Effect of seed biopriming techniques on moisture stress tolerance of sandal (Santalum album L.)

Abstract

Seed priming is a smart, innovative, and effective option for enhancing the germination rate, seed quality, and productive capability of crops. The present study investigated the efficacy of biopriming techniques on the seed germination and seedling growth of Santalum album L. Further, the bioprimed seedlings were evaluated for moisture stress tolerance (drought and flooding tolerance). Five biopriming agents (e.g. Effective microorganisms; Plant growth promoting rhizobacteria (PGPR-I and PGPR-II); Pseudomonas fluorescens and Piriformospora indica) were evaluated in the study. The highest germination percentage was obtained for the seeds subjected to biopriming with Pseudomonas fluorescens for eight days (70.67%), whereas the control seeds had only 28.67% germination. PGPR-I was found to be equally effective in increasing seed germination at higher duration of treatment. Pseudomonas fluorescens and PGPR-I treatment had lower imbibition period to 13 days compared to the control seeds' 24 days. Lowered the mean time of germination (MTG) and increased germination rate index (GRI), germination uniformity and higher speed of germination too were observed with these treatments. Biopriming techniques influenced the seedling growth and biomass production at 90 and 180 days after transplanting (DAT). All the treatments from Pseudomonas fluorescens group effectively enhanced the seedling growth attributes. This was followed by Piriformospora indica and PGPR-I treatments. Among all the priming treatments, Pseudomonas fluorescens for six days was the best treatment for increased biometric growth and biomass in sandal. This was followed by Piriformospora indica treatment for two days. Seed biopriming techniques influenced the seeds' biochemical composition, e.g., carbohydrate, crude fat, electrical conductivity, protein, total soluble sugar and α and β- amylases. Observations during the storage period revealed that seeds deteriorated at 60 and 90 days, with a reported higher electrical conductivity, a decrease in carbohydrate, crude fat content, and protein inactivation. Six-month-old sandal seedlings were exposed to drought and flooding conditions. Leaf samples were used to compare for screening out best performing treatments for moisture stress tolerance, considering physiological and biochemical parameters at three stages. Evaluation was done at three stages: normal stress-free stage, stress (drought or flood) stage, and recovery stage. Multivariate analysis of variance (MANOVA) was performed for each physiological and biochemical parameter at three stages for drought and flood experiment to measure the strength and significance of the relationship between the dependent and independent variables. Piriformospora indica followed by Pseudomonas fluorescens group showed excellent recovery for photosynthetic rate, relative water content, chlorophyll stability index and cell membrane stability index in physiological parameters. Osmotic adjustment (e.g. free amino acids, proline, glycine betaine and total soluble sugar) was found to be significantly higher in seedlings originated from Piriformospora indica and Pseudomonas fluorescens priming suggesting these biotic agents as a potential seed priming agent, in sandal for imparting drought tolerance. Correlation studies suggest that among the sixteen characters (physiological and biochemical) used for the screening study, under drought stress, most of the characters showed a strong negative correlation with canopy air temperature difference (CATD). Under the flood stress, the CATD showed a highly significant negative correlation with net photosynthetic rate (-0.81), stomatal conductance (-0.54) and transpiration rate (-0.79). The study highlights the role of seed biopriming techniques in enhancing abiotic stress (drought and flood) tolerance in sandalwood, a threatened species, due to overexploitation in its natural population. The use of low-cost, environmentally safe seed invigoration techniques, as demonstrated in the present study, will be helpful for nursery growers to ensure better germination and efficient seedling establishment in the field due to the stress tolerance characteristics in this era of environmental unpredictability due to climate change.