Assessing the efficacy of iodine seed priming in enhancing the tolerance of wheat (triticum aestivum L) genotypes to water stress conditions.

Abstract

Worldwide, wheat (Triticum aestivum L.) is a vital cereal crop that provides over 20% of daily protein intake and calories. However, research has predicted that its production will continue to decrease due to climate change which will accelerate environmental stresses such as drought stress. Drought remains a significant environmental factor that negatively impacts wheat growth and development from germination to maturity stages, ultimately affecting yield and seed quality traits. Although iodine application has the potential to stimulate growth and development and enhance responses to tolerate abiotic stresses, there is a lack of knowledge on its effects on agronomic and physiological traits under drought stress conditions. Therefore, this study aimed to evaluate the potential of iodine fertilizer on seed quality, growth, physiological traits, and yield of wheat genotypes under drought-stress conditions. The study was conducted through a series of trials, including laboratory, tunnel, and field trials, which were carried out Controlled Environment Research Unit (CERU) and Ukulinga Research Farm of the University of KwaZulu Natal, Pietermaritzburg. The laboratory experiment focused on determining the optimal iodate dose and its effects on seed quality parameters. The pot trials aimed to investigate the impact of iodine priming on wheat seed quality, yield and physiological traits under drought stress conditions. Finally, the field trial evaluated the efficacy of iodine fertilization on wheat yield and yield parameters under rainfed and irrigated conditions. In a laboratory experiment, a 3 x 5 factorial experiment was conducted in a randomized complete block design (RCBD) and replicated three times. The wheat genotypes (SST806, SST8135 and PAN3111) and five iodine concentration (0, 0.001, 0.01, 0.1 and 0.5 M IO3-) were used as treatment factors. The results revealed that wheat seeds primed with iodate doses higher than 0.01 M (IO3-) did not germinate, rendering concentrations of 0.1 and 0.5 M (IO3-) unsuitable for the experiment. However, the study found that iodate priming significantly (p < 0.05) influenced germination tests, such as germination rate index and meantime germination in wheat genotypes. The final germination percentage was not significantly (p > 0.05) affected by iodate concentration or wheat genotype. The vigour tests showed insignificant (p > 0.05) differences between the interaction genotypes and iodate concentrations, except for the cold test and seedling length. Despite these findings, genotype SST806 had higher seed quality than other genotypes. In the first pot trial, the experiment was laid out using a factorial design arranged in a complete block design (CRD), where irrigation (well-watered (WW) and water deficit (WD)), wheat genotypes (PAN3111, SST806 and SST8135) and iodine concentrations (0, 0.001 and 0.01 M IO3-) were the treatment factors replicated three times. Tolerance growth indices, membrane stability index (MSI), relative water content (RWC) and photosynthetic pigments were determined in the study. The results demonstrated that iodine priming during early stages of growth significantly (p < 0.05) improved plant height stress index (PHSI), root length stress index (RLSI) and dry matter stress index (DMSI) and decreased carotenoids compared to control. Between iodate concentrations, genotypes primed with 0.001

M IO3- performed better than genotypes primed with 0.01 M IO3- . Overall, genotype SST806 had more resistance to drought than other wheat genotypes. The second pot trial evaluated the agronomic and some physiological responses of wheat genotypes using iodine application (seed priming and foliar spraying) under drought stress conditions at different growth stages. The two season trails were conducted using a factorial design where wheat genotypes (SST806 and SST8135), iodine application [seed priming (0.001M) and foliar spraying (0.05% w/v)] of IO3- and water stress levels (water deficit (WD) at tillering, WD at flowering, well-watered (WW) at tillering and WW at flowering) were the treatment factors replicated three times. Data collected included plant height (PH), leaf gas exchange variables, relative water content (RWC) and yield and yield-related traits that were determined during the trial and at harvest. The findings showed that drought stress significantly (p < 0.05) affected all the studied traits, however, the application of iodine through seed priming and foliar applications significantly increased ((rate of photosynthesis (Pn), transpiration rate (Tr), number of tillers (NT), number of spikelets per spike (SPS), number of grains per spike (NGS), 1000 grain weight (TGW) and biological yield (BY)) under water stress and normal conditions in wheat genotypes. Nevertheless, some traits showed not only increases but also significant decreases (p > 0.05) compared to the control. Interestingly, genotype SST806 performed better than genotype SST8135. The two-season field trial was conducted to evaluate the efficacy of iodine fertilization on wheat yield and yield parameters under rainfed and irrigated conditions. The experiment was arranged in a split-split plot design with three replications. Irrigation (well-watered and water deficit) was assigned to main plots, while wheat genotypes (PAN3111, SST806, and SST8135) were assigned to subplots. Iodine concentrations (0, 0.001 and 0.01 M IO3-) were assigned to sub-subplots. Wheat genotype transplanted seedlings were irrigated for one week after planting thereafter irrigation was withdrawn for rainfed plots. Plant height, days to maturity and yield and yield-related parameters were collected during the trial. The results of the study showed that iodate seed priming in wheat genotypes ameliorated the negative effects of drought stress experienced by the genotypes by improving yield traits such as spike length, number of kernels per spike, spikelet per spike, number of productive tillers, and grain yield. Based on the findings, it was concluded that iodine application has a potential to improve wheat growth, development and yield under drought stress conditions and the effective iodate seed priming concentration recommended is 0,001 M IO3

In conclusion, this study demonstrated that iodine fertilization has the potential to enhance the tolerance of wheat genotypes to water stress conditions. The findings provided valuable insights into the use of iodine as a means to improve crop productivity and mitigate the effects of water stress on crop growth and development.