New PCR primers applied to characterize distribution of Botrytis cinerea populations in French vineyards

The phytopathogenic fungus Botrytis cinerea is a complex of two main genetic groups, Group-I and Group-II, the latter including different TE types distinguished by the presence or absence of two transposable elements (TE), Boty and Flipper. In populations from Bordeaux vineyards (n = 470), the frequency distribution into these genetic subdivisions showed that Group-I isolates were rare (2.3 %) whereas, within Group-II, four TE types were identified by dot blot in very different proportions: II-transposa (59.8 %), II-boty (21.3 %), II-vacuma (15.5 %) and II-flipper (1.1 %). To distinguish the TE types by PCR, a first primer pair was designed within the Flipper sequence which yielded a not-expected 2287 bp fragment. The 5’ extremity of this fragment was sequenced revealing a potential genomic insertion site of the Flipper element allowing the design of a new overlapping PCR primer. Detection of the Flipper element by two newly developed PCR tests and a published one (F300-F1550) was consistent with dot blot results in Group-I and II-transposa (concordance rates from 94.6 % to 100 %). However, discrepancies between PCR and dot blot were noticeable especially in II-boty, but also in II-vacuma (concordance rates from 33.3 % to 38.0 % and from 62 % to 81.2 %, respectively). On the basis of TE-type identification strengthened by combining different PCR and dot blot results, the spatiotemporal distribution of the Group-II isolates was assessed according to the developmental stage and the host organ of grapevine. In Bordeaux as in Loire valley vineyards, similar distribution patterns were described showing significant differences between the most sampled TE types. The II-transposa isolates predominated on grape berries at the end of the season, whereas the II-vacuma ones were detected mostly at flowering. Lastly, the II-boty isolates were more often detected on grapevine leaves than on flowers or berries.

A mutation in the 14 alpha-demethylase gene of Uncinula necator that correlates with resistance to a sterol biosynthesis inhibitor.

We investigated the molecular basis of resistance of the obligate biotrophic grape powdery mildew fungus Uncinula necator to sterol demethylation-inhibiting fungicides (DMIs). The sensitivity of 91 single-spore field isolates of U. necator to triadimenol was assessed by using a leaf disc assay. Resistance factors (RF) ranged from 1.8 to 26.0. The gene encoding the target of DMIs (eburicol 14 alpha-demethylase) from five sensitive and seven resistant isolates was cloned and sequenced. A single mutation, leading to the substitution of a phenylalanine residue for a tyrosine residue at position 136, was found in all isolates exhibiting an RF higher than 5. No mutation was found in sensitive or weakly resistant (RF, < 5) isolates. An allele-specific PCR assay was developed to detect the mutation. Among the 91 isolates tested, only isolates with RF higher than 5 carried the mutation. Three of the 19 resistant isolates and all sensitive and weakly resistant isolates did not possess the mutation. The mutation at codon 136 is thus clearly associated with high levels of resistance to triadimenol

Les stimulateurs de défense des plantes

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Importance of sterols acquired through host feeding in synovigenic parasitoid oogenesis.

Eupelmus vuilleti (Hymenoptera; Eupelmidae) is a host feeding ectoparasitoid of fourth-instar larvae or pupae of Callosobruchus maculatus (Coleoptera; Bruchidae) infecting Vigna unguiculata seed and pods (Fabacae). Parasitoid females are synovigenic, i.e. they are born with immature eggs and need to feed from the host in order to sustain egg production. In this study, the role of sterols obtained through host feeding in parasitoid oogenesis are examined. Quantitative and qualitative analyses of the sterol contents in each partner of the tritrophic interaction show that a parasitoid female's larval sterol contents is sufficient to produce only 30% of the total number of eggs laid throughout a female's life cycle. In a second step, by manipulating the composition of the sterols hemolymph in the host, it is shown that cholesterol obtained through adult nutrition plays a crucial role in the eggs viability but does not affect the egg production quantitatively. This result has important implications for understanding both the nutrient allocation strategy in this species and the impact of cholesterol in parasitoid reproduction

Biocontrôle : impacts écologiques et durabilité

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