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A series of laboratory, greenhouse, and field experiments were conducted to evaluate seven strains of plant growth-promoting rhizobacteria (PGPR). The PGPR were tested as suspensions of fresh cultures and talc-based powder formulations. Evaluations were conducted on pearl millet (Pennisetum glaucum) for growth promotion and management of downy mildew caused by Sclerospora graminicola. All treatments with fresh suspensions and powdered formulations showed enhancement in germination and vigor index over the respective untreated controls. With fresh suspensions, maximum vigor index resulted from treatments by Bacillus pumilus strain INR7 followed by B. subtilis strain IN937b (64 and 38% higher than the untreated control, respectively). With powdered formulation, treatment with strain INR7 also resulted in the highest germination and vigor indexes, which were 10 and 63%, respectively, over the untreated control. Under experimental plot conditions, prominent enhancement in growth also was observed in the disease tests. Yield was enhanced 40 and 37% over the untreated control by seed treatment with powdered formulations of strains INR7 and SE34, respectively. The same strains also increased yield by 36 and 33%, respectively, when applied as fresh suspensions. Studies on downy mildew management resulted in varied degrees of protection by the PGPR both under greenhouse and field conditions. With fresh suspensions, treatment with INR7 resulted in the highest protection (57%), followed by B. pumilus strain SE34 and B. subtilis strain GBO3, which resulted in 50 and 43% protection, respectively, compared with the untreated control. With powdered formulation, PGPR strain INR7 suppressed downy mildew effectively, resulting in 67% protection, while SE34 resulted in 58% protection, followed by GBO3 with 56% protection. Treatment with Apron (Metalaxyl) resulted in the highest protection against downy mildew under both greenhouse and field conditions. Thus, the present study suggests that the tested PGPR, both as powdered formulations and fresh suspensions, can be used within pearl millet downy mildew management strategies and for plant growth promotion.

No abstract

Inhibitory effect of 21 commercial and 6 experimental fungicides was assessed in model experiments against pearl millet downy mildew disease. Chemicals differed strongly by their anti-mildew activity, however neither the pathogen nor the host plant showed complete tolerance to any of compounds tested. Nevertheless, the plants outgrew depressant effect of compounds observed in germling stage and this activity did not significantly influence the yield. There was a significant correlation between yield performance and disease inhibitory effects assessed either in vitro or in vivo tests. The response of pathogen to investigated compounds varied during ontogeny, where zoosporangium formation was found to be the most sensitive ontogenetic event. When comparing responses of pathogen and host with fungicides by means of principal component analysis, the presence of two independent components has been demonstrated accounting for 86% of the total variation to which responses of host and pathogen contributed differently. The antisporulant activity of compounds evaluated on detached leaf segments and their positive effect on yield significantly correlated allowing to predict the expectable grain yield significantly (p>0.05). Beside acylanilides andoprim, drazoxolon and efosit offered efficacy on the level requested. Metalaxyl and tridemorph as well as andoprim and cymoxanil acted synergistically against S. graminicola.