1. Phenotypic variables measured
Helena L. Brochero
Faculty of Agricultural Sciences
Universidad Nacional de Colombia
Bogotá, Colombia
Bio-Protection Research Centre
Lincoln University
Lincoln, New Zealand
Michael Rostás, Travis Glare, Maya Raad, Aimee McKinnon
Bio-Protection Research Centre, PO Box 85084, Lincoln University, Lincoln 7647, New Zealand
Endophytic lifestyle of an insect pathogen causes isolate-specific differences in the development of the host plant but not in its herbivores
Background
Beauveria bassiana can act as entomopathogenic fungus killing insect populations or as true endophyte by colonizing plant tissues contributing to induced plant defence responses.
We assessed the effects of two B. bassiana isolates from New Zealand on the development of Arabidopsis thaliana Col-1.
We evaluated the performance of a leaf-chewing (Plutella xyllostella) and a phloem-sucking herbivore (Myzus persicae) when fed with endophyte-infected plants.
Methodology
Fifteen -day old Arabidopsis thaliana Col-1 plants were inoculated with 108 spores/mL solutions of B. bassiana strains BG11 and FRh2 by root dip inoculation.
Control plants were inoculated with 0.05% Tween 80.
Four and twelve weeks after inoculation, 11 different phenotypical variables were measured per plant (n=20 per group each time) (Boyes et al., 2001).
Fungus colonization was assessed through plating on a selective medium with antibiotics and qPCR using B. bassiana-specific markers (Castrillo et al., 2003)
Bioassays were carried out to test the effect of plant-endophyte association on the growth of Plutella xylostella caterpillars and on the fecundity of the aphid Myzus persicae. 1 2
Figure 1: Discriminant analysis representing variables between phenotypical traits in groups of Arabidopsis thaliana plants inoculated with Bauveria bassiana BG11 and FRh2 strains A
Figure 2: Effect of endophytic B. bassiana on herbivores:
(A-C) Endophytic B. bassiana effect on P. xylostella growth post-infestation with third instar caterpillars. Error bars represent the standard error of the mean (N=15-20). Caterpillars of the same age were used within one experiment.
(D) Endophytic B. bassiana effect on M. persicae population after 10 days post infestation. Error bars represent the standard error of the mean (N=12-14). No significant differences between treatments (P < 0.05). n.s. = not significant.
n.s.
(A)
(B)
(C)
(D) 2 1
BG11-inoculated plants showed delayed plant development affecting all growth stages. However, BG11-inoculated plants had greater plant biomass. Likewise, seeds from BG11-inoculated plants had slower germination rate and less uniform germination.
FRh2-inoculated plants were not significantly different to control plants in terms of phenotypic traits and developmental time. Likewise, controls and FRh2 –inoculated A. thaliana plants have similar rates of seed production and germination.
Endophyte presence did not have any antagonistic effects on the growth of P. xylostella and the fecundity of M. persicae (Figure 2). However the re-isolated fungus caused 100% mortality when applied topically on caterpillars.
Results
Group
Phenotypic variables measured
stem legth2
rosette radius
no leaves2
shoot f.w
root legth
root f.w
root dry.w
ratio r.s.f.w
stem daysb
no leavesb
stem lengthb
CONTROL
Mean
17.704
52.5
4.300
95.895
2.832
0.332
0.644
28.5
12.95
28.35
Median
16.65
54.5
4.337
93.915
2.738
0.333
0.606
30.00
13.00
32.545
Standard deviation
10.627
18.076
8.532
1.0919
18.297
1.492
0.163
0.281
4.335
1.317
23.915
Sample variance
72.789
1.192
2.226
0.026
0.079
18.790
1.734
Kurtosis
-0.919
-0.792
0.690
1.3178
2.507
-0.992
-0.918
-0.761
15.690
-0.952
-1.240
Skewness
0.173
-0.183
-1.042
-0.831
0.978
0.283
0.149
0.451
-3.800
0.408
0.0302
Minimum value
0.203
73.31
31.00
65.54
0.68
0.073
0.264
11.00
0.00
Maximum value
36.93
133.44
63.00
6.069
148.47
5.667
0.628
1.173
15.00
69.28
Confidence level (95%)
4.974
8.460
3.993
0.511
8.563
0.698
0.076
0.131
2.029
0.616
11.193
BG11
6.224
63.55
4.159
93.327
5.041
0.466
1.270
28.45
13.2
22.519
2.928
66.5
4.310
91.98
4.406
0.457
1.196
7.007
19.065
15.275
1.513
10.467
1.945
0.183
0.382
6.724
27.419
49.105
2.290
3.785
0.033
0.146
45.208
1.432
1.111
-1.002
0.273
-0.131
-1.063
-0.787
5.783
19.624
-0.063
-1.538
0.554
-0.107
-0.605
-0.383
0.198
0.211
0.326
2.012
-4.412
0.803
0.570
0.000
66.66
34.00
0.867
73.43
1.881
0.195
0.77
12.00
18.5
154.78
80.00
7.228
116.02
8.365
0.818
2.534
16.00
68.52
3.280
8.923
7.149
0.708
4.899
0.911
0.086
0.179
3.147
0.560
12.833
FRH2
15.096
99.766
53.65
3.500
3.120
0.311
0.894
29.35
12.05
28.294
17.6
97.415
54.00
3.524
2.748
0.279
0.879
29.00
23.865
8.614
14.739
10.801
0.932
20.961
1.433
0.119
0.305
1.226
1.356
21.749
74.196
0.869
2.053
0.014
0.093
1.503
1.839
-0.248
-0.754
-0.648
-0.564
2.180
1.601
2.307
0.604
-0.326
-0.476
-0.504
0.048
-0.178
1.377
1.061
0.967
0.005
0.463
0.523
67.7
37.00
2.013
1.445
0.141
0.39
27.00
10.00
129.18
73.00
5.216
143.61
7.157
0.64
1.761
32.00
68.94
4.0313
6.898
5.055
0.436
9.810
0.671
0.056
0.143
0.574
0.635
10.179
Table 1: Data of phenotypic variables in groups of Arabidopsis thaliana plants inoculated with Bauveria bassiana BG11 and FRh2 strains
Figure 2: Polar coordinates of total variables analysed to discriminate between control vs BG11 for phenotypical traits in groups of Arabidopsis thaliana Col-1 plants inoculated with BG11 and FRh2 Beauveria bassiana strains
Table B. Dunnett’s test in groups of Arabidopsis thaliana Col-1 plants inoculated with BG11 and FRh2
Beauveria bassiana strains after β Bonferroni correction (0.0051)
Conclusions
Beauveria bassiana BG11 and FRh2 were recovered as endophyte from Arabidopsis thaliana Col-1 plant tissue and detected by qPCR after inoculation by dip root method.
Each strain of Beauveria bassiana interacted differently with the Arabidopsis thaliana Col-1 plants.
The endophytic B. bassiana did not have any antagonistic activity on the performance of P. xylostella and M. persicae.
References
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