Characterization of Septoria brown spot disease development and yield effects on soybean in Illinois

Figures & data

Fig. 1 Development of Septoria brown spot of soybean in three locations in Illinois. Five treatments were applied: NIC means not-inoculated control; 0X is no fungicide application; 3X means three applications of chlorothalonil; 6X means six applications of chlorothalonil; 9X means nine applications of chlorothalonil. The per cent of four disease components (y-axes) were evaluated through the season. Bars are the standard error

Fig. 2 Mean values of vertical progress at R6 and chlorotic area at R7 caused by Septoria brown spot of soybean with five treatments and three locations in Illinois. Error bars are standard errors. Bars with the same letters indicate no significant difference according to Fisher’s Least Significant Difference (LSD) pairwise comparisons (P < 0.05)

Table 1. Analysis of variance for the effect of fungicide treatments on multiple components of the severity of Septoria brown spot of soybean at the end of the season and their AUDPC values in Illinois

Septoria brown spot severity component	F value	p-value
Vertical progress (R6)	7.67	0.0080*
AUDPC of vertical progress (V7 to R6)	17.81	0.0005*
Chlorotic area (R7)	4.47	0.0044*
AUDPC of chlorotic area (V7 to R7)	7.99	0.0086*
Necrotic area (R7)	1.99	0.1148
AUDPC of necrotic area (V7 to R7)	9.58	0.0047*
Defoliation rate (R7)	2.57	0.1196
AUDPC of defoliation rate (R1 to R7)	5.87	0.0166*

Table 2. Variance components for the response of Septoria brown spot of soybean to fungicide application, for disease and yield components evaluated at three locations in Illinois

Disease or yield component	Location	Block (location)	Location x treatment	Residual
Vertical progress (AUDPC)	78%	3%	0%	18%
Vertical progress (R6)	15%	2%	5%	78%
Chlorotic area (AUDPC)	0%	0%	52%	48%
Chlorotic area (R7)	23%	0%	5%	72%
Necrotic area (AUDPC)	33%	0%	35%	31%
Defoliation rate (AUDPC)	75%	0%	10%	15%
Yield	79%	0%	6%	16%
100-seed weight	75%	8%	8%	9%
Pods per plant	27%	17%	5%	51%
Seeds per plant	40%	17%	0%	43%

Table 3. Pearson correlation coefficients (top) and p-values (bottom) for selected components of Septoria brown spot of soybean, 100-seed weight, yield, and yield response for combined data from three locations in Illinois

	Vertical progress		Chlorotic area
	AUDPC	R6	AUDPC	R7	100-SW^a	Yield response
Yield	−0.45	−0.28	−0.31	0.08	−0.49	0.19
	<.001	0.034	0.0232	0.546	<0.001	0.220
Vertical Progress | AUDPC	-	0.85	0.74	0.11	0.34	−0.03
	-	<.001	<.0001	0.43	0.009	0.871
Vertical Progress | R6	-	-	0.62	0.21	0.12	−0.05
	-	-	<.0001	0.128	0.371	0.768
Chlorotic Area | AUDPC	-	-	-	0.66	0.03	−0.1
	-	-	-	<.001	0.804	0.561
Chlorotic Area | R7	-	-	-	-	−0.38	0.03
	-	-	-	-	0.005	0.838
100−SW^a	-	-	-	-	-	0.03
	-	-	-	-	-	0.859

^aWeight of 100 seeds.

Fig. 3 Linear relationships between two components of Septoria brown spot of soybean severity and yield. (a) Per cent of vertical progress at R6. (b) AUDPC (V7 to R6) of vertical progress. Trials were held at three locations in Illinois

Fig. 4 Mean yield (kg ha⁻¹) of soybean field trials inoculated with Septoria glycines and treated with fungicide sprays 9 times (9X), 6 times (6X) and 3 times (3X), or not-sprayed (0X) or not-inoculated control (NIC), at three locations in Illinois. Bars show the standard error. There were no significant differences between treatments (α = 0.05)

Fig. 5 Power curves simulated based on our data for the required number of locations to detect statistically significant yield response (80% power) for treatment differences (effect) of 134.5 (2), 269.0 (4) and 403.5 (6) kg ha⁻¹ (bu ac⁻¹), in experiments with soybean inoculated with Septoria glycines in Illinois