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P lant pathology and disease resistance. Who is Alison Robertson?. Who is Alison Robertson?. Who is Alison Robertson?. 1991 B.S. Plant Pathology Uni. of Kwazulu-Natal 1992-1999 Plant Pathologist Tobacco Research Board Zimbabwe

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who is alison robertson2
Who is Alison Robertson?

1991 B.S. Plant Pathology Uni. of Kwazulu-Natal

1992-1999 Plant Pathologist Tobacco Research Board

Zimbabwe

M.S. Plant Pathology University of Zimbabwe

2003 Ph.D. Plant Pathology Clemson University, SC

who is alison robertson3
Who is Alison Robertson?

2004 – present

Associate professor/Extension field crops pathologist, Iowa State U.

70% extension; 30% research

alisonr@iastate.edu

alisonrISU

research interests
Research Interests

Goss’s wilt and leaf blight of corn

research interests1
Research Interests

Seedling blights caused by Pythium

slide8

Biology and management

of Phytophthora sojae

Alison Robertson

slide9

Economic importance

  • Estimated yield loss due to Phytophthora root rot in US, 1996 to 2007

Wrather and Koenning. 2009. Plant Health Progress

  • 2003 - Iowa = 4 million bu; OH = 20.2 million bu

Wrather and Koenning. 2006. J. Nematol.

slide11

Management

  • Resistance
    • Single gene (Rps)  Rps1c, 1k or 3a
    • Partial resistance  multiple genes
  • Improve field drainage
  • Seed treatments
slide12

Goal of research program

3. Seed treatments

1. Diversity

Improve management systems

to minimize losses due to PRR

4. Resistance

2. Molecular interactions

i. Single gene

ii. Partial resistance

slide13

Soybean – P. sojae interaction

Host

Pathogen

  • There are 15 known resistant genes (Rps) in soybean
  • Disease is managed by deployment of cultivars with single gene resistance & partial resistance
  • Corresponding avirulence genes (Avr) in P. sojae
  • There are > 200 known pathotypes of this pathogen identified in standard 13 differential set (Dorrance, et al. 2003)
pathotyping1
Pathotyping

1a

1b

1c

C

1d

1k

2

3a

7

3b

3c

4

5

6

8

Therefore pathotype = (1b,1c, 1k, 7)

slide17

Screening for partial resistance

2/3 vermiculite

inoculum

1/3 vermiculite

slide18

Mapping QTL for resistance

PI399036

PI399036

Conrad

Conrad

AR2

Sloan

AR3

Sloan

slide20

P. sojaecontinues to evolve

  • In Iowa:
    • 1966-73: 1 pathotype (race 1; 7)
    • (Tachibana et al, 1975)
    • 1991-94: 11 pathotypes; race 3 predominant
    • (Yang et al, 1996)
    • 2001-02: 18 pathotypes; race 25 and 35 predominant (Niu, 2004)
    • 2005-2007: 11 races and 12 pathotypes not previously detected in the state(Robertson et al, 2009)
slide22

Diversity in a single field - IA

Robertson et al. 2009. Plant Health Progress

slide23

Why is P. sojae so diverse?

  • Identify factors that shape the genetic diversity of xxxP. sojae populations
slide24

SSRs

  • No. of SSRs highly variable between individuals
  • 25 SSRs identified in P. sojae

(Dorrance and Grunwald, 2009; Schena et al, 2008)

slide26

10 pathotypes

32 pathotypes

17 pathotypes

slide27

Do Rps genes affect diversity of P. sojae?

  • H0 : Continuous use cultivars with specific Rpsgenes imposes selection pressure on the pathogen
  • Demonstrated for P. nicotianaeand tobacco system
  • (Sullivan et al., 2005)
number of pathotypes per treatment per year
Number of pathotypes per treatment per year

1=S-S-S-S 2= S-R-S-R 3=R-PR-PR-R

4=R-R-R-R 5=PR-PR-PR-PR 6=R-R-R-R

Stewart and Robertson. XXXX

slide30

Number and pathotypes of P. sojae detected in rotation study

R-R-R-R

PR-PR-PR-PR

R-R-R-R

R-PR-PR-R

S-R-S-R

S-S-S-S

Stewart and Robertson. XXXX

slide31

How do Avrgenes evolve?

  • Characterize the genetic changes that occur within xxithe avirulence gene(s) of P. sojae that enable the xxipathogen to escape detection by the corresponding xxiresistant gene.

Stewart et al. XXXX

slide33

Other resources

The links here are to two resources that I have been developing in collaboration with Don Lee at the University of Nebraska-Lincoln.

The Oomycete Learning environment is primarily for agronomists and farmers but high school students should still learn something from it.

The journey of a gene is an app we are developing for Future Farmers of America kids, so should be perfect for high schoolers.

We welcome any feedback – positive and negative!. Thanks

Oomycete Learning Environment (Phytophthora sojae)

http://passel.unl.edu/communities/oomycete

Journey of a gene

http://passel.unl.edu/ge/