Evaluation of the Effect of Bio-Priming and Seed Coating on Seed Germination and Seedling Growth Indices of Chenopodium Quinoa in Cadmium Stress

Cadmium contamination limits biodiversity, the activity of microbes and enzymes in the soil, and threatens human health through the food chain. Seed pretreatment is a common way to improve seed germination under stress conditions such as heavy metal stress, which increases seedling resistance. This study aimed to investigate the effect of bio-priming with Bacillus subtilis and seed coating on seed germination and seedling growth indices of quinoa under cadmium stress.

This study was conducted in laboratory and greenhouse conditions in three separate factorial experiments by two factors in a completely randomized design with 4 replications at laboratory and greenhouse of Yasouj University in 2019. In the first experiment, the first factor is bio-priming with Bacillus subtilis bacteria in two levels of presence and absence of bacteria and the second factor is cadmium stress in three levels of zero, 0.3, and 0.6 mM cadmium nitrate, in the second experiment, the first factor is the coating on three levels of seed inoculation with bio-priming treatment, then coating them, mixing bacteria with coating materials, then coating the seeds and coating alone and the second factor is three levels of treatment a combination coating of vermiculite (V), kaolin (K) and perlite (P) including V10K2.5P5, V8K2P4, and V12K3P6. In the third experiment, the first factor is Uncoated ± bio-priming and coated ± bio-priming and the second factor is cadmium stress factor at three levels of 0, 100 and 200 mM was cadmium nitrate.

The results showed that cadmium stress decreased germination indices and this downward trend increased with increasing stress intensity. Seed bio-priming increased the longitudinal index of quinoa seedling vigor and improved seedling growth. Seed coverage somewhat reduced germination indices, but in many cases, the presence of bacteria improved this downward trend and increased the number of quinoa germination indices. Also, increasing cadmium in soil caused a 72% increase in root cadmium content and a decrease in seed rate and germination percentage. Cadmium inhibits water absorption in seeds and reduces the amount of water in seedlings, which affects seed germination. Exposure to cadmium prevents seed germination, seedling growth, etc. The most important disorders caused by cadmium were reduced growth of roots and leaves and damage to DNA, which subsequently disrupted the cell cycle and changed the structure of cell walls and even cell death. Bacillus subtilis activates systemic induction resistance (ISR) in many plant products, thereby increasing disease resistance caused by pathogenic organisms and plant growth. This bacterium acts as a PGPR and protects the plant against stress.

Consequently, cadmium did not prevent quinoa germination, but its destructive effects were visible in other traits and caused a decrease in seedling length and weight, as well as seedling stem length and weight vigur index. Also, the coating of quinoa seeds caused a decrease in the germination rate, which by increasing the compounds surrounding the seed mixed with bacteria and coating materials, it was able to increase the germination rate by 8% in the combination of V10K2.5P5 and 16% in the combination of V12K3P6 rather than without bacteria treatment.