Millet mycoses development processes under global climate change: measures to protect grain quality from mycotoxins

Author: Sholpan Sakenkyzy

ABSTRACT

This article examines the transformation of the phytosanitary situation in millet (Panicum miliaceum L.) agrocenoses, a grain crop with important nutritional value, under conditions of global climate change. Based on an analysis of recent international scientific data, the impact of rising temperatures and drought on the development dynamics of the main fungal diseases of millet—black rot (Sporisorium destruens), stripe bark rot (Rhizoctonia solani), and fusarium fungi—is systematized.

This article identifies the role of climate stress in increasing the toxicogenic activity of phytopathogenic micromycetes and, consequently, the risk of millet grain contamination with hazardous mycotoxins (aflatoxins, zearalenone, and deoxynivalenol). A comparative analysis of the effectiveness of an integrated plant protection system (IPS) is presented, combining modern agronomic, chemical, and biological (biocontrol) measures used in global agriculture to maintain grain quality and toxicological safety.

The importance of molecular genetic screening of millet mycobiota at the regional level and the development of biological products to stabilize phytosanitary conditions in the country is substantiated.

Keywords: millet, global climate change, agrocenosis, phytopathogenic micromycetes, mycoses, mycotoxins, integrated protection, biological control (biocontrol).

INTRODUCTION

Global climate change is one of the most serious challenges facing modern agriculture and global food security. Extreme temperature increases, unpredictable precipitation patterns, and soil aridity are reducing crop yields. In this context, the strategic importance of millet (Panicum miliaceum L.), a highly drought- and heat-tolerant, water-saving crop, is increasing worldwide.

Millet is a key component of sustainable agriculture, characterized by a short growing season and the ability to produce stable yields in extreme climatic conditions. However, the transformation of agroclimatic conditions has radically altered not only the plant habitat but also the population structure of micromycetes (fungi) in their agrocenoses.

Global warming has led to a shift in the ranges of phytopathogens, changes in their life cycles, and the transition of previously economically insignificant diseases to an aggressive phase [1]. In recent years, millet agrocenoses have seen an increase in the spread and severity of fungal diseases, such as black sooty mold (Sporisorium destruens), stripe bark rot (Rhizoctonia solani), and Fusarium wilt (Fusarium spp.) [2].

The spread of mycoses is not limited to yield losses; one of the most dangerous consequences is the accumulation of mycotoxins (aflatoxins, zearalenone, and deoxynivalenol), which are secondary fungal metabolites, in grain. Climate stress, particularly drought during plant maturation, is the primary trigger, increasing the toxicogenic activity of phytopathogens (e.g., Aspergillus and Fusarium genera) [3].

These toxins not only reduce grain quality but also pose a significant threat to human and animal health, which, in turn, creates significant barriers to international exports.

To address these issues, global science is moving away from the excessive use of chemical fungicides and toward modern integrated protection systems and biological control methods. The suppression of phytopathogen development using beneficial endophytic microorganisms and rhizospheric bacteria (PGPR) is being actively studied [7].

The aim of this study is to analyze the development and spread of major mycoses in millet agrocenoses in the context of global climate change, based on international scientific data, as well as to summarize and systematize modern agronomic, chemical, and biotechnological strategies for protecting the quality and safety of millet grain from mycotoxin contamination.

GLOBAL CLIMATE CHANGE AND THE TRANSFORMATION OF MYCOSES INTO MILE AGROSENOSES

1. The Impact of Climate Factors on the Biology of Phytopathogenic Microfungi

Global climate transformation is characterized by increasing atmospheric CO₂ concentrations, rising average temperatures, and unstable precipitation patterns. These changes have disrupted the balance in the plant-pathogen system (plant-pathogen interactions) and led to changes in the ecological habitats of phytopathogenic microfungi [1].

