The identities of Sclerotinia isolates obtained from chickpea plants showing stem and crown rot were determined using morphological characteristics, variations in group I introns, and internal transcribed spacer (ITS) sequences. Isolates could be separated into two groups based on growth rates at 22°C, fast growing (about 40 mm per day) versus slow growing (about 20 mm per day). All fast-growing isolates induced stronger color change of a pH-indicating medium than did slow-growing isolates at 22°C. The slow-growing isolates contained at least one group I intron in the nuclear small subunit rDNA, whereas all fast-growing isolates lacked group I introns in the same DNA region. ITS sequences of the slow-growing isolates were identical to sequences of Sclerotinia trifoliorum. Those of the fast-growing isolates were identical to sequences of S. sclerotiorum. Finally, the slow-growing isolates showed ascospore dimorphism, a definitive character of S. trifoliorum, whereas the fast-growing isolates showed no ascospore dimorphism. Isolates of both species were pathogenic on chickpea and caused symptoms similar to those observed in the field. This study not only associated the differences between S. sclerotiorum and S. trifoliorum in growth rates, group I introns, ITS sequences, and ascospore morphology, but also represented the first report that S. trifoliorum causes stem and crown rot of chickpea in North America.
Sclerotinia trifoliorum, an important pathogen of cool season legumes, displays both homothallism and heterothallism in its life cycle, unique among members of the genus Sclerotinia. Very little is known about its genetic diversity and population structure. A sample of 129 isolates of S. trifoliorum from diseased chickpea in California was investigated for genetic diversity, population differentiation and reproductive mode. Genetic diversity was estimated using mycelial compatibility (MCG) phenotypes, rDNA intron variation, and allelic diversity at seven microsatellite loci. Genetic analysis revealed high levels of genotypic diversity demonstrated by high genotypic richness (0Á88). Similarly, high levels of gene diversity (mean expected heterozygosity H E = 0Á68) were observed at the microsatellite loci. Geographic populations of S. trifoliorum were highly admixed as evident from low F ST values (0-0Á11), suggesting high contemporary or historical gene flow. Hierarchical analysis of molecular variance showed that more than 92% of the genetic variation occurred among isolates within populations. Bayesian clustering analysis identified four cryptic genetic populations that were not correlated to geographic location, and index of multilocus association was non-significant in each of the four genetic populations. However, the presence of identical haplotypes within and among populations indicates clonal reproduction. The high levels of haplotype diversity and population heterogeneity, a lack of correspondence between MCG and microsatellite haplotype, and low levels of population differentiation suggest that populations of S. trifoliorum in chickpea have been undergoing extensive outcrossing and migration events probably shaped by human-mediated dissemination, the underlying diverse cropping systems, and chickpea disease management practices.
Sclerotinia trifoliorum is an important pathogen of forage legumes and some grain legumes. Attempts to study its population biology using microsatellite markers developed for Sclerotinia sclerotiorum and Sclerotinia subarctica resulted in no amplification or low levels of polymorphism. This study reports the development and characterization of 33 microsatellite loci developed from a microsatellite-enriched library of S. trifoliorum. Based on a population of 42 isolates of S. trifoliorum, these microsatellite markers are highly polymorphic, with a mean of 6.5 alleles per locus (range 3-12) and a mean expected heterozygosity of 0.63 (range 0.26-0.9). Based on locations of these marker sequences in the S. sclerotiorum genome, these microsatellite loci are dispersed throughout the genome. However, 50% (265 of 528) of pairwise comparisons of the 33 microsatellite loci had significant linkage disequilibrium, which could be explained by the mixed mating systems (homothallism and heterothallism) and clonal reproduction of S. trifoliorum. Thirty of the 33 loci were successfully applied to S. sclerotiorum, and 28 loci were polymorphic. However, only 10 loci are applicable to Sclerotinia minor and 1 locus to Sclerotinia homoeocarpa. These markers are therefore useful for population structure assessment, QTL mapping, and ecological analyses in S. trifoliorum and potentially in other Sclerotinia species.
