentosa, hybrid lines P. tomentosa × P. fortunei (Mega, Ganter and Caroline), P. elongata and hybrid line P. elongata × P. fortunei). Nodal and shoot tip explants were used for micropropagation of Paulownia genotypes by manipulating plant growth regulators. The highest germination percentage for all genotypes was obtained for seeds inoculated on medium supplemented with 50 mg*L GA 3 (MSG2). On Thidiazuron containing media, the explants of hybrid line P. elongata × P. fortunei exhibited the highest frequency of axillary shoot proliferation following by P. tomentosa × P. fortunei. The results are discussed with the perspective of applying an improved protocol for in vitro seed germination and plantlet formation in several economically valuable Paulownia genotypes.