Optimising Zoospore Concentration - Statistics Project continued

Continued from Optimising Zoospore concentration post
Sorry that not all the graphs and figures are included.

Results:
Nested Analysis of Variance on Square Root Transformed Data: Linear model:
Y_ijkl = μ + τ_i + α_j + β_k(j) + e_ijkl Where Y_ijkl is the observation, α_j is the fixed effect of the i^th species, β_k(j) is the fixed effect of the j^th level isolate nested within species, τ_i is the fixed effect of treatment and e_ijkl is the random experimental error. i = 1, 2, 3, 4, j = 1, 2, 3, k = 1, 2, 3 (the 3 isolates for each species are different so there are a total of 9 isolates, 3 nested in each of the 3 species).

Conclusions

The analysis of variance clearly showed that there was a significant difference in the amount of zoospores obtained between the four different treatments (F_(3,24)=42.3, p<0.001)>(2,24)=6.75, p=0.005) and between the isolates nested within species (F_(6,24)=9.01, p<0.001). The 5mL treatment with SPW or n/s soil extract was identified as being the best treatment, yielding the highest concentration of zoospores to volume of inoculum produced (Table 4). There was no significant difference between the remaining three treatments (Figure 5).

No further analysis of the differences between species and isolates were carried out as these differences were not of interest to the research being undertaken. It may be interesting for future studies to investigate the extent of any significant differences between isolates of the same species; however this did not pertain to the research question for this study.

My aim for this experiment was to optimise the concentration of zoospores produced from a single Petri plate culture. These results show that the best treatment, out of the 4 treatments tested herein, was the 5mL application of SPW or n/s soil extract as this yielded the highest ratio of concentration of zoospores to volume of inoculum obtained. In answer to the research question posed; reducing the volume of SPW or n/s soil extract applied to the broth cultures does increase the concentration to volume ratio of zoospore inoculum obtained.

I will now be able to obtain the concentration of zoospore inoculum that I require for all of the eight Phytophthora spp. that I am working with. Previously P. citricola and P. cambivora had consistently been poor producers of zoospores and I was unable to achieve the desired concentration of inoculum for my plant inoculation experiments. The results of this experiment lead me to conclude that I should treat these species with only 5mL of SPW or n/s soil extract (respectively) rather than 10mL which I had used previously.

I am unable to suggest a biological reason for this stark difference between the 5mL treatment and the 10, 15 and 20mL treatments. The purpose of treating the broth cultures with this SPW or n/s soil extract is to induce sporangia (which release zoospores) production through starvation conditions and so I can only assume that for the species studied herein the reduction of this rinse volume to 5mL enhances the effect of the starvation conditions and promotes greater sporangia or zoospores production. It is unclear whether the changes in zoospore concentration result from greater sporangia production or increased zoospores produced per sporangia. It seems particularly interesting, and unexplained, however that there are no significant differences between the other three treatments so that the relationship between treatment volume and response is not linear. Further research into the factors involved in this response must be undertaken in order to ascertain the nature and cause of the relationship.