Phenolic compounds of sorghum [Sorghum bicolor (L.) Moench] and their allelopathic effect

Abstract

Purpose. To establish the quantitative composition of phytochemicals containing in vegetative and generative organs of sugar sorghum hybrids with high and medium sugar content ‘Sugargraze ARG’ (Argentina), ‘Sioux’ and ‘Mohawk’ (USA) and ‘Ananas’ and ‘Medovyi’ (Ukraine) and their allelopathic effect
 Methods. Allelopathic, physiological-biochemical, agrochemical and statistical methods were used. The content of phytochemicals in the vegetative and generative organs of the studied sugar sorghum hybrids was determined by the extraction method.
 Results. A high concentration of sorghum phenolic substances in the seeds at the mature plant stage was found. However, their concentration was species specific and depended on their quantitative component in the process of morphogenesis of vegetative and generative organs of sorghum of different genetic origin. The analysis of the total content of phytochemical compounds in the studied hybrids showed an increase in their number at the end of the vegetation season. The research was conducted in vitro. The manifestation of phenolic compounds was observed through manifestation of the allelopathic effect of cultivated sorghum plants. It was found that on the 7th day of cultivation, the plants actively secreted phenolic compounds; the increase in the number of leaves and the height of plants in hybrids did not change and amounted to 3–5 and 1.6–2.0 cm, respectively. On the 14th day of the experiment, the phenolic spots grew significantly, and yellowing of the lower leaves appeared. In the process of morphogenesis of sorghum plants (during 21 days), a more intense release of phenolic compounds led to suppression and slowing down of growth and subsequently to the death of the clone, regardless of the genetic origin of the hybrids. Phenolic compositions also influenced the formation of the root system of cultivated sorghum plants. A significant decrease in the number of lateral roots and the length of the root system was noted in all studied hybrids.
 Conclusions. The highest content of phenolic compounds was found in the seeds (grain) and stems of the studied sorghum hybrids. Thus, the quantitative composition of glycosides and tannins was 34–39 and 5.5–6.9 %, respectively, in the seeds and 25–29 and 0.3–1.4 %, respectively, in the stems of the studied hybrids. The highest content of hydroxycinnamic acids (from 7 % to 14 %) was found in the leaves of the studied sorghum hybrids. Phenolic compositions under in vitro conditions cause stress, which slows down the growth and development of cultivated plants, and subsequently lead to the death of clones.