Colonisation and histological changes in muskmelon and autumn squash tissues infected by <Emphasis Type="Italic">Acremonium cucurbitacearum</Emphasis> or <Emphasis Type="Italic">Monosporascus cannonballus</Emphasis> |
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| Authors: | Ana Alfaro-Fernández Amparo García-Luis |
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| Institution: | (1) Instituto Agroforestal Mediterráneo (IAM), Universidad Politécnica de Valencia (UPV), Camino de Vera s/n., 46022 Valencia, Spain;(2) Departamento de Biología Vegetal, Universidad Politécnica de Valencia (UPV), Camino de Vera s/n,, 46022 Valencia, Spain |
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| Abstract: | Muskmelon (Cucumis melo cv. Temprano Rochet) and autumn squash (Cucurbita maxima) seedlings were inoculated either with Acremonium cucurbitacearum or Monosporascus cannonballus, two of the soil-borne fungi implicated in ‘melon collapse’. Inoculation was achieved in two different ways: by growing the
plants in pots containing infested soil to study the histological changes produced in the infected tissues using light microscopy
and by growing seedlings in Petri dishes together with fungal colonies in order to observe the colonisation of the plant tissues
using scanning electron microscopy. Both muskmelon and autumn squash roots infected with A. cucurbitacearum showed a suberised layer in the epidermis and the outermost layers of the parenchymatic cortex, but these symptoms developed
earlier in the muskmelon plants. Muskmelon plants infected by this fungus also presented hypertrophy and hyperplasia, which
led to a progressive separation of the vascular bundles in the lower stems of the affected plants. This response was not observed
in autumn squash during the study. On the other hand, few histological changes were observed in tissues infected with M. cannonballus and only a slight increase in the size of cortical intercellular spaces was noted in the lower stems of muskmelon plants,
and infected autumn squash tissues remained free of these symptoms throughout the study. The scanning electron microscope
observations revealed that both fungi were able to colonise the tissues of the two host plants which were studied. A. cucurbitacearum colonised the epidermis and cortex of both muskmelon and autumn squash. The hyphae grew both inter- and intracellularly,
and the density of the colonisation decreased within the endodermis. The same colonisation of host plants was observed as
a result of M. cannonballus infection. The xylem vessel lumina of both muskmelon and autumn squash showed hyphae and tylose formation as a result of
both fungal infections. However, non-fungal structures were detected in the hypocotyl vascular tissues. The present study
demonstrates that both fungi are capable of infecting the tissues of a species which is resistant (autumn squash) and a species
which is susceptible (muskmelon) to melon collapse. |
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| Keywords: | Cucumis melo Cucurbita maxima Infection process Light microscopy Scanning electron microscopy Vine decline |
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