Genetic distance may underlie virulence differences among isolates of a bacterial plant pathogen

Certain pathogens evolve with their hosts in a stepwise arms race of virulence and resistance, mediated by one or a few genetic loci in their genomes. Other pathogens may retain the ability to colonize hosts through multiple small genetic changes, which do not necessarily occur solely at loci under selective pressure. The bacterial plant pathogen Xylella fastidiosa lacks classic indicators of pathogenicity such as a type III secretion system, which makes the identification of its virulence mechanism challenging. We tested the hypothesis that quantitative differences in virulence between pairs of X. fastidiosa isolates were correlated with their respective genetic distances. Isolates from two different X. fastidiosa subspecies were genetically typed using 20 loci, generating information on the genetic distance among pairs of isolates. Virulence data were obtained by determining the impact of these genotypes on the phenotype of alfalfa plant hosts. Results show significant or marginally significant correlations with respect to differences in infection level and alfalfa stunting, suggesting that genetic distance partially explains plant phenotypic differences in virulence among X. fastidiosa isolates. Furthermore, the data demonstrate substantial amount of phenotypic variation among X. fastidiosa isolates within subspecies fastidiosa and multiplex

Genetic distance may underlie virulence differences among isolates of a bacterial plant pathogen

Certain pathogens evolve with their hosts in a stepwise arms race of virulence and resistance, mediated by one or a few genetic loci in their genomes. Other pathogens may retain the ability to colonize hosts through multiple small genetic changes, which do not necessarily occur solely at loci under selective pressure. The bacterial plant pathogen Xylella fastidiosa lacks classic indicators of pathogenicity such as a type III secretion system, which makes the identification of its virulence mechanism challenging. We tested the hypothesis that quantitative differences in virulence between pairs of X. fastidiosa isolates were correlated with their respective genetic distances. Isolates from two different X. fastidiosa subspecies were genetically typed using 20 loci, generating information on the genetic distance among pairs of isolates. Virulence data were obtained by determining the impact of these genotypes on the phenotype of alfalfa plant hosts. Results show significant or marginally significant correlations with respect to differences in infection level and alfalfa stunting, suggesting that genetic distance partially explains plant phenotypic differences in virulence among X. fastidiosa isolates. Furthermore, the data demonstrate substantial amount of phenotypic variation among X. fastidiosa isolates within subspecies fastidiosa and multiplex

Addressing the new global threat of Xylella fastidiosa

Xylella fastidiosa is one of the most important threats to plant health worldwide. This bacterial pathogen has a long history, causing disease in the Americas on a range of agricultural crops and trees, with severe economic repercussions particularly on grapevine and citrus. In Europe, X. fastidiosa was detected for the first time in 2013 in association with a severe disease affecting olive trees in southern Italy. Subsequent mandatory surveys throughout Europe led to discoveries in France and Spain in various host species and environments. Detection of additional introductions of X. fastidiosa continue to be reported from Europe, for example from northern Italy in late 2018. These events are leading to a sea change in research, monitoring and management efforts as exemplified by the articles in this focus issue. X. fastidiosa is part of complex pathosystems together with hosts and vectors. Although certain X. fastidiosa subspecies and environments have been well studied, particularly those that pertain to established disease in North and South America, this represents only a fraction of the existing genetic, epidemiological, and ecological diversity. This focus issue highlights some of the key challenges that must be overcome to address this new global threat, recent advances in understanding the pathosystem, and steps toward improved disease control. It brings together the broad research themes needed to address the global threat of X. fastidiosa, encompassing topics from host susceptibility and resistance, genome sequencing, detection methods, transmission by vectors, epidemiological drivers, chemical and biological control, to public databases and social sciences. Open communication and collaboration among scientists, stakeholders, and the general public from different parts of the world will pave the path to novel ideas to understand and combat this pathogen

Influência da fase embrionária dos ovos da traça-das-crucíferas sobre fêmeas de Trichogramma pretiosum com diferentes idades Influence of diamondback moth embrionary egg stage on Trichogramma pretiosum females of different ages

Plutella xylostella é considerada a praga mais importante das crucíferas. O método de controle mais utilizado para essa praga é o químico. Contudo, esta espécie de inseto vem desenvolvendo resistência aos inseticidas aplicados. O controle biológico com espécies do gênero Trichogramma é considerado uma alternativa no controle dessa praga. Porém, poucos são os trabalhos que mencionam aspectos biológicos desse parasitóide sobre esta praga. Neste trabalho avaliou-se a influência da fase embrionária dos ovos do hospedeiro P. xylostella sobre fêmeas de T. pretiosum com diferentes idades. Fêmeas do parasitóide foram divididas em cinco lotes, compostos por espécimes recém-emergidos com 24; 48; 72 e 96 horas de idade. Cada lote continha dez fêmeas de T. pretiosum. Para cada fêmea de cada lote, foi oferecida uma cartela contendo 30 ovos de P. xylostella com um, dois e três dias de idade. As maiores taxas de parasitismo foram observadas em fêmeas com idade superior a 48 horas, independente do desenvolvimento embrionário do hospedeiro. Em ovos com três dias de desenvolvimento embrionário verificou-se que, para fêmeas recém-emergidas e com 48 horas de idade, a taxa de viabilidade foi superior apenas em relação àquelas com 96 horas de idade. Ao se avaliar os descendentes de T. pretiosum provenientes de ovos com um dia de desenvolvimento embrionário, verificou-se que os maiores valores de longevidade foram obtidos quando as fêmeas desse parasitóide eram recém-emergidas.<br>Plutella xylostella is one of the most important pests of Cruciferae. Chemicals have been used to control this insect, but the rapid development of resistance is a serious constraint to this method. Biological control with Trichogramma species has been reported as an alternative to control diamondback moth. However few works report biological parameters of this parasitoid interacting with this pest. This work was carried out to evaluate the influence of egg embryonary stage of P. xylostella on T. pretiosum females at different ages. Females of this parasitoid were organized in five groups. These groups were composed of females just emerged, 24 h; 48 h; 72 h, and 96 hours-old. Each group was formed of ten females. Each female received a card with thirty P. xylostella eggs, one, two and three day-old. Higher parasitism rates were observed with females older than 48 hours, with no influence of host embryonic development. In three day-old eggs it was verified that just emerged females and 48 hour-old, the viability index was superior just to those 96 hour-old. The progeny with one day of embryonary development, presented higher longevity values with just emerged females