Isolates treated by Johnston and Jones (1997) as Colletotrichum gloeosporioides Group I were placed by Damm et al. (2012) in their new species Colletotrichum constrictum. This same species was given the informal name 'tam 4' in many of the unpublished notes and culture databases of Johnston.

This species rarely develops a sexual state in culture but fertile perithecia were seen in a few cultures isolated from the field. Single ascospore isolates from at least one of these cultures (isolate C1000.6, stored as a conidial suspension in 10% glycerol at -80C in the ICMP lab) behaved like the plus/minus strains described by Edgerton in the early 1900's (see discussion in Struble & Keitt, 1950) and more recently from Colletotrichum fructicola in papers such as Liang et al. (2021).

The single ascospore cultures had two distinct cultural morphologies. One was typical of the cultures isolated from the field, with scattered, large enclosed, globose conidiomata, these splitting open irregularly to expose the orange conidial masses. The second cultural type had large numbers of small, dark-based acervuli, covered with orange conidial masses. When the two cultural types were grown together in a single petri dish a row of perithecia developed along the boundary between the two cultural types. Single ascospore isolates from these perithecia segregated approximately 1:1 into the two cultural types.

The minus cultural type was never (or perhaps very rarely) isolated from the field, suggesting it was not fit.

Similar behaviour was observed in some C. kahawae subsp. cigarro (= C. gloeosporioides Group B in Johnston & Jones 1997, refered to using the informal name 'glom-avocado' in many of the unpublished notes and culture databases of Johnston), e.g. isolate C918.5. Again, the minus cultural type was rarely or never isolated from the field.

Notes prepared by Johnston, around about 1997

C. gloeosporioides Group I sensu Johnston & Jones 1997
7 days
Growth rate 35-45 mm. Some fine. cottony aerial mycelium covering colony, but not obscuring agar colony surface, no mycelial conidia. Colony dominated by relatively few, large, scattered, stromatic, black acervuli, those toward centre of colony starting to split open to reveal dull orange conidial ooze. Very centre of colony with solid conidial ooze. Agar with characteristic slightly brownish orange pigment. Scattered setae.
14 days
Colony dominated by scattered, quite numerous, large, globose, stromatic acervuli, each of which is covered by a dense weft of cottony, dark grey mycelium. Even at 14 days only those acervuli toward the centre of the colony with conidial ooze. Aerial mycelium whispy, white to pale grey. In reverse agar with orange pigment, with dark spots showing through from acervuli. In some isolates a purplish-grey pigment is concealing the orange from the centre of the colonies.
Perithecia forming tight glomerate masses, with several individual, long, dark ostiolar necks protruding. Developing along margins between 2 colonies, either as a single or double band of perithecia.

Damm U, Cannon PF, Woudenberg JH, Johnston PR, Weir BS, Tan YP, Shivas RG, Crous PW. 2012. The Colletotrichum boninense species complex. Studies in Mycology 73:1-36. doi: 10.3114/sim0002.

Johnston PR, Jones D. 1997. Relationships among Colletotrichum isolates from fruit-rots assessed using rDNA sequences. Mycologia 89: 420-430. http://www.jstor.org/stable/3761036

Liang X, Yao L, Hao X, Li B, Kong Y, Lin Y, Cao M, Dong Q, Zhang R, Rollins JA, Sun G. 2021. Molecular Dissection of Perithecial Mating Line Development in Colletotrichum fructicola, a Species with a Nontypical Mating System Featuring Plus-to-Minus Switch and Plus-Minus-Mediated Sexual Enhancement. Applied and Environmental Microbiology 87:e00474-21. https://doi.org/10.1128/AEM.00474-21

Struble FB, Keitt GW. 1950. Variability and inheritence in Glomerella cingulata (Stonem.) S. and V.S. from appale. American Journal of Botany 37: 563-576.