Management of Potato Cyst Nematodes Using Host Resistance, Organic Amendments and Biocontrol Agents in Nyandarua County, Kenya

Abstract

Globally, potato cyst nematodes species (Globodera pallida and Globodera rostochiensis) are characterized by their invasive nature, efficient adaptability in most environments, and vast spread in potato fields. Given the invasive potential of this pest, its mitigation entails restricting the movement of soil, planting materials, and farm tools in established infested farms. Therefore, the study aims at determining the level of resistance in local potato cultivars, efficacies of organic amendments and bio-control agents (BCAs) in managing potato cyst nematodes. In achieving these objectives, experiments were conducted in the laboratory, greenhouse, and open field already infested with potato cyst nematodes. Laboratory and greenhouse experiments were conducted at Upper Kabete, University of Nairobi whereas the subsequent field experiments were conducted in selected farms in Nyandarua County. To determine the level of resistance of locally available potato cultivars to potato cyst nematodes, the following potato cultivars were used; Dutch Robijn, Shangi, Roslin Tana, Tigoni, Asante, Sherekea, Nyota, Unica, Chulu, Arka, Kenya Mpya, Desiree and Manito. Potato cultivar ‘Shangi’ was used to assess the efficacies of organic amendments (chicken, pig, cow, goat and green manure) and bio-control agents; Purpureocillium lilacinum, Trichoderma asperellum, Trichoderma atroviride, Trichoderma hamatum, Trichoderma harzianum and Bacillus subtillis on potato cyst nematodes, respectively. Data collected from the experiments was subjected to analysis of variance and their means separated using Tukeys multiple comparisons (p<0.05). Potato cultivars Sherekea and Nyota were considered partially resistant to PCN with a severity score of 4-6 (<25-3%) whereas cultivars Shangi, Tigoni, Dutch, Chulu, Asante, Unica, Arka, Kenya Mpya and Roseline Tana were susceptible with a severity score of 1-3(>100-5%). The reproductive index of PCN viable eggs of all the 11 potato cultivars either susceptible or partially resistant were < 1 compared to the positive control potato cultivar Desiree. xv For all organic amendments, potato cyst nematode count was reduced by 50% under greenhouse whereas the reduction was 85% with a reproductive index of <1 for cow, goat and green manure compared to the control in the open field. All commercial BCAs had < 25 potato cyst nematode count compared to the control which had 48-53 cysts under the greenhouse. In the open field, the BCAs namely T. asperellum, T. atroviride and P.lilacinus, had < 23 final cysts count from an initial count of 106-247 cysts in the first season whereas the second season had < 7 final cyst count from an initial count of 19-166 cysts across cultivars Desiree, Shangi and Markies. This study established two tolerant potato cultivars; Nyota and Sherekea. Additionally, all bio-control agents except Bacillus subtillis and organic amendments were effective in suppressing potato cyst nematodes population densities. Therefore, integration of tolerant potato cultivars, bio-control agents and organic amendments can be recommended for sustainable management of potato cyst nematodes.