Cereal Root Interactions with Soilborne Pathogens—From Trait to Gene and Back

Abstract

Realizing the yield potential of crop plants in the presence of shifting pathogen populations, soil quality, rainfall, and other agro-environmental variables remains a challenge for growers and breeders worldwide. In this review, we discuss current approaches for combatting the soilborne phytopathogenic nematodes, Pratylenchus and Heterodera of wheat and barley, and Meloidogyne graminicola Golden and Birchfield, 1965 of rice. The necrotrophic fungal pathogens, Rhizoctonia solani Kühn 1858 AG-8 and Fusarium spp. of wheat and barley, also are discussed. These pathogens constitute major causes of yield loss in small-grain cereals of the Pacific Northwest, USA and throughout the world. Current topics include new sources of genetic resistance, molecular leads from whole genome sequencing and genome-wide patterns of hosts, nematode or fungal gene expression during root-pathogen interactions, host-induced gene silencing, and building a molecular toolbox of genes and regulatory sequences for deployment of resistance genes. In conclusion, improvement of wheat, barley, and rice will require multiple approaches.

Chronic Sublethal Aluminum Exposure and Avena fatua Caryopsis Colonization Influence Gene Expression of Fusarium avenaceum F.a.1

“…These genes are promising candidates for host-induced gene silencing (HIGS), an RNAibased approach for pathogen suppression that has been deployed against Fusarium spp. (reviewed in Okubara et al, 2019). Additionally, these genes (and others identified here) may be utilized in identifying other fungal strains that may be even more effective in causing weed seedbank decay.…”

A new esophageal gland transcriptome reveals signatures of large scale de novo effector birth in the root lesion nematode Pratylenchus penetrans

“…The identification of a more complete roster of candidate effectors in P. penetrans, coupled with available genome and transcriptome sequences for many phylogenetically well-positioned species, provides an opportunity to investigate the evolutionary history of the effector repertoire. We reconstructed a robust multi-gene phylogenetic tree, based on 86 CEGMA (Core Eukaryotic Genes Mapping Approach) genes highly conserved in the following species: root lesion nematodes Pratylenchus coffeae [ 23 – 25 ], P. neglectus, and P. thornei (PRJNA512537 [ 26 ];), and the burrowing nematode Radopholus similis [ 27 ]; root-knot nematodes Meloidogyne incognita [ 28 ] and M. hapla [ 29 ]; cyst nematodes Globodera pallida [ 30 ], G. rostochiensis [ 11 ], and Heterodera glycines [ 31 ]; the false root-knot nematode Nacobbus aberrans [ 32 ], the reniform nematode Rotylenchulus reniformis [ 33 ], the migratory potato rot nematode Ditylenchus destructor [ 34 ]; the pinewood nematode Bursaphelenchus xylophilus [ 35 ]; and the free-living nematode Caenorhabditis elegans ( http://parasite.wormbase.org ). We then searched for the presence of putative homologs of the entire P. penetrans putative effector repertoire validated by in situ hybridization ( n = 53) in all these species using BLAST (e-values < 1 × 10 − 5 and coverage > 50, Fig.…”

Purinoceptor P2K1/DORN1 Enhances Plant Resistance Against a Soilborne Fungal Pathogen, Rhizoctonia solani

“…Further studies are required to understand the complete mechanism by which extracellular ATP enhances defense against this and other soilborne pathogens, which might provide leads to new management strategies for growers. Very recently, putative orthologs of P2K1/DORN1 have been reported in banana, camelina, and wheat (Li et al, 2016;Okubara et al, 2019;Shan et al, 2020). Such functional studies using crops other than Arabidopsis would allow us to directly use the resistance mechanism against the necrotrophic pathogens.…”

“…Rhizoctonia solani primarily infects the below-ground organs of the plant ( Weinhold and Sinclair, 1996 ; Keijer et al, 1997 ), resulting in damping-off, root rot and bare patch of cereals, brown patch of turfgrass, black scurf of potato, and sheath blight of rice ( Sneh et al, 1991 ; DeShields et al, 2018 ). For example, R. solani anastomosis group 8 (AG-8), causes chronic and acute yield losses from 10-30% in dryland cereal production systems of the Pacific Northwest, USA and up to 100% in parts of the world, amounting to billions of dollars of annual losses to agriculture worldwide ( Okubara et al, 2014 ; Okubara et al, 2019 ). It is a broad host range pathogen, causing disease on a variety of crop plants, including canola and other brassicas.…”

“…Management of Rhizoctonia root diseases has been under development for decades. Genetic resistance to R. solani AG-8 has been reported for wheat ( Okubara et al, 2009 ; Mahoney et al, 2016 ; Mahoney et al, 2017 ) but is not readily deployable in wheat breeding programs due to the multigenic nature of resistance and absence of molecular markers ( Okubara et al, 2019 ). However, a broad-spectrum resistance gene from rice that confers R. solani resistance in Arabidopsis has been recently described ( Maeda et al, 2019 ) and would be more readily deployable than multigenic resistance.…”