Effect of humic acid on germination characteristics of Lallemantia royleana and Cyamopsis tetragonoloba under salinity stress

 Lallemantia royleana is an annual herbaceous plant of Lamiaceae family in different parts of Europe, the Middle East, and especially Iran. Cyamopsis tetragonoloba L. is a plant of the legume family. A common feature between these two plants is hydrocolloid gums, which stabilize some food emulsions by absorbing water and increasing the viscosity or forming a gel in the aqueous phase. Due to its diverse and rich vegetation, Iran can produce countless types of plant gums, and many seeds such as Lallemantia royleana and Cyamopsis tetragonoloba contain valuable gums. Considering the important therapeutic and industrial applications of C. tetragonoloba and L. royleanaplants and the need for more information and reports on determining the best humic acid level and salt stress tolerance of these plants, the purpose of this research is to investigate the tolerance of two L.  royleana and C. tetragonoloba plants to salinity stress in the germination stage and the initial stages of the growth of two plants under the humic acid application.

The experiment was carried out as factorial in a completely randomized design with three replications at the seed laboratory of the Faculty of Agriculture of Zabol University in 1400. In this experiment, salinity stress was investigated using sodium chloride at control (no salinity), 70, 140, 210 mM levels and humic acid at (0, 40, 80, and 120 mg/L) levels. Humic acid solution at different salinity levels was added to each petri dish containing 25 seeds.

 The results showed that salinity stress decreased germination percentage, radicle length, plumule length, seedling length and seedling dry weight of C. tetragonoloba. In this plant, the germination percentage decreased by 35.34% compared to the control as the salinity stress level increased to 210 mM, and with the increase of the stress to more than 140 mM, a significant decrease in the germination percentage was observed. The maximum plumule length of L. royleanaplants was obtained in 70 mM salinity treatment and 40 mg/L fertilizer level. The maximum radicle length in the L.  royleanaplants plant was obtained in the treatment of 40 mg/L of humic acid at a 70 mM salinity stress level. Also, the results showed that the maximum radicle length (1.46 cm) in the C.  tetragonoloba plant was related to humic acid pretreatment at 70 and 140 mM salinity and fertilizer levels of 40 and 80 mg/L.

 In general, it can be stated that the germination indices significantly decreased under stress conditions, and this indicates that humic acid is a suitable pretreatment that can improve the growth indices of C. tetragonoloba and L.  royleanaplants under stressed and non-stressed conditions. With the application of humic acid at all salinity levels except 210 mM, the germination indices in the two mentioned plants were in a favorable condition.

1- The salinity stress tolerance threshold was studied in Cyamopsis tetragonoloba and Lallemantia plants.
2- Humic acid fertilizer in this study mitigated the destructive effects of salinity stress in Cyamopsis tetragonoloba and Lallemantia plants.