Nutritional factors modulating plant and fruit susceptibility to pathogens: BARD workshop, Haifa, Israel, February 25–26, 2018

32 p.-3 fig.The molecular dialog between fungal pathogens and their plant hosts is governed by signals from the plant, secreted pathogen effectors and enzymes, and the plant immune system. There is an increasing awareness that nutritional factors are also central to fungal-plant interactions. Nutritional factors include carbon and nitrogen metabolism, local pH and redox state, and manipulation of host metabolism by secreted pathogen effectors. A diverse combination of approaches from genetics, biochemistry and fungal and plant cell biology addresses these questions, and a workshop whose abstracts accompany this note was held in 2018 to bring these together. Questions were asked about how the lifestyles and nutritional strategies of eukaryotic filamentous phytopathogens are related to the metabolic architectures and pathogenic processes affecting both plant hosts and their pathogens. The aim for future work will be to provide metabolism-based strategies for pathogen control.We thank the US-Israel Binational Agricultural Research and Development Fund (BARD) for funding the workshop (number W-104-17).Peer reviewe

Physiological and population genetic analysis of Botrytis field isolates from vineyards in Castilla y León, Spain.

46 páginas, 8 figuras y 8 tablasGrey mould is reported in the vineyards of Castilla y León, in Spain, every year. However, the natural populations of the pathogen have yet to be properly characterized. We surveyed vineyards from six wine producing areas in 2002 and 2007, sampling from symptomatic and symptomless grape bunches. 283 Botrytis field isolates were selected for physiological and genetic analyses. B. cinerea isolates predominated in the population, although isolates belonging to B. pseudocinerea and B. prunorum were also identified. These two species are recorded for the first time in Spain in this work. In addition, two isolates closely related to B. californica were identified. Physiologically, the B. cinerea population is very diverse, displaying a normal distribution of aggressiveness values in Vitis vinifera leaves, suggesting a quantitative nature of this trait. Several isolates unable to cause infection were identified, most of them belonging to a mycelial morphotype. Population genetic analysis revealed that genotypic diversity is high and that multiple infections of the same bunch by different genotypes occur frequently. The high genotypic diversity observed, an even distribution of both mating types, and the linkage disequilibrium values detected support a mixed mode of reproduction with low levels of clonality. The wine producing area in which each isolate was collected imposed a low degree of population differentiation, an effect which does not depend solely on the geographic distances, but rather on the management practices used by growers and wine producer associations.This work was funded by grants SA-02-C2-1 from Instituto Tecnológico Agrario de Castilla y León, Spain, and AGL2012-39876-C02, AGL2015-66131-C2-1-R and AGL2016-76035-C21R from MINECO, Spain. WAM was recipient of a fellowship from MESCYT, República Dominicana. DS was recipient of a fellowship from SENACYT, Ecuador. FA was recipient of a fellowship from Junta de Castilla y León, Spain.Peer reviewe

Novel insights into the early stages of infection by oval conidia of Colletotrichum sublineolum

Anthracnose, caused by Colletotrichum sublineolum Henn. ex Sacc. & Trotter, is one of the most important sorghum [Sorghum bicolor (L.) Moench] diseases in Brazil. This fungus exhibits conidial dimorphism, producing either falcate or oval conidia on solid and liquid media, respectively. We compared patterns of the initial infection events by these two types of conidia on sorghum leaves using light microscopy and scanning electron microscopy. The infection events during the first 24 h were similar for both oval and falcate conidia. Globose and melanized apressoria were formed at 24 h after inoculation (hai) regardless of the conidia type. Dense mycelium and oval conidia developed from germinated falcate conidia at 32 hai. Hyphal mass displaying acervuli filled with falcate conidia and surrounded by setae, developed from germinated oval conidia at 48 hai. Oval conidia were as capable as falcate conidia of infecting sorghum leaves. The inherent ability to grow faster and the easeness with which oval conidia can be produced in vitro as compared to falcate, make the former a preferred choice for studies on the C. sublineolum-sorghum interaction. It would be instructive to further investigate the potential role of the oval conidia in epidemics

Lifestyle transitions in plant pathogenic Colletotrichum fungi deciphered by genome and transcriptome analyses

Colletotrichum species are fungal pathogens that devastate crop plants worldwide. Host infection involves the differentiation of specialized cell types that are associated with penetration, growth inside living host cells (biotrophy) and tissue destruction (necrotrophy). We report here genome and transcriptome analyses of Colletotrichum higginsianum infecting Arabidopsis thaliana and Colletotrichum graminicola infecting maize. Comparative genomics showed that both fungi have large sets of pathogenicity-related genes, but families of genes encoding secreted effectors, pectin-degrading enzymes, secondary metabolism enzymes, transporters and peptidases are expanded in C. higginsianum. Genome-wide expression profiling revealed that these genes are transcribed in successive waves that are linked to pathogenic transitions: effectors and secondary metabolism enzymes are induced before penetration and during biotrophy, whereas most hydrolases and transporters are upregulated later, at the switch to necrotrophy. Our findings show that preinvasion perception of plant-derived signals substantially reprograms fungal gene expression and indicate previously unknown functions for particular fungal cell types