Effect of Fortification with Biostimulants on Seed Germination Indices and Seedling Growth Parameters of Rhubarb (Rheum ribes)

Cultivation of rhubarb (Rheum ribes) plant is increasing rapidly all over the world. The need to cultivate these plants according to the nutritional value is fully felt. The most important issue for the production of agricultural plants is the choosing appropriate method to propagate them. Germination is one of the critical stages in the growth cycle of plants. Germination plays a major role in determining the final growth and density of the plant. Low and irregular germination is one of the main problems of reproduction of many medicinal plants. Considering that biological stimuli can improve seed germination and minimize soil pollution, they are environmentally friendly and suitable for producing of organic crops. The aim of the current study was to investigate the influence of seed priming with some biostimulants such as humic acid and extract of bean and chickpea sprout on germination indices and seedling growth parameters of rhubarb plant        

An experiment was carried out based on completely randomized design with three replications to investigate the influence of seed priming with some biostimulants such as humic acid and extract of black-eyed bean and chickpea sprout on germination indices (germination percentage, germination speed, seed vigour and allometric coefficient) and seedling growth parameters (length, and dry and fresh weight of plumule and radicle) of rhubarb plant. Black-eyed bean and chickpea sprouts were separately milled in a fresh state and their powder was mixed with distilled water twice in a 50 to 50 weight ratio, and then mixed. The prepared sprout extracts were considered as 100% mother extract and different concentrations (10%, 20% and 30%) of experimental extract were prepared from mother extract. Humic acid was prepared at three different concentrations including 1, 5 and 10 g L-1, and distilled water was also used as control treatment. After soaking the seeds in prepared biostimulants for 24 h, they were sown in the plastic pots. The number of germinated seeds was counted every three days until the end of the period (50 d). At the end of the experiment, the length, and dry and fresh weight of plumule and radicle were measured.

The results showed that the effect of all three treatments on germination indices of rhubarb seeds was significant. There was significant difference between humic acid 10 g L-1 and bean extract 10% with the control in terms of seed germination percentage. Also, there was a significant difference between chickpea extract 10% and the control in terms of allometric coefficient. Bean extract 30% increased the length of plumule, but on the other hand, this trait decreased in seeds treated with chickpea 10% comparing to control. In terms of radicle length, there was significant difference between humic acid 5 and 10 g L-1 with the control. Application of humic acid 5 and 10 g L-1 increased the radicle length. Using chickpea sprout extract 10% caused a 28% decrease in the germination rate, and using chickpea sprout extract 20% caused 22% decrease in this trait. Priming with bean extract 10% caused 10 and 21% decrease in plumule length and germination speed, and the other treatments of bean and chickpea extracts did not have a significant effect on germination indices. Seed priming with humic acid at a concentration of 10 g L-1 increased the germination rate by 8% and germination speed by 12.5%. Studies have shown that treatment with humic acid can positively affect cellular metabolism, photosynthetic rate, amino acids biosynthesis rate and phyto-hormones content leading to improving growth rate and qualitative and quantitative characteristics of crops.

According to the results of the current study, humic acid 10 g L-1 was the best treatment to improve germination indices and growth parameters of rhubarb plant. Therefore, it could be used as a priming solution for better and faster germination of rhubarb seeds. Also, the use of humic acid both in sustainable agriculture and healthy crop production is cost effective. Using this treatment could be introduced as efficient technique to reduce the use of chemical fertilizers and reduce environmental pollution. Also, the results demonstrated that priming with bean and chickpea extracts could not significantly affect the most important germination indices and growth parameters of rhubarb plant.