During a survey for broad bean viruses in Sohag Governorate, a virus was identified as Broad bean stain virus (BBSV), a member of the genus Comovirus, based on host reactions, symptomatology, electron microscopy and serologically by double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA) technique. The virus was mechanically transmitted to some members of Leguminosae and also through seeds. The ultraviolet absorption spectrum of the purified virus showed a typical curve of nucleoprotein with an A260/280 ratio of about 1.25–1.34. The yield of purified virus was 0.61–0.63 mg/kg infected tissue. Electron microscopy of purified preparations revealed the presence of isometric virus particles, 27 nm in diameter. The polyclonal antibodies against BBSV were produced and the antiserum titre of three bleedings was determined by indirect DAS-ELISA technique. Gross reduction of nodulation was achieved by virus inoculation on broad bean plants cv. Giza 402. It produced smaller, fewer nodules and reduced its leghaemoglobin content. As well as seed yield quality and quantity was strongly affected due to infection. When cells of root nodules in BBSV-infected broad bean plants were investigated by transmission electron microscopy, a decrease of number, volume of bacteroids in nodule cells and the space between the bacteroid and its membrane envelope (ME) were observed when compared with healthy cells. This difference was accompanied with the presence of BBSV particles in the root nodule cells. Seeds taken from these plants were tested for the presence of the virus by DAS-ELISA and symptoms development on the seedlings produced. There was a good correlation between ELISA detection of BBSV in tissue taken from single broad bean seeds and subsequent development of infected plants grown from the same seeds. The ELISA detected BBSV in the cotyledons and developing axis of the embryo, but not in seed coat tissues. When mixtures of infected and healthy seeds in different ratios were tested, BBSV was detected in mixtures up to 1:100 (infected: healthy). The ELISA technique is reliable for selecting BBSV-free stocks of broad bean seeds. |
