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.

When sap of asymptomatic or mealybug wilt-affected pineapple plants of the Smooth Cayenne group was negatively stained and examined in an electron microscope, clostero-like virus particles were occasionally seen. However, numerous clostero-like virus particles and occasionally some bacilliform particles were seen in partially purified preparations from both asymptomatic and wilted pineapple leaves. An antiserum, made by injecting partially purified preparations of clostero-like particles into a rabbit, trapped and decorated the clostero-like particles. Using this antiserum, the clostero-like particles (c. 1700 -1900x12 nm) were found in almost all plants tested of Smooth Cayenne selections C10, C13, C30 and F-180, the hybrid cv. 53-116 and a selection of the rough leaf Queen group. The particles were more readily trapped from extracts of roots of hybrid cv. 53-116 and Smooth Cayenne selection C10 than from leaves, crowns and fruits. They were not detected in seedlings of a cross between a Queen selection and the Smooth Cayenne selection C10. The clostero-like particles are similar to those reported to occur in pineapple plants in Hawaii and South Africa. This is the first report of their occurrence in Australia. Trapping and decoration tests of particles in pineapples in quarantine from Brazil, France, Malaysia and Taiwan indicated that a similar clostero-like virus occurs in all these countries. The bacilliform particles measured about 133x33 nm. They were trapped and decorated by the Queensland pineapple virus antiserum and also by an antiserum to sugarcane bacilliform badnavirus. They were detected occasionally in various smooth leaf and rough leaf pineapples in north and south Queensland and northern New South Wales. However, in one commercial planting of Smooth Cayenne selection C10 in south Queensland, bacilliform particles were trapped from 29/47 plants. This is the first report of a small bacilliform virus, probably belonging to the badnavirus group, occurring in pineapple plants. The relationship of the clostero-like and bacilliform viruses to yield loss and mealybug wilt in pineapples is unknown.

Papaya ringspot virus type W (PRV-W) causes foliar mosaic, deformed fruit and reduced yield in crops of Cucurbita maxima cv. Queensland Blue in Queensland. Cucurbita ecuadorensis is highly resistant to PRV-W. Using crosses between these 2 cucurbits we studied inheritance of resistance to PRV-W in mechanically inoculated parental, F1, F2, backcross and inbred backcross populations under glasshouse and/or field conditions. Disease severity was assessed on each plant as the proportion of the young leaf area which was chlorotic. Inheritance of resistance, following inoculation of cotyledons with either of 2 isolates that differed in the severity of symptoms produced, was most consistently described as polygenic. Analysis of means of generations indicated additive gene effects were predominant. However simpler inheritance could not be entirely discarded as a 13:3 digenic model based on epistasis and modifiers described some distributions. No strong associations existed between high resistance to PRV-W and undesirable characteristics so that transfer of high levels of resistance from C. ecuadorensis to commercially acceptable lines of C. maxima should be possible.

The eggplant little-leaf agent was graft transmitted to tomato causing big-bud symptoms. Transmission from the big-bud tomato to potato by grafting or the leafhopper Orosius argentatus resulted in the development of purple top wilt symptoms. Thin-section electron microscopy revealed mycoplasma-like organisms present in the phloem sieve elements of a big-bud tomato plant and purple top wilt potato plants infected by grafting or leafhoppers. When tubers from graft-infected potato plants were planted, 73% produced spindly shoots and 44% of these later developed purple top wilt symptoms. When scions from either field-infected or experimentally infected potato plants showing purple top wilt symptoms were grafted onto tomato plants, 24% and 62% respectively developed big-bud symptoms. The results provide strong evidence for the mycoplasmal aetiology of some, if not all, potato purple top wilt in Queensland.

ELISA tests showed that 40-7670 of the seeds of tomato (Lycopersicon esculenturn cv. Grosse Lisse) contained tobacco streak virus (TSV) when either the female (ovule) parent only, the male (pollen) parent only, or both parents were virus infected. When seeds with either or both parents infected were soaked in distilled water overnight and dissected, TSV was found more frequently in the endosperm (40-90%) than the embryo (10-50%), and little or no TSV was present in the seed coat. The seeds which had an infected female (ovule) parent were lighter in weight and had a lower germination rate (3-27%) than seeds which had either an infected male (pollen) parent or two healthy parents (germination rate of 88-96%). Only about 10% of seedlings which had one or both parents infected were found to be infected. TSV was not transmitted to the leaves of healthy tomato plants when flowers were pollinated with pollen from infected tomato plants.