''Fusarium mangiferae'' is a fungal plant pathogen that infects mango trees. Its aerial

mycelium Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrates. A typical single spore germinates ...

is white and floccose.

Conidiophore A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to the ...

s on aerial mycelium originating erect and prostrate from substrate; they are sympodially branched bearing mono and polyphialides. Polyphialides have 2–5 conidiogenous openings. Phialides on the aerial conidiophores mono- and polyphialidic. Sterile hyphae are absent.

Microconidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to th ...

are variable in shape, obovoid conidia are the most abundant type, oval to allantoid conidia occurring occasionally.

mostly 0-septate with 1-septate conidia occurring less abundantly. Sporodochia are present.

Macroconidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an Asexual reproduction, asexual, non-motility, motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are al ...

are long and slender, usually 3–5 septate.

Chlamydospore A chlamydospore is the thick-walled large resting spore of several kinds of fungi, including Ascomycota such as '' Candida'', Basidiomycota such as '' Panus'', and various Mortierellales species. It is the life-stage which survives in unfavourable ...

s are absent.

Host and symptoms

''Fusarium mangiferae'' is one of the causal agents of malformation disease that affects mango (''

Mangifera indica ''Mangifera indica'', commonly known as mango, is a species of flowering plant in the family Anacardiaceae. It is a large fruit tree, capable of growing to a height of . There are two distinct genetic populations in modern mangoesthe "Indian ty ...

,'' L.) growing regions and is economically important. It causes mango malformation disease (MMD) and induces vegetative development abnormalities in shoots that leads to misshaped buds, short internodes, dwarf and narrow leaves. Moreover, MMD causes hormone imbalances in the

inflorescence An inflorescence is a group or cluster of flowers arranged on a Plant stem, stem that is composed of a main branch or a complicated arrangement of branches. Morphology (biology), Morphologically, it is the modified part of the shoot of sperma ...

that leads to abnormalities such as an increase in size and numbers, especially for male flowers. They are usually sterile or, if fertilized, abort after fruit set. The malformation of flowers causes a decrease in fruit yields. A ''

Fusarium ''Fusarium'' is a large genus of filamentous fungi, part of a group often referred to as hyphomycetes, widely distributed in soil and associated with plants. Most species are harmless saprobes, and are relatively abundant members of the soil mi ...

'' toxin has been found to play a role in the malformation symptoms on mango. Rootstocks from seedlings used for grafting can also be infected.

Disease cycle

It is an ascomycete that produces mycelia with aerial

conidiophores A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to ...

that contain colored structures such as

macroconidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an Asexual reproduction, asexual, non-motility, motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are al ...

with up to five cells, microconidia in false heads and a sporodochium. The epidemiology of the disease is not completely understood and there have been some conflicting reports. Macro and microconidia are produced in live and dead malformed tissues and they are dispersed by wind. Once conidia are dispersed, they will infect primarily the flower and vegetative (apical) buds. Small fruits have also been found to be sources of inoculum in the outer flesh but not the seeds contributing to the spread of the fungus if moved from infected orchards. ''F. mangiferae'' can be spread over large distances by material used for propagation of mango. In terms of survival structures, ''F. mangiferae'' does not produce

chlamydospore A chlamydospore is the thick-walled large resting spore of several kinds of fungi, including Ascomycota such as '' Candida'', Basidiomycota such as '' Panus'', and various Mortierellales species. It is the life-stage which survives in unfavourable ...

s and conidia do not survive by itself in soil, only within infected

. Thus, it is not a typical soil-borne pathogen and ''

'' species.

Environment

Germination of conidia does not occur at low temperatures and high inoculum have been found in summer months. Although inoculum is high during the summer, MMD spreads slowly in orchards due to the sensitivity of conidia to sunlight that impedes their survival. The fungus spreads primarily by wind but there have been reports of an association with the mango bud mite, ''Aceria mangiferae'', that aids in spread either by wounding that facilitates infection or vectoring conidia. The bud mite could possibly enhance fungal colonization and severity. Humans can also spread the fungus through contaminated tools.

Management

Management of the MMD includes sanitation by removing infected flowers and branches once the disease is established in the orchard. Although it can be time consuming and difficult when the affected trees are large, but it’s an important component for management of disease. Furthermore, using clean nursery stock, no grafting with infected budwood, and decontamination of infected fruit prior to storage or shipping can help to lower disease and spread. Under experimental conditions, sprays with concoctions containing extracts from ''Datura stramonium'', ''Calotropis gigantea'' and ''Azadirachta indica'' (neem), showed antifungal activity and controlled the malformation symptoms on mango. Chemical control with fungicides is possible but there is no consensus over what chemical is most effective.

References

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