Management of Crown Gall Disease in Asteraceae Flower Cuttings in Nairobi, Kiambu and Nakuru Counties, Kenya
Loading...
Date
2023-05
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
Flower cuttings production in Kenya faces challenges in the marketing stage because of crown gall whose causal agent is Agrobacterium tumefaciens. Although crown gall is not a quarantine disease in Kenya, strict regulations in the market require that flower cuttings be free of the disease. The disease causes significant financial loss in nursery when large numbers of plants are affected. So far, losses of up to 80% have been recorded in nurseries. Crown gall disease can move systemically throughout the root system and destroy the plants completely. There are currently no effective management strategies for crown gall in the production of flower cuttings. This study aimed to determine the spread and effects of crown gall disease in the production of flower cuttings in Nairobi, Kiambu and Nakuru counties, Kenya and to evaluate the efficacy of various management strategies against the disease on Asteraceae family. A baseline survey was carried out between September and December 2018 while the laboratory and greenhouse experiments were carried out between November, 2018 and October, 2019. A laboratory experiment was set up in a flower cuttings production farm in Kiambu County to determine the action of various management strategies on Agrobacterium tumefaciens invitro. An innoculum density of 10 CFU/ml was immersed in 10mls the selected products and left to settle. After one day, 0.5mls of the suspension was pippeted and serial dilution done. A 0.5ml volume of the diluted cell suspension was plated on nutrient agar medium, incubated at 26°C for 5 days and the colony growth studied. A separate greenhouse experiment was set up at Kenyatta University to determine the effect of the various management strategies on crown gall on susceptible Argyranthemum frutescens. The plants were planted on peat and pumice media at a ratio of 25:75 in 3-litre plastic pots. Seedlings of Argyrathemum plants used in the experiment were obtained from a flower production farm in Kiambu County that grows them for export. The plants were prepared in a propagation chamber for 4 weeks before planting. The management strategies evaluated were Sunflower vegetable oil, KSP-Colloidal Copper, KOBEChrysophanol parietin, Copper oxychloride and Electro-Chemical Activated water. Innoculum was acquired from fresh galls and applied to plants by injuring using a hypodermic syringe then left to express symptoms for fourteen days. Application of the management strategies started after symptoms started showing. Data on disease severity and incidence was collected on a weekly basis in the greenhouse by counting galls and observing chlorotic symptoms development on the plants. In the laboratory, data on bacteria population on nutrient agar media was recorded for the different products tested. Survey data was analyzed using SPSS; laboratory and greenhouse data were subjected to ANOVA using SAS software and the treatments separated using Fisher’s protected Least Significant Difference (LSD) test at 5%. The survey results indicated that crown gall is prevalent in over 70% of the farms that produce flower cuttings. About 60% of the respondents reported the commonly applied management strategies of rouging and use of copper-based pesticides were not effective. Laboratory evaluation indicated Copper oxychloride and KOBE treatments were least effective (266 & 127 cells) compared to ECA water, KSP and oil treatments that recorded few cells (8, 16 & 37 cells). In the lab, combined application of ECA water and Oil killed all bacterial cells while oil alone suppressed bacterial growth partially (27 cells). KSP and oil combined appeared to antagonize each other and had 106 cells. In the greenhouse Copper oxychloride and KOBE were
Description
A Thesis Submitted in Partial Fulfilment of the Requirements for the Award of Master of Science in Crop Protection (Plant Pathology) in the School of Agricultural and Environmental Sciences, Kenyatta University, May 2023.
Supervisor
Maina Mwangi
Nicholas Korir