A comparison of stem rust in oats and yellow rust in wheat: A Swedish example
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A comparison of stem rust in oats and yellow rust in wheat: A Swedish example

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Jonathon Yuen, Department of Forest Mycology and Plant Pathology, SLU

Jonathon Yuen, Department of Forest Mycology and Plant Pathology, SLU

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A comparison of stem rust in oats and yellow rust in wheat: A Swedish example A comparison of stem rust in oats and yellow rust in wheat: A Swedish example Presentation Transcript

  • A comparison of stem rust in oats and yellow rust in wheat: A Swedish example J. Yuen, A. Berlin, K. Gillen Department of Forest Mycology and Plant Pathology, SLU Y. Jin, USDA Cereal Disease Laboratory
  • Disposition o  Comparison of two rust diseases in Sweden o  Stem rust (primarily on oats) o  Stripe rust (primarily on wheat)
  • Where did he work?
  • The ’Botanical Section’
  • From Eriksson and Henning, Die Getrideroste (1896)
  • Stem rust in oats grown in Sweden shows the variation expected from a sexually reproducing population Photos: Anna Berlin
  • A collection of oat stem rust samples from Sweden Population   Location   Variety   Day of collectiona   N   G/N   Na   FIS   Ho   He   Ia   p   1   Fransåker   Belinda   01.08.08   27   1.00   62   0.487   0.329 (0.062)   0.618 (0.044)   0.509   0.563   2   Ingvasta   Ivory   06.08.08   29   1.00   45   0.333   0.363 (0.074)   0.526 (0.062)   0.341   0.045   3   Evertsholm   Ingeborg   11.08.08   30   0.93   41   0.133   0.472 (0.085)   0.533 (0.057)   0.184   0.145   4   Skarpenberga   Belinda   11.08.08   28   1.00   46   0.250   0.388 (0.061)   0.503 (0.045)   0.129   0.290   5   Bettna   Belinda   13.08.08   28   1.00   44   0.057   0.470 (0.087)   0.487 (0.065)   0.164   0.098   6   Bränne Övregård   Svava   13.08.08   30   0.90   44   0.054   0.436 (0.090)   0.449 (0.074)   -0.003   0.485   7   Pattala   Belinda   13.08.08   27   1.00   38   -0.028   0.501 (0.091)   0.477 (0.058)   0.108   0.125   8   Ultuna   Ivory   22.08.08   22   1.00   44   0.167   0.413 (0.071)   0.481 (0.063)   0.089   0.281   9   Hjälmarsholm   Kerstin   26.08.08   26   1.00   56   0.333   0.350 (0.066)   0.510 (0.062)   0.073   0.832   10   Götala   Ivory   26.08.08   25   1.00   56   0.244   0.443 (0.087)   0.567 (0.054)   -0.215   1.000   11   Skarpenberga   Belinda   30.07.09   28   1.00   60   0.277   0.419 (0.067)   0.564 (0.061)   0.389   0.149   12   Stäholm   Kerstin   04.08.09   28   1.00   50   0.262   0.398 (0.059)   0.524 (0.061)   0.024   0.649   13   Fransåker   Belinda   04.08.09   30   1.00   61   0.306   0.424 (0.050)   0.593 (0.053)   -0.083   0.665   14   Ingvasta   Ivory   05.08.09   26   1.00   55   0.449   0.330 (0.047)   0.578 (0.042)   0.063   0.661   15   Bränne Övregård   Kerstin   06.08.09   29   1.00   55   0.266   0.422 (0.047)   0.560 (0.047)   -0.096   0.584   16   Klostergården Dala   Belinda   07.08.09   30   1.00   38   0.130   0.421 (0.067)   0.474 (0.066)   0.332   0.002   17   Evertsholm   Belinda   17.08.09   29   1.00   54   0.164   0.438 (0.065)   0.511 (0.067)   -0.049   0.852   Table 2. Details of population genetic diversity in Puccinia graminis f.sp avenae at 11 microsatellite loci Abbreviations: N, Number of samples; G/N, number of genotypes divided by number of samples; Na, number of observed alleles; FIS, inbreeding coefficient in relation to subpopulation; Ho, observed heterozygosity (s.e. in parenthesis); He, expected heterozygosity (s.e. in parenthesis); IA, Index of Association and its p-value. aDay of collection, dd.mm.yy Berlin et al, 2012
  • Most variation within fields Source   df   SS   MS   Est. Var.   %   p-value   Among Populations   16   698.7   43.7   1.3   13%   <0.001   Within Populations   450   3975.3   8.8   8.8   87%     Totala   466   4674.0     10.1   100%     Among Varieties   4   96.2   24.1   0.2   2%   <0.001   Within Varieties   411   3990.4   9.7   9.7   98%     Totala   415   4086.6     9.9   100%     Among Years   1   97.2   97.2   0.4   4%   <0.001   Within Years   438   4315.4   9.9   9.9   96%     Totala   439   4412.6     10.3   100%     Table 4. Analysis of Molecular Variance (AMOVA) within and among Puccinia graminis f.sp avenae populations, collected from different varieties and collected 2008 and 2009 based on 11 microsatellite markers. a Clone correction prior to each AMOVA yields different numbers of total observations Berlin et al, 2012
  • Barberry is common in Sweden since the repeal of the ’Barberry eradication law’ in 1994.
  • Puccinia graminis on Berberis vulgaris Photographs A. Djurle
  • f.sp avenae f. sp. tritici/ secalis Puccinia arrhenatheri Photos: Anna Berlin and Iuliia Kyaschenko
  • The material from the grass host can be related to the aecia Berlin et al, 2012
  • From Eriksson and Henning, Die Getrideroste (1896)
  • Photograph Kerstin Gillen
  • Analysis of P. striiformis with microsatellite markers
