Mechanism of Resistance

Resistance to V. dahliae shown by certain strawberry lines is a polygenic trait controlled by both additive and dominant genes which can be observed in the bell curve pattern of Figure 4. 6  

Strawberry plants have gained resistance to V. dahliae by restricting the flow of the infectious structures through vegetative matter. Within susceptible plants, V. dahliae is easily transmitted within the stolons of strawberry plants, resulting in high levels of damage despite the low prevalence of the disease. The possession of this trait reduced yield loss in susceptible plants from 73 - 75% down to 7% -15% for resistant plants. The ability to tolerate the infection also prevents the fungus from spreading from mother plants to runners. As indicated by petiole assay 80.7%  infection rate was present in susceptible mothers and  59.8% infected runners. In comparison to resistant mothers who had 77.3% infection rate, but passed the disease to only 25.1% of the infected runners. 5

Fig. 4 The percentage resistant and tolerant strawberries from susceptible (S) and resistant (R) plants. More than 2,300 seedlings were tested in this study.  (Image credit Stephen Wilhelm, UC Berkeley.   Copyright © 1955 The Regents of the University of California.)



Question : True or false? 5 was the highest level of resistance developed by UC Davis.

Looks Good! Correct: UC Davis had the highest success for resistance at the level of 5

Question: How much improvement in yield loss due to verticillium wilt is typically seen in a resistant strawberry plant?

Looks Good! Correct: The strawberry crop with a previous harvest loss of 75% will typically see this loss ratio cut down to 15% when using a resistant strawberry plant.