Submitted to: Plant Disease Management Reports
Publication Type: Experiment Station
Publication Acceptance Date: 2/14/2013
Publication Date: 5/11/2013
Citation: Anders, M.M., Zhou, X., Jia, Y., Liu, G. 2013. Evaluation of brassica cover crop and PGPR strain for suppression of sheath blight of rice in Arkansas, 2012. Plant Disease Management Reports. 7: FC048 doi:10.1094/PDMR07. Interpretive Summary: Rice sheath blight disease is largely managed by the use of fungicides integrated with culture practices. A field experiment involved in brassica cover crop, plant growth promoting rhizobacterium (PGPR), and fungicide Quadris was conducted in Arkansas in 2012. Sheath blight severity was lower in plots seeded to brassica cover crop than in plots left fallowed the spring. The brassica cover crop did not affect grain yield. Application of the PGPR alone had no effect on disease severity or yield. Quadris reduced disease severity when applied at the low or high rate without yield gain, increase yield was only observed at the high rate or when the low rate was applied in combination with the PGPR. This research demonstrated that some combinations of cover crop, PGPR and fungicide are useful for crop protection.
Technical Abstract: An experiment was established in a field of Stuttgart silt loam soil at the University of Arkansas’s Rice Research and Extension Center, Stuttgart, AR. Plots consisted of six 17-ft rows, and spaced 7.5 in. between rows. The experiment was conducted as a split plot design with four replications. Whole plots consisted of two spring cover crop treatments: 1) mustard (brassica) ‘Caliente 199’ and 2) fallow. Subplots were five treatments: 1) Bacillus subtilis strain MBI-600 at 108 cfu/ml, 2) combination of B. subtilis strain MBI-600 with Quadris (azoxystrobin) at 4.5 fl oz/A, 3) Quadris at 4.5 fl oz/A, 4) Quadris at 9 fl oz/A, and 5) unsprayed control. B. subtilis strain MBI-600 is a plant growth-promoting rhizobacterium (PGPR) that has demonstrated growth promoting effects on rice and other crops. Strain MBI-600 is an active ingredient in the biofungicide Integral. Mustard ‘Caliente 199’ is a biofumigant cover crop containing high levels of glucosinolates toxic to many plant pathogens including R. solani. Mustard was seeded at 5 lb/A on 19 Mar and was plowed down on 30 Apr. All plots were inoculated with the sheath blight pathogen by manually broadcasting 1200 ml/plot of rice grain and rice hull mixture (1:3 vol/vol) containing R. solani prior to planting of brassica. Seeds of rice were treated with the Bacillus strains at 108 cfu/ml prior to planting. Rice was drill seeded at 80 lb/A on 17 May. Plots received 180 lb/A of urea fertilizer (46-0-0, N-P-K) prior to permanent flood. Permanent flood was established on 16 June. Control of weeds and harmful insects as well as irrigation followed local recommendations. On 20 July, plots were sprayed with the Bacillus strain MBI-600 at 108 cfu/ml and with Quadris at 4.5 or 9.0 fl oz/A using a CO2 pressurized sprayer equipped with a boom of three TeeJet 8002 nozzles spaced 16 in. apart and delivered at 32 gal/A. The Bacillus strain was grown in nutrient broth on a shaker (120 rpm) at room temperature for 2 days. On 21 Sep, sheath blight severity was rated on a scale of 0 to 9, where 0 represents no symptoms and 9 represents most severe symptoms. Rice was harvested using a plot combine on 25 Sep. Grain yield and moisture were determined and rice yields were adjusted to 12% moisture content. Sheath blight developed slowly and reached low levels at the end of the season. Sheath blight severity tended to be lower in plots seeded to brassica cover crop than in plots left fallowed the spring. However, the brassica cover crop treatment did not affect grain yield. Application of the PGPR alone had no effect on disease severity or yield. Quadris reduced disease severity when applied at the low or high rate, but only increased yield at the high rate or when the low rate was applied in combination with the PGPR. No phytotoxicity was observed in all treatments.