Light- and electron-microscopic observations of Cladosporium sp. growing on basidia of Exobasidum camelliae var. gracilis

Abstract

Basidia of the plant-pathogenic fungus Exobasidium camelliae var. gracilis Shirai became exposed on the abaxial side of an infected leaf of Camellia sasanqua Thunb. following the sloughing of the undersurface of the leaf. Basidia were formed in tremendous numbers in a distinct hymenium that appeared as a white, felt-like layer. Subsequently, colonies of another fungus, Cladosporium sp. appeared, initially as tiny dark dots on this white layer, but quickly increased in size to form larger circular colonies that were olive-brown to dark brown in color. Adjacent colonies sometimes merged to form larger growths with irregular margins that often covered much of the hymenium on the underside of an E. camelliaeinfected leaf. The hyphae that made up a young Cladosporium sp. colony were primarily confined to the surface of the E. camelliae hymenium, and we found no evidence that hyphae actually penetrated living basidia. However, E. camelliae basidia overrun by Cladosporium sp. eventually showed signs of necrosis and finally collapsed and died, creating a slightly sunken area in the hymenium. Hyphae of Cladosporium sp. grew throughout the remains of the dead basidia, but did not appear to spread into the leaf tissue above the pseudoparenchymatous layer of hyphae that gave rise to the basidia. Based upon our observations, it is clear that Cladosporium sp. is a necrotrophic mycoparasite. More specifically, it qualifies as a contact necrotrophic, since it kills basidia without first penetrating them with its hyphae.Résumé : Les basides du champignon phytopathogène Exobasidium camelliae var. gracilis Shirai, apparaissent du côté abaxial des feuilles infectées du Camellia sasanqua Thunb., suite au décollement de la surface inférieure de la feuille. Les basides se forment en très grand nombre sur un hyménium distinct, qui apparaît sous forme d'une couche blanche feutrée. Les colonies du Cladosporium sp. apparaissent d'abord comme de petits points, sur cette couche blanche, mais augmentent rapidement de dimension pour former de larges colonies circulaires, allant du brun olivâtre au brun foncé. Des colonies adjacentes se fusionnent occasionnellement les unes aux autres pour former des colonies plus larges aux pourtours irréguliers, lesquelles recouvrent souvent une bonne partie de l'hyménium, sur la face inférieure des feuilles infectées par l'E. camelliae. Les hyphes constituant une jeune colonie sont surtout confinées à la surface de l'hyménium, mais on observe aucune preuve que les hyphes du Cladosporium sp. pénètrent effectivement les basides vivantes. Cependant, les basides recouvertes de Cladosporium sp., montrent éventuellement des signes de nécrose et s'affaissent avant de mourir, créant ainsi une faible dépression dans l'hyménium. Les hyphes du Cladosporium sp. poussent parmi les résidus de basides mortes, mais ne semblent pas s'étendre dans les tissus foliaires au-delà de la couche parenchymateuse des hyphes qui donnent naissance aux basides. Sur la base de ces observations, il est clair que le Cladosporium sp. est un ...

Moniliophthora perniciosa, the Causal Agent of Cacao Witches’ Broom Disease Is Killed in vitro by Saccharomyces cerevisiae and Wickerhamomyces anomalus Yeasts

“…There are several types of mycoparasites, including the necrotrophic which are very aggressive organisms that may act upon a broad range of fungal preys. They can attack filamentous fungi at a distance by secreting toxins or lytic enzymes into the surrounding environment ( Junker et al, 2019 ), or they can act by direct physical contact, although they do not necessarily invade the target cell ( Mims et al, 2007 ). The ones that do are known as invasive necrotrophs or predatory mycoparasites.…”