In vitro treatment of tissue cultures of two garlic cultivars with crude culture filtrates from Sclerotium cepivorium was used to select somaclonal variants with enhanced resistance to white rot disease. The crude culture filtrate had a negative effect on callus induction and growth. It also inhibited the differentiation of adventitious buds. The inhibitory effects were greater at higher culture filtrate concentration. With increase in concentration of crude pathogen culture filtrate, rate of callus induction, callus survival, relative growth rate of callus, callus differentiation and number of divided shoots per callus decreased. The inhibitory effect for all the parameters was more visible when crude pathogen culture filtrate was used at 50% concentration or more. However, the performance of disease resistant cultivar Hangzhong Red Skin was better than Gailiang (disease susceptible cultivar) at higher concentrations of crude pathogen culture filtrate. Some somaclonal lines and plantlets (predominantly from Hangzhong Red Skin) that showed resistance to Sclerotium cepivorum were obtained at 50%concentration level of crude pathogen culture filtrate.

WRKY transcription factors play an important role in plant growth, development and immunity. In our study, a WRKY family member gene designated BoWRKY6 was isolated from broccoli (Brassica oleracea var. italica), and its expression was induced by downy mildew (Hyaloperonospora parasitica). Five transgenic broccoli lines over-expressing BoWRKY6 driven by the CaMV 35S promotor were obtained by Agrobacterium tumefaciens mediated transformation, and they demonstrated significant increased resistance to downy mildew, with resistant levels from low to very high. Real time-qualitative PCR analysis indicated that expressions of both BoWRKY6 and the pathogenesis-related gene 1 (BoPR1) in transgenic plants were obviously higher than those in WT plants after H. parasitica treatment. Lines of BWK14 and BWK31 exhibited very high resistance to downy mildew, and may serve as promising candidate materials for broccoli molecular breeding in the near future.

Ethylene-mediated flower abscission caused by Botrytis infection afflicts cut Geraldton waxflower stems. Preharvest spray applications of three known host plant defence elicitors, benzothiadiazole (BTH), methyl jasmonate (MeJA) or silicon (Si), were applied to Geraldton waxflower cvv. Mullering Brook and My Sweet Sixteen. Their individual efficacy in postharvest suppression of Botrytis disease developmentwas assessed. Field applications of BTH or Si generally had no significant (P>0.05) effect on Botrytis disease severity on either cultivar. MeJA sprays did not significantly (P>0.05) reduce disease severity on cv. Mullering Brook, but slightly and significantly (P<0.05) suppressed Botrytis on cv. My Sweet Sixteen at concentrations of 500 and 750 μM MeJA. One Si treatment, 1500 mg SiO₂/L, significantly (P<0.05) reduced floral abscission on cv. Mullering Brook. Overall, field applications of these three host plant defence elicitor chemicals as spray treatments had little effect on vase life, water uptake and relative fresh weight of the cut flower sprigs. Moreover, they did not suppress Botrytis or associated postharvest floral abscission in cut Geraldton waxflower flowers.

The host resistance of walnut (Juglans spp.) against Xanthomonas arboricola pv. juglandis (Xaj) was evaluated for 18 walnut genotypes in 2016 and 2017 at Chengdu, Sichuan, China, using three assays: one under natural conditions (field investigations) and two under controlled conditions (detached leaflet assay and whole plant assay). Field investigations were used as a benchmark for comparing the other two assays. Five genotypes, ‘JS 91’, ‘JS 92’, ‘JS 86’, ‘Qingxiang’ and ‘JS 71’, displayed partial resistance in all assays, suggesting that they may be good candidates for further evaluation. The rankings for resistance among the 18 genotypes showed significant correlations between field investigations and both the detached leaflet assay and whole plant assay. However, low determination coefficients indicated that assays under controlled conditions should be considered as complementary methods and not as a substitute for field analysis when evaluating resistance to walnut blight.

Candidatus Phytoplasma australiense (Ca. P. australiense) is associated with the plant diseases strawberry lethal yellows (SLY), strawberry green petal (SGP), papaya dieback (PDB), Australian grapevine yellows (AGY) and Phormium yellow leaf (PYL; New Zealand). Strawberry lethal yellows disease is also associated with a rickettsia-like-organism (RLO) or infrequently with the tomato big bud (TBB) phytoplasma, the latter being associated with a wide range of plant diseases throughout Australia. In contrast, the RLO has been identified only in association with SLY disease, and Ca. P. australiense has been detected only in a limited number of plant host species. The aim of this study was to identify plant hosts that are possible reservoirs of Ca. P. australiense and the SLY RLO. Thirty-one plant species from south-east Queensland were observed with disease between 2001 and 2003 and, of these, 18 species tested positive using phytoplasma-specific primers. The RLO was detected in diseased Jacksonia scoparia and Modiola caroliniana samples collected at Stanthorpe. The TBB phytoplasma was detected in 16 different plant species and Ca. P. australiense Australian grapevine yellows strain was detected in six species. The TBB phytoplasma was detected in plants collected at Nambour, Stanthorpe, Warwick and Brisbane. Ca. P. australiense was detected in plants collected at Nambour, Stanthorpe, Gatton and Allora. All four phytoplasmas were detected in diseased Gomphocarpus physocarpus plants collected at Toowoomba, Allora, Nambour and Gatton. These results indicated that the vector(s) of Ca. P. australiense are distributed throughout south-east Queensland and the diversity of phytoplasmas detected in G. physocarpus suggests it is a feeding source for phytoplasma insect vectors or it has a broad susceptibility to a range of phytoplasmas.

Chlorotic ringspot symptoms were noted on Cuban royal palms (Roystonea regia) from two locations in south-east Queensland. A virus, provisionally named Roystonea palm virus (RoPV), was isolated from these plants. It was mechanically transmitted to Chenopodium amaranticolor, C. quinoa, Nicotiana benthamiana, N. clevelandii and Vicia faba in which it caused systemic infections and to Cucumis sativus and N. tabacum in which it caused only local lesions. The characteristics of RoPV were consistent with its classification as a potyvirus: i.e. transmission by the aphid Myzus persicae, flexuous rod-shaped particles approx. 740 nm long, positive reaction with the AGDlA potyvirus group monoclonal antibody and the presence of pinwheel inclusions and laminated aggregates in infected plant cells.

Alternaria blotch of apple caused by Alternaria alternata apple pathotype has a severe negative effect on apple production. It can cause tissue necrosis on leaves, young shoots and fruit. Recent studies on this pathogen have mostly focused on phytotoxicity and pathogenicity. There are few reports on the roles of signaling and metabolism in the process of infection. In this paper, a filial generation with substantial differences in resistance between individuals with similar genetic background was used as a host. An aggressive strain of A. alternate, that can complete the infection process 72 h after inoculation, served as the pathogen. A reproducible and reliable in vitro inoculation system for plant growth regulator determination was established to overcome the difficulties of inoculation of attached leaves. Alterations in growth regulator concentrations were detected, including indole-3-acetic acid (IAA), zeatin riboside (ZR), gibberellin A₃ (GA₃), abscissic acid (ABA) and the polyamines, putrescine (Put), spermidine (Spd) and spermine (Spm). Results indicated the plant growth regulators interacted with each other to modulate signaling and metabolic networks. A biotrophic-like phase was inferred to exist before necrosis developed. Gibberellin A₃ and ABA appeared to be involved in the phase transformation from the biotrophic-like stage to the necrotrophic stage. Cytokinin, Put and Spd appeared to be related to disease resistance. This study advances our knowledge of the pathological mechanisms of Alternaria blotch on apple and provides useful resources for development of disease control and prevention.