Morphological diversity of Ganoderma species and its host trees in Mezam Division, Northwest Region, Cameroon

Ganoderma P. Karst. is a pathogen that causes root and stem rot in trees, ultimately leading to their death. It can be used to treat various conditions of human diseases. This fungal species often grows on economically significant trees. Its morphological' diversity and host range need to be better understood due to their similarity in morphological resemblance. This research aims to identify the phenotypic diversity of Ganoderma species and their host trees. Opportunistic sampling was used to collect samples from nine villages in Mezam Division, Northwest Region of Cameroon.


Introduction
The genus Ganoderma is a common and widespread Basidiomycota species that can be parasitic and saprobic (Kinge & Mih 2011;Tchotet Tchoumi et al. 2019).These fungi are known for their brownish, woody, or leathery brackets (Gryzenhout et al. 2021).Certain species have been recognized as the causative agents of plant diseases Ganoderma P. Karst. is a pathogen that causes root and stem rot in trees, ultimately leading to their death.It can be used to treat various conditions of human diseases.This fungal species often grows on economically significant trees.Its morphological' diversity and host range need to be better understood due to their similarity in morphological resemblance.This research aims to identify the phenotypic diversity of Ganoderma species and their host trees.Opportunistic sampling was used to collect samples from nine villages in Mezam Division, Northwest Region of Cameroon.Morphological identification of Ganoderma species was done based on morphological characters such as colour, length, and width, laccate or non-laccate, the type of basidiocarp, margin shape, microscopical structures, and hyphae.The morphological characters of basidiocarps collected from different host trees revealed eleven distinct Ganoderma species, including Ganoderma applanatum, G. australe, G. brownii, G. cupreum, G. gibbosum, G. lucidum, G. multipileum, G. multiplicatum, G. orbiforme, G. resinaceum and G. weberianum.This study identified nine host tree species.Ganoderma resinaceum was host specific to Elaeis guineensis.G. cupreum on Ficus sp., and Persea americana, and G. orbiforme on Cola acuminata.G. multiplicatum, G. lucidum, G. gibbosum, and G. applanatum had multiple hosts.Ganoderma typically grows on dead tree stumps based on host preferences.However, three species were collected from living trees; one on Albizia adianthifolia and two on Persea americana, confirming their nature as saprophytes and plant pathogens.(Edy et al. 2022), including root and stem rots, which can lead to the death of significant economic trees like oil palm (Elaeis guineensis Jacq.), rubber (Hevea brasiliensis (Willd.ex Juss.)Muell.Arg.), tea (Camellia sinensis (L.) Kuntze), ornamental plants (Kinge & Mih 2011;Coetzee et al. 2015), and forest trees like Acacia, Albizia, Populus, and Macadamia species (Lee and Chang 2016).Most dead woody plants in forests are broken down by Ganoderma, making it ecologically significant for decomposition and delignification (Lee & Chang 2016 and having medicinal and cultural values (Bishop et al. 2015).Ganoderma growing on Acacia erioloba E. Meyer and Combretum imberbe var dielsii treats nosebleeds, boosts infant and maternal immunity during gestation, and strengthens infant cranial bones (Ekanjo & Chimwamurombe 2012).Ganoderma extract possesses anti-tumor, immune-boosting, antimicrobial, and cardiovascular properties and may have anti-aging effects (Chen and Miles 1996;Mshigeni & Chang 2001;McMeekin 2004;Sun et al. 2006).
Most reports on the identification of Ganoderma species in Cameroon were based solely on morphology but from the publication of Douanla-Meli & Langer (2009), Teke et al. (2018), Kinge (2012), and Kinge et al. (2012).There is a need to get more knowledge on the diversity of Ganoderma in the western highlands of Cameroon (Kinge & Mih 2015); as a result, valuable information is required to fill research gaps.Basidiocarps, the sexual structures in Ganoderma, typically grow on living or dead tree trunks, with the latter being the more common occurrence or branch of a tree in the form of a bracket (Mawar et al. 2020).Two types of basidiocarps are produced depending on the species: a laccate fruiting body with a shiny upper surface or a non-laccate fruiting body with a dull upper surface (Smith & Sivasithamparam 2000a, Pilotti et al. 2004).
Specialists have faced several controversies while attempting to classify Ganoderma, which has made the taxonomy of this species challenging (Moncalvo et al. 1995a).Several species have been misidentified due to taxonomic controversies and inconsistencies under this genus (Mueller et al. 2007) since Ganoderma species exhibit significant genetic heterogeneity due to outcrossing and geographical diversity (Miller et al. 1999;Pilotti et al. 2003).The morphology of organisms can vary even within the same species, leading to differences in their physical characteristics.(Hong et al. 2001).Identifying a species can be challenging due to several factors, such as environmental influences, variation, hybridization, and differences in individual morphology (Zheng et al. 2007).Traditional taxonomic methods based on morphology must be more conclusive in establishing a stable classification system for species within a genus (Hseu et al. 1996;Hong et al. 2002).Different mycologists use varying criteria for fungi identification.Some criteria focus on host specificity, geographic distribution, and macro-morphology of basidiomes, while others emphasize spore characteristics (Sun et al. 2006;Ekandjo 2012).This study aims to determine the diverse morphology of Ganoderma species and their host trees in the Mezam Division of the Northwest Region in Cameroon.