Increasing temperatures and prolonged periods of drought subject plants to physiological stress, weakening their natural immunity (the production of phytoalexins and protective proteins). At the same time, the number of generations (alternation of generations) of thermophilic fungi increases during the growing season due to spore germination and growth and a shortened incubation period. Conversely, sudden heavy rains at the end of the growing season sharply increase air humidity, creating favorable conditions for the massive dissemination of spores by airborne and droplet transport (epiphytoty) [2].

Furthermore, data from international mycological monitoring has revealed a trend toward the migration (range shift) of southern pathogens, previously considered non-specific to cold and temperate regions, toward northern latitudes.

2. Major mycoses in millet agrocenoses and current trends in their development

Globally, the following transformation is occurring in the development patterns of the main fungal diseases that cause significant damage to the yield and grain quality of millet:

• Black rot of millet (Sporisorium destruens / Sphacelotheca destruens)

This is the most destructive disease of millet. The infection persists on the surface of seeds or in the soil as spores (chlamydospores). A sharp rise in temperature in spring slows millet seed germination, making this a favorable time for the pathogen Sinus to penetrate the plant shoots. Dry weather accelerates the maturation of black mold spores, allowing them to spread widely to healthy plants during harvest [4].

• Striped rot of leaf sheaths (Rhizoctonia solani)

This pathogen damages the stems and leaf sheaths of millet, causing lodging of the plant and incomplete grain maturation. Rhizoctonia solani is a soil-dwelling fungus highly resistant to high temperatures (+28°C and above). Summer heat and high soil temperatures increase the aggressiveness of this pathogen, leading to premature rotting of millet stems and yield losses of up to 30-40% [5].

• Fusarium and Alternaria spp. (Fusarium spp., Alternaria spp.)

This fungal complex damages the root system, stems, and, most importantly, the panicle and grain of millet (smut). If high temperatures and subsequent high humidity occur during flowering and grain set, the development of Fusarium and Alternaria smut increases exponentially. These micromycetes not only destroy the outer shell of the grain but also penetrate the endosperm, completely destroying the germination of the grain [6].

RISK OF MILLET GRAIN CONTAMINATION WITH MYCOTOXINS (QUALITY AND SAFETY)

1. Toxigenicity of phytopathogenic microfungi and major mycotoxins

The spread of phytopathogenic microfungi in millet agrocenoses is not limited to a reduction in production volumes but also leads to a decline in the quality and sanitary and hygienic properties of the product. In the field and during post-harvest storage, fungi release secondary metabolites—mycotoxins (fungal poisons)—as part of their vital activity [9]. Mycotoxins are heat-stable, chemically stable, low-molecular compounds; therefore, they are not destroyed even during industrial grain processing (grinding, cooking), but remain in the final product.

The main groups of mycotoxins common in millet grains and particularly dangerous to humans and animals include:

1. Aflatoxins (B1, B2, G1, G2): They are primarily synthesized by the fungi Aspergillus flavus and Aspergillus parasiticus. They have strong hepatotoxic and carcinogenic effects, causing severe liver damage.

2. Zearalenone (ZEA): This mycotoxin is produced by the micromycetes Fusarium oxysporum and Fusarium graminearum. It has estrogenic activity and causes reproductive system disorders in animals (especially pigs and cattle).

3. Deoxynivalenol (DON / Vomitoxin): Produced by pathogens of the genus Fusarium. It disrupts the digestive system, weakens the immune system, and causes animals to refuse food.

2. The Role of Climate Stress in Accelerating Mycotoxin Synthesis

International studies over the past five years have shown that global climate change (high temperatures and water shortages) greatly increases the toxin-producing properties of fungi [3]. This process occurs through a dual mechanism:

Global Warming / Drought

1. Weakening of plant immunity — Easier pathogen penetration into grain

2. Genetic stress in the fungus — Activation of toxin-producing genes (stress signal)

First, prolonged drought stresses the millet plant, causing the outer grain shell to thin. This allows phytopathogens to easily penetrate the grain endosperm. Second, unfavorable environmental factors (e.g., heat above 30°C and critical soil moisture deficits) also cause genetic stress in the fungus itself.

