A fungus-eat-fungus world: Digitopodium, with particular reference to mycoparasites of the coffee leaf rust, Hemileia vastatrix

Abstract

Digitopodium hemileiae was described originally in 1930 as Cladosporium hemileiae; growing as a mycoparasite of the coffee leaf rust (CLR), Hemileia vastatrix, in a sample of diseased leaves of Coffea canephora collected in the Democratic Republic of Congo. No cultures from this material exist. More recently, the type material was re-examined and, based on morphological features, considered to be incorrectly placed in Cladosporium. The new genus Digitopodium was erected to accommodate this species. Interest in fungal antagonists of H. vastarix, as potential biocontrol agents of CLR, led to comprehensive surveys for mycoparasites, both in the African centre of origin of the rust, as well as in its South American exotic range. Among the rust specimens from Ethiopia, one was found to be colonized by a fungus congeneric with, and similar to, D. hemileiae. Pure cultures obtained from the Ethiopian material enabled a molecular study and for its phylogenetic position to be elucidated, based on DNA sequence data from the ITS and LSU regions. Molecular data showed that two members of the recently erected genus Hyalocladosporiella (Herpotrichiellaceae: Chaetothyriales) are congeneric with Digitopodium from Ethiopia and morphologically similar to both D. hemileiae and the two Ethiopian isolates. These isolates were found to be morphologically and genetically identical to H. tectonae, described previously from Brazil. Thus, species of Hyalocladosporiella are re-allocated to Digitopodium here; including D. tectonae, and a novel species, D. canescens, recently found in Brazil growing as a mycoparasite of Puccinia thaliae. The potential use of D. hemileiae and D. tectonae for classical biological control of CLR is discussed.

Differential Physiological Prerequisites and Gene Expression Profiles of Conidial Anastomosis Tube and Germ Tube Formation in Colletotrichum gloeosporioides

“…To study the effect of conidial age on GT formation and CAT fusion and their mutual exclusiveness in C. gloeosporioides , the GT and CAT induction assays were carried out by following a protocol developed in our lab [ 11 ]. The C. gloeosporioides (CBS 953.97) culture was inoculated on bean pod agar medium (autoclaved French bean pods submerged in 2% water agar) and was incubated in the dark at 25 °C to induce conidiation.…”

“…In contrast, for CAT induction, different concentrations of 17-day-old conidia were incubated in dH 2 O for 72 h in the dark. The concentrations of conidia tested were 4 × 10 2 , 4 × 10 3 , 4 × 10 4 , 4 × 10 5 , and 4 × 10 6 per mL [ 11 ].…”

“…The CAT fusion versus GT formation were independent of conidial age in N. crassa and F. oxysporum [ 4 , 5 , 9 ]. Interestingly, older conidia were optimal for CAT fusion while younger conidia were suitable for GT formation in C. lindemuthianum, C. gloeosporioides, and C. siamense [ 10 , 11 ]. The CAT fusion might play a vital role in the life cycle of fungi by improving the chances of colony establishment during nutrient starvation [ 7 ].…”

“…The heterokaryotic progenies have been generated through CAT fusion with distinct phenotypes compared to parental strains in F. oxysporum and C. lindemuthianum [ 9 , 13 ]. Inter-specific CAT fusion between C. lindemuthianum and C. gossypii resulted in the formation of some hybrids, which exhibited phenotypic variations; one hybrid was highly pathogenic [ 14 ] Furthermore, we have demonstrated that an inter-specific CAT fusion between C. gloeosporioides and C. siamense generated genetic and phenotypic diversity in these fungal pathogens [ 11 ]. Pathogen populations with higher genetic variations tend to show increased mean fitness, resilience, expansion of host range, and fungicide resistance.…”

“…C. gloeosporioides starts its usual life cycle from conidial germination to the formation of melanized infection structures, appressoria [ 15 ]. The formation of GTs and CATs in C. gloeosporioides were reported in both in vitro and in vivo conditions [ 11 , 16 ]. Despite having legitimate morphological variations between GT and CAT, their whole transcriptome comparison has never been reported.…”