Abstract
Bacterial blight (X. oryzae pv. oryzae) is a serious disease in rice across the world. To better control the disease, it is important to understand its epidemiology and how key aspects of this (e.g. infection efficiency, and spatial spread) change according to environment (e.g. local site conditions and season), management, and in particular, variety resistance. To explore this, we analysed data on the disease progress on resistant and susceptible varieties of rice grown at four sites in the Philippines across five seasons using a combination of mechanistic modelling and statistical analysis. Disease incidence was generally lower in the resistant variety. However, we found no evidence that the primary infection efficiency was lower in resistant varieties, suggesting that differences were largely due to reduced secondary spread. Despite secondary spread being attributed to splash dispersal which is exacerbated by wind and rain, the wetter sites of Pila and Victoria in south Luzon tended to have lower infection rates than the drier sites in central Luzon. Likewise, we found spread in the dry season can be substantial and should therefore not be ignored. In fact, we found site to be a greater determinant of the number of infection attempts suggesting that other environmental and management factors had greater effect on the disease than climate. Primary infection was characterised by spatially-random observations of disease incidence. As the season progressed, we observed an emerging short-range (1.6 m–4 m) spatial structure suggesting secondary spread was predominantly short-range, particularly where the resistant variety was grown.
Highlights
Bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae (Ishiyama, 1922) is one of the most important diseases of rice (Choi et al, 1998; Savary et al, 2000a; Savary et al, 2000b)
We found that there was significant spatial structure in the data for almost all observations made at Malayantoc and Maligaya, whereas for data from Pila and Victoria there were more occasions where the random model fitted the data better than the model with spatial structure (Table 5) this was true in the resistant varieties and suggests there was no evidence of secondary infection
We have further clarified how any differences in disease dynamics between the resistant and susceptible varieties were affected by site and season
Summary
Bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae (Ishiyama, 1922) is one of the most important diseases of rice (Choi et al, 1998; Savary et al, 2000a; Savary et al, 2000b). Oryzae (Ishiyama, 1922) is one of the most important diseases of rice (Choi et al, 1998; Savary et al, 2000a; Savary et al, 2000b). The pathogen infects wounds and water pores in the plant It multiplies in intercellular spaces and bacterial ooze is produced on the leaf which can be passed to other plants by direct contact of foliage and through irrigation water (Mundt et al, 1999; Cottyn and Mew, 2004; White and Yang, 2009). Lesions that result from infection still occur on resistant varieties but to a lesser extent, as the pathogen is enveloped by plant polymers making the bacteria unable to colonise the intercellular spaces (Cottyn and Mew, 2004)
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