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Rhizobacteria closely related to two recently described species of pseudomonads, Pseudomonas brassicacearum and Pseudomonas thivervalensis, were isolated from two geographically distinct wheat field soils in South Australia. Isolation was undertaken by either selective plating or immunotrapping utilizing a polyclonal antibody raised against P. brassicacearum. A subset of 42 isolates were characterized by amplified 16S ribosomal DNA restriction analysis (ARDRA), BIOLOG analysis, and gas chromatography-fatty acid methyl ester (GC-FAME) analysis and separated into closely related phenetic groups. More than 75% of isolates tested by ARDRA were found to have >95% similarity to either Pseudomonas corrugata or P. brassicacearum-P. thivervalensis type strains, and all isolates had >90% similarity to either type strain. BIOLOG and GC-FAME clustering showed a >70% match to ARDRA profiles. Strains representing different ARDRA groups were tested in two soil types for biological control activity against the soilborne plant pathogen Gaeumannomyces graminis var. tritici, the causative agent of take-all of wheat and barley. Three isolates out of 11 significantly reduced takeall-induced root lesions on wheat plants grown in a red-brown earth soil. Only one strain, K208, was consistent in reducing disease symptoms in both the acidic red-brown earth and a calcareous sandy loam. Results from this study indicate that P. brassicacearum and P. thivervalensis are present in Australian soils and that a level of genetic diversity exists within these two novel species but that this diversity does not appear to be related to geographic distribution. The result of the glasshouse pot trial suggests that some isolates of these species may have potential as biological control agents for plant disease.

The release of effective inocula for new perennial clovers into cropping zones where subterranean clover is important might compromise N2 fixation by this valuable annual clover if symbiosis between the new inoculants and subterranean clover is not optimal. To assist our understanding of the interactions between clovers and their microsymbionts, rhizobial strains and clovers from South and equatorial Africa, North and South America, and the Euro–Mediterranean regions were tested. Glasshouse-based studies of the cross-inoculation characteristics of 38 strains of Rhizobium leguminosarum bv. trifolii associated with 38 genotypes of annual and perennial Trifolium spp. from these world centres of diversity were undertaken. Less than 7.5% of the perennial clover symbioses were effective whereas 40% of associations were effective for many of the annual clover species of Euro–Mediterranean origin. There was substantial specificity within the African clovers for effective nodulation. Rhizobial strains from the South American perennial T. polymorphum or from the African clovers were unable to nodulate subterranean clover effectively. Also, 7 of the 17 strains from these regions were unable to form nodules with the less promiscuous Mediterranean annual clovers, T. glanduliferum and T. isthmocarpum. Fifty-three of about 400 cross-inoculation treatments examined, which included annual and perennial clovers, were incapable of forming nodules, while only 65 formed effective nodules. There are 2 barriers to effective nodulation: a ‘geographic’ barrier representing the broad centres of clover diversity, across which few host-strain combinations were effective; and, within each region, a significant ‘phenological’ barrier between annual and perennial species. Clovers and their rhizobia from within the Euro–Mediterranean region of diversity were more able to cross the phenological barrier than genotypes from the other regions. It appears that only the relatively promiscuous clovers, whether annual or perennial, have been commercialised to date. The data indicate that, for perennial clovers, it will be a substantial challenge to develop inocula that do not adversely affect N2 fixation by subterranean clover and other annual clovers available commercially, especially if the perennial clovers were originally from Africa or America. Some future strategies for development of inoculants for clovers are proposed.

The phosphate solubilizing fungi Penicillium radicum, Penicillium bilaiae (strain RS7B-SD1), and an unidentified Penicillium sp. designated strain KC6-W2 were tested for their ability to increase the growth and phosphorus (P) nutrition of wheat, medic, and lentil in three soils of neutral to alkaline pH reaction. The strongest plant growth promoting (PGP) strain was Penicillium sp. KC6-W2, which stimulated significant increases in shoot growth and dry mass in seven of the nine experiments conducted. Levels of PGP by Penicillium sp. KC6-W2 ranged from 6.6% to 19% and were associated with increased uptake of P to the shoot. The PGP properties of Penicillium sp. KC6-W2 were evident on each of the three different plant species and soil types, a level of reliability not observed in other strains tested. Inoculation of seed with P. radicum increased lentil growth by 5.5% (P < 0.05) in soil from Tarlee but did not affect plant growth in the eight other experiments. Inoculation of plant seed with P. bilaiae RS7B-SD1 resulted in significant PGP in two of the nine experiments conducted. However, when significant, stimulation of PGP by P. bilaiae RS7B-SD1 was strong and resulted in increases in medic dry matter (19%) and lentil shoot dry matter (15%). A soil microcosm experiment investigated the effect of Penicillium fungi on cycling of soil P. Penicillium bilaiae RS7B-SD1 was the only fungus to significantly increase HCO3-extractable P (23% increase; P < 0.05). Production of phosphatase enzymes was not associated with increased HCO3-extractable P. Addition of carbon in the form of ryegrass seed significantly increased microbial respiration and movement of P to the microbial biomass (P < 0.05), but these parameters were irrespective of Penicillium treatment. This work has established the potential for use of Penicillium inoculants to increase plant growth on alkaline soils in Australia. The role of Penicillium fungi in plant P uptake and soil P cycling requires further exploration.

