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plant surface microbiology.pdf

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538<br />

Frank B. Dazzo<br />

Table 2. In situ plot-based spatial distribution analysis of corn phyllosphere prokaryotic<br />

microbial communities<br />

Parameter Control BT corn Interpretation<br />

corn (Pioneer<br />

(Pioneer 3573)<br />

36N05)<br />

Spatial density (cells/mm 2 ) 214,615 172,692 Higher on control corn<br />

Morista dispersion value 1.3086 1.7805 Clumped distribution<br />

Variance/mean ratio 7.7346 13.6624 Clumped distribution<br />

Negative binomial K distribution 1.9238 0.6779 Clumped distribution<br />

Lloyd’s patchiness value 1.3144 1.7931 Clumped distribution<br />

Nonfilamentous microbial cover (%) 2.2 0.4 Higher on control corn<br />

The spatial distribution of prokaryotic microorganisms on the phylloplane<br />

<strong>surface</strong> of these two corn varieties was compared by analyzing several CMEIAS<br />

in situ plot-based measurement features on a sample set of 104 quadrat images<br />

(52 quadrats each). The mean values of their spatial density (cells/unit of <strong>surface</strong><br />

area) and percent nonfilamentous microbial cover indicated a significantly<br />

higher level of bacterial colonization on the phylloplane of the Pioneer<br />

36N05 (control corn) variety (Table 2). An ascending sort plot of the entire<br />

range of spatial density for each image quadrat provided further insight into<br />

the basis for this difference in spatial distribution,with clear indication that the<br />

overall density of bacteria on the BT-corn phylloplane was lower because that<br />

habitat contained more image quadrats with no bacterial cover (Fig. 14).<br />

Table 2 lists several other computations that define the patterns of spatial<br />

distribution for microbes that colonize these <strong>plant</strong> leaf <strong>surface</strong>s, all derived<br />

from in situ plot-based data extracted from image quadrats by CMEIAS and<br />

computed in EcoStat. The Morista Index measures the degree of dispersion,<br />

with values 1 for a clumped pattern. The variance/mean ratio from the<br />

observed pattern of frequencies (proportion of quadrats that contain organisms)<br />

to those predicted by a Poisson distribution is approximately 1 for randomly<br />

spaced populations, significantly >1 for clumped spacing, and

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