Investigation of Indigenous Plant Root Associated Bacteria and Yeast Isolates for Plant Growth Promoting Ability

Several bacteria (BSP41, BSP42, BSP51, BPL41 and BPL51) and yeast (YSP11, YSP31, YSP41 and YPL21) were isolated from the rhizosphere (SP) and rhizoplane (PL) of marigold (Tagetes erecta L.) obtained from local nurseries. Each isolate was identified and classified to genus and species levels. BSP41 was Stenotrophomonas maltophilia, and the other isolates belonged to Aeromonas veronii. The yeasts YSP11 and YPL21 were identified as Cryptococcus humicolus, YSP31 as Candida famata and YSP41 as Cryptococcus laurentii. Marigold seedlings, at the third leaf stage, were treated by dipping their root system in cell suspensions of the isolated bacteria or yeast or bread yeast (Saccharomyces cerevisiae) and observed for growth and nutrient composition. The effect of nutrient levels at the ambient solution was also investigated. Results indicated that there was a high degree of inconsistency in plant growth response and tissue nutrient contents of treated plants. However, the yeast isolate YSP31 (Candida famata) showed consistency in enhancement of plant growth over the untreated control plants. All tested isolates were found to be able to produce IAA in the culture medium.