Does rootstock choice affect ToBRFV resistance?

Rootstock-scion interaction trial results.

Understandably, growers around the world still have a lot of questions about tomato brown rugose fruit virus (ToBRFV). One key question involves the impact of ToBRFV resistant rootstocks on the performance of the scion. Does it make sense to choose a resistant rootstock, and will doing so help protect the crop against the disease? Bayer has conducted specific additional research to help answer this question.

The short answer, according to Bayer’s most recent research, is that the choice of rootstock does not affect ToBRFV symptoms in the crop, confirming the results of previous work in this area. According to our latest research, the rootstock does not appear to bring additional value to the crop in terms of ToBRFV. Resistant rootstocks might give peace of mind to the grower, but in practice the severity of fruit and leaf symptoms are determined by the scion: the resistance status of the rootstock seems irrelevant.

 For our latest trial, in November 2023 we sowed 10 different rootstocks in the Netherlands. These included rootstocks which are known to be resistant to ToBRFV (including a competitor’s variety), and those which are known to be susceptible, such as Maxifort and DRO141TX. Five crop varieties with different levels of ToBRFV resistance were then grafted onto each of these rootstocks, including well-known intermediate resistant variety Ferreira, and susceptible variety Marinice.

The crops were planted in early January and 8 days later, all the scions were vaccinated with Pepino Mosaic Virus, then inoculated with ToBRFV after another 9 days.  Every combination of rootstock and scion was planted in 3 plots, each containing 4 plants. The plants were grown hydroponically in a peat substrate without artificial light – and the severity of ToBRFV symptoms was assessed on leaves as well as ripe fruit.

Five factors were analyzed in terms of their possible influence on the severity of ToBRFV symptoms in each plant:

1.     How much does the scion influence the expression of ToBRFV? Is it the main factor?

2.     How much does the rootstock influence the expression of ToBRFV and can it prevent symptoms?

3.     Does the combination of rootstock and scion, or the interaction between them, play a role in the crop’s performance against ToBRFV?

4.     Were there any location or block effects? This is because the conditions may vary slightly across the glasshouse.

5.     Other statistical errors, i.e., any variation in symptom severity that can’t be assigned to other variables above.

A statistical technique known as Analysis of Variance (or ANOVA) was used to assess which of the above variables were significant in the different expression of ToBRFV symptoms in the 50  possible combinations of varieties and rootstocks.

(whereby ns means not significant, * means significant at p < 0.01 and ** means significant at p < 0.001):

These results clearly show that leaf symptoms were only affected by the resistance level of the scion and that the rootstock had no significant impact on leaf symptoms. Very similar results were also seen in terms of fruit symptoms. Once the block effect is discounted (i.e. any differences which occurred due to the location of the plots within the greenhouse) the fruit symptoms were shown to only have been impacted by the resistance level of the scion, not the rootstock.

The various combinations of scion and rootstock were analyzed separately so we could consider possible interaction effects between the two, but the results supported our initial position that varieties do not appear to perform differently with various rootstocks. This can be seen in the table below.