Population density and spatial pattern of sclerotia of Sclerotinia sclerotiorum in desert lettuce production fields

Figures & data

Table 1. Descriptive statistics for sclerotia populations of Sclerotinia sclerotiorum in six lettuce fields

				Indices of dispersion^a
Field	Range^a	Mean^a	Variance	V/M	Morisita’s Index	Lloyd’s Index
A	0–35	1.2	54.6	8.9*	8.9*	7.9*
B	0–42	2.9	51.1	17.7*	6.8*	16.7*
C	0–24	2.9	18.8	6.4*	2.9*	5.4*
D	0–11	0.27	1.00	3.66*	10.81*	2.66*
E	0–4	0.08	0.13	1.63*	9.17*	0.63
F	0–8	0.36	1.09	3.06*	6.85*	2.06*

The statistics were performed for each field using the sclerotia data from composite samples (192).

^aSclerotia/100 g of soil.

Values followed by an asterisk (*) are significantly greater than 1.0 at P ≤ 0.05, indicating an aggregated distribution. V/M = Variance/Mean. The detailed statistics for each plot per field are given in the supplement Table.

Fig. 1. Frequency distribution of sclerotia densities of Sclerotinia sclerotiorum in six lettuce fields.

Table 2. Distribution patterns of sclerotia of S. sclerotiorum within two diagonals of the same plots of six lettuce fields

	Variance peak (radius of population aggregate)a
	Plot
	1		2		3		4		5		6		7		8
Field	d1	d2	d1	d2	d1	d2	d1	d2	d1	d2	d1	d2	d1	d2	d1	d2
A	1	1	3	R	4	U	4	R	4	U	4	2	1	R	1	U
B	4	R	4	U	6	U	6	1	4	R	5	U	1	6	1	U
C	6	U	2	U	2	6	6	R	6	4	6	U	4	R	4	R
D	3	U	R	U	1	2	2	U	−	−	R	−	R	1	6	4
E	−	−	2	2	2	U	−	−	−	4	1	−	−	R	−	R
F	R	U	2	−	4	6	U	4	R	4	4	U	−	4	4	4

^aRadius of population aggregate (in metres) was obtained by plotting the variance of different blocks calculated using TTLQV method against block sizes. d1 and d2 are the two diagonal paths of each plot. R = variance fluctuates randomly with the different block sizes which indicates random distribution, U = variance is low and does not fluctuate at different block sizes which indicates uniform distribution, – = no sclerotia recovered from the diagonal.

Fig. 2. Graph of variance peaks for random, uniform and clumped patterns of sclerotia of Sclerotinia sclerotiorum from two diagonals of the same plot for representative plots from field A (A), field B (B) and field C (C) lettuce fields.

Table 3. A precision of sampling size used in estimating sclerotia populations of Sclerotinia sclerotiorum in six lettuce fields

Field	No. of soil samples taken	No. of soil samples required with 20% SE	Sampling error with 192 samples (%)	No. of plots sampled	No. of plots required with 20% SE	Sampling error with 8 plots (%)
A	192	178	19	8	15	27
B	192	152	18	8	10	22
C	192	55	10	8	3	10
D	192	334	25	8	32	40
E	192	499	31	8	21	33
F	192	214	20	8	9	22

Table 4. Goodness of fit of the distribution of sclerotia of Sclerotinia sclerotiorum in six lettuce fields to statistical distribution

		χ^2 value
Field	No. of samples used	Poisson^a	Negative binomial^a	Neyman type A^a
A	192	93.3*	89.2*	444.0*
B	192	77.0*	33.4*	16.8*
C	192	12.7*	18.9*	852.0*
D	192	7.1*	19.7*	170.3*
E	192	x	x	5.9*
F	192	9.1*	10.7*	83.3*

^aChi square value. Asterisk (*) indicates chi square statistic was highly significant (P < 0.01) and that the composite soil core frequency data was not adequately described by the corresponding frequency distribution. x indicates that the frequency of sclerotia was not enough to calculate a χ². Goodness of fit was also performed separately for sclerotia data from each plot per field, and the results are listed in supplement table.