Fungi associated with common bean (Phaseolus vulgaris) wilt in Costa Rica

Root rot limits the performance of beans ( Phaseolus vulgaris ), and although they are frequent in Costa Rica, the identity of the fungi associated with them is uncertain. The objective of this research was to molecularly identify the fungi associated with root rot and wilt of beans in the two main producing areas of the country. Between 2017 and 2020, 120 plants were collected in 20 farms in the Huetar Norte and Brunca regions. Experimental lines (IBC 302-29 and ALS 0536-6) and commercial varieties (Brunca, Cabecar, Changuena, Guaymi, Nambi and Tayni) were sampled. The symptoms observed in the field were described and isolates were made on chloramphenicol bengal rose water agar, then pure hypha-tip cultures on water agar, which were transferred to potato dextrose agar to determine morphotypes with the use of taxonomic keys. Isolated fungi were also identified by sequencing the ITS region of ribosomal nuclear DNA. The percentage of relative frequency of morphotypes was calculated. The most frequent were Macrophomina phaseolina (26.7%), Fusarium oxysporum (13.6%) and Athelia rolfsii (5.6%). From the wilt symptoms observed in the field, the fungi commonly described in beans for these pathologies were isolated. It is necessary to perform pathogenicity tests to confirm that they are the cause of the infections.