Ultrastructure of the early stages of Colletotrichum acutatum infection of strawberry tissues

Abstract

Abstract:The early stages of the infection of attached leaves and petioles of strawberry (Fragaria ×ananassa Duch. 'Camarosa') by Colletotrichum acutatum Simmonds were studied using scanning and transmission electron microscopy. Pre-penetration events of these tissues were similar, but the production of secondary conidia (microcyclic conidiation) was detected only on leaves. At the ultrastructural level, different stages of maturation of appressoria were observed and described. In young appressoria, the cell wall was composed of two layers and the plasma membrane displayed a wavy appearance. In the following stage, the appressorium developed a third electron-transparent layer between the cell wall and the plasma membrane. This new electron-transparent material was especially visible in the region of the appressorium near the cuticle. The plasma membrane of this appressorium showed a smooth appearance. Afterwards, a penetration peg emerged through the pore penetrating the cuticle and reached the epidermal wall where it enlarged to form an intramural infection vesicle. Both structures of infection, the penetration peg and the intramural infection vesicle, produced during the early phases of infection of strawbery tissues by C. acutatum, have not been previously reported and confirm that its invasion strategy is that of a subcuticular intramural pathogen. Once the infection was well established, abundant subcuticular and intramural hyphae were produced on petioles, causing severe degradation of the host cell walls. Occasionally, the cuticle appeared disrupted in those regions where the host walls were very degraded and dilated. Differences between colonization of petioles and leaves were observed.Key words: Colletotrichum acutatum, Fragaria ×ananassa, infection vesicle, invasion strategy, penetration peg.Résumé : À l'aide de la microscopie électronique par balayage et par transmission, les auteurs ont étudié les premiers stades de l'infection des feuilles attachées et des pétioles du fraisier (Fragaria ×ananassa Duch. 'Camarosa'), par le Colletotrichum acutatum Simmonds. Les évènements de pré-pénétration de ces tissus sont similaires, mais la production de conidies secondaires (conidiation microcyclique) ne s'observe que sur les feuilles. Les auteurs ont observé et décrivent les ultrastructures, aux différents stades de maturation des appressoriums. Chez les jeunes appressoriums, la paroi cellulaire est composée de deux couches et la membrane plasmique montre une apparence ondulée. Au stade suivant, l'appressorium développe une troisième couche transparente aux électrons, entre la paroi cellulaire et la plasmalemme. Ce nouveau matériel transparent aux électrons est particulièrement visible dans la région de l'appressorium voisin de la cuticule. La plasmalemme de cet appressorium est d'apparence lisse. Par après, l'hyphe de pénétration émerge à travers le pore et pénètre la cuticule pour atteindre la paroi épidermique, où il s'élargit pour former une vési-cule d'infection intramurale. Les deux structures d'infection...

Histopathology of Colletotrichum gloeosporioides on guava fruits (Psidium guajava L.)

“…This structure is an extension of the penetration peg wall and may act on the hydrostatic pressure at the penetration spot. However, in this study the appressorial cone was not observed, which is also the case of C. sublineolum (WHARTON et al, 2001), C truncatum (O'CONNELL et al, 1993) and C. acutatum (ARROYO et al, 2005). The lack of a cone in some species and its presence in others suggests that mechanism of infection by species of Colletotrichum depends on the host species.…”

“…The area of contact between the appressoria and the fruit surface was relatively narrow (Figure 1 I-K). After the formation of the penetration peg, the cuticle structure remained intact in the region near the pore, supporting the hypothesis that penetration occurs mainly through mechanical force, as reported for C. acutatum in strawberry (ARROYO et al, 2005). However, other factors, such as enzyme activation during the process need to be considered (O'CONNELL et al, 1985;KÖLLER, 1991).…”

“…In coffee plants inoculated with C. gloeosporioides and C. dematium, the conidial germination started 5 and 12 h.a.i, respectively (LINS; ABREU; ALVES, 2007). Conidia of Colletotrichum acutatum germinated 4 h.a.i on strawberries (ARROYO et al, 2005) and C. destructivum took 12 h to germinate on tobacco (SHEN; GOODWIN; HSING, 2001).…”

“…In coffee plants inoculated with C. gloeosporioides and C. dematium, the conidial germination started 5 and 12 h.a.i, respectively (LINS; ABREU; ALVES, 2007). Conidia of Colletotrichum acutatum germinated 4 h.a.i on strawberries (ARROYO et al, 2005) and C. destructivum took 12 h to germinate on tobacco (SHEN; GOODWIN; HSING, 2001).Colletotrichum gloeosporioides conidia are normally aseptate, however they develop septa during germination (Figure 1B-C) due to mitosis (MOULD et al, 1991a;O'CONNELL et al, 1993).The germ tube growth was not affected by the presence or location of stomata on the fruit surface ( Figure 1D). There was no penetration via the stomata.…”

Histological and ultrastructural characterization of the leaf infection events of Colletotrichum fructicola on Malus domestica ‘Gala’

“…The employment of both intracellular and subcuticular intramural infection strategies was reported in C. acutatum , C. gloeosporioides , and C. truncatum (Perfect et al , ; De Silva et al , ). Of these, only C. acutatum was observed to form subcuticular intramural infection vesicles in strawberry leaf tissues (Arroyo et al , ).…”