Plant pathology and disease resistance

Who is Alison Robertson?

1991B.S. Plant Pathology Uni. of Kwazulu-Natal Plant Pathologist Tobacco Research Board Zimbabwe 1999 M.S. Plant PathologyUniversity of Zimbabwe 2003Ph.D. Plant Pathology Clemson University, SC

Who is Alison Robertson? 2004 – present Associate professor/Extension field crops pathologist, Iowa State U. 70% extension; 30% research alisonrISU

Research Interests Goss’s wilt and leaf blight of corn

Research Interests Seedling 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 Wrather and Koenning Plant Health Progress Iowa = 4 million bu; OH = 20.2 million bu Wrather and Koenning 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 treatments 1. Diversity 2. Molecular interactions 4. Resistance i. Single geneii. Partial resistance

Disease Cycle of Phytophthora root and stem rot Dorrance et al Plant Health Instructor

 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) 1a1b1c 1k 23a 3b3c d C Pathotyping

Identifying novel resistance genes

Screening for partial resistance 1/3 vermiculite inoculum 2/3 vermiculite

AR2 AR3 PI Conrad Sloan PI Conrad Mapping QTL for resistance

BUT……P. sojae is extremely diverse

In Iowa: : 1 pathotype (race 1; 7) (Tachibana et al, 1975) : 11 pathotypes; race 3 predominant (Yang et al, 1996) : 18 pathotypes; race 25 and 35 predominant (Niu, 2004) : 11 races and 12 pathotypes not previously detected in the state (Robertson et al, 2009) P. sojae continues to evolve

Furthermore ………..

Robertson et al 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

10 pathotypes 32 pathotypes 17 pathotypes

 H 0 : 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?

YearTreatment Susceptible Rps1k Partial RRps1k 2008SusceptibleRps1kPartial RRps1cPartial RRps1k 2009Susceptible Partial RRps3aPartial RRps1k 2010SusceptibleRps1k Partial RRps1k How do Rps genes affect diversity of P. sojae? Stewart and Robertson. 2014

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

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) Journey of a gene

Thanks for your attention.