In many heterothallic fungal pathogens, mating types are found to be associated with variation in virulence and some other ecological traits. Sclerotinia trifoliorum is unique from other Sclerotinia species in that it is heterothallic with two mating types. The mating type gene has pleotropic effect on ascospore size; large ascospore isolates are phenotypically homothallic (L-type), and small ascospore isolates are heterothallic (S-type). The possible association of variation in virulence with the two mating types and hence the ascospore size in S. trifoliorum is investigated using isolates collected from naturally infected chickpea plants and isolates generated from controlled crosses. Chi-square tests showed that 57 field isolates collected from crown lesions (infection initiated by mycelium) had a 1:1 distribution of L-type (29 isolates) and Stype (28 isolates), whereas 14 isolates from stem lesions (infection initiated by ascospores) had a distribution of 10 L-type isolates and 4 S-type isolates not significantly different from 1:1. Greenhouse tests using mycelial plugs as inoculum of field and laboratory-derived isolates did not show significant difference between the two mating types in causing stem rot of chickpea. The sample size of ascosporeinitiated infection was small, and the controlled pathogenicity assays in the greenhouse only tested mycelial infection. Thus, whether the two types of ascospores have equal capability of infecting chickpea remains to be further investigated. Strong evidence of both field and greenhouse data showed that mycelia of both mating types of S. trifoliorum were equally capable of infecting chickpea.
Waitea circinata var. circinata was first reported as the causal agent of brown ring patch on annual bluegrass (Poa annua L.) in the United States in 2007 (2). In early April to mid-June of 2009, circular to irregularly shaped yellow rings resembling symptoms of this disease were observed on an annual bluegrass putting green at Rutgers University in North Brunswick, NJ. Severely infected foliage eventually turned brown as the disease progressed. During the same time period, similar disease symptoms were observed on creeping bentgrass (Agrostis stolonifera L.) from a golf course in Bedminster Township, NJ. The disease reappeared in both locations in April of 2010. Five additional samples with similar symptoms on creeping bentgrass and annual bluegrass were received at Rutgers Diagnostic Laboratory from Paramus, Madison, Allamuchy, and Farmingdale, NJ between late April and early May of 2010. Portions of diseased leaf and sheath tissue that displayed symptoms of the disease were disinfested for 1 min in 0.5% NaOCl, rinsed with sterile distilled water, and plated on potato dextrose agar (PDA) amended with 50 mg/liter of streptomycin sulfate. At the first sign of fungal growth, single hyphal tips were transferred to PDA. After 1 week at 25°C, white-to-orange mycelial colonies formed in culture and eventually turned brown with age. Minute sclerotia (≤3 mm), which followed the same color development pattern, formed within 10 days. These features are consistent with those described of W. circinata var. circinata (2,3). The internal transcribed spacer (ITS) region of the ribosomal RNA gene was amplified using primer pair ITS1/ITS4 and sequenced with ITS4 (GenBank Accession Nos. HQ166065 to HQ166071). BLASTn analysis of the ITS sequences showed a 99 to 100% similarity to W. circinata var. circinata sequences deposited in GenBank (1,2). Pathogenicity tests were conducted in 2010 using 6-week-old creeping bentgrass seedlings cv. Declaration inoculated with colonized oat grain that had been autoclaved and then infested with the Bedminster Township isolate. Eight colonized oat grains were uniformly spread around the crowns of seedlings grown in 10-cm-diameter pots. Control plants were treated with autoclaved grain. Plants were incubated at 25°C and high humidity maintained by misting the plants three times per day. Within 3 days postinoculation, foliage near infested grain turned chlorotic. All foliage in pots became completely blighted and spherical orange-brown sclerotia were observed on leaf sheaths by the eighth day. W. circinata var. circinata was consistently reisolated from inoculated plants (as confirmed by isolate morphology and ITS sequencing) but not from control plants. The ITS sequence data, morphological characters of the isolates, and pathogenicity tests demonstrate that W. circinata var. circinata is present in New Jersey. To our knowledge, this is the first report of W. circinata var. circinata infecting turfgrass in New Jersey. References: (1) C. M. Chen et al. Plant Dis. 93:906, 2009. (2) K. A. de la Cerda et al. Plant Dis. 91:791, 2007. (3) T. Toda et al. Plant Dis. 89:536, 2005.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.