| Abstrakt: |
Rhizopus species are important pathogens associated with vegetables, fruits and root crops. They are ubiquitous and have been implicated in soft rot disease of sweetpotato roots, which accounts for huge economic losses. However, there is paucity of information on accurate identification of Rhizopus spp. infecting sweetpotato in Nigeria using modern tools. In this study, characterization and pathogenicity of Rhizopus isolates were investigated. Diseased tuber samples were collected during the dry season in 2019 from potato fields in Oyo Sate, Nigeria. Isolation, purification of fungal cultures and pathogenicity of selected, representative isolates were conducted. Morphological identification of Rhizopus isolates was carried out using sporangia fruiting bodies and hyphal structures, while molecular identification and characterization were accomplished through amplification of the internal transcribed spacer (ITS) region of ribosomal DNA. ITS sequences of rDNA 18S, ITS, and 28S D1/D2 of all Rhizopus species were analyzed and compared with standard database for identification to species level. All the 20 isolates were morphologically similar and identified as Rhizopus oryzae and R. stolonifer. Molecular analysis, however, confirmed 16 of the 20 isolates as R. oryzae, two as Aspergillus brasiliensis and the remaining two as Lasiodipodia pseudotheobromae. Phylogenetic analysis distinguished all the 20 isolates into three major clades and intraspecies variation among isolates and reference strains was minimal. All Rhizopus isolates were pathogenic on re-inoculation with lesions identical to field symptoms. This study provides an invaluable information for effective breeding for resistance to soft rot disease in sweetpotato. [ABSTRACT FROM AUTHOR] |
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