Rhizoctonia solani AG-8 is a major wheat root pathogen; however, soils can become suppressive to the expression of disease under intensive cropping with retention of crop residues. This is in part due to the action of soil microorganisms. A step-wise approach was used to determine which microorganisms contributed to suppression of R. solani induced disease in a disease-suppressive soil. Using wheat-soil-pathogen bioassays it was determined that the interaction between 3 phylogenetically diverse groups of bacteria, Pantoea agglomerans, Exiguobacterium acetylicum, and Microbacteria (family Microbacteriaceae), was a major contributor to disease suppression. Inoculation of a sterilised soil with the combination of these groups resulted in greatly increased seedling shoot dry weight and reduced infection compared with diseased control plants with no bacterial inoculation, or inoculated with individual types of bacteria. These groups, however, did not reduce levels of pathogen DNA, although inoculation with suppressive soil (at 10% w/w) did reduce pathogen DNA. Root associated P. agglomerans and E. acetylicum promoted the growth of infected wheat plants and soil associated Microbacteria reduced root infection by R. solani.

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Most pathogenic strains of Agrobacterium are able to induce crown gall or hairy root on both the apical surface (facing the root tip) and the basal surface (facing the shoot) of carrot (Daucus carota L.) root discs. Tumorigenic strains carrying mutations in the shoot inhibition region of the T-DNA (TL-DNA genes 1 and 2) are markedly attenuated on the basal surface but remain virulent on the apical surface. Coinoculation of two attenuated tumorigenic strains, with mutations in gene 1 and gene 2, respectively, resulted in restoration of virulence on the basal surface. Wild type hairy root-inducing strains can be divided into two groups: those that are virulent on both apical and basal surfaces and those that are virulent only on the apical surface. a-Naphthalene acetic acid stimulated virulence of hairy root strain TR7, belonging to the latter group, on the basal surface. Attenuated virulence on the basal surface can be explained in terms of an auxin deficiency in the basal tissues and unidirectional auxin transport to the apical surface.Crown gall and hairy root diseases are caused by the soil bacteria Agrobacterium tumefaciens, A. rhizogenes, and A. rubi and affect many dicotyledonous plants. Tumor-inducing (Ti') and root-inducing (Ri) bacterial plasmids are the infectious agents (30,31). The nomenclature of Holmes and Roberts (10) is used in this paper. In this system, biotypes 1, 2, and 3 of Keane et al. (14) and Kerrfand Panagopoulos (15) are given the specific epithets A. tumefaciens, A. rhizogenes, and A. rubi, respectively, regardless ofwhether the plasmids cause crown gall or hairy root. To distinguish between the two diseases, strains are referred to as containing Ti or Ri plasmids.Wounding of the plant tissues is required for transformation by the bacteria. During plant cell transformation, part of the plasmid, the T-DNA, is inserted into plant nuclear DNA (4, 5). Expression of this T-DNA results in tumor or hairy root formation and also in the synthesis of opines, compounds found specifically in transformed tissue. Several genes in the TL-DNA (the left component of octopine T-DNA) which are common to both octopine and nopaline T-DNA code for tumor morphology functions (3). TL-DNA genes 1 and 2 have been implicated in the control of the auxin balance of transformed tissue (1,3,22). The normal function of these genes has been termed shoot inhibition, as mutations in these genes cause shoot formation on tobacco tumors (17). A cytokinin-like function has been ascribed to an adjacent root inhibition gene which, when mutated, gives ' Abbreviations: Ti, tumor-inducing; Ri, root-inducing; pTi, tumorinducing plasmid; pRi, root-inducing plasmid; NAA, a-naphthalene acetic acid.rise to root formation (16,22).The object of the work was to study the crown gall and hairy root transformation process. Differences in virulence properties between wild type strains and strains with mutations in the T-DNA tumor morphology region led to the identification of T-DNA functions differentially affecting virulence on ...