Four strains of sugarcane mosaic virus infecting cereals and other grasses in Australia

Abstract

Viruses of the sugar-cane mosaic virus (SCMV)-type were isolated from 23 naturally infected species of Gramineae in Queensland, New South Wales, or the Northern Territory. The virus isolates were placed in four groups or strains on the basis of host reactions. Each strain was named after an important perennial host, viz. (1) Johnson grass (Sorgltum halepense), (2) sugar-cane (Saccharum officinaruin), (3) sabi grass (Urochloa mosambicensis), and (4) Queensland blue couch grass (Digitaria didactyla). The strains could be distinguished on the basis of mosaic or necrotic reactions in Yates NK220Y and Atlas sorghums, on abi!ity to cause systemic infection of Johnson grass or sugar-cane, or local infection of French bean (Phaseolus vulgaris cv. Bountiful). This ability of the sabi grass strain to infect a dicotyledonous host is previously unreported for any strain of SCMV . All four virus strains had a normal particle length of 736¦17 nm, but the variability in particle length was greater for the sugar-cane and Queensland blue couch grass strains than for the other two. The Johnson grass strain was only distantly serologicaliy related to the sugar-cane, sabi grass, and Queensland blue couch strains, but the latter three were very closely related amongst themselves. Five aphid species, Aphis craccivora, A. gossypii, Macrosiphum euphorbiae, Rhopalosiphum maidis, and R. padi mere shown to transmit at least one strain of SCMV. A. craccicora and R. maidis were each able to transit all four strains. The Johnson grass strain of SCMV is the major strain infecting maize and sorghum crops in Australia. It was probably the cause of the maize ringspot mottle disease first observed in 1948 and of the mosaic and necrotic diseases of Sorghum almum first observed in 1960. These early records and its distinctive host reactions and serological properties make it unlikely that it is z recent introduction to Australia.