Distribution of plant parasitic nematodes associated with bananas and severity of their damage in Democratic Republic of Congo
Kamira, Bacishoga Muller
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The importance of parasitic nematodes as a constraint to production of banana and plantain has for long been emphasized. Banana and plantain parasitic nematodes can significantly weaken root systems, reduce yields, topple plants before harvest, make plants more prone to wind knockdowns, reduce fertilizer uptake and utility, and reduce the banana-growing lifespan of a given piece of land. In most regions of the world, nematodes are recognized as important pests of bananas. Detection and identification of parasitic nematodes is the first step in controlling them and checking their spread. In recognition of the importance of bananas and plantains and the existing data indicating the importance of nematode damage on banana and plantain, the general objective of this study was to evaluate the species distribution and damage severity of the major root parasitic nematode species associated with banana and plantain in DR Congo. Specifically, the study assessed the abundance and distribution of plant parasitic nematodes associated with banana and plantain production systems in DR Congo, determined the severity of root damage to banana and plantain caused by plant parasitic nematodes and established the relationship between banana and plantain cultivars commonly grown in DR Congo and the nematode damage. The study was conducted in the provinces of Bas Congo, where the sampled fields were located at altitudes ranging between 9 m to 646 m above the sea level (m asl) and in South Kivu where the sampled fields located at altitudes 1043 m to 2005 m asl. The nematode populations were recovered from the commonly cultivated Musa in Bas Congo which are dessert and plantain cultivars, while in south Kivu, the most widespread Musa cultivars are typically beer and cooking banana types. Collection of samples was carried out according to methodology described by Speijer and De Waele (1997). Nematode densities were determined for each nematode species recovered as the number of nematodes per 100 g root fresh weight, and root necrosis as average of percentage of root cortex damaged in each of the score roots. Seven parasitic nematodes species Helicotylenchus multicinctus, Helicotylenchus spp., Meloidogyne spp., Radopholus similis, Pratylenchus goodeyi, Pratylenchus spp. and Rotylenchulus reniformis were associated with banana and plantain cultivars in DR Congo. In addition, other nematode species belonging to the genus Hoplolaimus, Scutellonema, Aphelenchus and Rotylenchulus occurred, though their importance and pathogenic effect on Musa genotypes is not yet clearly documented. The geographical distribution of the nematode populations in DR Congo was found very closely linked to altitude. For instance, P. goodeyi, H. multicinctus and R. similis population densities were significantly correlated with the altitude at (P ≤ 0.05). Pratylenchus goodeyi was not recovered from the assessed fields within Bas Congo, as Radopholus similis was not found in South Kivu. Cooler temperatures at higher elevations were hypothesized as the most important factor that limits the establishment of R. similis in South Kivu at higher elevations. The study indicated significant differences among locations (territories) in terms of nematode population densities. The total population of each nematode species recovered from the roots of plantain and dessert cultivars in Bas Congo was significantly (up to P ≤ 0.001) influenced by locations (territories), while there was no significant difference in terms of nematode population densities recovered on roots of cooking and beer cultivars in the South Kivu between territories, except for P. goodeyi population densities, which significantly varied (P ≤ 0.01) between territories. In addition, the correlation analysis revealed a highly positive (P ≤ 0.01) relationship between root necrosis damage and nematode population densities, especially H. multicinctus and P. goodeyi. It is recommended that this investigation be extended to other provinces of DR Congo where bananas and plantains are commonly grown as important crops, including the assessment of the yield loss in banana and plantain production caused by nematodes in the DR Congo.