Sorghum yellow banding virus

Abstract

Sorghum (Sorghum bicolor L. Moench) cultivars were mechanically inoculated with sorghum yellow banding virus (SYBV) to determine their reaction to the virus. Of the 378 cultivars tested, 129 were susceptible and 249 were resistant to SYBV. Field testing revealed that 14 hybrids were susceptible and four hybrids were resistant to sorghum yellow banding virus. Of the 19 inbreds screened in the field, seven were susceptible to the virus. Twelve were resistant to SYBV. A disease rating scale based on disease severity in the field and different stages of disease development was developed. Virus was viable and infectious after being frozen at -19 C for more than 36 months in sap. Virus was serologically detected in infected plant leaves maintained at room temperature for 34 days. Mixed infections of SYBV and maize dwarf mosaic virus (MDMV) were observed in the field. A pathogenic interaction between SYBV and MDMV was proven. Co-infection by the viruses affected plant height. Sorghum cultivars Hegari, RT x 430 and BT x 378 doubly infected exhibited initial SYBV symptoms 9 days after inoculation with SYBV, while singly-infected plants developed symptoms 11-17 days after inoculation. Plants singly-infected with SYBV developed yellow bands on half leaves, while sorghum leaves infected with maize dwarf mosaic virus developed chlorotic mosaic patterns. Doubly-infected plants developed disease symptoms different from those induced by either virus alone. By day 17 post-inoculation, all doubly-infected plants were dead. High antiserum titers were obtained from sorghum yellow banding virus. Purified virus was obtained as a total of 17.5 mg/100 ml of crude sap. Purified virus concentration was 3.5 mg/ml. Enzyme-linked immunosorbent assay (ELISA) detected purified virus to 7.2 ng/ml. Plant height was effective as a predictor of resistance or susceptibility only in the late stages of plant development. Sorghum yellow banding virus was serologically detected in roots, leaves, green panicles and external part of the stem by gel double diffusion assay (Ouchterlony). SYBV was undetectable in internal pith. No virus was detected in either immature or mature seed. Virus particles were observed in the cell cytoplasm in infected root tissues but not the nucleus with the electron microscope.