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Occurrence, abundance and distribution of nematodes of banana linked to altitude in selected banana production areas with focus on pathogenicity of Pratylenchus goodeyi in Kenya
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Banana (Musa spp.) is a popular fruit crop in Kenya, where it is largely cultivated by smallholder farmers. However, plant pathogens, such as plant parasitic nematodes, have been blamed for the fall in output (PPN). A survey of bananabased subsistence farming systems in Kenya's banana-growing counties was done with the objective to a) assess farmers' awareness regarding PPN, b) explore the variability regarding PPN species associated with banana genotypes in Kenya and if the prevalence and abundance of these PPN species vary with altitude and c) differential ability of Pratylenchus goodeyi populations to infect banana. One hundred and eighty (180) farms from 12 major banana producing areas with varying altitudes ranging from 1100-2000 m above sea level were surveyed. Farms were selected following a purposive sampling method. A structured questionnaire was administered to every farmer whose orchard was selected for sampling. From each production area, 30 soil and 30 root samples were randomly collected from 15 banana farms. On each farm, one soil and one root sample were collected from both dessert (Cavendish) and cooking (EAHB) banana cultivars. A total of 720 samples were collected from the survey study. Nematode damage was scored on five functional roots randomly selected and scored for the extent of necrosis in the root cortex as a percentage. Nematodes were extracted from 5g of roots and 100 ml soil using a modified Baermann technique and identified to the genus level. Besides, two pot experiments were set up to assess the differential ability of Pratylenchus goodeyi derived from diverse altitudinal gradients to infect banana. Mean values of root necrotic indices (RNI %) from the survey and pot trials were arcsine (√x) transformed. Nematode relative abundances and genera diversity were computed. The nematode counts were subjected to log10(x+1). Data were subjected to a two-way ANOVA using R- version 3.5.1 system statistical software and means separated by the Tukey's test at P≤0.05. Results showed that only 2.3% of the farmers were aware of nematode damage and symptoms, with none applying any management measures. The highest abundance of PPN was recorded at an altitude range of 1601-2000 masl with Pratylenchus, Meloidogyne and Helicotylenchus spp. as the predominant genera. Across mid and high altitudes, EAHB showed higher numbers of nematodes than Cavendish. Screening tests on P. goodeyi revealed that populations from Embu had higher plant infectivity as they recorded the highest reproduction rates. Ng‟ombe showed higher infectivity than Sukari Ndizi banana in both trials. The results revealed that nematode damage is more common at higher altitudes and on the EAHB genotype. The findings suggest that strengthening farmers' awareness of pathogen dissemination mechanisms and increasing their availability to disease-free planting supplies should be part of Kenya's banana nematode management strategy. The findings from our study can be used to advise farmers on nematode management techniques suitable for different altitudes.