Results and Discussion
Figure 4. CART (classification and regression tree analysis) output examining the effect of breeding class, treatment and block on seedling height.
In Figure 4 based on the CART analysis we can see that breeding class is the most significant contributor to the differences in height we can observe. Block is the second most significant contributing factor, indicating that the block effect was higher than the treatment effect in this case. This is an interesting result because it appears that although different environmental stressors were applied to the seedlings (drought and western gall rust fungal inoculation), their breeding class (whether they were elite, improved or unimproved) still contributed the most to their differences in height. There does not appear to be an environmental trade off in terms of ability to cope with environmental stressors and height growth in this experiment.
Figure 5. CART (classification and regression tree analysis) output examining the effect of breeding class, treatment and block on seedling intrinsic water use efficiency.
The output of this CART analysis (Figure 5) tells a similar story to Figure 4. The breeding class was the most significant contributor to the variation in water use efficiency that was observed in the seedlings. Beyond that first split, both block and treatment play a role in the variation observed. This is not a particularly clear result, but it is telling us that within the unimproved seedlings, treatment had more of an effect but in the elite and improved seedlings block had a more significant effect.
Figure 6. CART (classification and regression tree analysis) output examining the effect of breeding class, treatment and block on seedling stomatal conductance.
In this figure (Figure 6), the nodes are different than Figures 4 and 5. The most significant factor affecting the differences in stomatal conductance is the treatment group, and then breeding class and block are secondary. This makes sense particularly in terms of the treatment groups with drought. Seedlings experiencing drought conditions will keep stomata closed in order to conserve water, and stomatal conductance should decrease in these seedlings.
Table 1. ANOVA results tables for seedling height, water use efficiency and stomatal conductance.