Molecular Identification of Secreted Effector Genes Involved in African Fusarium oxysporum f.sp. elaeidis Strains Pathogenesis During Screening Nigerian Susceptible and Tolerant Oil Palm (Elaeis guineensis Jacq.) Genotypes

Abstract

Fusarium wilt is caused by Fusarium oxysporum f. sp. elaeidis, and constitutes a severe threat to the oil palm industry in Africa. This study is aimed at surveying, identifying the secreted effector genes responsible for virulence during pathogenesis, and investigating the level of genetic diversity and cluster resolutions of alleles accountable for virulence in pathogenic strains of F. oxysporum f.sp. elaeidis from African countries. Fifty-eight fungal strains were isolated from acute and chronic Fusarium wilt diseased oil palms in Nigeria, Ghana and Cameroon. Morphological and sequencing analysis of the Internal Transcribed Spacer (ITS) region grouped all strains into nine dominant strains with a majority (41.37%) belonging to F. oxysporum, followed by F. solani (20.68%), F. equiseti (20.68%), F. verticilliodes (5.17%), F. proliferatum (3.44%), F. chlamydosporum (3.44%), F. nelsonii (1.72%), Fomes fomentarius, and Penicillium simplicissimum (1.72%). Disease incidence and severity showed varying levels of virulence with some Fusarium strains causing severe symptoms while others exhibited slight symptoms. ISSR evaluation disclosed a considerable level of genetic diversity among pathogenic F. oxysporum f.sp. elaeidis strains. Molecular characterization using defense gene primers revealed that the oil palm genotypes screened did not amplify defense genes. During pathogenesis, Fusarium strains produced GMC oxidoreductases, hypothetical proteins, FOIG 16629, FOXG 14258, and Pyranose dehydrogenase 3-like proteins using virulent effector gene primers. Polymerase Chain Reaction analysis using specific gene primers revealed that PRK02106, beta and BetA effector genes were secreted explicitly by F. oxysporum f.sp. elaeidis (4) and F. oxysporum f.sp. elaeidis (CRT) strains while screening tolerant oil palm genotypes. During screening susceptible oil palm genotypes, F. oxysporum f.sp. elaeidis (4) and F. oxysporum f.sp. elaeidis (CRT) strains produced FGGY_L-XK1, PRK10939, FGGY_N1, XylB1, XylB2, FGGY_L-XK2, XylB3, FGGY_N2, and XylB4 effector genes. Identifying these effector genes will provide the platform to study the basis of pathogenesis which will help breeders to modify breeding techniques for the improvement of oil palm genotypes in order to reduce oil palm loss in plantations and enhance food security.

Keywords: Fusarium oxysporum f.sp. elaeidis; Fusarium wilt; genetic diversity; incidence; oil palm; pathogenesis; severity; virulence.