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Bacterial halo blight Disease symptoms, aetiology and dissemination Pseudomonas syringae pv. garcae (Psgc), the causal agent of bacterial halo blight (BHB) of coffee, was first described in 1955 by Amaral et al. (1956) in the munici- pality of Garc
a in the Brazilian state of S~ao Paulo.High increases in disease incidence have occurred after frost, for example after the 1973-1975 period in the state of Paran
a (Kimura et al., 1973; Mohan, 1976), which could be facilitated by the ice-nucleation activity exhib- ited by Psgc (Gonc
alves & Massambani, 2011; Ara
ujo et al., 2018).Bacterial halo blight has been reported in Kenya (Ramos & Shavdia, 1976), Ethiopia (Korobko & Wondinagegne, 1997), Uganda (Chen, 2002) and China (Chen, 2002; Bai et al., 2013).Although the disease was initially considered of minor importance, recurrent outbreaks have occurred in coffee plantations in several Brazilian states, mainly at higher altitudes (Kimura et al., 1973; Mohan, 1976; Cafepoint, 2011; Zoccoli et al., 2011; Rodrigues et al., 2013).Under severe infection, the disease can cause blackening of twigs and blighting of branch tips, resulting in dieback, defoliation, and apical meris- tem death, which in turn induces over-branching (Fig. 1a).

Bacterial halo blight
Disease symptoms, aetiology and dissemination
Pseudomonas syringae pv. garcae (Psgc), the causal agent of bacterial halo blight (BHB) of coffee, was first described in 1955 by Amaral et al. (1956) in the munici- pality of Garc
a in the Brazilian state of S~ao Paulo. It was also reported in the states of Paran

a (Mohan et al.,
1978) and Minas Gerais (Kimura et al., 1973; Zoccoli et al., 2011) in Brazil. Bacterial halo blight has been reported in Kenya (Ramos & Shavdia, 1976), Ethiopia (Korobko & Wondinagegne, 1997), Uganda (Chen, 2002) and China (Chen, 2002; Bai et al., 2013). Although the disease was initially considered of minor importance, recurrent outbreaks have occurred in coffee plantations in several Brazilian states, mainly at higher altitudes (Kimura et al., 1973; Mohan, 1976; Cafepoint, 2011; Zoccoli et al., 2011; Rodrigues et al., 2013).
Characteristic symptoms of the disease include the formation of necrotic spots surrounded or not by chlorotic haloes (Fig. 1a). The lesions are more evident on the leaf borders, but flowers, fruits and branches can also be affected. Under severe infection, the disease can cause blackening of twigs and blighting of branch tips, resulting in dieback, defoliation, and apical meris- tem death, which in turn induces over-branching (Fig. 1b,c) (Zambolim et al., 1999, 2005; Rodrigues et al., 2013). Disease development is favoured by mild temperatures, high wind intensity and rain, especially hail stone rain, which produces injuries that facilitate bacterial penetration (Rodrigues et al., 2013). High increases in disease incidence have occurred after frost, for example after the 1973–1975 period in the state of Paran

a (Kimura et al., 1973; Mohan, 1976), which
could be facilitated by the ice-nucleation activity exhib- ited by Psgc (Gonc
alves & Massambani, 2011; Ara
ujo et al., 2018).
It has been estimated that BHB can cause losses of up to 70% in nurseries and in the field, predomi- nantly in regions above 1000 m a.s.l. in the presence of severe wind (Zoccoli et al., 2011). The bacterium survives mainly as an epiphyte and associated with plant debris. It penetrates the host tissue through nat- ural openings (stomata) or wounds and is mainly dis- seminated by water and wind-driven aerosol particles (Zoccoli et al., 2011). A recent study suggests that coffee seed may also be a source of inoculum (Belan et al., 2016).