Determination of <i>Fusarium</i> Species Associated with Onion Plants (<i>Allium cepa</i>) in Field in Burkina Faso Causing Damping-Off and Bulb Rots

Abstract

Onion (Allium cepa L.) is the second most important vegetable crop in Burkina Faso and provides an important source of income for those involved in the sector. However, producers are facing significant pre-harvest and post-harvest losses. To date, knowledge of major diseases of the crop is limited, limiting the development of effective control strategies. The objective of this study was to test the pathogenicity of some species of Fusarium. To this end, 33 fungal isolates collected from onion plants in 17 localities and belonging to five Fusarium species were used to inoculate onion seeds and bulbs to determine the pathogenic species responsible for damping-off on seedlings and basal bulb rot in Burkina Faso. The virulence of pathogenic isolates was determined according to the percentages of seedling damping-off evaluated 28 Days After Sowing, and the extent of rot in millimetres on inoculated bulbs. The evaluation of isolates on seedlings revealed that the most pathogenic isolates belong to the species F. proliferatum (I29, I21, I37, I33, I31), F. thapsinum (I35) and F. solani (I38) which resulted in 58.33% -70.83% of seedling damping-off. The most pathogenic isolates on bulbs belong to the species F. proliferatum (I4, I29, I32) and F. oxysporum (I52, I50, I16) which caused 21.67 to 25 mm of rot on bulbs. Isolate I29 was very virulent on both seedlings and bulbs. The isolates of F. fujikuroi species were all low pathogenic on seedlings but one of them, (I27), expressed average pathogenicity on bulbs.

Fusarium basal rot: profile of an increasingly important disease in Allium spp.

“…Such is for instance the case in Vietnam, where co-infection by F. solani, F. proliferatum, and F. oxysporum was reported on onion, but while F. solani was only highly virulent on seedlings, F. proliferatum and F. oxysporum severely affected bulbs as well as seedlings (Le et al 2020). Similarly, reports from Iran, Finland, and Burkina Faso suggest that F. solani and F. redolens typically results in lesions on seedlings while occurring in asymptomatic infections on bulbs (Ghanbarzadeh et al 2014;Haapalainen et al 2016;Kintega et al 2020). Given that natural FBR epidemics are rarely found to be associated with a single species, identifying key species at a specific stage of host development can be useful in adjusting effective control strategies.…”

“…In early stages of germination, the infection results in a delay of seedling emergence (Gutierrez and Cramer 2005;Gutierrez et al 2006) or damping-off of the seedlings (Fig. 1f) (Galeano et al 2014;Kintega et al 2020;Saxena and Cramer 2009). Fusarium pathogens also cause a loss of transplanted seedlings (Fig.…”

“…Some infected seedlings can still survive but are poorly developed and stunted in growth. Occasionally, the pathogens infect plants in the seedling stage, but symptoms become more conspicuous during crop maturity or after harvest (Kintega et al 2020). This was observed with several specific isolates of Fusarium spp., which were inoculated at the seedling stage (Kintega et al 2020).…”

“…The susceptibility of a cultivar is a variable factor (Taylor et al 2013). Indeed, the specialization of pathogens, which is influenced by host phenology, is likely to exist among Fusarium population, leading to some Fusarium isolates being only pathogenic in a certain set of Allium cultivars and even at specific growth stages of the host plants (Cramer 2000;Galván et al 2008;Kintega et al 2020). For example, some isolates of F. oxysporum f. sp.…”

“…(Bayraktar et al 2010;Stankovic et al 2007). It is sometimes referred to "damping-off" or "dieback" disease of the seedlings (Kintega et al 2020).…”