Changes in the Sensitivity of Erwinia amylovora Populations to Streptomycin and Oxolinic Acid in Israel.

A survey of streptomycin resistance in the fire blight pathogen, Erwinia amylovora, conducted in pear, apple, and quince orchards in Israel during 1998 to 2001 revealed a decrease in the frequency of locations with streptomycin-resistant strains, from 57% in 1998 to 15% in 2001. In 2001, streptomycin-resistant strains were detected in only five locations in two restricted areas in western Galilee and the Golan Heights, compared with 16 locations found in 1998 throughout the northern part of the country. Since the use of streptomycin for fire blight control was terminated in 1997, this antibiotic has been replaced with oxolinic acid (Starner) in commercial orchards. Strains resistant to oxolinic acid were isolated from two pear orchards in the northern part of Israel in 1999. In a nationwide survey conducted during the spring and winter of 2000 and 2001, 51 and 47 pome fruit orchards, respectively, were sampled. Oxolinic acid-resistant strains were detected in several orchards located in two restricted areas in northern Galilee. Strains with resistance to both streptomycin and oxolinic acid were not found during 2000 to 2001. Results of this survey are used in managing fire blight with bactericides.

Characterization of Colletotrichum acutatum causing anthracnose of anemone (Anemone coronaria L.).

Anthracnose, or leaf-curl disease of anemone, caused by Colletotrichum sp., has been reported to occur in Australia, western Europe, and Japan. Symptoms include tissue necrosis, corm rot, leaf crinkles, and characteristic spiral twisting of floral peduncles. Three epidemics of the disease have been recorded in Israel: in 1978, in 1990 to 1993, and in 1996 to 1998. We characterized 92 Colletotrichum isolates associated with anthracnose of anemone (Anemone coronaria L.) for vegetative compatibility (72 isolates) and for molecular genotype (92 isolates) and virulence (4 isolates). Eighty-six of the isolates represented the three epidemics in Israel, one isolate was from Australia, and five isolates originated from western Europe. We divided these isolates into three vegetative-compatibility groups (VCGs). One VCG (ANE-A) included all 10 isolates from the first and second epidemics, and 13 of 62 examined isolates from the third epidemic in Israel, along with the isolate from Australia and 4 of 5 isolates from Europe. Another VCG (ANE-F) included most of the examined isolates (49 of the 62) from the third epidemic, as well as Colletotrichum acutatum from strawberry, in Israel. Based on PCR amplification with species-specific primers, all of the anemone isolates were identified as C. acutatum. Anemone and strawberry isolates of the two VCGs were genotypically similar and indistinguishable when compared by arbitrarily primed PCR of genomic DNA. Only isolate NL-12 from The Netherlands, confirmed as C. acutatum but not compatible with either VCG, had a distinct genotype; this isolate represents a third VCG of C. acutatum. Isolates from anemone and strawberry could infect both plant species in artificial inoculations. VCG ANE-F was recovered from natural infections of both anemone and strawberry, but VCG ANE-A was recovered only from anemone. This study of C. acutatum from anemone illustrates the potential of VCG analysis to reveal distinct subspecific groups within a pathogen population which appears to be genotypically homogeneous by molecular assays.

Molecular analyses of colletotrichum species from almond and other fruits.

ABSTRACT Isolates of Colletotrichum spp. from almond, avocado, and strawberry from Israel and isolates of the pink subpopulation from almond from the United States were characterized by various molecular methods and compared with morphological identification. Taxon-specific primer analysis grouped the avocado isolates within the species C. gloeosporioides and the U.S. almond and Israeli strawberry isolates within the species C. acutatum. However, the Israeli almond isolates, previously identified morphologically as C. gloeosporioides, reacted with C. acutatum-specific primers. Arbitrarily primed polymerase chain reaction and A+T-rich DNA analyses determined that each population from almond and strawberry was distinct and clonal. Sequence analysis of the complete internal transcribed spacer (ITS) region (ITS 1-5.8S-ITS 2) revealed a similarity of between 97.03 and 98.72% among almond isolates from Israel, C. acutatum almond isolates from the United States, and C. acutatum strawberry isolates from Israel. Similarity of the above populations to that of C. gloeosporioides of avocado was between 92.42 and 92.86%. DNA sequence analysis of the entire ITS region supported the phylogeny inferred from the ITS 1 tree of 14 different Colletotrichum species. Although morphological criteria indicated that the Israeli isolates from almond are unique, this population was grouped within the C. acutatum species according to molecular analyses.

Characterization of Colletotrichum gloeosporioides isolates from avocado and almond fruits with molecular and pathogenicity tests.

One hundred twenty isolates of Colletotrichum gloeosporioides from avocado (6 U.S. and 57 Israeli isolates) and almond (57 Israeli isolates) fruits were compared by various molecular methods and a pathogenicity assay in order to determine the genetic diversity and host specificity between and among the different populations. DNA from eight additional U.S. almond anthracnose isolates were also compared. PCR amplification of genomic DNA with four primers produced uniform banding patterns for all the Israeli almond isolates from different geographic locations in Israel. DNAs from the U.S. almond isolates were distinct from DNAs of the Israeli isolates. In contrast, the avocado isolates from Israel and the United States were more diverse, with numerous arbitrarily primed-PCR phenotypes being observed. HaeIII digestion patterns of A+T-rich DNA distinguished between the almond and avocado isolates. Southern hybridization of the repetitive nuclear-DNA element GcpR1 to PstI-digested genomic DNA of almond and avocado isolates revealed no polymorphic fragments among the almond isolates, whereas polymorphic fragments were observed among the avocado isolates. Amplification and subsequent restriction enzyme digestion of the internal transcribed spacer 4 and 5 regions between the small and large nuclear subunits of DNA encoding rRNA failed to distinguish between C. gloeosporioides isolates from a diverse host range. In artificial inoculations, avocado isolates produced various lesions on avocado and almond fruits, whereas the almond isolates infected both fruits at a lower rate.