GWAS provides biological insights into mechanisms of the parasitic plant (Striga) resistance in sorghum

Jacinta Kavuluko,Mark Wamalwa,Titus Magomere,Sylvia Mutinda,Willy Kibet,Steven Runo,Irine Sugut,Magdaline Kibe,Joel Masanga,Damaris Odeny

doi:10.1186/s12870-021-03155-7

Abstract

BackgroundSorghum yields in sub-Saharan Africa (SSA) are greatly reduced by parasitic plants of the genus Striga (witchweed). Vast global sorghum genetic diversity collections, as well as the availability of modern sequencing technologies, can be potentially harnessed to effectively manage the parasite.ResultsWe used laboratory assays – rhizotrons to screen a global sorghum diversity panel to identify new sources of resistance to Striga; determine mechanisms of resistance, and elucidate genetic loci underlying the resistance using genome-wide association studies (GWAS). New Striga resistant sorghum determined by the number, size and biomass of parasite attachments were identified. Resistance was by; i) mechanical barriers that blocked parasite entry, ii) elicitation of a hypersensitive reaction that interfered with parasite development, and iii) the inability of the parasite to develop vascular connections with hosts. Resistance genes underpinning the resistance corresponded with the resistance mechanisms and included pleiotropic drug resistance proteins that transport resistance molecules; xylanase inhibitors involved in cell wall fortification and hormonal regulators of resistance response, Ethylene Response Factors.ConclusionsOur findings are of fundamental importance to developing durable and broad-spectrum resistance against Striga and have far-reaching applications in many SSA countries where Striga threatens the livelihoods of millions of smallholder farmers that rely on sorghum as a food staple.

Highlights

Sorghum yields in sub-Saharan Africa (SSA) are greatly reduced by parasitic plants of the genus Striga
Consistent with the ‘zigzag’ model for Strigahost interactions [35], we identified genes encoding different components of pathogen activated immunity including: i) DNA repair and peroxidases; ii) Downy mildew resistant 6 (DMR6) that participates in salicylic acid homeostasis and required for susceptibility to downy mildew in Arabidopsis [36] and P. infestans potato [37]; iii) and genes involved in induction of the Systemic Acquired Resistance (SAR) pathway which in Striga-rice interactions is regulated by both jasmonic acid (JA) and salycilic acid (SA) in a cross talk mediated by WRKY45 [38] and regulated by (AP2/ Ethyleneresponsive transcription factor (ERF)) [39]
Taken together, we report on new sources of Striga resistant sorghum obtained from a diverse collection

Summary

Introduction

Sorghum yields in sub-Saharan Africa (SSA) are greatly reduced by parasitic plants of the genus Striga (witchweed). Yield losses due to Striga in Africa are Striga control methods are limited These include cultural and agronomic practices [3], seed treatment with herbicides [4], use of trap crops [5] and deployment of resistant varieties [6, 7]. These strategies have been used for a long time, they are either ineffective or poorly adaptable by African smallholder farmers [8]. An effective resistance breeding approach will be one that combines several

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