Evaluating the susceptibility of some common bean cultivars to Fusarium solani species complex causing bean root rot in Iran

Legumes are one of the primary protein sources in human and livestock diets worldwide. There are five different types of legumes (i.e., beans, peas, peanuts, lentils, and lupines), with beans as the most important. Fusarium root rot (FRR) is among the most challenging diseases of common beans (Phaseolus vulgaris). While soil-borne diseases are difficult to control, resistant bean cultivars significantly help reduce the losses caused by the disease. This study was conducted in a greenhouse to investigate the susceptibility of different bean cultivars to FRR caused by the F. solani species complex (FSSC).

Several bean fields in Fars, Kohgilouyeh and Boyer-Ahmad, Chaharmahaal and Bakhtiari, Hamdan, Lorestan, Markazi, Qazvin, Zanjan, East Azerbaijan, and Mazandaran provinces were explored during summer from 2017 to 2019. Infected plants were sampled, and the fungi were isolated in the laboratory. Once appeared on the culture medium, the fungal isolates were purified using single-spore isolation or hyphal tip methods. Fungal DNA extraction was performed using Doyle and Doyle’s method for molecular identification of the isolates. A part of the internal transcribed spacer (ITS) region of the ribosomal RNA (rRNA) gene and a translation elongation factor 1-alpha (EF-1α) were amplified from the polymerase chain reaction (PCR). PCR-amplified fragments were sent to the Cardiogenetics Department of Rajaie Cardiovascular, Medical and Research Center (Tehran, Iran) for sequence analysis. After editing, the Basic Local Alignment Search Tool (BLAST) was applied to ITS and EF-1α sequences of the isolates in the GenBank data set in the National Center for Biotechnology Information (NCBI) database. A preliminary pathogenicity test was performed on the Sadri bean cultivar-pathogenicity tests were fulfilled in 400ml plastic pots. An inoculum was prepared by pooling the isolates in a pot experiment utilizing Bilgi et al.’s (2008) method to evaluate bean cultivars. Ten representative isolates of F. solani with the highest pathogenicity were selected from different regions. The cultivar susceptibility was assessed in 3-liter pots as described in the preliminary pathogenicity test. Saleh, Sadri and Koosha chiti (pinto) bean cultivars, Akhtar, Goli and Sayyad red bean cultivars, Dorsa, Shekoofa white bean cultivars, and Valentino and Sanri green bean cultivars were compared based on disease severity and yield correlates (shoot/root fresh and dry weight).

Fusarium isolates from the sampled provinces were identified using authentic scientific sources and Fusarium identification keys based on morphological properties. A Blast search of ITS and EF-1α sequences in GenBank yielded 100% nucleotide identity with the sequences of strains of FSSC. In the preliminary pathogenicity test, leaf yellowing and falling symptoms appeared on the Sadri cultivar in the greenhouse three weeks after inoculation. All FSSC isolates caused root rot on the tested bean cultivar. To evaluate the susceptibility of bean cultivars to the selected isolates, the plants were carefully removed from the 3-liter pots two months after inoculation. The results showed statistically significant differences (p=0.01) among the cultivars. Koosha chiti bean, green Sanri and Valentino cultivars with the lowest root rot severity (19.5%, 22.62% and 23.81%, respectively) and red Goli and Dorsa white bean cultivars with the highest root rot severity (66.67% and 70.24%, respectively) were the least and most susceptible bean cultivars to the pooled FSSC isolates, respectively. The results also indicated relatively significant differences in yield correlates (shoot/root fresh and dry weight) among the cultivars. Besides, the Koosha cultivar was shown to be the most resistant to the disease, followed by Akhtar, Sanri, Valentino and Saleh cultivars. Dorsa white bean and Goli red bean cultivars were demonstrated to be the most susceptible to the disease. This study identified several cultivars with low susceptibility to bean root rot caused by FSSC isolates. A good variation was observed in the spectrum of bean plant responses to the disease. Koosha, Akhtar, Valentino, Sanri and Saleh cultivars with low susceptibility to the selected FSSC isolates may be considered for further studies. Proper soil management with cultivating resistant cultivars is an integral part of any disease management program for FRR.