Evaluation of the effect of water regime on the growth processes of Oryza sativa subsp. japonica Kato seeds for optimizing rice cultivation using herbicide-free technology

Relevance. Along with germination, the ability of rice seedlings to overcome a layer of water in order to form an optimal density of seedlings and a good harvest is of fundamental importance. Rice is a hygrophite, and in the Kuban region, it is grown using the technology of flooding with a layer of water to improve the environmental friendliness of the rice industry and reduce the use of herbicides. The field germination of seeds is significantly lower than the laboratory germination, which is associated with the varietal characteristics of their germination physiology and the morphological parameters of the seedlings to overcome the layer of flooded soil. It is important to determine the tolerance of rice varieties to flooding during the germination phase. Purpose of research. To evaluate the features of morphological parameters of rice varieties seedlings under conditions of humidification and flooding, the rate of growth at the initial stage and the intensity of plant growth throughout the rice vegetation for the optimization of approaches in cultivation. Materials and Methods. The research was conducted on the basis of the USU (Unique Scientific Unit) group of the Federal Scientific Rice Center, with the involvement of 15 varieties from the Rice Bioresource Collection in the experiment. Laboratory experiments on assessing the viability of seeds and the growth intensity of seedlings were conducted in two variants: in a 10 cm layer of water in glass containers and on moistening in Petri dishes at the same temperature. The cultivation of these same varieties in a field on an irrigated plot was carried out according to the generally accepted methods and technologies of rice cultivation in the Krasnodar Territory. Results. The analysis of the obtained data showed that when growing rice, it is necessary to take into account the reaction of the varieties to the irrigation regime and the intensity of growth in the initial germination phase. In almost all varieties, flooding with a layer of water led to a decrease in the length of the seedling and the main embryonic root. On average, over a period of 14 days, the growth of the rice seedling under a layer of water was 2.36 cm shorter and the root was 6.72 cm shorter compared to the moistened variant. However, in a number of varieties, the seedlings successfully overcame the water layer, the percentage of such was 80-100 for varieties: Avangrad, Kuban 3, Yakhont and Strombus; more than 50 % for varieties: Victoria, Aral 22, Kauris, Fast and Furious and Leader. In the field, a high rate of increase in stem length per day over the entire growing season was observed in tall varieties: Kuban 3, Avangard, Marzhan and Strombus (0.89-1.01 cm/day). It was recorded that the lowest seed germination rate in a 10 cm layer of water was observed in the Marzhan, Flagman, Polus-5, and Junior varieties.