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The effect of two plant growth-promoting rhizobacteria (PGPRs) on the germination and growth of pepper seedlings was investigated in a culture chamber. The two strains showed metabolic capacities related to their potential PGPR action. Two different patterns of inoculation were carried out. In the first, strains were inoculated when seeds were sown, and in the second when seedlings showed fully developed cotyledons. In both cases the following parameters were measured: aerial and root surface, aerial and root length and aerial and root weight. In the first pattern of inoculation no aerial parameters were modified, probably because the bacteria did not colonize the root. In the second pattern of inoculation, all parameters were significantly modified by Chryseobacterium balustinum, except root surface, which indicated that this bacterium was able to colonize the root. Serratia fonticola did not modify any parameter. In both inoculation patterns root length was reduced by both bacteria probably due to a hormonal effect. C. balustinum enhanced aerial surface, aerial length and also the dry aerial and root weight. This resulted in stronger and more robust plants with a higher adaptative capacity and a greater resistance against pathogens. [ABSTRACT FROM AUTHOR]

The effects of three Plant Growth-Promoting Rhizobacteria (PGPRs) on tomato and pepper seedlings grown in two types of peat (brown and black, each sterilized or unsterilized) were studied. After sterilization, the seeds were unable to germinate in the brown peat. All three bacteria had the capacity to modify the growth, but tomato seedlings responded better than pepper seedlings, possibly indicating better root colonization in the former. All bacteria increased total stem length of tomato seedlings in nonsterilized brown peat, nonsterilized black peat and sterilized black peat. Plant shoot surface was also increased in nonstenlized brown peat and in sterilized black peat. The results show that plants, especially tomato, grown in nonsterilized black peat are smaller than in nonsterilized brown peat. The results obtained in sterilized peat show that there are no differences between sterilized and nonsterilized peat. Therefore, factors other than competition with other microorganisms must be more important in the performance of the bacterial inoculants. Root growth was only modified in nonsterilized black peat with two bacteria, in pepper it increased, and in tomato, decreased. These different effects could be due to a hormonal effect of the auxins, which influence root growth. [ABSTRACT FROM AUTHOR]