Symptoms of pistachio bacterial dieback include decline, dieback, internal staining, trunk and limb lesions and, in some instances, tree death. The causal agent is Xanthomonas translucens. The main mode of transmission of the bacteria from tree to tree is through pruning tools. We report here results from experiments aimed to elucidate aspects of the disease cycle. To study the colonisation of woody tissue we inoculated young potted trees and assessed the presence of the bacteria at intervals from the inoculation point over time, and recorded when the vascular tissue became discolored (internal staining). To test the effect of the infection on water uptake we measured the water conductivity of infected and non-infected potted and field trees. Based on the results from these experiments we hypothesised that the infection is localised to the vascular tissue active in the year of infection and that, in consequence, very diseased trees must have had several infection events. Accordingly, we established one field and one glasshouse experiment in which trees are being inoculated repeatedly, and a second field experiment in which trees were pruned severely using disinfested pruning tools and the wounds simultaneously drenched with a bactericide. Results to date are reported.

Xanthomonas bacteria have been found in association with dieback of pistachio trees in Australia. Identification of the bacterial species and/or pathovar and epidemiological studies are in progress.

The onset of the production of nuts in commercial quantities in Australia (1996) coincided with the advent of symptoms of decline, dieback, internal staining, trunk and limb lesions and, in some instances, tree death. This disease has been termed "pistachio dieback". Bacteria of the genus Xanthomonas have been identified as the most probable causal agents of pistachio dieback in Australia. Xanthomonas bacteria were consistently recovered from shoots (1-2 years old) with internal staining. No other plant pathogens have been isolated consistently from diseased tissue. Koch's postulates have been only partially fulfilled, as the complete set of symptoms has not yet been observed on young trees inoculated in the glasshouse.Identification by GC-FAME and Biolog suggested that the species involved is X translucens, although the similarity indices were low. Likewise, 16S IRNA sequencing of one isolate showed it to be X translucens. Whole-genome DNA fingerprinting using AFLP will be applied to identify the bacteria to species and pathovar.Epidemiological studies are in progress to provide a basis for the development of disease management strategies. The pattern of spread of the disease in the orchard is being examined and trees at different stages of the disease have been dissected to trace possible entry point/s of the bacteria and determine the pattern of colouration of the tissue.

of these nematodes, it seems unlikely that they are all indigenous to the island. Some species have almost certainly been introduced in the past, in the absence of any quarantine measures. The widespread occurrence of infected wild Tobacco and Lantana bushes on the outskirts of cultivated land appears to provide a constant source of inoculum for new crops. These observations are in agreement with results obtained by Orton Williams (1), in which he referred to the widespread occurrence of Meloidogyne spp. in the islands of the central and South Pacific regions. Other nematodes, although representing economically important genera, were found in small numbers and did not appear to contribute to any detectable damage. However, some of them such as Xiphinema and Paratrichudors are known as vectors of virus diseases of plants which makes them potentially more important.

Effect of Soil Moisture on Decline of Pinus radiata