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<p>The widespread use of chemical fungicides to combat fungal infections in plants poses significant risks to both the environment and human health. This ongoing concern drives the search for eco-friendly fungicide alternatives that can help produce healthier food. In the current study, nineteen <i>Bacillus</i> strains were isolated from the rhizosphere of healthy tomato plants. From these, isolates showing over 60% reduction against <i>Alternaria solani</i> (AS) were chosen for further identification using MALDI-TOF spectroscopy and were evaluated as potential fungicide alternatives to Rizolex. The selected isolates—KA2, KA36, and KA50—were identified as <i>Bacillus megaterium, Bacillus thuringiensis</i>, and <i>Bacillus subtilis</i>, respectively. The most promising isolates, acting as prospective alternative fungicides, were chosen based on their <i>in vitro</i> antifungal efficacy against common tomato phytopathogens and based also on their plant growth-promoting characteristics. Among them, <i>Bacillus thuringiensis</i> (Bt) KA36 demonstrated the most significant antifungal activity against a range of tested tomato pathogenic fungi, including <i>Aspergillus niger, Fusarium oxysporum, Botrytis cinerea, Rhizoctonia solani, Alternaria solani</i>, and <i>Podosphaera xanthii</i>, with inhibition zones ranging from 35 to 61&#xa0;mm. Further investigation involved applying <i>B. thuringiensis</i> KA36 as a foliar spray on both healthy and AS-infected tomato plants at four concentrations (50, 100, 150, and 200&#xa0;mg/L). The results clearly showed that KA36 was the most effective isolate in alleviating AS disease symptoms and enhancing plant’s physicochemical characteristics and yield. Specifically, <i>B. thuringiensis</i> KA36 significantly reduced the disease severity score (DSS) caused by AS in tomatoes by 91.7 %. This reduction was linked to the upregulation of tomatoes’ defense gene expression, including <i>PR1a, PR7, PDF1.2, WRKY,</i> and <i>ef1α</i>. Additionally, KA36 significantly improved fruit weight by 21.54% to 72.31% and total yield by 31.08% to 72.00% compared to the positive control. The use of the KA36 strain also effectively reduced levels of stress indicators, including MDA and proline. Moreover, the foliar application of <i>B. thuringiensis</i> KA36 (50–150&#xa0;mg/L) significantly improved several quality parameters of tomatoes, including pH, total soluble solids (TSS), total sugars (TS), total flavonoids (TF), total phenolic content (TPC), β-carotene, lycopene, and ascorbic acid. Notably, TSS was increased by 8.70% to 23.19%, total sugars by 4.35% to 14.38%, β-carotene by 50% to 250%, lycopene by 26.19% to 64.29%, and ascorbic acid by 5.66% to 37.33% when compared to infected and Rizolex-treated tomatoes. Based on these comprehensive findings, <i>Bt</i> KA36 is strongly endorsed as a promising biocontrol agent for phytopathogenic fungi, offering a safe and effective alternative to chemical fungicides.</p>

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Effects of Bacillus thuringiensis KA36 as an environmentally sustainable fungicide alternative on the morphological, physicochemical, and qualitative attributes of Alternaria solani-infected tomatoes

  • 期刊论文

  • 发表日期：

    2025年8月7日

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  • Eman A. Beyari,
  • Naheda M. Alshammari

摘要

The widespread use of chemical fungicides to combat fungal infections in plants poses significant risks to both the environment and human health. This ongoing concern drives the search for eco-friendly fungicide alternatives that can help produce healthier food. In the current study, nineteen Bacillus strains were isolated from the rhizosphere of healthy tomato plants. From these, isolates showing over 60% reduction against Alternaria solani (AS) were chosen for further identification using MALDI-TOF spectroscopy and were evaluated as potential fungicide alternatives to Rizolex. The selected isolates—KA2, KA36, and KA50—were identified as Bacillus megaterium, Bacillus thuringiensis, and Bacillus subtilis, respectively. The most promising isolates, acting as prospective alternative fungicides, were chosen based on their in vitro antifungal efficacy against common tomato phytopathogens and based also on their plant growth-promoting characteristics. Among them, Bacillus thuringiensis (Bt) KA36 demonstrated the most significant antifungal activity against a range of tested tomato pathogenic fungi, including Aspergillus niger, Fusarium oxysporum, Botrytis cinerea, Rhizoctonia solani, Alternaria solani, and Podosphaera xanthii, with inhibition zones ranging from 35 to 61 mm. Further investigation involved applying B. thuringiensis KA36 as a foliar spray on both healthy and AS-infected tomato plants at four concentrations (50, 100, 150, and 200 mg/L). The results clearly showed that KA36 was the most effective isolate in alleviating AS disease symptoms and enhancing plant’s physicochemical characteristics and yield. Specifically, B. thuringiensis KA36 significantly reduced the disease severity score (DSS) caused by AS in tomatoes by 91.7 %. This reduction was linked to the upregulation of tomatoes’ defense gene expression, including PR1a, PR7, PDF1.2, WRKY, and ef1α. Additionally, KA36 significantly improved fruit weight by 21.54% to 72.31% and total yield by 31.08% to 72.00% compared to the positive control. The use of the KA36 strain also effectively reduced levels of stress indicators, including MDA and proline. Moreover, the foliar application of B. thuringiensis KA36 (50–150 mg/L) significantly improved several quality parameters of tomatoes, including pH, total soluble solids (TSS), total sugars (TS), total flavonoids (TF), total phenolic content (TPC), β-carotene, lycopene, and ascorbic acid. Notably, TSS was increased by 8.70% to 23.19%, total sugars by 4.35% to 14.38%, β-carotene by 50% to 250%, lycopene by 26.19% to 64.29%, and ascorbic acid by 5.66% to 37.33% when compared to infected and Rizolex-treated tomatoes. Based on these comprehensive findings, Bt KA36 is strongly endorsed as a promising biocontrol agent for phytopathogenic fungi, offering a safe and effective alternative to chemical fungicides.