Phoma glomerataas a Mycoparasite of Powdery Mildew

Abstract

Ampelomyces and Phoma species are frequently confused with each other. Isolates previously attributed to the genus Ampelomyces were shown to be Phoma isolates through studies of their morphology and life cycle and ribosomal DNA internal transcribed spacer region 1 sequence analysis. Phoma glomerata can colonize and suppress development of powdery mildew on oak and may have utility as a mycoparasitic agent.Powdery mildews are widespread plant pathogens that are conspicuous by their white mycelia and powder-like conidia (20). The fungus Ampelomyces quisqualis Ces. is the only fungus that has been demonstrated to be generally effective as a biocontrol agent of powdery mildew (4, 9, 16). Many morphologically similar species may be confused with A. quisqualis (10). To evaluate this possibility, we examined and identified Ampelomyces-like fungi isolated from powdery mildew and compared these cultures with isolates identified as Ampelomyces in culture collections.Isolation and growth. Leaves of sycamore trees (Platanus occidentalis L.) bearing infections of powdery mildew (Microsphaera penicillata (Wallr.:Fr.) Lèv.) were located in South River, New Jersey, in July 1998. Microscopic examination of the leaves revealed two types of pycnidia: stipitate pycnidia, typical of A. quisqualis, and sessile pycnidia, typical of the genus Phoma (Fig. 1) (17). Both types of pycnidia were removed from leaves with fine needles and placed on potato dextrose agar (Difco, Inc., Detroit, Mich.) containing the antibiotics gentamicin (40 mg/liter), streptomycin (40 mg/liter), and penicillin (20 mg/liter) (PDA ϩ 3). Two different fungi were consistently recovered. The stipitate pycnidia developed into slow-growing colonies whose characteristics corresponded to those expected for A. quisqualis (5, 11). The sessile pycnidia developed into rapidly growing colonies whose characteristics corresponded to those of Phoma glomerata (Cda) Wollenw. (2,19).Agar plugs (6 mm in diameter) of mycelia cut from the margins of rapidly growing colonies of both the South River Ampelomyces and South River P. glomerata isolates were transferred to five plates each of PDAϩ3 and incubated at room temperature (21 to 22°C) for 3 weeks to measure growth rates. We measured an average growth of 8 Ϯ 1 mm/day for the P. glomerata isolates and an average growth of 0.8 Ϯ 0.1 mm/day for the Ampelomyces isolates. With age, cultures of P.

Existence of different physiological forms within genetically diverse strains of Ampelomyces quisqualis

“…Until recently, A. quisqualis was often confused with several other species: A. quercinus, A. humuli, A. heracli and Phoma glomerata. Unlike A. quisqualis, these other powdery mildew mycoparasites do not produce intracellular pycnidia and they also grow more quickly, with in vitro radial growth rates of 3-4 mm d −1 (Kiss et al 2004;Sullivan and White 2000). In the past, scientists identified all of these fast-growing strains as A. quisqualis (e.g.…”

Genetic variability and mycohost association of Ampelomyces quisqualis isolates inferred from phylogenetic analyses of ITS rDNA and actin gene sequences

“…Genetic diversity and heterogeneity within various A. quisqualis isolates have been shown by several molecular studies on restriction fragment length polymorphism (RFLP) (Kiss 1997), single-stranded conformation polymorphism (SSCP) (Szentivá nyi et al 2005), and phylogenetic sequence analyses of ITS rDNA region (Kiss & Nakasone 1998;Sullivan & White 2000;Liang et al 2007). In addition, Kiss (1997), Nakasone (1998), andSzentivá nyi et al (2005) showed that genetically diverse Ampelomyces isolates were largely divided into two distinct clades, each of which was characterized by fast or slow growth in culture.…”

“…In addition, Kiss (1997), Nakasone (1998), andSzentivá nyi et al (2005) showed that genetically diverse Ampelomyces isolates were largely divided into two distinct clades, each of which was characterized by fast or slow growth in culture. It was suggested that fast-growing Ampelomyces isolates be reidentified as Phoma glomerata based on the results of molecular analysis and the difference of pycnidia formation (Sullivan & White 2000).…”

Phylogenetic analysis of manganese-oxidizing fungi isolated from manganese-rich aquatic environments in Hokkaido, Japan

“…Most Phoma species are cosmopolitan species and have been recognized as common plant pathogens. P. gromerata and P. macrostoma in the same clade with KY-1 in the ITS1-5.8S rRNA-ITS2 distant tree are noted because of the interesting characteristics in agriculture (Sullivan and White 2000;Zhou et al 2004). However, Mn oxidation is not among their characteristics.…”