Description of the study area
This research focused on the Mezam Division, located in the Northwest region of Cameroon.Mezam Division is between latitudes 5°04' and 7°05' North and longitudes 9°08' and 11051' East of the Greenwich Meridian (UNDP 1999).The area's population is over 524,127, with a total surface area of 1,841.45km 2 .The study area comprises seven sub-divisions: Bamenda I, Bamenda II, Bamenda III, Bafut, Bali, Santa, and Tubah (Mbangari et al. 2019), and includes nine villages in this sub-division: Mbatu, Mankon, Nkwen, Bambili, Bambui, Bafut, Mendankwe, Nsongwa, and Santa.The study area is illustrated in Figure 1.

Climate dynamic of the seven sub-divisions
The region has a cool, temperate climate, mountainous terrain, and rugged topography.It receives an average rainfall of 2400 mm and has an average temperature range of 15°C to 32°C.This region has two seasons: the rainy season, lasting from March to October, and the dry season, which lasts from November to February (Olayiwola et al. 2011;Mukete et al. 2018).

Sample collection and morphological identification
Samples were collected from forests in the Mezam division between November 2021 and August 2023 using opportunistic sampling.Each sample was snapped from above-ground and below-ground positions, and the geographic coordinates were accurately marked using GPS.Ziplock bags were labeled and used to collect the samples after wrapping them in aluminum foil.Later, the samples were affixed to A4 papers with a ruler beside them, along with pictures.The basidiocarps were oven-dried at a temperature of 35°C.Morphological characters such as the type of basidiocarp (whether it was laccate or non-laccate and whether it was stipitate, sessile, or dimidiate), length and width, concentric zones, margin shape (lobed, rounded/acute), margin colour (brown, white, reddish, etc.), pore colour, and tube colour were recorded.The morphological characters recorded were compared with those of Ganoderma species described by various authors (Ryvarden & Johansen 1980;Corner 1983;Ryvarden 1995;Moncalvo & Ryvarden 1997;Ryvarden 2000;Kinge & Mih 2011).
Samples were prepared for micromorphological analyses by slicing thin sections of dried basidiocarps and passing through the hymenium.The sections were mounted in 5% KOH and observed under a compound microscope.Twenty randomly selected basidiospores from each specimen were measured, and ornamentation was noted.To determine the size and shape of basidiospores, their length and width were measured, and the spore length and width (Q) quotient was calculated using the formula Q=L/W.This was done for at least 20 basidiospores from each basidioma, with the mean length and width used for the calculation done using the method by Miettinen & Larsson (2006) with some modifications.Fungal identification was done using taxonomic keys (Zhao et al. 1983).The host trees were identified at the National Herbarium in Yaounde, Cameroon.

