Microparticles containing gallic and ellagic acids for the biological control of bacterial diseases of kiwifruit plants

Journal of Plant Diseases and Protection - Over the last decades, kiwifruit cultivation has gained increasing importance all over the world, but some bacterial diseases seriously threaten its...     

A recombinant flagellin fragment,which includes the epitopes flg22 and flgII-28, provides a useful tool to study flagellin-triggered immunity

Plants and animals independently evolved the ability to recognize flagellin (also called FliC), the building block of the bacterial flagellum, as part of their innate immune response. While animals recognize a relatively large region of FliC, most plants recognize one or two short epitopes of FliC: flg22 and flgII-28. However, since most research in plants has focused on flg22 and flgII-28 and not the actual FliC protein, the importance of any FliC region beyond the two epitopes in plant immunity is poorly understood. Here we report cloning, overexpression, and purification of a Pseudomonas syringae FliC fragment from amino acid 1 to 143, which includes both FliC epitopes and the adjacent alpha helices. Exposing Arabidopsis thaliana leaves to FliC_1–143 did not reveal any additional FliC recognition capabilities beyond flg22. However, while the kiwifruit species Actinidia arguta did not respond to either flg22 or flgII-28, treatment of A. arguta leaves with FliC_1–143 triggered a significant reactive oxygen response, indicating recognition. This result suggests that in some plant species, recognition of FliC requires regions of FliC beyond the two well-known epitopes and that FliC_1–143 represents a useful tool in the study of plant immunity.     

Natural antimicrobials in spray-dried microparticles based on cellulose derivatives as potential eco-compatible agrochemicals

Journal of Plant Diseases and Protection - It has been demonstrated that some aromatic substances synthesized by plants serve as plant defense mechanisms. However, natural extracts are difficult to...     

Bacterial canker on kiwifruit in Italy: anatomical changes in the wood and in the primary infection sites

The bacterial canker of kiwifruit caused by Pseudomonas syringae pv. actinidiae is a severe threat to kiwifruit production worldwide. Many aspects of P. syringae pv. actinidiae biology and epidemiology still require in-depth investigation. The infection by and spread of P. syringae pv. actinidiae in xylem and phloem was investigated by carrying out artificial inoculation experiments with histological and dendrochronological analyses of naturally diseased plants in Italy. We found that the bacterium can infect host plants by entering natural openings and lesions. In naturally infected kiwifruit plants, P. syringae pv. actinidiae is present in the lenticels as well as in the dead phloem tissue beneath the lenticels, surrounded by a lesion in the periderm which appears to indicate the importance of lenticels to kiwifruit infection. Biofilm formation was observed outside and inside plants. In cases of advanced stages of P. syringae pv. actinidiae infection, neuroses of the phloem occur, which are followed by cambial dieback and most likely by infection of the xylem. Anatomical changes in wood such as reduced ring width, a drastic reduction in vessel size, and the presence of tyloses were observed within several infected sites. In the field, these changes occur only a year after the first leaf symptoms are observed suggesting a significant time lapse between primary and secondary symptoms. It was possible to study the temporal development of P. syringae pv. actinidiae-induced cambial dieback by applying dendrochronology methods which revealed that cambial dieback occurs only during the growing season.     

Modification of a multiple‐locus variable number tandem repeat analysis (MLVA) for typing isolates of Erwinia amylovora

Erwinia amylovora, the causal agent of fire blight that affects economically important rosaceous plants, is reported among the most important plant pathogenic bacteria. The low genetic diversity within E. amylovora and the lack of simple and high‐resolution genotyping techniques make epidemiology and evolutionary studies challenging for this pathogen. A multiple‐locus variable number tandem repeat analysis (MLVA) based on a set of nine variable number tandem repeat loci was successfully used to type 46 E. amylovora isolates collected from different host plants in 16 countries, mainly Mediterranean. The nine polymorphic loci proved to have high discriminatory power and to increase the resolution of the MLVA. Thirty‐eight haplotypes clustered in seven clonal complexes. The results identified potentially useful genetic markers among the Mediterranean strains, particularly from the Balkan Peninsula and the Eastern Mediterranean countries. Different MLVA types were observed amongst Italian strains only, indicating the possibility of multiple introductions of the disease. MLVA can be used effectively as a fast, cheap, and simple tool to track E. amylovora infection sources, to gain insight into geographic diversity, and to understand the dynamic evolution of the pathogen.     

Use of random amplified polymorphic DNA (RAPD) for detection of genetic variation and proof of the heterothallic mating system in Hypoxylon mediterraneum

The efficiency of RAPD analysis in the evaluation of genetic variability in Hypoxylon mediterraneum has been tested on 49 monoascospore isolates of the fungus from different localities. A large genetic variability was detected within single stromata and among monoascospore isolates in a restricted area. The large variability in restricted populations can be explained by the heterothallic mating system and the life cycle of the fungus and its ecological adaptations. RAPD markers can discriminate monoascospore isolates both in the single stromata and among stromata. The application of RAPD markers for epidemiological studies is discussed.