Biology of flowering, diversity of sexual types and seed production in Salsola orientalis S.G. Gmel

Reproductive biology of many cultivated plants has been studied in detail whereas in newly introduced, especially arid fodder species, different aspects of flowering, pollination, reproduction, seed production, etc., should be understood. Salsola orientalis S.G. Gmel. is a dwarf semi shrub haloxerophyte plant vegetated for a long period (250-254 days), 35-55 cm in height, with the root system of the generic type that penetrates the soil to a depth of 5-8 m. The species is extremely drought-resistant and tolerant to salt stress so this is a valuable fodder pasture plant in the deserts of Central Asia, well eaten by sheep and camels, especially in autumn and winter. Salsola orientalis is a polymorphic species consisting of a plurality of intraspecific ecotypes, populations and biotypes which differ in environmental sustainability and fodder productivity. S. orientalis is considered promising for breeding due to intraspecific plant polymorphism on adaptiveness and productivity. Here we report the data on flowering, intraspecific diversity of sexual types in population, and seed reproductive function of S. orientalis. The seeds were collected in arid, geographically and environmentally distinct areas of Tajikistan, Kyrgyzstan, Uzbekistan, and sown in the Desert Karnabchul (Uzbekistan, Samarkand region, Karnab). Karnabchul is characterized by hot summers (+40-45 °C in June-July) and dry climate (annual precipitation of 180 mm with 100-250 mm fluctuations). The soil is grey-brown, middle-saline. This study was carried out in the nursery (each plot of 100 m2 in size) by the method of A.N. Ponomarev. The number of functionally female flowers on each plant in all populations was estimated. The type of pollination was determined in experiments with isolation of individual plants and flowers. Embryonless seeds were found among the specimen collected in different eco-geographical areas and in three tested S. orientalis varieties (Perventz Karnaba, Solnechnyi and Salang). The seed of these varieties were divided into three fractions by size (large, medium and small) and weight of 1000 seeds. We found that the flowers in S. orientalis were cross-wind-pollinated. Self-pollination does not occur, since by the time of stamen appearance in bisexual flowers the pistil turns brown and dry. S. orientalis flowering begins in June and lasts until mid-July, the hottest season. However, the disclosure and the dusting of the flowers occur in the cooler morning hours (at a temperature of 25-26 °С and relative humidity of 26-65 %). In S. orientalis, self-incompatibility to avoid self-fertilization is not limited to dichogamy (i.e., non-simultaneous maturation of male and female generative structures of hermaphrodite individuals), and also combined with other adaptations to cross-pollination. These are the presence of female flowers and intermediate flowers with long stigma lobes of the pistil, and emergence of the plants with only functionally female flowers. The cross-pollination in S. orientalis is provided by both genetic incompatibility and structure of the flower. We attributed S. orientalis species to trioecious plants because i) only staminate flowers, ii) hermaphrodite and pistillate flowers, and iii) only pistillate flowers were characteristic of the individuals in the population. A wide variation on embryoless seed ratio (from 0-2 % to 98-100 %) was found in S. orientalis. Hence, selection makes it possible to increase the number of plant with low embryoless seed ratio in the population. Similar result can be achieved when using the parental forms with low percentage of embryoless seeds in breeding to obtain population with more frequent female forms. In both cases, you can get perspective parental forms for breeding varieties with low percentage of embryoless seeds and increased seed germination. Our findings are essential for development of S. orientalis breeding and seed production in the arid zones of Central Asia and Russia.