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Biological Control of Seed Rot and Damping-off Pathogens in Corn (Zea mays L.) with Bacillus spp
Thesis Abstract:
One hundred eighteen putative Bacillus strains isolated from healthy corn roots obtained from Baguio, Bukidnon, La Union, Los Baños, Misamis Oriental, and Nueva Ecija were evaluated for antagonistic activity by co-cultivation against Diplodia macrospora Earle (DM), Fusarium moniliforme J. Sheld. (FM) and Pythium graminicolum Subr. (PG) causing seed rot and post emergence damping-off in corn. Of these isolates evaluated, only three isolates were found antagonistic to the test pathogens, namely: Ba-UPR 30 on PG, Ba-NER 1, and Ba-NER 23 on DM; and Ba-NER 1, Ba-NER 23, and Ba-UPR 30 on FM. Both agar-diffusible and volatile metabolites toxic to the pathogens were produced by the antagonists. Rhizoctonia solani (RS) from corn was also found sensitive to the antagonists.
The antagonists (Ba-NER 1, Ba-NER 23, and Ba-UPR 30) were evaluated as biological seed treatment materials on sweet corn (IPB Supersweet var.) against FM, PG, and RS. In these tests, the seeds were coated with bacteria prior to sowing in artificially infested pasteurized and non-pasteurized field soils. In seed treatment against DM, the seeds were coated first with antagonists then inoculated with the pathogen before sowing in pasteurized soils. When compared with the controls, seeds treated with Ba-NER 1 and Ba-NER 23 against DM had reduced percent seedling infection by 77.97 and 78.71 percent, respectively.
Seeds treated with Ba-NER 1, Ba-NER 23 and Ba-UPR 30 against FM resulted in significantly higher seed germination and seedling height than that of the controls. Reductions of pre-emergence damping-off in corn for the three antagonists ranged from 93.77 to 98.48 percent in pasteurized soils, and 82.31 and 91.81 percent in nonpasteurized soils.
Seed treatment using Ba-UPR 30 effectively suppressed the pre- and postemergence seed infection of corn by PG. Compared with the control, the treatment reduced pre- and post-emergence infection by 42.81 and 90.71 percent, respectively in pasteurized soils and 51.47 and 69.20 percent, respectively in non-pasteurized field soils.
All the three Bacillus isolates were found active against RS. Pre-emergence infection by the pathogen was significantly reduced by 67.75 and 82.26 percent in pasteurized soils, and 57.65 to 78.82 percent in non-pasteurized field soils.
The controls afforded by seed treatment with the three Bacillus isolates were all comparable or even better than Captan seed treatment.
On the basis of morphological and biochemical characteristics, Ba-NER 1, Ba- NER 23, and Ba-UPR 30 were identified as strains of Bacillus subtilis (Ehrenberg) Cohn.
Data indicated that the three B. subtilis strains could be advanced for field testing to determine their true potential as biocontrol seed treatment materials against major seed rot and damping-off pathogens in corn and their development prospects as possible biocontrol product for commercialization.