  • A comparison of 2 pathosystems in Sweden o  Oat stem rust o  Spring sown crop o  Localized infection o  Hard to survive as uredinia or urediniospores o  No green bridge o  Early infections seen after aecia production o  Early populations are from sexual reproduction o  Wheat stripe rust o  Both fall and spring sown o  Systemic infection o  Easy to survive in plants due to systemic infection o  Green bridge o  Earliest infection seen on fall sown crops o  Early infections are from clones
  • The role of sexual reproduction in the disease epidemiology o  For some pathosystems sexual reproduction is required •  White mold on oil-seed rape caused by Sclerotinia sclerotiorum o  For others, sexual reproduction is not necessary or is even unknown •  Soybean rust caused Phakopsora pachyrhizi o  For some, sexual reproduction can take place but it can have a varying effect on disease epidemiology •  Rust diseases in cereals caused by different Puccinia species •  Phytophthora infestans on potato and tomato
  • Facultative sexual reproduction o  Pathosystems that can have sexual reproduction o  Obligate sexual reproduction? o  Classification has to be based on pathogen biology as well as cropping system o  Oats is only spring sown in Sweden o  Thus stem rust on oats in Sweden has ’obligate sexual reproduction’ o  Spring sown oats in a warmer climate or fall-sown oats could have survival as uredinia and thus have ’facultative sexual reproduction’ if the alternate host was present
  • A model comparing early and late infection shows that the earlier infections will dominate in the population
  • Can we classify P. striiformis? o  Is the alternate host present (??) o  Both fall and spring sown wheat crops in Sweden o  Examination of aecia from barberry in nature has revealed only P. graminis and P. arrhenatheri o  Facultative sexual reproduction o  How easy would it be to see the immediate results of sexual reproduction?
  • Can address this question with mathematical models o  Expand the model previously described (based on a Lotka- Volterra model for competition) o  Original model addressed early versus late infection •  The individuals that come early will dominate in the epidemic •  Infections from aeciospores of Pst would have difficulty in competing with the urediniospores from the overwintering crop o  Expand the model to many seasons and many clones •  Varying fitness, introduction of new individuals, and Muller’s ratchet can duplicate what we see with the appearance (and subsequent disappearance) of dominant clones
  • Model Multiple seasons and many clones o  Begin with population of 200 clones with varying fitness —each randomly drawn from a distribution with fixed mean and distribution o  Simulate 100 seasons allowing for competition with Lotka-Volterra o  Muller’s ratchet slightly decreasing the fitness of each individual each year o  Initial inoculum each year a function of the final clone population size the previous year o  Add a new individual each year with random fitness drawn from the original distribution, replacing the least fit individual.
  • Results of a model that simulates the appearance, persistence, and displacement of dominant clones of a plant pathogen
  • Changes in dominant clones of P. striiformis and P. infestans
  • What would we see with P. striiformis? o  Can P. striiformis reproduce sexually in Sweden? •  Alternate host present •  Both fall and spring sown wheat crops in Sweden •  Facultative sexual reproduction o  How easy would it be to see the immediate results of sexual reproduction? •  Difficult to see immediately, but the introduction of a clone with better fitness (possibly via sexual reproduction) will allow it to eventually dominate in the population •  It would take several years before the new clone could be detected o  This more fit clone can also be an immigrant clone!!
  • Söllingen, Niedersachsen 2013 Photograph courtesy Andreas Jacobi, Strube Research
  • Where is stem rust on wheat? o  Stem rust is rarely seen in wheat o  Alternate host of the pathogen is present o  Sexual reproduction of P. graminis s.l. clearly takes place o  Two possible reasons: •  Swedish wheat cultivars have sufficient resistance genes that stem rust is not a problem •  Pgt has been eliminated from the pathogen population •  The stem rust we see is caused by another f.sp. that has infected the wrong host....
  • Why no stem rust on wheat in Sweden? •  Barberry present •  Severe epidemics on oats and natural grasses •  Some stem rust on rye •  Large genotypic variation within and between fields •  P. graminis is clearly completing its sexual cycle •  How closely related are Pgt and Pgs? •  Does wheat grown in Sweden have effective resistance genes? •  Preliminary tests by the CDL indicates very few stem rust resistance genes are present in Swedish wheat varieties
  • o  How does the pathogen survive? o  How is the crop grown? o  How do the different individuals in the pathogen population interact (compete) with each other? o  Understanding these relationships is the key to controlling the disease