Measuring a Population's Response to Dicamba

When Javier collected kochia plants for his research he sampled at least 40 random plants from a field, representing the broader population that occurred in the field. 

Figure 6: Kochia plants growing in the greenhouse. (R. J. Crespo, University of Nebraska-Lincoln)



 Because Javier conducted his study in a greenhouse and carefully measured the rates of dicamba used in each treatment…

Looks Good! Correct: Yes! The environment was controlled, so differences were caused by genetics.

The phenotype of a plant is controlled by the genotype (genetic make-up) plus how the genotype responds to the environment where the plant is grown.  In the greenhouse Javier did his best to make the environment uniform for all plants, and he carefully applied the dicamba so that the doses received by the plants were consistent within each treatment.  Any variation he measured among plants and across populations would be expected to be due to differences in the genetic makeup.

All of the populations were initially treated with a single dose of dicamba (Figure 7). 

Figure 7: Visual injury estimates 21 DAT of 67 Nebraska kochia populations treated with 560 g ae ha-1 dicamba. (R. J. Crespo, University of Nebraska-Lincoln)



Did all the populations respond similarly to dicamba (see Figure 7)?

Looks Good! Correct: The answer is no. Population 11 was on average, far less susceptible to the the recommended field rate than population 23. The error bars surrounding the mean for Population 219 were very large because the individuals within the population responded very differently – some were killed by dicamba while others were only mildly affected.

Now let’s review the hypothesis: All populations of a given species will respond the same to a given dose of dicamba.  Was Javier able to accept or reject his hypothesis based on the data in Figure 7?

The hypothesis was rejected.  This data shows that there is great variability in kochia response to dicamba across populations in Nebraska, and even within some of the populations.  This suggests that repeated applications of dicamba without the use of other effective control measures may select for less-resistant individuals, and shift populations towards those that are not susceptible to dicamba.