A single amino acid change in the Tomato brown rugose fruit virus (ToBRFV) has successfully breached a specific virus resistance. Researchers report their findings in the scientific journal Frontiers in Plant Science. This discovery pertains to an isolate found in a new resistant variety planted in a commercial greenhouse.
In this commercial greenhouse, the grower had planted the new resistant varieties in two rows, interspersed among other susceptible varieties. The susceptible varieties planted in this commercial greenhouse had naturally contracted ToBRFV. Analysis of the new resistant varieties revealed, contrary to expectations, high concentrations of ToBRFV were also present in this variety, once again through natural means.
Using High-throughput sequencing (HTS), the sequences of the isolate present in the susceptible varieties and the isolate present in the new resistant varieties were compared. It emerged that the sequences were not entirely similar – there was a one base pair difference. To confirm that this naturally occurring isolate with a one base pair difference could indeed break the resistance of the new resistant variety, this isolate was purified and reintroduced into a new resistant variety with the same resistance and monitored in the growth chamber under controlled conditions.
Mutated virus can bypass resistance
It was confirmed that this isolate with the mutation could indeed cause high virus concentrations and clear virus symptoms in the new resistant variety. In contrast, the isolate without this mutation showed no symptoms and no virus multiplication in the new resistant variety. The researchers, from KU Leuven, Scientia Terrae, and DCM, deduce from this that the mutation at position 82 of the movement protein of ToBRFV can enable ToBRFV to bypass the resistance present in these new resistant varieties.
The researchers emphasize that these are naturally occurring isolates of ToBRFV for which they have only mapped the sequence. The mutation also occurred naturally.
Thus, a resistance-breaking isolate has been found, and the researchers have not, as mistakenly stated in an earlier version of this article, broken a ToBRFV resistance.
View the full research report from a team of researchers from Belgium here. The study was conducted by KU Leuven in collaboration with Scientia Terrae and DCM.