RESUMEN
Fusarium oxysporum f. sp. cubense is one of the most destructive soilborne fungi causing Fusarium wilt disease in banana. Generally, F. oxysporum f. sp. cubense race 1 (R1) severely affects most of the banana varieties, except Cavendish banana (AAA). Here, we present the draft genome of an isolate of VCG 0124, a novel virulent R1 strain that severely affects the Cavendish group of banana isolated from the Theni district of Tamil Nadu, India. The genome assembly of R1 comprises 61,471,473 bp with 88 contigs and 18,377 protein-coding regions. The genome contains homologs of F. oxysporum f. sp. cubense race-specific secreted-in-xylem (SIX) genes SIX1, SIX5, SIX9, and SIX13. The absence of SIX4 and SIX6 and deletion of a peptide in SIX1 virulence factor genes in the R1 (VCG 0124) strain might be the contributing factor for strains infecting Cavendish banana in India.
Asunto(s)
Fusarium , Musa , Fusarium/genética , India , Enfermedades de las PlantasRESUMEN
Fusarium wilt caused by Fusarium oxysporum f.sp. cubense (Foc) is the most devastating disease affecting commercial and subsistence cultivation of banana (Musa spp.) worldwide. Generally, the Cavendish bananas are resistant to Foc race 1 that destroyed cv. 'Gros Michel' (AAA) and susceptible to tropical race 4 (TR4), which is causing severe epidemics in different banana-growing countries including India (Thangavelu et al. 2019). In 2019, a roving survey was conducted in major banana growing states of India such as Bihar, Uttar Pradesh, Gujarat and Tamil Nadu to assess the incidence of Fusarium wilt disease in Cavendish bananas and also to characterize the pathogens by different methods including Vegetative Compatibility Grouping (VCG) and molecular methods. The Fusarium wilt incidence in cv. Grand Naine (Cavendish group-AAA) was 6-65% in Bihar, 30-45% in Uttar Pradesh, 5-15% in Gujarat and 15- 21% in Tamil Nadu. For characterization, a total of 61 samples from the Fusarium wilt infected Cavendish bananas were collected and single spore culture of Foc was obtained. The morphological characterization revealed the presence of one to two oval- to kidney-shaped cells in false heads and sickle-shaped macroconidia and a foot-shaped basal cell. The pathogenicity was demonstrated by adopting randomized block design with five replications on cv. Grand Naine. The Koch's postulate was successfully completed by re-isolation of the inoculated Foc pathogen and characterization by PCR method. The VCG analysis carried out using nit-M testers of all known VCGs indicated the presence of VCG 0125 from the Foc samples collected from cv. Grand Naine grown in Uttar Pradesh (Siswabazar of Maharakanj district) and Tamil Nadu (Cumbum of Theni district), VCG 01220 from the Foc samples collected from cv. Grand Naine grown in Uttar Pradesh (Siswabazar of Maharakanj district) and Gujarat (Kamrej of Surat district,) and VCG 01213/16 from Foc samples collected from Uttar Pradesh (Siswabazar of Maharakanj district) and Bihar (Falka village of Katihar district) . The molecular confirmation of these VCGs 0125, and 01220 (Foc R1) isolates was carried out by PCR method using the primer set SIX6b_210_F and SIX6b_210_R (Carvalhais et al. 2019) for Foc R1, primer sets Foc TR4-F & Foc TR4 -R (Dita et al. 2010) for Foc TR4 and primer set Foc-1/Foc -2 (Lin et al. 2009) for Race 4. The results showed that only the primer set for Foc R1 has generated the expected amplicon size of 210 bp in the Foc isolates of VCG 0125 and 01220. Besides, the sequencing of Translation Elongation Factor (TEF) 1-α gene and BLAST searches in Genbank for the representative Foc isolates of VCG 0125 (Genbank no. MW 286800) showed 99.84% similarity to Foc R1 (KX365393.1) and Foc isolates of VCG 01220 (Genbank no. MW 286803) showed 99.69% similarity to Foc R1 (KX365413.1). Further, a phylogenetic analysis performed using the TEF1-α gene sequences showed that the Foc race 1 isolates (VCGs 0125 and 01220) from India were grouped with known Foc race 1 isolates from Tanzania and Australia. Based on the experimental results the study has confirmed the presence of VCGs 0125 and 01220 of Foc Race 1 in cv. Grand Naine in India. As these VCGs are most widely distributed and do not found to infect Cavendish bananas so far (Mostert et al. 2017), this report is very important from the quarantine and management perspectives. To the best of our knowledge, this is the first report of the occurrence of VCGs 0125 and 01220 of Foc Race 1 in cv. Grand Naine in India.
RESUMEN
Fourteen isolates of Fusarium were isolated from wilt affected tomato samples collected from 10 different states of India. Characterization of the fungal cultures based on morphology and sequencing of ITS rDNA revealed that they belonged to Fusarium oxysporum f.sp. lycopersici (Fol). Pathogenicity assay on two susceptible tomato cultivars showed all the 14 isolates were pathogenic and categorized in high-, moderate- and low-virulent groups. Differential host assay on Bonny Best (no resistant gene), UC82-L (harboring I-1), Fla.MH1 (harboring I-1 and I-2) and I3R-1 (harboring I-1, I-2 and I-3) tomato genotypes and PCR amplification with race-specific primers indicated that all the Fusarium isolates infecting tomato in India were belonging to race 1. Molecular diversity analysis based on ISSR markers revealed the presence of 3 distinct groups of Fol isolates. Abundant diversity was observed among the Fol isolates in harboring the virulence-related genes (endo-polygalacturonase gene pg1 and tomatinases) and toxin production (fumonisin). However, presence of pg1 does not correlate with virulence and the isolates carrying tomatinase 4 (tom-4) in combination with other tomatinase genes were of virulent group. Detection of fumonisin gene in six isolates of Fusarium infecting tomato indicated their toxigenic nature.