Effect of bean common mosaic virus on seed germination and yield of cowpea ( [L.] Walp.) breeding lines and characterisation of virus strains.

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The study was conducted to characterise bean common mosaic virus strain Blackeye (BCMV-BICM) and determine the likelihood of seed transmission in cowpea breeding lines. F6 cowpea lines obtained from crosses between 'Ife-Brown' and 'IT-95 K-193-12' were planted at five locations in Southwest Nigeria for multilocational evaluation. Virus symptoms were observed on leaves of the breeding lines planted in Ibadan at eight weeks after planting. Enzyme-linked immunosorbent assay (ELISA) was used to determine the presence of six viruses: BCMV-BICM, cowpea aphid-borne mosaic virus, cucumber mosaic virus, cowpea mottle virus, southern bean mosaic virus and cowpea mild mottle virus. Seed transmission tests were carried out to determine virus transmission by seeds while growth and yield components of the cowpea lines were obtained. Reverse transcription polymerase chain reaction, sequencing and phylogenetic analyses were also used to characterise the BCMV-BICM isolates. The observed symptoms, leaf curling and mosaics, were typical of BCMV-BICM infection and ELISA results confirmed the presence of only BCMV-BICM. Line 'L-22-B' had the highest yield of 1653.9 kgha followed by 'L-43-A' (1072 kgha). A non-significant relationship existed between the virus and germination parameters and similarly, the relationship between virus titres and yield parameters was not significant. Sequence analysis of the virus coat protein (CP) gene revealed the presence of three isolates with 96.87-97.47% nucleotide and 98.2-98.65% amino acid similarities and a 99.10-99.55% match with BCMV-BICM CP genes in GenBank. The deduced CP gene sequences showed unique changes at specific sites, while phylogenetic inferences revealed at least two separate origins for the isolates. Seed transmission is evident in all the cowpea breeding lines and 'L-22-B' and 'L-43-A' showed significant tolerance to BCMV-BICM. Thus, it is recommended that seeds from infected fields should not be used for further planting to prevent the introduction of viruses into new areas where their effect could be devastating in susceptible lines.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13337-023-00812-3.