Evaluating the Reaction of different Species of Beans to Macrophomina phaseolina, Rhizoctonia solani and Fusarium solani In Vitro

 Every year, soli-borne pathogens of beans cause a lot of damage to this crop. Caudex and root rot of beans caused by Macrophomina phaseolina, Rhizoctonia solani, and Fusarium solani are among the most common diseases of this plant. Cultivating resistant species and maintaining shifting cultivation are among the most effective methods of controlling this disease Disease caused by Rhizoctonia solani include seedling death and in some cases cause rot of aerial parts. Macrophomina phaseolina is a plant-borne pathogen that has a wide range of hosts and causes extensive damage to farmers around the world each year. This fungus is a polyphage and causes disease in more than 500 different plant species such as soybeans, peas, pines, kiwis, cotton and sesame, peanuts, cotton, sunflower, melon. Fusarium solani f.sp. phaseoli Burk, is a fungus isolated from peas and red beans, it is present in most soils and causes disease on legumes and plants that grow in hot and humid conditions.

 A factorial experiment in the form of Completely Randomized Design is conducted in order to evaluate the resistance level of beans species to these fungi. The factors consisted of species (five levels, containing Sadri, Shazand, Saleh, Dorsa, and Goli species) and fungi species (8 levels: each of three fungi alone, combined with each other, and a control sample without any fungus). The reaction of beans species was by calculating the severity of disease and evaluating dry and fresh weight of aerial organs and root and height of the bushes. Steps to perform the test: 1- Preparation of seedbed for planting and sowing seeds of bean cultivars 2- Planting seeds and start growing seedlings 3- Inoculation of seedlings 4- Determining the severity of the disease 5- Measuring the height of aerial parts of seedling.

 Plants are equipped with several defense mechanisms to resist the attack of various pathogens. These include pre-existing structural or biochemical defenses that prevent pathogens from invading, or a series of induced structural and biochemical defenses after an attack. In natural ecosystems, most of the existing pathogenic models are the result of long-term evolution of both the host and the pathogen, and there is usually a high genetic diversity between plants and microbial populations. Today, with the widespread cultivation of cultivars with a uniform genetic background, it has led to the increasing development of susceptible strains of pathogens and the occurrence of widespread epidemics of plant diseases. Therefore, there is a great need to produce lasting resistance to pathogens in plants. Rhizoctonia solani, Macrophomina phasolina and Fusarium solani are fungi with widespread global damage to crops. Therefore, strategies to reduce the quantitative and qualitative damage of these fungi should be studied. In this study, it was observed that beans infected with Macrophomina phasolina, the first symptoms after about four weeks, were yellowing of leaves, wilting of the plant and discoloration of root vascular tissue to reddish-black brown. Also, plants infected with Fusarium solani and Rhizoctonia solani turned the root skin brown. With the spread of disease-causing fungi, necrosis of the crown and roots of tissues was observed. In this case, the color of the vessels changed and turned yellow to brown. Restriction of root development, slow growth of plant shoots, symptoms of leaf yellowing and paleness similar to the symptoms of nutrient deficiency and wilting and leaf fall were the obvious symptoms of these diseases. The results of this study showed that Sadri and Darsa cultivars had relative resistance to all three fungi alone, but Sadri cultivar also showed relative resistance to binary combinations of fungi. But none of the cultivars used were resistant to all three fungi. The experimented species reacted differently to the pathogenic fungi. The maximum and minimum severity of the disease was observed in Goli and Sadri species respectively. The maximum height of seedling was observed in Sadri and Shazand species infected with R. solani and M. phaseolina pathogenic fungi and the combination of these two fungi with Shazand. The maximum dry and fresh weight of aerial organs and roots of infected seedlings was observed in Sadri species infected with F. solani fungus.

The research results indicated that Sadri species, with minimum severity of disease and maximum height and fresh and dry weight of aerial organs and root, was the most resistant species to all three fungi solely and combined.