L rpd 3 66; p : ; Bayoud, the Fusarium wilt of date palm, was first detected in southern Morocco (Draa Valley), after which it spread to most of the Moroccan palm groves. To assess whether the epidemic results from the spread of a single virulent clone, 42 isolates of Fusarium oxysporunz f. sp. albedinis were collected from several cultivars of wilted palms at different locations in Morocco; two isolates were included from Algeria, where the disease also occurs. The isolates were tested for vegetatjWcompatibility group (VCG), restriction fragment length polymorphism .(RFLP), and random amplified polymorphic DNA (RAPD). No polymorphism was observed either in RFLP studies on mitochondrial DNA o;ih RAPD analysis, and all strains belonged to a single VCG (0170). Sequences homologous to the DNA transposable element Fotl were found in the genome of the F: oxysporum f. sp. albedinis strains. Repetitive DNA patterns were produced when EcoRI-digested DNA of the isolates was probed with Fotl; 23 distinct hybridization patterns were established among the 44 isolates. Of these patterns, 4 accounted for more than 50% of the isolates, 1 was found twice, and 18 were represented by a single isolate each. Common hybridization patterns were found in the Moroccan palm groves surveyed; the two Algerian isolates had a pattern that also was found in the Draa Valley. Cluster analysis grouped most of the E oxysporurn f. sp. albedinis strains at a genetic distance of 0.11. Such close genetic relationships between the isolates provides evidence that Moroccan E ogsporum f. sp. albedinis populations may belong to a single clonal lineage that originated in Moroccan palm groves and eventually reached the Algerian oases.
Populations of Fusarium oxysporum f. sp.albedinis, the causal agent of Bayoud disease of date palm, are derivatives of a single clonal lineage and exhibit very similarFot 1 hybridization patterns. In order to develop a sensitive diagnostic tool for F. oxysporum f. sp.albedinis detection, we isolated several DNA clones containing a copy of the transposable element Fot 1 from a genomic library of the date palm pathogen. Regions flanking the insertion sites were sequenced, and these sequences were used to design PCR primers that amplify the DNA regions at several Fot 1 insertion sites. When tested on a large sample of Fusariumisolates, including 286 F. oxysporum f. sp.albedinis isolates, 17 other special forms, nonpathogenicF. oxysporum isolates from palm grove soils, and 8 otherFusarium species, the primer pair TL3-FOA28 allowed amplification of a 400-bp fragment found only in F. oxysporum f. sp. albedinis. Sequence analysis showed that one of the Fot 1 copies was truncated, lacking 182 bp at its 3′ terminus. The primer pair BI03-FOA1 amplified a 204-bp fragment which overlapped the Fot 1 truncated copy and its 3′ site of insertion in the F. oxysporum f. sp.albedinis genome and identified 95% of the isolates. The primer pairs BIO3-FOA1 and TL3-FOA28 used in PCR assays thus provide a useful diagnostic tool for F. oxysporum f. sp.albedinis isolates.
The roots of date palm contain four cell wall‐bound phenolic acids identified as p‐hydroxybenzoic, p‐coumaric, ferulic and sinapic acids. The ferulic acid represents the major phenolic compound since it constitutes 48.2–55.8% of cell wall‐bound phenolic acids. All these phenolic acids were present in the resistant cultivar (BSTN) and the susceptible cultivar (JHL). However, the pre‐infection contents of p‐coumaric, ferulic and sinapic acids were greater in the resistant cultivar than in the susceptible one. For the contents of p‐hydroxybenzoic acid, there was no significant difference between the resistant cultivar and the susceptible cultivar. Similarly, the pre‐infection contents of lignin were approximately equal for both cultivars. Inoculation of the date palm roots by Fusarium oxysporum f. sp. albedinis induced important modifications to the contents of the cell wall‐bound phenolic compounds and lignin, which made it possible to distinguish between resistant and susceptible cultivars. The post‐infection contents of cell wall‐bound phenolic compounds underwent a rapid and intense increase with a maximum accumulation on the tenth day for p‐hydroxybenzoic acid (1.54 μmol/g), p‐coumaric acid (2.77 μmol/g) and ferulic acid (2.64 μmol/g) and on the fifteenth day for sinapic acid (1.85 μmol/g). The maximum contents accumulated in the resistant cultivar were greater than those in the susceptible cultivar, namely, 11 times for p‐hydroxybenzoic acid, 2.6 times for p‐coumaric acid, 1.8 times for ferulic acid and 12.3 times for sinapic acid. In the susceptible cultivar, p‐coumaric acid and ferulic acid contents also increased after inoculation although they did not reach the pre‐infection contents of the resistant cultivar. The contents of p‐hydroxybenzoic acid in the susceptible cultivar roots did not present post‐infection modification and those of sinapic acid decreased instead. The lignin contents increased in both cultivars with a maximum accumulation on the fifteenth day. However, the maximum contents accumulated in the resistant cultivar roots were 1.5 times greater than those of the susceptible cultivar. These results showed clear differences between the resistant BSTN and the susceptible JHL cultivars. The implication of cell wall‐bound phenolic compounds and lignin in the resistance of date palm to F. oxysporum f. sp. albedinis appears to be dependent on the speed and intensity of their accumulation with greater contents in the first stage of infection.
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