Field-based plant bioassays were employed to assess the potential for pre-and post-emergence loss of seedlings and for root damage affecting Trifolium subterraneum L. (subterranean clover) during autumn-winter at 17 pasture sites across a broad agricultural area of temperate southern Australia. Between 9 and 93% (median 21%) of T. subterranean seedlings failed to emerge at the 14 locations where soil moisture was considered adequate for germination. Post-emergence losses were lower (range 0-32%; median 7%). Moderate damage (lateral roots) to severe damage (taproots) was recorded on surviving test plants at all of the sites. Sublethal damage to pasture roots constitutes a potentially large, but underestimated cost to production because it was so widespread and because the damage occurs during autumn-winter when pasture yield limits stocking rate. Potential for the loss of Lolium rigidum · multiflorum (annual ryegrass) seedlings was also demonstrated at some of the sites. DNA assays for common root rot disease pathogens (Pythium irregulare, Phytopthora clandestina and Rhizoctonia) were used for the first time to construct cost-effective profiles of fungal and oomycete pathogens at each site. These assays may be useful for indicating disease risks and guiding plant cultivar selection and appropriate use of pesticides. DNA assays for arbuscular mycorrhizal fungi were also used and have the potential to provide novel insights into the soil biology of farming systems.

Almond anthracnose was reported for the first time in Australia in 1998 and has since been observed in all of the major almond-growing regions. The organism causing anthracnose was confirmed as Colletotrichum acutatum using taxon-specific polymerase chain reaction (PCR). Three main morphotypes of C. acutatum from almond in Australia were identified (namely, pink, orange, and cream colony color) and the optimum temperature for mycelial growth of representative isolates was 25 degrees C. Australian isolates of C. acutatum were more similar morphologically to the pink subpopulation of C. acutatum from California than to the gray Californian subpopulation and the isolates of Colletotrichum from Israel. Inter-simple-sequence-repeat (ISSR) PCR analysis revealed that the majority of Australian isolates shared an identical banding pattern whereas Australian isolates of C. acutatum from almond were distinct from isolates of the pink and gray subpopulations of C. acutatum from almond in California and of Colletotrichum spp. from almond in Israel. Sequence analysis of the internally transcribed spacer (ITS1-2) ribosomal DNA region of representative isolates differed from the results of ISSR-PCR in that polymorphisms were revealed among isolates, indicating that some genetic variation may be present. Pathogenicity experiments on detached leaves and fruit revealed pathogenic variation among representative isolates of C. acutatum from almond in Australia, California, and Israel; however, all isolates tested caused disease. Distinct subgroups among Australian isolates of C. acutatum from almond were not supported on the basis of morphology, mycelial growth rates, ISSR-PCR, and pathogenicity.

BACKGROUND: Botrytis bunch rot, caused by Botrytis cinerea, is an economically important disease of grapes in Australia and across grape-growing regions worldwide. Control of this disease relies on canopy management and the application of fungicides. Fungicide application can lead to the selection of resistant B. cinerea populations, which has an adverse effect on the management of the disease. Characterizing the distribution and severity of resistant B. cinerea populations is needed to inform resistance management strategies.RESULTS: In this study, 724 isolates were sampled from 76 Australian vineyards during 2013-2016 and were screened against seven fungicides with different modes of action (MOAs). The resistance frequencies for azoxystrobin, boscalid, fenhexamid, fludioxonil, iprodione, pyrimethanil and tebuconazole were 5%, 2.8%, 2.1%, 6.2%, 11.6%, 7.7% and 2.9%, respectively. Nearly half of the resistant isolates (43.8%) were resistant to more than one of the fungicides tested. The frequency of vineyards with at least one isolate simultaneously resistant to one, two, three, four or five fungicides was 19.7%, 7.9%, 6.6%, 10.5% and 2.6%. Resistance was associated with previously published genotypes in CytB (G143A), SdhB (H272R/Y), Erg27 (F412S), Mrr1 (D354Y), Bos1 (I365S, N373S + Q369P, I365S + D757N) and Pos5 (V273I, P319A, L412F/V). Novel genotypes were also described in Mrr1 (S611N, D616G), Pos5 (V273L) and Cyp51 (P347S). Expression analysis was used to characterize fludioxonil-resistant isolates exhibiting overexpression (6.3-9.6-fold) of the ABC transporter gene AtrB (MDR1 phenotype).CONCLUSION: Resistance frequencies were lower when compared to most previously published surveys of B. cinerea resistance in grape and other crops. Nevertheless, continued monitoring of critical MOAs used in Australian vineyards is recommended.

Thirty-seven South Australian native plant species from 11 families, including 15 threatened species in the state (of which six are listed as threatened under the federal Environment Protection and Biodiversity Conservation Act 1999) were assessed for response to infection by Phytophthora cinnamomi. Seedlings, 3-6 months old and grown in a greenhouse, were inoculated by placing infested pine wood plugs in the potting mix, maintained in moist conditions and assessed for mortality and disease symptoms for between 3 and 10 months. Thirty species were found to be susceptible, of which nine were highly susceptible, 15 moderately susceptible and six slightly susceptible. Three species were found to be resistant and results for four species were inconclusive. Six of the 15 threatened, rare or locally endangered species tested (Eucalyptus viminalis var. viminalis, Correa aemula, C. calycina, Olearia pannosa ssp. pannosa, Pomaderris halmaturina ssp. halmaturina and Prostanthera eurybioides) were moderately susceptible, while two (Allocasuarina robusta and Pultenaea graveolens) were highly susceptible. Significant populations of at least five of the threatened species susceptible to the disease are located close to confirmed or suspected Phytophthora-infested areas or growing in areas conducive for P. cinnamomi. An effective management strategy is therefore required to avoid extinction of such species due to infection by the phytophthora dieback pathogen.