Browsing by Author "del Río-Mendoza, L."

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Genetic diversity and population differentiation of Sclerotinia sclerotiorum collected from canola in China and in U.S.A.
(Phytopathology, 2011) Attanayake, R.N.; del Río-Mendoza, L.; Chen, W.; Jiang, D.
Sclerotinia sclerotiorum is an important pathogen of canola and many other crops worldwide. Genetic diversity and population differentiation of S. sclerotiorum collected from canola fields in Anhui Province, China (30 isolates) and in North Dakota, U.S.A. (29 isolates) were investigated in terms of genetic variation in 8 simple sequence repeat (SSR) marker loci, mycelial compatibility groups (MCGs) and three phenotypic traits: sensitivity to fungicides benomyl, iprodione and fluzinam, oxalic acid production, and pathogenicity. Significant genetic differences were observed; there were no shared SSR haplotypes and no shared MCGs between the two populations. Population differentiation was significant (p = 0.000) indicating lack of gene flow between the two populations. There were also significant differences between the two populations in oxalic acid production and in fungicide sensitivity. The Chinese population displayed high levels of insensitivity (faster growth rate) to benomyl and fluzinam and higher levels of oxalic acid production per unit dry weight of mycelium than did the U.S. population. However, there was no significant difference in pathogenicity between the two populations as measured by colonization of detached canola leaves. Data Vol. 101, No. 6 (Supplement), 2011 S11 suggest that despite geographic and genetic isolation the two populations of S. sclerotiorum were equally adapted to colonizing canola plants, and pathogenicity is under different selection pressure than the other genetic and phenotypic traits.
Inferring outcrossing in the homothallic fungus Sclerotinia sclerotiorum using linkage disequilibrium decay
(Heredity, 2014) Attanayake, R.N.; Tennekoon, V.; Johnson, D.A.; Porter, L.D.; del Río-Mendoza, L.; Jiang, D.; Chen, W.
The occurrence and frequency of outcrossing in homothallic fungal species in nature is an unresolved question. Here we report detection of frequent outcrossing in the homothallic fungus Sclerotinia sclerotiorum. In using multilocus linkage disequilibrium (LD) to infer recombination among microsatellite alleles, high mutation rates confound the estimates of recombination. To distinguish high mutation rates from recombination to infer outcrossing, 8 population samples comprising 268 S. sclerotiorum isolates from widely distributed agricultural fields were genotyped for 12 microsatellite markers, resulting in multiple polymorphic markers on three chromosomes. Each isolate was homokaryotic for the 12 loci. Pairwise LD was estimated using three methods: Fisher?s exact test, index of association (IA) and Hedrick?s D?. For most of the populations, pairwise LD decayed with increasing physical distance between loci in two of the three chromosomes. Therefore, the observed recombination of alleles cannot be simply attributed to mutation alone. Different recombination rates in various DNA regions (recombination hot/cold spots) and different evolutionary histories of the populations could explain the observed differences in rates of LD decay among the chromosomes and among populations. The majority of the isolates exhibited mycelial incompatibility, minimizing the possibility of heterokaryon formation and mitotic recombination. Thus, the observed high intrachromosomal recombination is due to meiotic recombination, suggesting frequent outcrossing in these populations, supporting the view that homothallism favors universal compatibility of gametes instead of traditionally believed haploid selfing in S. sclerotiorum. Frequent outcrossing facilitates emergence and spread of new traits such as fungicide resistance, increasing difficulties in managing Sclerotinia diseases.
Sclerotinia sclerotiorum Populations Infecting Canola from China and the United States Are Genetically and Phenotypically Distinct
(Population Biology, 2013) Chen, W.; Attanayake, R.N.; Carter, P.A.; Jiang, D.; del Río-Mendoza, L.; Weidong
Genetic and phenotypic diversity and population differentiation of Sclerotinia sclerotiorum isolates infecting canola from China and the United States were investigated. Genetic diversity was assessed with eight microsatellite markers and mycelial compatibility groups (MCGs). Phenotypic diversity was assessed with sensitivity to three fungicides, production of oxalate and sclerotia, growth rate, and virulence on two canola cultivars. No shared MCGs or multilocus haplotypes were detected between the two populations, and populations differed significantly (P < 0.001). Recombination was detected in both populations but was greater in the Chinese population. A polymerase chain reaction detection assay showed that ~60% of the isolates were inversion-plus at the mating type locus. The two populations differed significantly (P < 0.05) for all of the phenotypic traits except for sensitivity to fungicide fluazinam and virulence. Isolates in the Chinese population were unique in several aspects. Despite the phenotypic differentiation, heritabilities of the phenotypic traits were similar for both populations. Significant correlations were found among five phenotypic traits. Cross resistance to benomyl and iprodione was detected. Virulence was not significantly correlated with any other phenotypic trait and had the least heritability. However, both populations were equally virulent on either a susceptible or a moderately resistant canola cultivars.