The effects of maize dwarf mosaic virus (MDMV) infection, variety, temperature, and light on the ultrastructure and red pigment expression of sorghum bicolor (L.) moench

Abstract

Five varieties of grain sorghum (AKS614, Tx414, Tx412, B378, and Tx09) were selected for growth-room studies of the red-leaf phenomenon. Plants were inoculated with MDMV-A and after virus symptoms appeared, the temperature was lowered to 13 C during the day and 20 C at night. Two days later, AKS 614 (infected) and B378 (infected and control) plants turned very red. Control AKS614 plants shoved very little red coloration. The tolerant varieties, Tx414 and Tx09 (infected and control) plants, showed slight marginal red color. Tx412 (infected and control) plants did not turn red. Further studies showed that constant low temperatures also caused the production of red pigment. Lower temperatures (13 C) caused the production of more red color than did higher temperatures (23 C). Treatment at 28 C produced no red leaf color. Studies of the effect of light duration on pigment production revealed that light must be received by the plants for pigment production. Cold-treated plants (healthy and infected) in the dark produced no red pigment. Lower temperatures also caused necrosis in AKS614 and B378. The necrotic response seemed to be greater in infected plants than in healthy plants. Electron microscope studies of plants infected with MDMV-A revealed the presence of "pinwheel" and "bundle-type" inclusions. Very few individual rods were observed. Cells of susceptible varieties contained more of the inclusions than did cells of tolerant varieties. The inclusions were found exclusively in the cytoplasm..