In such cases, the fungi actively express a group of genes responsible for mycotoxin synthesis (e.g., the AflR gene, which produces aflatoxin) as a defense mechanism [1]. As a result, millet grains grown in arid regions may appear intact, but the amount of latent mycotoxins in them can be several times higher than the permissible concentration. This situation requires enhanced phytosanitary and toxicological monitoring in arid steppe regions.

MODERN MEASURES FOR PROTECTING GRAIN QUALITY FROM MYCOTOXINS (GLOBAL EXPERIENCE)

Under climate change, protecting millet crops from phytopathogens using only one method (e.g., chemical pesticides) is ineffective. Current global practice requires the use of an integrated protection system (IPS) covering all stages, from sowing to storage [8].

1. Agronomic and Breeding Measures

Agronomic methods are aimed at eliminating primary sources of infection and increasing plant resistance to climatic stress.

Planting millet after legumes and green manure crops, rather than after other grains that are often affected by Fusarium or Rhizoctonia pathogens, significantly reduces the pool of fungal spores in the soil.

The introduction of modern millet varieties that are drought-resistant and prevent fungal spores from penetrating plant tissue (e.g., with closed flowers and thick seed coats) can reduce mycotoxin accumulation by up to 50%.

2. Chemical Control (Chemical Fungicides)

In the context of global warming, the use of new-generation fungicides is of great importance for disease prevention [8].

Pre-sowing seed treatment with systemic fungicides (e.g., fludioxonil, tebuconazole, or triazoles) is the most effective way to prevent black rot of millet (Sporisorium destruens) and early root rot.

During millet flowering and tillering (a critical phase when pathogens attack the grain), the use of a combination of strobilurins and triazoles suppresses the development of Fusarium and Aspergillus and blocks mycotoxin formation.

3. Biological protection and biocontrol

International studies have shown that the use of environmentally friendly biological agents is promising [7].

4. Post-harvest technologies

Most mycotoxins actively form after grain harvesting in improperly dried warehouses [9]. Therefore, after millet harvesting, quickly reducing its moisture content to a critical level (12-13%) completely inhibits the metabolism of Aspergillus and Fusarium fungi. Maintaining warehouse temperatures below 15°C and using automatic ventilation systems prevent the development of "self-heating" processes and mold in enclosed spaces.

CONCLUSION

In the context of global climate change and the associated increase in phytosanitary risks, ensuring stable productivity and safety of millet (Panicum miliaceum L.) crops is one of the strategic tasks facing modern agricultural science. As a result of a comprehensive analysis of foreign scientific research, the following main conclusions were made:

1. Transformation of the pathogenic complex: Global warming and extreme drought processes increase the biological activity of micromycetes in millet agrocenoses. Increased temperature and fluctuations in the humidity regime reduce the incubation period for the development of dangerous mycoses such as black soot (Sporisorium destruens), striped bark rot (Rhizoctonia solani), and fusarium, and increase their ability to survive epiphytically.

2. Toxicological safety issue: It has been proven that environmental climatic stresses (especially drought) are the main factors that provoke the massive accumulation of secondary metabolites of phytopathogenic fungi — mycotoxins (aflatoxins, zearalenone, deoxynivalenol) — in grain. This situation not only reduces the nutritional and feed quality of the product but also poses a hidden toxicological threat to human and animal health.

3. The priority of complex protection: In conditions of climate change, treating millet with chemical fungicides alone does not give a positive result. As world best practice shows, the most effective results are achieved by integrated systems (IPM), which combine agrotechnical measures (crop rotation), breeding achievements (resistant varieties), new-generation systemic fungicides, and innovative biological control agents (rhizobacteria and endophytes). Immediate drying of grain after harvest to 12-13% moisture content is a decisive step in inhibiting the growth of toxins in storage.

Future research directions: Based on the results obtained, it is necessary to deepen the work on screening the mycobiota of local millet varieties at the molecular-genetic level and developing domestic biological preparations that inhibit the expression of virulence genes of phytopathogens, taking into account specific regional (including West Kazakhstan and Aktobe regions) climatic features.

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