Evaluation of rice cultivars for resistance to rice yellow mottle virus

H Kam,M.-N Ndjiondjop,A Ghesquiere,M.D Laing,N Ouedraogo

doi:10.4314/acsj.v26i1.4

Abstract

Rice yellow mottle virus (RYMV), which is only found in Africa, threatens rice farming on the continent. A local Oryza sativa cultivar collected from Burkina Faso (named BM24), was evaluated with that of well known highly resistant and tolerant cultivars. Firstly, three RYMV isolates were used to characterise the differential interaction within the cultivars. Secondly, disease kinetics of symptom expression and virus titer on leaves at 21 days after inoculation were assessed using the BF1 isolate. Thirdly, the allelic profile of O. sativa varieties using SSR marker RM101 located on chromosome 12 was also assessed. IR64 showed susceptibility to all isolates; while Tog5681 was resistant to all isolates. Ng122 overcame the resistance of Gigante, with mild leaf symptoms at 42 dpi. Azucena and BM24 had, therefore, different resistance level regarding the three isolates (Ng117b, Ng122 and Ng144). When infected with the isolate, BF1, BM24 and Azucena exhibited same resistance patterns in early growth stages with delayed of symptoms appearance, but BM24 outperformed Azucena at later stages. The virus content in the two accessions, at 14 days post inoculation, was statistically different with BM24, showing less virus compared to Azucena. However, the two accessions depicted an identical allelic profile at RM101 locus. Key words: Azucena, Burkina Faso, local variety, Oryza sativa

Highlights

In Africa, two rice species are cultivated, the African rice (Oryza glaberrima) and the Asian rice (Oryza sativa)
Screening with BF1 further corroborated the previous finding, and suggests that BM24 and Azucena could have same genotype at the RM101 locus, which is associated with QTL12 that provides partial resistance to Rice yellow mottle virus (RYMV) (Ioannidou et al, 2000; Boisnard et al, 2007)
BM24 could be used for QTL12 fine mapping, which has been difficult in offspring derived from IR64 and Azucena (Boisnard et al, 2007)

Summary

Introduction

In Africa, two rice species are cultivated, the African rice (Oryza glaberrima) and the Asian rice (Oryza sativa). These two rice species are affected by Rice yellow mottle virus (RYMV) disease, which is only found on this continent (Kouassi et al, 2005). Partial resistance is expressed only at the early stages of infection It is characterised by delayed and reduced virus accumulation in leaves, and delayed virus invasion in bundle sheath tissues (Ioannidou et al, 2003). The tolerance in Azucena was apparent at the later stages of infection, and was characterised by reduced symptom expression, despite high virus titer (Ioannidou et al, 2000). Partial resistance was reported previously in cultivar Azucena (Albar et al, 1998; Pressoir et al, 1998; Ahmadi et al, 2001; Boisnard et al, 2007)

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