Abstract
The root-knot nematode Meloidogyne graminicola is one of the most serious nematode pests worldwide and represents a major constraint on rice production. While variation in the susceptibility of Asian rice (Oryza sativa) exists, so far no strong and reliable resistance has been reported. Quantitative trait loci for partial resistance have been reported but no underlying genes have been tagged or cloned. Here, 332 accessions of the Rice Diversity Panel 1 were assessed for gall formation, revealing large variation across all subpopulations of rice and higher susceptibility in temperate japonica accessions. Accessions Khao Pahk Maw and LD 24 appeared to be resistant, which was confirmed in large pot experiments where no galls were observed. Detailed observations on these two accessions revealed no nematodes inside the roots 2 days after inoculation and very few females after 17 days (5 in Khao Pahk Maw and <1 in LD 24, in comparison with >100 in the susceptible controls). These two cultivars appear ideal donors for breeding root-knot nematode resistance. A genome-wide association study revealed 11 quantitative trait loci, two of which are close to epistatic loci detected in the Bala x Azucena population. The discussion highlights a small number of candidate genes worth exploring further, in particular many genes with lectin domains and genes on chromosome 11 with homology to the Hordeum Mla locus.
Highlights
The genus Meloidogyne has been identified as the most scientifically and economically important group of nematodes (Jones et al, 2013)
At 2 days after inoculation (DAI), on average less than two J2 of M. graminicola had penetrated the TOG5674 roots and no J2 had penetrated the roots of linkage disequilibrium (LD) 24 and Khao Pahk Maw (Fig. 5 A, B)
We found significant variation in the degree of susceptibility of O. sativa accessions to infection
Summary
The genus Meloidogyne (root-knot nematodes) has been identified as the most scientifically and economically important group of nematodes (Jones et al, 2013). It has been clearly shown to cause substantial damage to the rice root system (Plowright and Bridge, 1990). Losses to upland, lowland, and deepwater rice as well as in rice nurseries (Bridge et al, 2005; Pokharel et al, 2010; Win et al, 2011) It is considered one of the biotic causal agents of yield failure in tropical aerobic rice (Kreye et al, 2009; De Waele et al, 2013). M. graminicola infestation of rice-based agrosystems is only a serious problem in the tropics (Jones et al, 2013) but the geographic areas affected might be expected to expand owing to climate change (Bebber et al, 2013)
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