Favorable conditions for Xanthomonas axonopodis infection in Eucalyptus spp.

Abstract

Currently, Xanthomonas axonopodis is one of the main foliar pathogens for Eucalyptus spp. in Brazil. It induces leaf blight and defoliation of seedlings in the nursery and young plants in the field. However, little is known about the favorable conditions for infection. The establishment and development of bacterial leaf blight caused by X. axonopodis in eucalyptus was studied for different leaf ages, temperatures and leaf wetness durations. Disease severity increased with leaf age, and the highest severity was observed on the fourth pair of completely expanded leaves (from the apex to the base). A higher level of bacterial colonization was also observed on the fourth pair of leaves quantified as bacterial cells/cm 2 of leaf area. Twelve hours of free water on the leaf surface, prior to inoculation, was essential to promote a severe infection. However, with the increase in the leaf wetness duration, a decrease in disease severity was observed. The optimal temperature for disease development was 26-30ºC.

Severity of Xanthomonas axonopodis leaf blight on eucalypt cuttings under different levels of nutrients

“…Diseased eucalypt cuttings are unsuitable for planting in the field due to the reduced photosynthetic area and potential for the spread of the pathogen into previously unaffected areas (Neves, Guimarães, Ferraz, & Alfenas, 2014).…”

Temporal Analysis of Bacterial Leaf Blight in Clonal Eucalyptus Plantations in Brazil

“…In other studies, incidence and severity of symptoms caused by bacteria rise with increasing temperatures [30,31]. According to Neves et al [17], the optimum temperature range for development of bacterial leaf blight in eucalyptus is between 26 and 30 • C.…”

“…Foliar bacterial diseases are pathosystems polycyclic, in which the bacterial spreads between leaves and plants, mainly by water splash [15,16]. Several other studies with bacterial diseases have shown the above-mentioned models as a better fit for pathogen incidence data, both in the nursery and in the field [15,[17][18][19].…”

“…Growth indicators, when correlated with incidence and AUDPC values, were influenced by the disease incidence, confirming the deleterious effect of bacterial infection on the initial growth of the clones. Bacterial leaf blight decreases the photosynthetic area of leaves in the plant and causes severe defoliation, resulting in decelerating plant growth [17]. Palladino et al [28], studying products for bacterial leaf blight control in young plantations of E. dunni and E. grandis in Uruguay, observed that nine months after planting, even in plants with disease severity between 16% and 36%, plant growth was not different between treatments, specifically regarding plant height.…”

“…However, at the beginning of this study, rainfall and air relative humidity were high, favoring bacteria spread and penetration through water film on the leaves. Even after a significant decrease in rainfall and air relative humidity, 100 days of after planting of seedlings, incidence continued to increase, since leaf wetting prior to infection is more critical than in the post-infection stage [17]. According to Fukui et al [29], water availability is solely essential at the pathogen penetration stage, rather than after infection and colonization by bacteria.…”