Pyramiding rust

Enhancing soybean rust resistance through Rpp2, Rpp3 and Rpp4 pair wise gene pyramiding

M. Maphosa, Talwana, H & Tukamuhabwa, P

Introduction

•Soybean rust is an obligate fungal parasite with multiple hosts

•It is a polycyclic disease with multiple re-infections

•Genetic resistance is a long term solution

•However, single genes have been overcome in certain areas whilst others show increasing susceptibility

•To enhance single gene resistance & broaden the base for available resistance genes

Introduction

•Conventional gene pyramiding is a challenge

•It is not practically feasible in some cases

•Marker assisted gene pyramiding may be a possible solution

•Given that some of the resistance genes have markers

associated with them

•No attempt has be done to use identified SSR for MAS

pyramiding & effect of pyramiding genes

Study 1

•Validate the use of SSR in pyramiding resistance genes Rpp2, Rpp3 and Rpp4

Study 1

Marker Linkage Group Position1

(cM)

Resistance Gene Reference

Sat_255 J 43.85 Rpp2 Silva et al. (2008)

Satt620 J 53.71 Rpp2 Silva et al. (2008)

Satt460 C2 111.87 Rpp3 Hyten et al. (2009)

Sat263 C2 118.78 Rpp3 Hyten et al. (2009)

Satt288 G 76.77 Rpp4 Yamanaka et al. (2008)

AF162283 G 87.94 Rpp4 Yamanaka et al.(2008)

Study 1

Study 1

Study 2

•Evaluating the most effective resistance gene combination using sporulation & severity indices

Study 2

• All parents has severities higher that the pair wise combinations

•In the F3 generation

Major Findings

• Complementary gene interactions occurred resulting in

enhanced resistance

• The effectiveness of resistance is influenced by the genetic

background of introgression

• Independent genetic control of severity and sporulation in

soybean rust

• Disproportinate contribution of resistance, Rpp3 more

dominant

Recommendations

• MAS gene pyramiding is feasible

• Introgression to elite lines

• Evalution of pairwise genes in other areas

• Assessing for durability of the resistance

Acknowledgements

•RUFORUM

•International Foundation for Science (4968-1)

•Makerere University Soybean breeding programme