Screening of Endophytic Colonizing Bacteria for Cytokinin-Like Compounds: Crude Cell-Free Broth of Endophytic Colonizing Bacteria Is Unsuitable in Cucumber Cotyledon Bioassay

Endophytic microorganism live inter or intra cellularly in most of the plant tissues without causing any disease symptoms. Endophytes are known to produce plant growth promoting compounds. Cytokinin is a group of plant growth regulators (PGRs) and can be exploited in agriculture for both pre-harvest and postharvest management of leafy vegetables, fruits and cut flowers. The objective of this study is to isolate cultivable endophytic bacteria from local plants and to screen them using cucumber cotyledon bioassay for cytokinin-like compounds. In this study, one hundred fifteen cultivable endophytic colonizing bacteria were isolated from seventy two different plant species. Putative bacterial endophytes were grown separately in Luria Bertani (LB) medium. Cell-free broth was used without dilution in the cucumber cotyledon bioassay. In bioassay, the total chlorophyll content in cucumber cotyledon samples was estimated by spectrophotometry and compared with positive and negative controls. Bioassay results showed that the total chlorophyll content was less in all 115 samples of cotyledons (treated with crude cell-free broth) in comparison to both negative and positive control. Results clearly show that crude cell-free broth of cultivable endophytic bacteria is unsuitable in their screening for cytokinin-like compounds using cucumber cotyledon bioassay.