Abstract
The adoption of tool sterilization using either 3.5% sodium hypochlorite (household bleach) or fire, a core element of the cultural control packages for Xanthomonas wilt (XW) of banana has been poorly adopted hampering XW control in East and Central Africa. Household bleach is costly and not accessible to the rural poor while repeated heating weakens metal blades of garden tools (machetes, knives, and hoes). Identification of economically viable tool sterilization options is thus crucial for XW management. We explored a range of practices including tool insertion for varying time periods into cold and hot ash, fire and boiling water; tool exposure over varying time periods to the sun while under black or transparent plastic sheets; and washing tools with cold water and laundry soap or detergent. Cleaning with household bleach served as a negative control while uncleaned tools as positive control. Like for household bleach, no Xanthomonas vasicola pv. musacearum (Xvm) the causal agent of XW was recovered from tools washed with cold water and different laundry soaps or detergents. Culturing Xvm in varying detergent and soap concentrations (0.00125–0.035 g/mL), only resulted in growth at lower concentrations of 0.00125 and 0.0025 g/mL. The cleaning effect of soap could thus be due to both an anti-bacterial effect and dislodgment of bacteria from tools. Laundry soaps/detergents are cheaper than household bleach and used for various purposes within and across households, including the resource poor and rural households, hence a cheaper and convenient tool sterilization alternative. Tool insertion into boiling water was effective from the 40th second and thus a viable alternative. Heating tools in fire required up to a minute to clear all bacteria. The currently recommended 20–40 s heating could thus be inadequate. Repeated heating for 1 min may also damage tools. Other practices (washing with cold water only, use of solar radiation, repeatedly and forcefully inserting tools into the soil, tool insertion into hot and cold ash for up to 5 min) only reduced Xvm populations on tools, thus not independently recommended. We recommend expanding the tool sterilization options to include washing with soap/ detergents and tool insertion into boiling water for at least 1 min.
Highlights
Xanthomonas wilt (XW) of banana is an important disease of banana in the east and central African region (Kalyebara et al, 2006; Biruma et al, 2007; Tripathi et al, 2009; Blomme et al, 2014, 2017a; Ocimati et al, 2019)
This suggests that the available laundry soaps and detergents in the [Ugandan] market can potentially eliminate the bacteria from farm tools
Similar estimates for the fixed effects (i.e., Xanthomonas vasicola pv. musacearum (Xvm) incidence on tools and Colony Forming Units (CFU) recovered from tools) were attained for washing tools with cold water and laundry soap; cleaning with 3.5% sodium hypochlorite; tool insertion into boiling water for at least 40 s, 60 s, 3 min and 5 min; and tool insertion into fire for about 60 s, 3 min and 5 min (Tables 2, 3; Figures 1A,B)
Summary
Xanthomonas wilt (XW) of banana is an important disease of banana in the east and central African region (Kalyebara et al, 2006; Biruma et al, 2007; Tripathi et al, 2009; Blomme et al, 2014, 2017a; Ocimati et al, 2019). A 35% drop in sales and doubling of bunch prices due to XW have been reported in Tanzania and Rwanda (Nkuba et al, 2015) It might not be a coincidence that the period 2001–2014 has seen a 50% and a 39% decline in banana production and area with banana, respectively, in Uganda (FAO, 2020). The core cultural control practices promoted include the rouging of entire diseased mats and/ or singly cutting at soil level of diseased plants, sterilization of farm tools by flaming/heating with fire or cleaning with 3.5% sodium hypochlorite (NaOCl/ household bleach), timely removal of the floral male buds with a forked stick and the use of clean planting materials (Karamura et al, 2008; Blomme et al, 2014, 2019; PROMUSA, 2020). The main packages include the (i) complete diseased mat uprooting (CDMU) which comprises uprooting entire mats, farm tool sterilization and male bud removal; and (ii) single-diseased stem removal (SDSR) which consists of the removal of single diseased stems, farm tool sterilization and early male bud removal
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