23 Oct Gilbertella

Gilbertella

Background

The monotypic genus Gilbertella belongs to the family Choanephoraceae and subfamily Gilbertelloideae (Mucorales, former Zygomycota). It was established by Hesseltine (1960) for species described earlier as Choanephora persicaria by Eddy (1925), and consequently, the type species of the genus is Gilbertella persicaria. Benny (1991) proposed a new family, Gilbertellaceae to accommodate this genus. Currently, the genus belongs to the family Choanephoraceae and subfamily Gilbertelloideae that can be distinguished from Choanephoroideae (Voigt and Kirk 2012) by ornamented zygospores and opposed suspensors (Voigt 2012). Although G. persicaria was originally described as Choanephora persicaria (Eddy 1925), its separate position within the family has been confirmed in several studies (Papp et al. 2003; Hoffmann et 2013).

In tropical and subtropical regions Gilbertella is a common postharvest pathogen, causing rots of pears (Mehrotra 1963a), peaches (Hesseltine 1960; Mehrotra 1963b; Ginting et al. 1996) and tomatoes (Mehrotra 1966). It was reported by Butler et al. (1960) and Hesseltine (1960) from mulberry (Morus sp.) in the USA. It was also recently isolated from pitaya fruits (Hylocereus undatus, Cactaceae) in Japan (Taba et al. 2011) and China (Guo et al. 2012).

Species identification and numbers

Currently, Gilbertella persicaria is the only species within the genus. Although another species–Gilbertella hainanensis–has been described (Cheng and Hu 1965), after recent molecular studies of its ITS sequence, it is not currently recognized as a separate species (Walther et al. 2013). Two varieties of G. persicaria have been described: G. persicaria var. persicaria and G. persicaria var. indica, however only the former was accepted in the monograph published by Benny (1991).

Gilbertella persicaria produces sporangia with a persistent wall that ruptures at preformed sutures in two halves. Ellipsoid, smooth-walled, hyaline sporangiospores with polar appendages are released in a droplet of fluid. Light brown ornamented zygospores are formed on opposed suspensors (Hesseltine 1960). The examination of morphology is usually enough for correct species identification. Moreover, morphological identification may be easily confirmed by ITS sequencing (Table, Fig.).

Table Gilbertella. Details of the isolates used in the phylogenetic tree

Molecular phylogeny

The phylogenetic relationships based on the complete ITS region of Gilbertella representatives and related Mucorales taxa were completed by Papp et al. (2003). All Gilbertella cultures available in the CBS culture collection have been sequenced for their ITS region and were included in a molecular analysis by Walther et al. (2013). These studies showed that the universal fungal DNA barcoding marker–the ITS region (Schoch et al. 2012)–is sufficient for Gilbertella species identification (Fig. 16). The multi-marker phylogenetic analysis including representatives of this genus performed by Hoffmann et al. (2013), confirmed a distinct, well-supported position of Gilbertella within Choanephoraceae family.

Recommended genetic markers

• The internal transcribed spacer (ITS) region–generic and species level

The large and small subunits (LSU and SSU) of nrDNA– placement within the Mucorales order, higher-level phylogeny