Revival of the name Streptomyces scabies is proposed for the predominant species causing common scab of potato. Common scab strains from the northeastern United States, Atlantic Canada, and Hungary were differentiated by a phenotypic analysis of 42 criteria from six atypical pathogen strains, three saprophytic streptomycetes isolated from scab lesions, and reference strains of Streptomyces griseus and Streptomyces tendae. The 12 S . scabies strains formed a homogeneous group characterized by smooth grey spores borne in spiral chains, melanin production, and usage of all International Streptomyces Project sugars. Most S . scabies isolates did not degrade xanthine and were susceptible to 25 pg of oleandomycin per ml, 10 IU of penicillin G per ml, 20 pg of streptomycin per ml, 10 pg of thallous acetate per ml, and 0.5 pg of crystal violet per ml. The type strain of S . scabies is strain RL-34 (= ATCC 49173).

A new bacterial species is described, for which we propose the name Streptomyces acidiscabies. This organism causes a scab disease of potatoes (Solanurn tuberosurn) which may occur in soils with pH values below 5.2. The acid scab symptoms caused by this organism are indistinguishable from the symptoms of commn scab caused by Streptomyces scabies. In culture, S . acidiscabies is distinct from S. scabies, having flexuous spore chains, a growth medium-dependent spore mass color ranging from white to organish red, and a red or yellow, pH-sensitive diffusible pigment rather than melanin. S. acidiscabies grows on agar media at pH 4.0 (versus pH 5.0 for S. scabies), does not use raffinose as a carbon source, and tolerates higher concentrations of crystal violet (0.5 pg/ml), thallium acetate (10 pg/ml), streptomycin (20 pg/ml), oleandomycin (25 pg/ml), and penicillin G (10 IU/ml) than S. scabies. The type strain of S. acidiscabies is strain RL-110 (= ATCC 49003).

Mycorrhizae increase the uptake of Zn and Cn by many plants, but mycorrhizal activity is suppressed by P fertilization. Soybean (Glycine max Mer.) and two lines of corn (Zea mays L.) were used to determine if this mechanism is a major cause of P-induced Zn and Cu deficiencies. Shoot dry weights and concentrations or total uptake of P, Zn, Cu, Fe, Mn, K, Ca and Mg were determined for mycorrhizal and nonmycorrhizal plants given 0, 25, 75, or 200 ppm P. Phosphorus fertilization significantly reduced Zn and Cu concentrations in mycorrhizal soybeans, but concentrations in nonmycorrhizal treatments were not affected. Concentrations of Zn and Cu in mycorrhizal and nonmycorrhizal corn were reduced by P fertilization, but the reduction for mycorrhizal plants was significantly greater than the decrease for nonmycorrhizal plants. Reductions in Zn and Cu concentrations in nonmycorrhizal corn were the result of a dilution effect and could be attributed to increased plant size rather than increased P fertility per se. The concentrations of the other analyzed elements were all affected by P level and/or mycorrhizal condition. In general, mycorrhizal and nonmycorrhizal dry weights and element concentrations converged as soil P was increased. Patterns of response to P and mycorrhizae differed slightly between corn lines, and such differences were marked for certain elements when corn was compared with soybean.

SummaryOne hundred and eighty-nine Thoroughbred horses that had won Graded Stakes races in North America were genotyped with the Illumina Equine SNP50 bead chip. Association tests using PLINK to determine whether any SNPs were associated with optimum racing distance (7 furlongs and under compared to 8-10 furlongs) identified a locus on ECA18 that was statistically significant ()log 10 EMP2 = 1.63) at the genome-wide level following permutation analysis (10 000 permutations). Bioinformatic analysis revealed that the two ECA18 SNPs with the highest statistical significance spanned the MSTN (myostatin) locus. Mutations in myostatin in several mammalian species have been associated with increased muscling, with a preferential increase in fast glycolytic type IIB fibres, which would increase power potential. Thoroughbred horses that race over sprint distances, which are 5-7 furlongs, are often characterized by impressive hind quarter musculature, strongly suggesting that the association observed between the ECA18 SNPs and optimum race distance is mediated through MSTN.

The levels of DNA-DNA hybridization among members of the three major groups of Streptomyces spp. that cause potato scab did not exceed 20% for any pair. The majority of the Streptomyces scabies strains which we examined exhibited greater than 70% relatedness to the type strain, although values as low as 21% were obtained. The levels of homology between S . scabies and nonpathogenic type strains belonging to the Diastatochromogenes group ranged from 10 to 42 9% , while the reciprocal values obtained with labeled DNAs from Streptomyces bottropensis ATCC 25435T (T = type strain) and Streptomyces eurythermus ATCC 14975T ranged from 37 to 74% and from 2 to 24%, respectively. In contrast to S . scabies, the levels of relatedness between Streptomyces acidiscabies isolates and their type strain were high (83 to 111%). The levels of DNA relatedness within the Streptomyces aZbidoJlavus group were uniformly low. These results are consistent with phenotypic data which indicate that pathogens in the three groups are not related. The genetic diversity of strains referred to as S . scabies exceeds the genetic diversity found at the species level, and some of these strains appear to be related to phenotypically similar nonpathogens.Scab diseases of potatoes (Solanum tuberosum) and certain other root crops are caused by streptomycetes, including the major species Streptomyces scabies, which was first described by Thaxter in 1891 (11, 22), the acid-tolerant species Streptomyces acidiscabies (12), and other strains whose characteristics are consistent with those of the Streptomyces albidojlavus group of Williams et al. (11, 24). S. scabies is most closely related to the Diastatochromogenes group of Elesawy and Szabo (2), while the S. albidoflavus strains have been associated with Streptomyces griseus and Streptomyces tendae (7). The results of studies of 42 phenotypic traits (11, 12) have suggested that these three pathogen groups are not closely related and that the levels of strain diversity are lowest for S . acidiscabies and greatest for the S . albidoflavus group. The purposes of this study were to confirm these relationships, to determine the genomic relationship of S . scabies to the Diastatochromogenes group, and to interpret the significance of common pathogenicity mechanisms among potato scab pathogens. MATERIALS AND METHODSStrains. The isolates which we used are listed in Table 1 DNA extraction. Total DNAs were isolated from Streptomyces strains by using the method of Hintermann et al. (6), with some modifications. Mycelia grown in Trypticase soy broth shake cultures were homogenized, centrifuged, rinsed, and suspended in 5 ml of cold TS buffer (50 mM Tris, 0.75 M sucrose; pH 8.0). Lysozyme hydrochloride and EDTA were added to concentrations of 5 mg/ml and 0.1 M, respectively.After incubation at 37°C for 1 h, 1 mg pronase E per ml was added, and incubation was continued for 15 min. Sodium dodecyl sulfate was added to a concentration of 1%, and the suspensions were incubated at 37°C until full lysis was achieved (30 to 6...

No abstract

No abstract

No abstract