Plant 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

1999 M.S. Plant Pathology University of Zimbabwe

2003 Ph.D. Plant Pathology Clemson University, SC

Who is Alison Robertson?2004 – presentAssociate professor/Extension field crops pathologist, Iowa State U.

70% extension; 30% research

alisonr@iastate.edu alisonrISU

Research InterestsGoss’s wilt and leaf blight of corn

Research InterestsSeedling blights caused by Pythium

Biology and management of Phytophthora sojae

Alison Robertson

Economic importance

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

19961998

20002002

20042006

010,00020,00030,00040,00050,00060,000

1000

bus

hels

Wrather and Koenning. 2009. Plant Health Progress

• 2003 - Iowa = 4 million bu; OH = 20.2 million buWrather and Koenning. 2006. J. Nematol.

Phytophthora root and stem rot

Resistance― Single gene (Rps) Rps1c, 1k or 3a― Partial resistance multiple genes

Improve field drainage

Seed treatments

Management

Goal of research program

Improve management systems to minimize losses due to PRR

3. Seed treatments1. Diversity

2. Molecular interactions 4. Resistance

i. Single gene ii. Partial resistance

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)

Host Pathogen

Soybean – P. sojae interaction

Pathotyping

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

1a 1b 1c 1k 2 3a

3b 3c 4 5 6 7 8

1d C

Pathotyping

Identifying novel resistance genes

Screening for partial resistance

1/3 vermiculite

inoculum

2/3 vermiculite

AR2

AR3

PI39

9036

Conr

ad

Sloa

n Sloa

n

PI39

9036

Conr

ad

Mapping QTL for resistance

BUT……P. sojae is extremely diverse

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)

P. sojae continues to evolve

Furthermore ………..

Robertson et al. 2009. Plant Health Progress

Diversity in a single field - IA

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

Why is P. sojae so diverse?

No. of SSRs highly variable between individuals

25 SSRs identified in P. sojae (Dorrance and Grunwald, 2009; Schena et al, 2008)

SSRs

Evaluating population diversity

R14R17

R2R25

Iowa Ohio South Dakota Checks

Coord. 1

Coor

d. 2

10 pathotypes 32 pathotypes 17 pathotypes

H0 : Continuous use cultivars with specific Rps genes imposes selection pressure on the pathogen

Demonstrated for P. nicotianae and tobacco system(Sullivan et al.,

2005)

Do Rps genes affect diversity of P. sojae?

Year Treatment1 2 3 4 5 6

2007 Susceptible Susceptible Rps1k Rps1k Partial R Rps1k2008 Susceptible Rps1k Partial R Rps1c Partial R Rps1k2009 Susceptible Susceptible Partial R Rps3a Partial R Rps1k2010 Susceptible Rps1k Rps1k Rps1k Partial R Rps1k

How do Rps genes affect diversity of P. sojae?

Stewart and Robertson. 2014

Number of pathotypes per treatment per year

1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6planting harvest planting harvest planting harvest planting

2007 2008 2009 2010

0

2

4

6

8

10

12

race 1 others

Treatments

No.

isola

tes

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-RStewart and Robertson. XXXX

Number and pathotypes of P. sojae detected in rotation study

Stewart and Robertson. XXXX

S-S-S-S

R-R-R-R

PR-PR-PR-PR

S-R-S-R

R-R-R-R

R-PR-PR-R

How do Avr genes evolve?

Stewart et al. XXXX

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.

How does Avr change to escape detection by Rps?

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 genehttp://passel.unl.edu/ge/

Thanks for your attention.