Document Type : Research Article
Authors
Department of Biotechnology and Plant Breeding, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran
Abstract
Introduction
Soil salinity is a major abiotic stress limiting agricultural productivity worldwide, threatening food security particularly in arid and semi-arid regions where irrigation practices and poor drainage exacerbate salt accumulation in the root zone. It is estimated that over 800 million hectares of land are affected by salinity, a figure that continues to rise due to climate change and unsustainable farming practices. High salt concentrations in the soil disrupt plant water uptake, induce ionic toxicity, and cause oxidative damage, ultimately reducing crop yields. Breeding crops for increased tolerance to abiotic stresses is very difficult due to the complexity of inheritance of traits related to tolerance to these stresses, which often involve multiple genes with minor effects and strong interactions with environmental conditions. Consequently, conventional breeding programs have made limited progress in developing salt-tolerant crop varieties. In recent years, non-breeding or non-transgenic approaches such as the use of symbiotic microorganisms in plants have been considered, which has led to increased tolerance to abiotic stresses and achieved promising results. These beneficial microbes can alleviate stress effects through various mechanisms, including phytohormone production, nutrient solubilization, and induction of host defense responses.
Plants have distinct microbial communities in their different organs, including roots, stems, leaves, and seeds, collectively referred to as the plant microbiome. There is a lot of evidence about the role of the microbiome in growth, development, response to biotic and abiotic stresses, and increased adaptation to the environment. In particular, endophytic microorganisms, those that reside within plant tissues, have gained attention as natural partners that can enhance host resilience. Halophytes, plants naturally adapted to high-salinity environments, harbor unique microbial communities that have co-evolved with their hosts under extreme conditions. These halophyte-associated microbes have shown remarkable ability to confer stress tolerance to conventional crops, but the mechanisms remain poorly understood, limiting their practical application. This study investigated the potential of Penicillium chrysogenum, an endophytic fungus isolated from seeds of the halophyte Bassia scoparia, to improve salinity tolerance in maize (Zea mays L.), a globally important cereal crop sensitive to salt stress. Our research aimed to (1) characterize the salt tolerance of P. chrysogenum under in vitro conditions, (2) evaluate its effects on maize growth under salt stress, and (3) analyze physiological responses in inoculated plants, including ion content and photosynthetic performance.
Materials and Methods
The fungal strain was isolated from surface-sterilized B. scoparia seeds collected from saline regions in Iran. Surface sterilization was performed using ethanol and sodium hypochlorite to ensure that only endophytic microorganisms were recovered. Molecular identification was performed using ITS sequencing of the ribosomal DNA region, and the sequence was compared against public databases to confirm taxonomic affiliation. The salinity tolerance of the fungus was evaluated on potato dextrose agar (PDA) medium containing NaCl concentrations ranging from 0 to 4 M, with radial growth measured daily. Maize seeds (cv. Hido) were surface-sterilized and inoculated with a fungal spore suspension (10⁶ spores/mL) or sterile water for controls. Seeds were grown under controlled conditions with three salinity levels (0, 30, and 60 mM NaCl) in a growth chamber. Subsequently, greenhouse tests were conducted under two treatments of 150 mM NaCl and normal irrigation to evaluate performance under more realistic stress levels. Drought tests were also conducted on plants in the greenhouse by withholding irrigation for defined periods. Growth parameters including germination rate, root length, shoot length, and fresh and dry biomass were recorded. Ion content (Na⁺, K⁺) was determined using flame photometry, and photosynthetic parameters such as chlorophyll content and net photosynthetic rate were measured using a portable photosynthesis system. Experiments included laboratory, growth chamber, and greenhouse trials with five replicates per treatment arranged in a completely randomized design. Data were analyzed using analysis of variance (ANOVA) followed by Tukey's honestly significant difference test (p < 0.05) for mean comparisons.
Results and Discussion
In this study, an endophytic fungus, identified by ITS sequencing as Penicillium chrysogenum, was isolated from the seed microbiome of the halophyte B. scoparia. This fungus exhibited optimal growth at 1 M NaCl, with substantial mycelial development even at 2 M, indicating strong halotolerance superior to many soil saprophytes. Although it did not significantly affect seed germination percentage or rate, fungal inoculation improved early seedling growth traits and biomass under both saline and normal conditions, suggesting that the primary benefits occur after emergence. Greenhouse experiments confirmed its positive effects on shoot and root development under salt stress, while no beneficial effects were observed under drought conditions, indicating a stress-specific mechanism rather than a general growth promotion effect.
Interestingly, photosynthetic performance and Na⁺/K⁺ ratios remained unchanged in inoculated plants compared to non-inoculated controls, suggesting that the fungus may enhance salt tolerance through mechanisms such as salt detoxification via osmotic adjustment, enhancement of antioxidant enzyme activity, or production of fungal metabolites that protect cellular structures, rather than altering ion uptake or transport. Given the fungus’s native origin from a halophyte host and its potential role in stress adaptation, P. chrysogenum represents a promising candidate for developing biological solutions to improve crop resilience in saline environments. Further field trials and molecular studies are recommended to optimize its application, including dose-response experiments and transcriptomic analysis of host plant responses.
Conclusion
This study demonstrated that Penicillium chrysogenum, an endophytic fungus isolated from the halophyte Bassia scoparia, can promote maize growth under salt stress. Despite no significant effect on germination rate, fungal inoculation improved seedling establishment and biomass production in both normal and saline conditions. The fungus showed strong halotolerance and may enhance salt stress resilience through mechanisms unrelated to ion uptake or photosynthetic changes, potentially involving detoxification pathways or antioxidant activity. Given its native origin and efficacy under saline conditions, P. chrysogenum holds potential as a bio-inoculant for improving crop performance in salt-affected soils. Further field trials and molecular studies are recommended to better understand and harness its functional mechanisms for agricultural application.
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