Species diversity
Seventy-one Ganoderma samples were collected (Table 1).The various host trees of Ganoderma, the place of collection, the collection date, and the collection sites' GPS points were noted.Eleven Ganoderma species were identified from their morphology which include G. applanatum, G. australe, G. brownii, G. cupreum, G. gibbosum, G. lucidum, G. multipileum,
Wight, Croton macrostachyus, and Eucalyptus globulus, Labill.as well as eight unidentified tree stumps, were registered in the study area.Also, from the 71 samples, 11 species were identified, with one that often grows on oil palm and seven on forest trees.January had the highest number of collections (11), while March and July had the least (01) Ganoderma species.Collections were made in all seasons, confirming that Ganoderma species bear fruit throughout the year.Most of the collections were from dead tree stumps.At the same time, only a few Ganoderma species were from living trees, such as Persea americana (02) and Albizia adianthifolia (01).Table 2 shows the host trees and Ganoderma species diversity with the plant families of host trees in the study: Lauraceae, Fabaceae, Anacardiaceae, Moraceae, Malvaceae, Rhamnaceae, Arecaceae, Euphorbiaceae, and Myrtaceae.

Morphological characteristics
Below are the descriptions of each species of Ganoderma based on their morphology.

Ganoderma weberianum (Bres. and Henn.)
Basidiocarp strongly laccate, stipitate, stipe up to 4.5 x 2.5 cm, pileus colour reddish brown (8E8-5), yellowish red, 1 -3 concentric zones.The margin is thin and incurved; the margin colour white to yellow, with some rounded.The context colour is brown and light yellow, and one resinous layer is present in the woody context of the pileus.Tube length 0.5 -0.7 cm.The diameter of the pileus ranges from 5 -10 cm.The pore surface is cream white, circular, pores 2 -5 per mm.Context is 4 cm long and light brown with a few gasterospores.The hyphal system of this organism is trimitic.The generative hyphae are thin-walled, aseptate, and 2-5 µm thick.They rarely branch.The skeletal hyphae are clampless, septate, thick-walled, and branched.They are 3-5.5 µm thick.The binding hyphae are of the bovista type, clampless, aseptate, thick-walled, and much branched.They are 1-5 µm thick.The basidiospores are light yellowish and broadly ellipsoid.They measure 3.0-3.5 × 2.0-3.0 µm.This comprised the isolate labeled NJM07 (Figure 21).Ganoderma is characterized by high morphological variability (Moncalvo & Ryvarden 1997;Douanla-Meli & Langer 2009).The variability in morphology could be due to environmental factors.Also, the lack of distinct morphological features makes it challenging to accurately identify and classify Ganoderma species.Different host plants and geographic conditions may affect the diversity of Ganoderma species and the morphology and pigmentation of their fruiting bodies (Smith & Sivasithamparam 2003;Kinge et al. 2015).This study identified G. multipileum, G. applanatum, G. orbiforme, G. brownii, and G. gibbosum for the first time in Cameroon because of the gap in Ganoderma diversity.
This study identified nine host trees.Some species were host-specific, while others were on multiple hosts.G.  (Mawar et al. 2020;Morera et al. 2021), Ficus sp.(Mawar et al. 2020;He et al. 2022), Mangifera indica (Foroutan and Jafary, 2007), Edy et al. (2022) reported Persea americana to be a host tree to Ganoderma species.Persea americana, Albizia adianthifolia, and Mangifera indica were this study's most susceptible host trees.Kinge et al. (2015)  Ganoderma is a type of fungus that usually grows on dead tree stumps, depending on the preferences of its host.However, three species of Ganoderma (G.brownii, G. gibbosum, and G. australe) inhabited living trees, Albizia adianthifolia and Persea americana, which confirms that they are saprophytes and plant pathogens.This study and observations have revealed a need for more information on the diversity and distribution of Ganoderma in Cameroon, which conforms with the point made by Douanla-Meli & Langer (2009) about the insufficient knowledge of macrofungi in Cameroon.The diversity of Ganoderma may have affected their distribution across different sites and hosts.According to Kinge (2012), the spores may not have had enough time to expand into other habitats, which could explain why certain species in this study inhabited specific locations and hosts.
Additionally, some species may have a habitatspecific nature or short-lived spores, which could also contribute to their limited distribution.However, despite these factors, species of Ganoderma are generally well distributed.Certain species, such as G. lucidum, G. applanatum, G. gibbosum, and G. orbiforme, can remain dormant during unfavorable periods, which may explain their abundance.Symptoms of basal stem rot disease occurred in various hosts, including Persea americana (avocado), Albizia adianthifolia, Mangifera indica (mango), Cola acuminata, Elaeis guineensis (oil palm), Maesopsis eminii, Ficus sp., and unidentified hardwoods.Numerous studies worldwide investigate basal stem rot disease affecting oil palms caused by various species of Ganoderma, such as in Malaysia (Lau et al. 2022;Mooralitharan et al. 2023), Indonesia (Rahayu et al. 2021;Edy et al. 2022), Papua New Guinea (Gorea et al. 2020;Wong et al. 2022), andCameroon (Kinge et al. 2015;2017).A recent survey by Edy et al. (2022) highlighted the ability of these Ganoderma species (G.lucidum, G. austral and G. resinaceum) to survive on different hosts, including living and dead trees.Although there may be limitations with morphological characters, it is still crucial to study Ganoderma species from Cameroon using morphological characters supplemented with molecular methods where possible.

