Colonisation and histological changes in muskmelon and autumn squash tissues infected by Acremonium cucurbitacearum or Monosporascus cannonballus

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.

Untitled

“…Our results of the varietal sensitivity study of C. sativus to P. melonis strain 502 are in agreement with the studies of American and Spanish isolates of P. melonis, which state that the pathogen brings the worst damage to plant roots in the initial stages of growth and development (Alfaro-Fernández and García-Luis, 2009;Biernaki and Bruton, 2001). Young sprouts have a low resistance to the infection, since some mechanisms, present in plants on later stages of development, are absent from their recently formed tissues (Alfaro-Fernández and García-Luis, 2009;Bruton et al, 2000b). Previously we have demonstrated that the plants of Nizhynskyi 12 variety are susceptible on the stage of two actual leaves (after two weeks of growing plants on the AIB of P. melonis 502) (Kopilov et al, 2021).…”

Gene Expression in Cucurbita spp. Root and Crown during Phytophthora capsici Infection

“…However, most studies have used Fusarium oxysporum and other crops in the Cucumis genus [9,10], while molecular studies of Phytophthora capsici have used horticultural crops such as pepper [11,12]. Many of the plant defensive tools against soilborne pathogenic fungi are enzymes that act directly on pathogens, such as chitinases, 1,3-glucanases/glucosidases, and peroxidases [13][14][15]; are involved in the production of defense structures such as lignin [16], tylose [17], and suberin [18]; are antimicrobial molecules (phytoalexins) [19]; or are oligopeptides (defensins) [14].…”

Root transcriptional responses of two melon genotypes with contrasting resistance to Monosporascus cannonballus (Pollack et Uecker) infection

“…Studies on the specificity of M. cannonballus showed that germination of ascospores is extremely host specific and occurs only in the rhizosphere of certain genera and species of plants belonging exclusively to the Cucurbitaceae family [4]. In a histological study using artificial inoculation with active mycelium, Alfaro-Fernandez and García-Luis [5] examined the early colonization of M. cannonballus in two cucurbit species that differed in their sensitivity to this disease: a highly sensitive muskmelon ( C. melo ) and a tolerant squash ( Cucurbita maxima ). Results showed that M. cannonballus was capable of infecting the tissue of both host plants, colonizing the epidermis and cortex with decreased density of mycelium at the endodermis level.…”