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<p>Brazil is responsible for approximately 40% of the total soybean produced in the world, earning the country the title of the largest producer and exporter of soybeans. In the 2023/2024 harvest, 46 million hectares were planted, producing approximately 150 million tons. However, Brazilian production faces challenges that can lead to significant productivity losses, such as plant diseases. The main and most devastating disease is Asian soybean rust (ASR), caused by the fungus <i>Phakopsora pachyrhizi</i>, and without efficient management, losses can reach up to 100%. For the control of ASR, fungicides from the chemical groups QoI, SBI, and SDHI are recommended, however, loss of sensitivity to these fungicides has already been identified in some isolates of <i>P. pachyrhizi</i> in Brazil. For this reason, the control of ASR should not consist solely of the use of fungicides but rather be conducted in an integrated and rational manner, with the use of resistant cultivars being the most effective strategy against ASR. Resistance can be expressed by dominant or main recessive genes (vertical), but this resistance may not be durable, due to the limitation of genes to certain isolates. Thus, soybean breeding programs aim to develop plants with partial (horizontal) resistance expressed by minor genes, increasing the longevity of the cultivars. These genes act by regulating biochemical pathways and mechanisms developed to combat biotic stress, as well as creating structural barriers for plant defense. The objective of this study was to evaluate the activity of enzymes (peroxidases – POX and phenylalanine ammonia liase—PAL), formation of horizontal barriers (epicuticular wax and cell wall thickness) and photosynthetic parameters in soybean plants infected with <i>P</i>. <i>pachyrhizi</i> under greenhouse conditions. Six genotypes, with partial resistance to soybean Asian rust (ASR), and one commercial cultivar (Desafio RR 8473 RSF—Susceptible) were tested. The layers of adaxial and abaxial epicuticular wax of the leaflets were analyzed structurally by a scanning electron microscope (SEM) to determine their role in forming physical barriers against ASR. There are differences among genotypes during the progress of ASR severity in two assays. Genotypes 2, 3 and 6 showed signals of partial resistance and obtained the lowest levels of severity and the cultivar Desafio 8473SFR demonstrated higher susceptibility with higher levels of severity. Photosynthetic parameters were impaired by <i>P</i>. <i>pachyhizi</i> infection in the susceptible genotype, but not in its resistant counterpart, because of structural and biochemical constraints derived of partial resistance. Impairments to photosynthesis were proportional to the development of the ASR in the susceptible genotypes. The leaf cell wall was thicker in the resistant genotypes (0.89–0.95&#xa0;µm) compared to the susceptible control (0.35&#xa0;µm). Lignin content was significantly higher in the resistant genotypes before inoculation and the content was equalized four days after inoculation. During 24 to 72&#xa0;h after inoculation the activity of the PAL enzyme was greatly increase in the resistant genotypes. The genotypes that stood out with lower severity values, maintained overall a higher enzyme activity (PAL and POX). This study highlighted the importance of chemical and physical responses that confer partial resistance in soybean plants. They can be considered in soybean breeding programs for the development of plants resistant to ASR. Partial resistance can increase the longevity of cultivars in the field, efficiently reducing the rate of ASR progression and, therefore, reducing fungicide applications.</p>

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The value of chemical and physical barriers against Asian rust in soybean genotypes with partial resistance

  • 期刊论文

  • 发表日期：

    2025年3月19日

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  • Breno Cezar Marinho Juliatti,
  • Ana Cristina Andrade Monteiro,
  • Deila Magna dos Santos Botelho,
  • Felipe Douglas Soares Leal,
  • Mário Lúcio Vilela de Resende,
  • Fernando Cezar Juliatti,
  • Edson Ampélio Pozza

摘要

Brazil is responsible for approximately 40% of the total soybean produced in the world, earning the country the title of the largest producer and exporter of soybeans. In the 2023/2024 harvest, 46 million hectares were planted, producing approximately 150 million tons. However, Brazilian production faces challenges that can lead to significant productivity losses, such as plant diseases. The main and most devastating disease is Asian soybean rust (ASR), caused by the fungus Phakopsora pachyrhizi, and without efficient management, losses can reach up to 100%. For the control of ASR, fungicides from the chemical groups QoI, SBI, and SDHI are recommended, however, loss of sensitivity to these fungicides has already been identified in some isolates of P. pachyrhizi in Brazil. For this reason, the control of ASR should not consist solely of the use of fungicides but rather be conducted in an integrated and rational manner, with the use of resistant cultivars being the most effective strategy against ASR. Resistance can be expressed by dominant or main recessive genes (vertical), but this resistance may not be durable, due to the limitation of genes to certain isolates. Thus, soybean breeding programs aim to develop plants with partial (horizontal) resistance expressed by minor genes, increasing the longevity of the cultivars. These genes act by regulating biochemical pathways and mechanisms developed to combat biotic stress, as well as creating structural barriers for plant defense. The objective of this study was to evaluate the activity of enzymes (peroxidases – POX and phenylalanine ammonia liase—PAL), formation of horizontal barriers (epicuticular wax and cell wall thickness) and photosynthetic parameters in soybean plants infected with P. pachyrhizi under greenhouse conditions. Six genotypes, with partial resistance to soybean Asian rust (ASR), and one commercial cultivar (Desafio RR 8473 RSF—Susceptible) were tested. The layers of adaxial and abaxial epicuticular wax of the leaflets were analyzed structurally by a scanning electron microscope (SEM) to determine their role in forming physical barriers against ASR. There are differences among genotypes during the progress of ASR severity in two assays. Genotypes 2, 3 and 6 showed signals of partial resistance and obtained the lowest levels of severity and the cultivar Desafio 8473SFR demonstrated higher susceptibility with higher levels of severity. Photosynthetic parameters were impaired by P. pachyhizi infection in the susceptible genotype, but not in its resistant counterpart, because of structural and biochemical constraints derived of partial resistance. Impairments to photosynthesis were proportional to the development of the ASR in the susceptible genotypes. The leaf cell wall was thicker in the resistant genotypes (0.89–0.95 µm) compared to the susceptible control (0.35 µm). Lignin content was significantly higher in the resistant genotypes before inoculation and the content was equalized four days after inoculation. During 24 to 72 h after inoculation the activity of the PAL enzyme was greatly increase in the resistant genotypes. The genotypes that stood out with lower severity values, maintained overall a higher enzyme activity (PAL and POX). This study highlighted the importance of chemical and physical responses that confer partial resistance in soybean plants. They can be considered in soybean breeding programs for the development of plants resistant to ASR. Partial resistance can increase the longevity of cultivars in the field, efficiently reducing the rate of ASR progression and, therefore, reducing fungicide applications.