**3. Causal organism**

Panama disease is brought about by the soilborne hyphomycete, *Fusarium oxysporum* Schlect. f. sp. *cubense*. It is one of more than 100 special forms of *F. oxysporum* that reason vascular wilt of flowering plants. It contains pathogenic and saprophytic strains that cannot be recognized morphologically. Fungus grow 4–7 mm/day on Potato Dextrose Agar medium at 24°C, with slight to significant fluffy mycelium, and have white to pink pigmentation. Sporodochia are tan to orange, and sclerotia are blue and submerged. Conidia and macroconidia are delivered on extended and unbranched monophialides. Microconidia are 5–16 × 2.4–3.5 μm, one or twocelled, oval to kidney shaped, and are borne in false heads. Macroconidia are 27–55 × 3.3– 5.5 μm, four to eight sickle celled formed with foot shaped basal cells. Terminal and intercalary chlamydospores are 7–11 μm size, normally globose and formed independently or two by two in hyphae or conidia (**Figure 2**). Atypically for the species, chlamydospores are not distributed by isolates of *F. oxysporum* f. sp. *cubense* in vegetative compatibility group (VCG) 01214.

Four races of *F. oxysporum* f. sp. *cubense* have been revealed, just three of which affect banana (race 3 is a pathogen of Banana). Race 1 caused the pandemics on Gros Michel and furthermore affects the cultivars Maqueño, Silk, Pome, Pisang Awak. Race 2 affects cooking bananas *viz.*, Bluggoe, and some reared tetraploids. Race 4 is most dangerous since it affects race 1 and race 2 powerless clones just as the Cavendish cultivars. Up to this point, it had been accounted for just in subtropical regions where cold weather during winter are believed to be a predisposing factor. In any case, inside the most recent decade, remarkable harm was observed in Cavendish monocultures in tropical South-East Asia. A particular populace of the pathogen, VCG 01213-01216, is responsible for these flareups. Despite the fact that it is as of now limited to Asia and northern Australia, it caused critical disease in the western exchanges because of their dependence on the Cavendish clones. Vegetative or substantial similarity has been utilized widely to describe overall populaces of this pathogen. More than 20 VCGs have been accounted which is a pointer for the incredible genetic diversity that happens inside this taxon.

**Figure 2.** *Pure culture and spore of* Fusarium oxysporium *f. sp.* cubense.
