Evaluating resistance in test plots
A strawberry plant’s resistance rating and yield were plotted each year on a regression line graph as seen in figure 6. A research field was designated to each of the tests performed. There are 2 methods of evaluating resistance that were used in this study: Runner inoculation and direct genotype evaluation.
During this study the researchers were looking for single parents to find which of them has moderate to high levels of resistance to verticillium. Multiple runners were taken from strawberry plants in order to form a family group for testing the level of genetic resistance to the disease. The submersion of runners within a medium containing the fungal spores is the primary method for family selection within the study (see Figure 7). So what Shaw’s team did was took a sample of runners from each family and inoculated them with the verticillium fungus. After treatment the strawberry runners were then transplanted into an assigned test plot. This test allows for the evaluation of traits with minimal genetic influence.
This direct root inoculation technique allows for greater amounts of plant material to be screened because several clone plants can be obtained in the form of runners. In this way, the researchers were able to replicate the strawberry genetics being tested for resistance, since each runner clone would have the exact same genetic makeup. These clone plants can then be evaluated for resistance by progeny tests. This technique has the most thorough inoculation procedure and therefore allows for a high probability of disease transmission. The issue with this method is the low amounts of genetic diversity within the strawberry cultivars being tested. This narrow view is unfavorable due to the high level of diversity present that leads to resistance.3