Effect of Broad bean mottle bromovirus and its DI-RNAs on productivity and yield components in broad bean

Defective interfering RNA molecules (DI-RNAs) are being studied to get a better understanding about how they are formed and how they can regulate their helper virus replication. However, the effect of defective interfering molecules on yield has not been well established. Preliminary observations in broad beans and peas suggest that Broad bean mottle bromovirus (BBMV) DI-RNAs could affect productivity, exacerbating the yield reduction produced by the virus alone. To quantify the effect of BBMV and its DI-RNAs on components of grain yield and productivity, broad bean plants growing under field conditions in a screenhouse, were inoculated, 3 weeks after sowing, with the transcribed genomic RNA of the virus, plus, depending on the treatment, the small DI-RNA (1900 nt) or the large DI-RNA (2400 nt). Some plants were inoculated only with a DI-RNA-free virion RNA preparation of the helper virus at different phenological stages (19, 38, 52, 66 and 80 d after sowing (DAS)). The plants were harvested 130 d later. The results obtained indicated that the virus had an important effect on productivity, reducing yield between 75% (inoculation 38 DAS) and 36% (inoculation 52 DAS). All the plants inoculated with BBMV produced less grain, statistically different from the treatment without inoculation. Presence of the large and small DI-RNAs reduced grain yield even more than the loss in productivity caused by the virus without DI-RNAs.