INTRODUCTION
In sub-Saharan Africa, the destruction of forests year after year by the improper felling of trees and shrubs has manifold ecological consequences. In Côte d'Ivoire in agrosystems, the woody species spared in orchards for the shade they provide to crops have over time become focal point of Loranthaceae infestation commonly called ‶African mistletoe'' for these crops (Amon et al., 2010). Today, few trees and shrubs are not parasitized by Loranthaceae (Amon, 2006). Indeed, these epiphytoid hemiparasitic phanerogams attack and invade in large numbers the shade species encountered particularly in cocoa field (Soro et al., 2009). According to Boussim (2002), the Loranthaceae, once implanted on the trunk or the branches of the host, take with the helper of a system called sucker, the water and the mineral salts of the latter to ensure their own development. By this process of infestation, they are able to produce their own photosynthesis and live as long at the expense of this host; which makes these parasitic plants real dangers for any cultivated or spontaneous woody species that they parasitize (Salle, 2004; Soro, 2006). Despite the numerous inventories carried out in Côte d'Ivoire, in order to understand these parasitic plants and their host plants (Traoré et al., 2003, Soro, 2010; Amon, 2014), no specific study on the degree of infestation of species shading by these same phytoparasites in cocoa-based agrosystems has not been carried out to our knowledge in the Central-West of Côte d'Ivoire, an important cocoa production area (N'Guessan et al., 2014). It therefore seems important to carry out a qualitative inventory of woody plants tolerated as shade species in the experimental cocoa growing field on the site of the University Jean Lorougnon Guédé and to assess their state of infestation by species of the family of Loranthaceae.
MATERIAL AND METHODS
Study area
The study area is located in the department of Daloa, in the Central-West of the Côte d'Ivoire between 06º51′40.7″ North latitude and 006º21′22.6'′ West longitude (Fig. 1). It is in the Guinean domain characterized by an equatorial type climatic regime comprising two rainy seasons and two dry seasons (Eldin, 1971). Monthly precipitation varies between 1300 mm and 1800 mm. Its vegetation is from the mesophilic sector of the Guinean domain, today, made up of a mosaic of forests and savannas (Guillaumet & Adjanohoun, 1971; Monnier, 1983).
Material
The plant material was composed of Loranthaceae and woody plants found in the experimental field of cocoa. The technical equipment includes a geographical positioning device (GPS), a digital camera, a tape measure, sisal wires and data sheets.
METHODS
Data collection
For the floristic inventory of shade species, hosts of vascular plants of the Loranthaceae family, the surface survey method which consists of listing shade trees and shrubs encountered on square or rectangular areas (Hall & Swaine, 1981), coupled by direct observations in order to note the presence or absence of Loranthaceae species (Soro, 2010) were adopted in the experimental cocoa field on the Jean Lorougnon Guédé University site. The inventory consisted of counting the non-parasitized individuals and those parasitized of shade trees and shrubs, the parasitic species and the number of their tufts on each woody plant was carried out from three survey plots of 20m×20m (400m²) delimited in the field. The total height of individuals of shade trees and shrubs and their diameter at breast height (DBH at 1.30 m from the ground) were also registered. The presence or absence of the parasite and the number of its clumps by these woody plants have been noted. The data collected made it possible to determine the rate and intensity of infestation of Loranthaceae in the experimental cocoa cultivation plantation according to the formula used by Amon (2006):
§ Infestation rate (Txi):
with Txi - Infestation rate; Nip - Number of parasitized individuals; Nti - Total number of individuals identified;
§ Intensity of infestation (Ii):
with Ii - Intensity of infestation; Nt - Total number of Loranthaceae tufts; Ntii - Total number of infected individuals identified.
Statistical analysis
The data generated were subjected to one-way analysis of variance (ANOVA) to compare the mean values of the infestation rates and intensities of Loranthaceae on shade species. Statistical analysis was performed using STATISTICA version 7.1 software. This program provides, in the event of significant differences, for a comparison of the means (Dagnelie, 1980), by Duncan's test at the 5% threshold (α < 0.05).
RESULTS
Loranthaceae species encountered
Two species of Loranthaceae were found on cocoa trees and woody shade plants in the orchard. These are Phragmanthera capitata (Spreng.) Ballé (Fig. 2) and Tapinanthus bangwensis (Engl. And K. Krause) Danser (Fig. 3). T. bangwensis is the most common and abundant species with 77% of the host spectrum registered.
DISCUSSION
The study identified two species of Loranthaceae (Phragmanthera capitata and Tapinanthus bangwensis), parasites of shade trees and shrubs in the experimental cocoa cultivation field at the Jean Lorougnon Guédé University site. The number of two species encountered is lower than the four Mrankpa species (2018) inventoried on the University Jean Lorougnon Guédé site. The difference noted could be explained by the size of the prospected area. Indeed, Mrankpa (2018) made an inventory over the entire Jean Lorougnon Guédé University site.
Twenty-two (22) shade host species of Loranthaceae belonging to 20 genera and 15 families were inventoried in this experimental field. This number is significantly lower than those of the 41 host species and 21 families obtained by Sako (2019) in the village fields in the surrounding areas of the University Jean Lorougnon Guédé. These results also corroborate those of Amon (2006), in Côte d'Ivoire and Houenon (2012), in Benin who have already reported the polyphagous character of parasitic vascular plants of the Loranthaceae family which parasitize different families of trees and shrubs in sub-Saharan Africa.
The rate of infestation of shade species by Loranthaceae registered in the experimental cocoa field is of the order of 27.62%. This value of the infestation rate obtained is significantly lower than that of 35.25% registered by Sako (2019) in cocoa agrosystems in surrounding areas of the University Jean Lorougnon Guède. This observed difference could be explained by the level of cared of the plots. Indeed, the field studied by this author were fewest cared and aged.
The enumerated cohort of shade host species exhibited numerically high infestation rate values according to diameter and height classes. These results confirm the work of Mranpka (2018).
The infestation rate of the experimental cocoa field is of the order of 15.97±6.81%. This rate is clearly lower than the 42.86±7.02% of Amon et al. (2020) obtained by in agrosystems based on cocoa trees in riparian areas of the University Jean Lorougnon Guédé. This difference could be justified by the age of the farms as well as by the care. Indeed, the plantations studied by this author are older and poorly cared.
CONCLUSION
Loranthaceae pose a serious threat to cocoa trees and other woody shade plants in orchards. The experimental cocoa farming field at the Jean Lorougnon Guédé University site parasitized by two species of Loranthaceae (P. capitata and T. bangwensis). This field abounds within 22 species of shade hosts of Loranthaceae belonging to 20 genera and 15 families. The infestation rate values of these woody plants by Loranthaceae vary from species to species and also according to their diameter and height classes. The field presented an infestation rate of the order of 15.97±6.81% and an infestation intensity of 2.39±0.34 tufts/tree. The results of this study could be used as an implement in making decisions concerning the conservation of certain species in fields for a sustainable agriculture.
Acknowledgements
Authorities from Jean Lorougon Guédé University in Daloa, Côte d'Ivoire.
Conflict of Interests
Authors declare that they have no conflict of interest.
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