An unprecedented study conducted by the Agronomic Institute (IAC) has shown that the bacteria that causes sugarcane leaf scald, the main bacterial disease of this crop, is transmitted by the root spittlebug. The insect vector carries the bacteria Xanthomonas albilineans and transfers it to healthy plants, transmitting this disease that has no control and, in most cases, is asymptomatic.
According to IAC researcher Silvana Creste, with this discovery, the development of varieties resistant to the root spittlebug could be one of the strategies for controlling leaf scald. “This discovery brings a new perspective on the pest and also the disease because it allowed us to know that the spittlebug, in addition to being one of the main pests of sugarcane, also carries a hidden enemy of sugarcane,” she says.
The bacteria, by colonizing mainly the xylem vessels, hinders the absorption of water and raw sap by the plant. The damage includes low germination of buds, a drop in productivity and sugar content of the sugarcane, in addition to a reduction in the longevity of sugarcane fields. The damage depends on the variety, crop cycle, age of the sugarcane field, environmental conditions, aggressiveness of the bacterial isolate and the interaction between all these factors.
“In susceptible varieties, the disease causes the death of buds/shoots and, consequently, of the plant”, says the researcher from IAC, from the São Paulo Agency for Agribusiness Technology (Apta), from the Secretariat of Agriculture and Supply of the State of São Paulo.
In addition to the IAC team, the following professors participated: Guilherme Duarte Rossi from Unesp Jaboticabal, Claudia Barros Monteiro-Vitorello and Luis Eduardo Aranha Camargo from Esalq, Marie Anne Van Sluys from the Botany Institute/USP, Andressa Peres Bini from FAPESP, Izadora Farina Pastore from Fundag, and Carolina Veluci Brondi, a master's student from Unesp Jaboticabal and Marina Carnaz Duarte Serra from the Ribeirão Preto School of Medicine/USP.
Next phases of studies
The next stages of the research aim to evaluate whether other species of root spittlebug that infest sugarcane crops are also hosts of Xanthomonas albilineans. It is also intended to establish new management strategies for the pest and disease, since, currently, the use of healthy seedlings and disinfection of cutting instruments during planting and harvesting are recommended.
According to the researcher, once infected, a variety can only be recovered through clonal cleaning in tissue culture laboratories, followed by health checks using advanced molecular biology methods in laboratories. The reference laboratory unit of the IAC Sugarcane Center, in Ribeirão Preto, is the only laboratory in Brazil with ultrasensitive technology to detect the presence of this bacteria in sugarcane.
“We developed this technology about a decade ago, when we realized that the materials intended for planting were not healthy enough to deliver high productivity throughout the cultivation cycles of a variety,” comments Silvana Creste.
Based on the development of health checking technologies, Silvana and her team developed the Invicta IAC technology, which consists of producing seedlings in a meristem culture laboratory, in which the health of diseases transmitted by seedlings is certified by molecular biology techniques, in addition to the genetic identity attested by DNA fingerprinting.
The researcher reports that the discovery was only made possible by Invicta technology. “We were convinced that we had delivered healthy seedlings to the producer when we identified the occurrence of scalding in the nurseries. In the history of this nursery, there was no practice of using mechanical instruments - until then described as the only form of transmission of the disease - but there was a high infestation of root spittlebugs in this area. We had a new perspective, designed a new project focused on this finding and ended up uncovering this transmission”, reports the IAC scientist.
Understanding the disease's transmission methods allows us to define strategies to prevent its occurrence or minimize the damage it causes. The research has not yet generated a recommendation for controlling the disease, but the scientist says that the discovery has opened up a new opportunity for debate, focusing on management strategies for controlling it in seedling nurseries and sugarcane fields, aiming to reduce losses.
The discovery of this transmission was published in the scientific journal Journal of Insect Science and is available at https://doi.org/10.1093/jisesa/iead116. The projects that made this discovery possible were funded by the São Paulo Research Foundation (FAPESP) and the Agricultural Research Support Foundation (Fundag).