Conclusion
This study observed the different morphological characters of Ganoderma species collected from nine villages and identified eleven morphological basidiocarps of Ganoderma around households and forests in the Mezam division, which includes G. cupreum, G. weberianum, G. multiplicatum, G. lucidum, G. multipileum, G. australe, G. applanatum, G. resinaceum, G. brownii, G. orbiforme, and G. gibbosum implying that the Mezam division is diverse in terms of Ganoderma species.It also listed nine economically significant trees to be hosts to Ganoderma species, which were Persea americana, Elaeis gineensis, Mangifera indica, Maesopsis eminii, Cola acuminata, Ficus sp., Albizia adianthifolia, Eucalyptus globulus, and Croton macrostachyus, still implying that Ganoderma can grow on diverse hosts.

Fig 1 .
Fig 1. Map of Ganoderma species collection sites in Mezam division, Northwest region, Cameroon.

Fig 4 .
Fig 4. Ganoderma australe (NJS20) (A-B) Basidiome pilear and hymenial surfaces (C) Transverse section of the basidiome showing context and stratified tube layers (D) Close view of the hymenial surface showing pore shape.

Fig 10 .
Fig 10.Ganoderma gibbosum (NJM41) (A-B) Basidiome pilear and hymenial surfaces (C) Transverse section of the basidiome shows context and stratified tube layers (D) Close view of the hymenial surface showing pore shape.

Fig 16 .
Fig 16.Ganoderma multiplicatum (NJM05) (A-B) Basidiome pilear and hymenial surfaces (C) Transverse section of the basidiome showing context and stratified tube layers (D) Close view of the hymenial surface showing pore shape.

Fig 18 .
Fig 18. Ganoderma orbiforme (NJM37) (A-B) Basidiome pilear and hymenial surfaces (C) Transverse section of the basidiome showing context and stratified tube layers (D) Close view of the hymenial surface showing pore shape.

Table 1 :
Species, place of collection, date of collection, G.P.S. points, and host trees of the species identified (Source:

Table 2 :
Diversity of host trees, their families, and species of Ganoderma in the Mezam division Ganoderma species associated with G. australe, G. cupreum, and G. resinaceum in South Africa.Ganoderma resinaceum is related to basal stem rot disease in oil palms.This study highlights the significant impact of this genus on horticulture and forestry, including fruit trees (Avocado, Mangoes) and forest trees (Albizia adianthifolia, Cola acuminata, Maesopsis eminii, and Ficus sp.).