Plant parasitic nematodes associated with sugarcane in western kenya and their management using host resistance and crop mixtures
Plant parasitic nematodes associated with sugarcane are known to cause losses in yields of up to 50% thus ranking among the most damaging pests. However, their occurrence, abundance and distribution in western Kenya sugarcane zones is not known. Therefore, this study was conducted to determine occurrence of the nematodes, the host resistance status of the varieties used and the influence of different intercrops on the population dynamics of the parasites. The survey and field trials were carried out in the western sugarcane zones of Nzoia, Mumias, West Kenya and Busia while the greenhouse experiment was conducted at Kabete field station. Samples were collected from farms in the four zones and nematodes extracted from 200 crn' soil. Nematodes were identified up to the genus level and then counted. Seven sugarcane varieties were selected for evaluation to determine their host resistance status to nematodes. These were C0421, C0617, C0945, EAK70-97, KEN83-737, KEN82-808 and KEN82-216. N14 was used as the standard due to its known tolerance status. The experiment was carried out in a glasshouse at Kabete in a completely randomized design with three replications. Data on nematode populations and shoot length were collected at 0, 60 and 120 days after planting (DAP). At termination, data on root length and weight were taken and subjected to Analysis of Variance and means separated by Least Significant Difference test. The field trial to evaluate the effect of different intercrops on plant parasitic nematodes associated with sugarcane was carried out at Kibos, Kisumu in western Kenya. Five food crops namely bean, soya bean, pigeon pea, maize, and cowpea. The experiment was laid down in split-plot designwith variety as the main plot. The dominant genera of nematodes associated with sugarcane were Pratylenchus, Scutellonema and Meloidogyne with percentage densities of 21, 18 and 13 respectively. Soils in Nzoia were more heavily infested with plant parasitic nematodes given that 55% of the nematodes were recovered from the zone compared to 45% in all the other zones combined. Sandy soils haboured 40% more nematodes compared to clay soils. The varieties tested showed a higher level of resistance to plant parasitic nematodes compared to N14. Crop cycle, altitude, AEZ, management types and organic products were found to influence the parasites. Most nematodes are concentrated in Nzoia sugarcane scheme which is a marginal sugarcane zone as opposed to Mumias which is a typical sugarcane zone (LM1). The highest density of nematodes in the rhizospheres of all varieties screened were those of Pratylenchus spp. at 188 per 200cm3 of soil while the least were Hoplolaimus spp. at 92. Numbers of plant parasitic nematodes were 81% lower when variety C0421 was interplanted with beans compared to variety N14 with beans. Significant differences were also observed when different sugarcane varieties were interplanted with soya beans. Intercropping resulted in reduction of numbers of plant parasitic nematodes with the exception of members of the genus Scutellonema whose numbers increased in sugarcane interplanted with common bean. This study has established the presence of 15 genera of plant parasitic nematodes associated with sugarcane in the western zones of Nzoia, Mumias, West Kenya and Busia with Pratylenchus, Scutellonema and Meloidogyne being the most predominant. It has also revealed the influence of soil texture, crop cycle and anthropogenic factors on abundance and distribution of these nematodes in western Kenya sugarcane zones. It has therefore set the justification of further work to determine the economic importance of the nematodes to sugarcane production.