Role of host specificity in the speciation of Ascochyta pathogens of cool season food legumes

Peever, Tobin L.

doi:10.1007/978-1-4020-6065-6_12

Cited by 8 publications

(13 citation statements)

References 27 publications

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“…A good example is provided by Ascochyta pathogens. Recent multilocus phylogenetic analyses of Ascochyta fungi causing blights of chickpea, faba bean, lentil, and pea have revealed that fungi causing disease on each of these hosts form distinct species [56] (Fig. III).…”

Section: Resultsmentioning

confidence: 99%

Linking the emergence of fungal plant diseases with ecological speciation

Giraud

Gladieux

Gavrilets

2010

Trends in Ecology & Evolution

295

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Emerging diseases represent a growing worldwide problem accompanying global environmental changes, and there is tremendous interest in identifying the factors controlling the appearance and spread of these diseases. Here, we discuss emerging fungal plant diseases, and argue that they often result from host shift speciation, a particular case of ecological speciation. We consider the factors controlling local adaptation and ecological speciation and show that certain life-history traits of many fungal plant pathogens are conducive for rapid ecological speciation, thus favoring the emergence of novel pathogen species adapted to new hosts. We argue that placing the problem of emerging fungal diseases of plants within the context of ecological speciation can significantly improve our understanding of the biological mechanisms governing emergence of such diseases.

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Section: Resultsmentioning

confidence: 99%

Linking the emergence of fungal plant diseases with ecological speciation

Giraud

Gladieux

Gavrilets

2010

Trends in Ecology & Evolution

295

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“…Indeed, M. pinodes is a polyphagous fungus that can infect different wild legumes (9,40,50). Wild legumes have sometimes been assumed or shown to be involved in the transmission of inoculum from field borders into fields.…”

Section: Discussionmentioning

confidence: 99%

“…Gerard et al (21) and Frenkel et al (19) showed that an exchange between wild and domesticated plants could exist in nature. Moreover, Peever (40) showed that as wild host populations are generally more diverse, they could influence the genetic structure of the plant pathogen populations. Although primary inoculum can also be generated by volunteers in neighboring fields (8), the initiation of disease in the winter crops could therefore be due mainly to wild hosts acting as reservoirs.…”

Section: Discussionmentioning

confidence: 99%

A Single, Plastic Population of Mycosphaerella pinodes Causes Ascochyta Blight on Winter and Spring Peas (Pisum sativum) in France

May

Guibert

Leclerc

et al. 2012

Appl Environ Microbiol

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c Plant diseases are caused by pathogen populations continuously subjected to evolutionary forces (genetic flow, selection, and recombination). Ascochyta blight, caused by Mycosphaerella pinodes, is one of the most damaging necrotrophic pathogens of field peas worldwide. In France, both winter and spring peas are cultivated. Although these crops overlap by about 4 months (March to June), primary Ascochyta blight infections are not synchronous on the two crops. This suggests that the disease could be due to two different M. pinodes populations, specialized on either winter or spring pea. To test this hypothesis, 144 pathogen isolates were collected in the field during the winter and spring growing seasons in Rennes (western France), and all the isolates were genotyped using amplified fragment length polymorphism (AFLP) markers. Furthermore, the pathogenicities of 33 isolates randomly chosen within the collection were tested on four pea genotypes (2 winter and 2 spring types) grown under three climatic regimes, simulating winter, late winter, and spring conditions. M. pinodes isolates from winter and spring peas were genetically polymorphic but not differentiated according to the type of cultivars. Isolates from winter pea were more pathogenic than isolates from spring pea on hosts raised under winter conditions, while isolates from spring pea were more pathogenic than those from winter pea on plants raised under spring conditions. These results show that disease developed on winter and spring peas was initiated by a single population of M. pinodes whose pathogenicity is a plastic trait modulated by the physiological status of the host plant. P lant parasites can quickly adapt to their hosts and overcome resistance genes used in crop protection. This process occurs both in agroecosystems, where hosts (cultivars) are typically quite uniform genetically, and in wild pathosystems, where hosts and parasites show high levels of diversity and are structured as metapopulations (12). However, a number of crop plants are grown in complex ecosystems rather than as the monocultures which characterize modern agriculture; this is particularly the case for species grown as both winter and spring cultivars and for which wild relatives occur as weeds or in field margins.From a plant pathology point of view, such complex ecosystems are usually characterized by one or more of the following parameters: (i) spatial and temporal heterogeneity of hosts, which creates patchiness and an often complex age structure, (ii) intraand interspecific diversity, and (iii) multiple host-pathogen interactions. These features favor niche partitioning, as they allow the coexistence on the same host species of different pathogen populations separated in space and/or time. Indeed, ecological differences that lead to niche partitioning can occur in three basic ways: resource partitioning, temporal niche partitioning, and spatial niche partitioning (4, 14, 36). For plant-pathogenic species able to exploit the same host, separation in space and/or time mi...

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“…These regions were used previously to estimate the phylogeny among Ascochyta spp. and proved to be informative at or below the species level (48). Primers EF1-728F and EF1-986R (14) were used to amplify a portion of the translation elongation factor 1 alpha gene (EF1␣).…”

Section: Methodsmentioning

confidence: 99%

“…Plant pathogens are dependent upon the abiotic environment as well as on their host plants and are subjected to strong selective forces exerted by their hosts. This process is shaped especially (but not exclusively) by genetic variation at loci controlling differential host specificity, which may ultimately be an important driver in speciation (37,48,49).…”

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confidence: 99%

Ecological Genetic Divergence of the Fungal PathogenDidymella rabieion Sympatric Wild and DomesticatedCicerspp. (Chickpea)

Frenkel

Peever

Chilvers

et al. 2010

Appl Environ Microbiol

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For millennia, chickpea (Cicer arietinum) has been grown in the Levant sympatrically with wild Cicer species. Chickpea is traditionally spring-sown, while its wild relatives germinate in the autumn and develop in the winter. It has been hypothesized that the human-directed shift of domesticated chickpea to summer production was an attempt to escape the devastating Ascochyta disease caused by Didymella rabiei. We estimated genetic divergence between D. rabiei isolates sampled from wild Cicer judaicum and domesticated C. arietinum and the potential role of temperature adaptation in this divergence. Neutral genetic markers showed strong differentiation between pathogen samples from the two hosts. Isolates from domesticated chickpea demonstrated increased adaptation to higher temperatures when grown in vitro compared with isolates from the wild host. The distribution of temperature responses among progeny from crosses of isolates from C. judaicum with isolates from C. arietinum was continuous, suggesting polygenic control of this trait. In vivo inoculations of host plants indicated that pathogenic fitness of the native isolates was higher than that of their hybrid progeny. The results indicate that there is a potential for adaptation to higher temperatures; however, the chances for formation of hybrids which are capable of parasitizing both hosts over a broad temperature range are low. We hypothesize that this pathogenic fitness cost is due to breakdown of coadapted gene complexes controlling pathogenic fitness on each host and may be responsible for maintenance of genetic differentiation between the pathogen demes.

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Role of host specificity in the speciation of Ascochyta pathogens of cool season food legumes

Cited by 8 publications

References 27 publications

Linking the emergence of fungal plant diseases with ecological speciation

Linking the emergence of fungal plant diseases with ecological speciation

A Single, Plastic Population of Mycosphaerella pinodes Causes Ascochyta Blight on Winter and Spring Peas (Pisum sativum) in France

Ecological Genetic Divergence of the Fungal PathogenDidymella rabieion Sympatric Wild and DomesticatedCicerspp. (Chickpea)

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