Characterization and integrated management of Fusarium oxysporum f.sp. cubense (E.F. Smith) synder and hansen causing fusarium wilt disease of banana
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Date
2020
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Department of Plant Pathology, College of Horticulture, Vellanikkara
Abstract
Fusarium wilt of banana caused by the soil borne fungus Fusarium oxysporum f. sp. cubense (Foc) is a serious constraint to banana cultivation in Kerala. The fungal species constitute four pathogenic races, of which Race 1 is the prevalent one in our country and Race 4 is one of the emerging threats, though not reported from Kerala yet. The present study was undertaken to characterize the associated pathogenic races and to develop an integrated package for the disease management. The project initiated with purposive sampling surveys in various districts viz., Thiruvananthapuram, Ernakulam, Thrissur, Palakkad, Kozhikode and Wayanad representing different agroclimatic zones of Kerala. The per cent disease incidence (PDI) and the per cent disease severity (PDS) ranged from 1.52 to 43.65 per cent and 20.34 to 49.57 per cent. The correlation analysis of PDI with weather parameters showed a positive correlation with rainfall. However, it was negatively correlated with temperature. The study on symptoms under natural as well as artificial conditions showed characteristic external and internal symptoms. The number of days taken for complete wilting under artificial inoculation was 29.67 in Rasthali (AAB), 47.99 in Njalipoovan (AB), 31 in Kadali (AA) and 37.67 in Chenkadali (AAA). Among the thirty isolates of the Foc collected, twenty three isolates were from Rasthali variety, four isolates from Kadali, two isolates from Njalipoovan and one from Chenkadali. Studies on identification of Foc races with the differential host assay revealed that the varieties such as Cavendish (assay host to Race 4), Nendran (assay host to Race 4), Heliconia sp. (assay to Race 3) and Monthan (assay to Race 2) did not produce any type of symptoms whereas, all the isolates produced symptoms on Rasthali (assay host to Race 1) variety. A non polymerase chain reaction (PCR) based quick molecular diagnostic technique with loop mediated isothermal amplification (LAMP) assay was developed for the detection of Races of the pathogen. All isolates showed positive reaction to the LAMP assay for Race 1 and negative for Race 4. A PCR was also standardised for the confirmation of the races. It is concluded that all the isolates collected from different agroclimatic zones belonged to the Race 1 category of the pathogen only. Cultural and morphological characterization of the isolates revealed white coloured aerial mycelium with pink pigmentation and cottony and fluffy mycelial mat. The mycelial growth rate in half strength potato dextrose agar (PDA) medium ranged from 0.83 to 2.40 cm/day and the length and breadth of macroconidia and microconidia measured about 15.01 - 20.20 μm x 2.14 - 5.07 μm and 4.49 - 7.42 μm x 1.35 - 3.13 μm respectively. The inter-septal length and breadth of hyphae ranged from 16.14 to 22.94 μm and 4.22 to 6.57 μm respectively and the size of chlamydospores varied from 5.68 to 9.58 μm in diameter. The PCR based molecular characterization of isolates using ITS (internal transcribed spacer) primers produced single bands of size approximately 580 bp. In silico analysis of the sequences showed 96 to 100 per cent homology to Foc. Based on cultural, morphological and molecular characters, the pathogen was identified as Fusarium oxysporum f. sp. cubense. The screening of accessions maintained in the germplasm of Banana Research Station (BRS), Kannara was done to assess their disease resistance to Foc Race 1 and were grouped into six categories. Fifteen immune varieties viz., Attunendran, Zanzibar, Big Ebanga, Nedunendran, Nendran, BRS II, Thiruvananthapuram, Pachanadan I, Cultivar Rose, Pisang Lilin, Pisang Jari Buaya, Yangambi Km5, Grand Naine, Chinese Cavendish and Nendran Hybrid and four highly susceptible varieties viz., Cheriya Poovan, Valiya Poovan, Kadali and Rasakadali were identified. The estimation of biochemical parameters for the assessment of host plant disease resistance against Foc Race 1 revealed that the activity of total phenols and defense related enzymes was more in resistant varieties compared to susceptible varieties and the activity of reducing and non reducing sugars was more in susceptible varieties. An in vitro experiment was conducted for the evaluation of chemical fungicides, biocontrol agents and botanicals for control of the pathogen. The effective treatments from in vitro evaluation were carried over to pot culture and field experiments for the disease management. Among the various treatments, an integrated package comprising of Pseudomonas fluorescens + arbuscular mycorrhizal fungi and Trichoderma enriched cow dung + tebuconazole (T6) was proved to be the best for yield and disease management. It is concluded that the present study has enlightened our knowledge on characterization, race identification and management of Fusarium wilt pathogen infecting banana.
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PhD