We studied the behaviour of tomato mosaic tobamovirus (ToMV) in a recirculating nutrient solution. Particles of tomato mosaic virus were found in the nutrient solution 3 days after leaf inoculation of plants and we demonstrated that the level could increase to a concentration readily detectable by electron microscopy. Virions remained infective in nutrient solution for at least 6 months, could infect bait plants and induced systemic symptoms within 10 days. This is the first report of measurement of infective virions in recirculating nutrient solutions. Hydroponic producers should be aware of the potential for rapid spread of virus diseases in soilless growing systems as one infected plant can serve as a source of inoculum that can ultimately result in an epidemic.

SUMMARYA tobamovirus infection of Capsicum annuum is recorded for the first time in New South Wales, Australia. The causal virus is described and shown to differ from tobacco (TMV) and tomato (ToMV) mosaic viruses in its host reactions and serology.Seventeen capsicum cultivars were tested for reaction to the Australian isolate and ranked according to symptom severity. Field and glasshouse observations indicated that the virus causes a decrease in height and weight of plants, fruit malformation and leaf mosaic symptoms.It is proposed that the capsicum tobamovirus strains are sufficiently distinctive from TMV and ToMV to be grouped together and designated a separate virus: capsicum mosaic virus (CaMV).

Virus disease limit glasshouse production of capsicums in the Supraysia District of New South Wales. Symptoms develop on plants about 4 weeks after planting; and up to 83° of plants are infected. The major virus is cucumber mosaic (CMV) with some pepper mild niottle (PMMV) also present. Evidence is presented to show that the primary source of intection of both viruses is most likely to be debris from previous crops remaining in the soil. It demonstrates a previously unconsi‐dered mechanism tor survival and spread of labile viruses such as CMV and the ecological ecological consequence of these results are considerable.

Two isolates of maize dwarf mosaic virus originating from maize (MDMV(M)) and Johnson grass (MDMV(J)) were distantly related to an Australian and a Californian strain of sugar-cane mosaic virus (SMV). MDMV(M) was shown to be distantly related serologically to a Californian strain but not to an Ohio strain of MDMV; MDMV(J) was not shown to be related serologically to either the Californian or the Ohio strain of MDMV. MDMV(M), MDMV(J), and the Australian SMV produced similar symptoms on sweet corn (Zea mays var. saccharata (Sturtev)), which under glasshouse conditions included an initial necrotic phase not previously described for MDMV. The three isolates showed different characteristics when purified from sweet corn by an identical procedure. The yields of MDMV(M) and MDMV(J) were higher than that of SMV, and these two isolates produced strong zones in density gradients whereas SMV produced a very weak zone. The normal length of MDMV(M) was 773 ± 6.35 mµ and that of MDMV(J) 778 ± 6.35 mµ and the particles of both were uniform. By contrast the particles of SMV were very uneven in length; the most common length was 650–750 mµ, but many longer and shorter particles were observed.

Although lettuce mosaic virus (LMV) has been studied from many points of view, as summarized by Tomlinson (1970), there has been no published record of the effects of this virus on the fine structure of its host's cells. Edwardson (1966) noted that LMV induced cytoplasmic inclusions in host cells but did not record any effects on organelles. This communication reports the effects of LMV on fine structure of mesophyll cells of C. quinoa. Materials and MethodsGlasshouse-grown seedlings of O. quinoa were mechanically inoculated on the three lower leaves with sap from lettuce (Lactuca 8ativa L.) seedlings infected with LMV. After 8-9 days the inocula.ted leaves developed yellow local lesions and 17 days after inoculation the younger leaves of the new growth had developed areas of yellow tissue (systemic symptoms). Uninoculated plants were grown under the same conditions as the inoculated plants, as controls.Seventeen days after inoculation samples were taken from the centres of local lesions, from green tissue on the same leaves, from the centres of yellow systemically infected tissue, from the centres of green areas on systemically infected leaves, and from comparable leaves on the control plants.Tissue pieces were fixed in 3% glutaraldehyde, post-fixed in 2% OS04, both in phosphate buffer. Samples were then stained for 1 hr in 2% uranyl acetate in water, dehydrated in a graded ethanol series, and embedded in Durcupan ACM. Sections were cut with glass knives, stained for 8-9 min in lead citrate (Reynolds 1963), and examined in a Philips EM 300 electron microscope at 60 kV. Observations were made on three blocks from each tissue type.