Bio-inoculant formulations for enhanced seedling emergence and pasture growth

Soil-borne damping-off diseases are a major constraint limiting pasture seedling emergence and yield. Large scale laboratory and glasshouse screening of beneficial micro-organisms against several host/pathogen systems was conducted to identify efficient bio-control and growthpromoting microbes. This was followed by field-testing of the best microbes and their formulations for efficient application techniques. The research identified a number of fungal (Trichoderma spp.) and bacterial (Paenibacillus spp.) isolates which suppressed damping-off diseases and promoted plant growth of various pasture species. Preliminary field-trials with granule and seed-coat formulations confirmed the glasshouse results. Intensive research trials with a mix of four T. atroviride isolates, providing growth promotion and disease control activity, led to the development of a prototype pasture seed additive product. Keywords: damping-off diseases, Paenibacillus spp., seed-coating, Trichoderma spp.

Perennial legumes for the high rainfall zone of eastern Australia. 1. Evaluation in single rows and selection of Caucasian clover (Trifolium ambiguum M. Bieb.)

A range of perennial legume species, including Trifolium ambiguum, T medium, Astragalus cicer, Coronilla varia, Lotus corniculatus, L. pedunculatus, and Lespedeza cuneata, were evaluated in glasshouse and field trials in 1989-92 at Armidale, New South Wales. Hexaploid germplasm of T. ambiguum was subjected to selection for increased seedling vigour, early biomass production and profuse flowering in glasshouse screening and spaced plant field nurseries. On an acid, solodic soil, T. ambiguum and T. medium grew modestly, Lotus spp. grew vigorously initially, but died out within 3 years, A. cicer and C. varia failed to persist beyond 1 year, but isolated plants of Lespedeza cuneata thrived. On an acid, freedraining, red-basalt soil, all accessions grew vigorously until early 1991. During the succeeding drought, Lotus sp. died out, A. cicer thinned out on the acid soil, but T. ambiguum, T medium, and C. varia remained persistent and productive. A large nursery of A. cicer accessions on the same soil limed to 5 t/ha before planting remained vigorous to the present. Superior hexaploid material of T ambiguum selected from spaced plants, originated chiefly from CPI 43909 and the ARS-2678 germplasm collection from Utah, USA.

Adaptability and virulence specificity in Australian strains of blackleg [Leptosphaeria maculans (Desm.) Ces. et De Not.] on different host genotypes of rapeseed (Brassica napus L.)

Five clone-lines of rapeseed (Brassica napus L.) were artificially inoculated with 24 isolates of blackleg (Leptosphaeria maculans (Desm.) Ces. et De Not.) from 12 sites around Australia to determine the proportion of virulence genes in L. maculans which interacted with genes for specific resistance in B. napus. Resistance/susceptibility was evaluated both as external lesion size (%G) and internal lesion area (%II) of individual plants of the clone-lines. Using two different regression techniques (stability analysis) involving levels of infection caused by the isolates on the clone-lines, isolates were ranked according to levels of specific virulence. There were differences in stability between isolates in their capacity to exhibit consistent virulence over the range of genotypes used. Using deviations from regression as an indicator of the proportion of genes for specific- and non-specific virulence, it was observed that a third of all isolates used possessed significant levels of specific virulence. The significance of this finding in relation to glasshouse screening programs for blackleg resistance is discussed.

Effect of Kabatiella caulivora isolates and host growth stage on symptom expression and resistance in Trifolium subterraneum

Occasional severe clover scorch disease outbreaks from Kabatiella caulivora have occurred in the 2 partially resistant Trifolium subterraneum cultivars, Karridale and Meteora. All K. caulivora isolates screened, including isolates taken from severely damaged field swards of Karridale and Meteora, were highly pathogenic, but there was variation in the pathogenicity of some isolates and there was a significant cultivar x isolate interaction in 1 of 2 studies. Plant age affected development of disease. Cultivars Karridale, Mt Barker and Woogenellup were least susceptible when inoculated 10 weeks from sowing, and there was a strong plant age x cultivar interaction. However, there was no suggestion that severe disease in Karridale was due to increased susceptibility at a particular plant growth stage. In resistance screening studies, the resistance rankings of subterranean clover varieties sometimes changed markedly depending upon the test isolate, and in 1 of 2 studies, there was a significant cultivar x isolate interaction. While there was significant overall correlation between glasshouse and field data, this only accounted for 49.9 and 20.5%, respectively, of the variation. Glasshouse screening was not suitable for replacing field screening but it was useful for confirming the field resistance of some highly resistant genotypes.

Effect of Host Genotype on Incubation Period, Receptivity, Lesion Diameter, and Leaf Area Damage of Didymella arachidicola on Peanut1

The effect of host genotype on incubation period, receptivity, lesion diameter and leaf area damage of Didymella arachidicola on nine peanut (Arachis hypogaea L.) genotypes was investigated under monocyclic infection in the glasshouse. The genotypes, Florunner. P 84/5/256, C 347/5/6, C 346/5/8 and P 105/3/7, resistant to the pathogen in field trials, had a longer incubation period, reduced receptivity, lesion diameter, and percentage leaf area damage, than susceptible genotypes. Among the susceptible genotypes, Tamnut 74 had the shortest incubation period, and highest receptivity, the largest lesion diameter, and percentage leaf area damage. The other susceptible genotypes. Egret, 38/7/20, and P 84/5/112, were intermediate for these variables. Production of pycnidia and pseudothecia of the pathogen could not be demonstrated in infected leaf tissues of any of the genotypes studied. There was significant interaction between plant age and disease development. Younger plants had a shorter incubation period, higher receptivity, larger lesion diameter, and percentage leaf area damage than older plants. Correlation coefficients among incubation period, receptivity, lesion diameter, and leaf area damage were highly significant. The possible role of these variables in disease epidemics and their use in glasshouse screening of peanut germplasm for resistance to D. arachidicola are discussed.