Hydroponics originally came about to eliminate many of the variables that contribute to disease in the field, but other negative variables may have been created in the process. At present, Pythium causing root rot is a real problem in recirculating hydroponic systems as they provide ideal condition for rapid growth and spread of infectious propagules. Besides, it is an opportunistic disease which means that it is looking for weak or injured plants. Biological-based approach to hydroponic cultivation may probably provide a helping hand in managing the root disease and maintaining a more sustainable and hydroponic crop ecosystem. Therefore, the research was conducted to improve the hydroponic crop production against root rot disease of lettuce (Lactuca sativa L.) through biological and cultural measures. The research consisted of four parts. First, the evaluation were made on the efficacy of the four formulations of commercial fungal bioproducts presently available for conventional crops and the four reported-beneficial rhizosphere bacteria having high antagonistic potential in suppressing important pathogens for controlling Pythium root rot of lettuce grown in hydroponics. It was found that the four formulations of fungal bioproducts for soil-grown crops were in effective against Pythium root rot disease of lettuce in NFT which are not in line with recent observation with other DFT crops suggesting that the products might be host specific in controlling. Besides, it is possible that NFT might not provide the ideal condition to maintain the population of biocontrol agent in the system sufficient enough to control the disease compared to that in DFT. The unsuited formulation to hydroponics as well as quality of the product would possibly be attributed to the experiment. For the four reported-beneficial rhizosphere bacteria, directly applying them into the hydroponic nutrient solution gave unsatisfactory result in controlling Pythium root rot of lettuce since their survival in the system were hardly detected. Applying the beneficial rhizosphere bacteria as seed treatment, Pseudomonas fluorescens (SP007s) gave the best result in terms of percent seed germination and growth of green oak seedling under laboratory condition. Seed treatment + directly adding into nutrient solution gave the best result in decreasing the disease incidence and increasing the crop growth. Due to the efficacy limit of the forementioned-bioproducts for conventional crops to be used in hydroponics, therefore, the second and third parts of the research were conducted to find out and determine the new indigenous microorganisms including PGPR from hydroponic systems as biocontrol agents which would be an alternative biological-based approach for sustainable disease management. It was found that 60 indigenous fungal isolates were obtained from hydroponics and some of them showed the in vitro antagonistic ability against the mycelial growth of Pythium sp. at 3 days less than 40 percent growth inhibition which was rather low. This might due to the slow growth rate of these indigenous fungi. Hence, competition was not responsible for this regard. However, the in vitro abilities of fungal antagonists A003, A018 and A019 became quite satisfactory at 20 days since Pythium colony was almost covered by these 3 indigenous fungi and exploitation was observed. Furthermore, the three isolates of fungal antagonists also gave good results in decreasing the Pythium root rot disease severity and increasing shoot fresh weight of lettuce in hydroponics compared to that in inoculated control without tested antagonists. Regarding the new indigenous rhizobacteria, it was found that 468 strains of miscellaneous endophytic and epiphytic bacteria were obtained from recirculating hydroponic systems and some strains were shown to be effective in inhibiting the in vitro growth of Pythium about 65.8-87.9 percent. KUKL205 showed the best potential to produce secondary metabolite equivalent to commercial strain Pseudomonas fluorescens SP007s for suppressing the target pathogen in bi-culture test. In hydroponic trial, all the bacterial treated plants as seed treatment (KUKL205 included) showed no symptom of root rot compared to the non-treated plants. In line with disease incidence, it was found that the accumulation of .-1, 3 glucanase, a defense-related enzyme was greater in bacterial antagonists-treated plants compared to that in inoculated control. To our knowledge, this is the first report about induced systemic resistance under hydroponics with plant growth promoting rhizobacteria. The fourth part was conducted to determine the efficacy of the obtained-beneficial indigenous fungal antagonists (3 isolates) together with the indigenous PGPR (KUKL205) for controlling Pythium root rot of lettuce grown in the DFT. The emphasis was placed on synergistic effect between antagonistic bacterium and antagonistic fungus. Indigenous KUKL205 was used as seed treatment (106 CFU/ml), while the 3 isolates of indigenous fungal antagonists were applied as root-dip solution and added into DFT nutrient solution at the concentration of 108 CFU/ml (10 ml per plant). The results showed that the application of the indigenous KUKL205 alone (T1) and with the 3 isolates of indigenous fungal antagonists (T2, T3 and T4) did provide significant control (on 21 dpi) of root rot disease compared to that in the inoculated control. No synergistic effect between the indigenous KUKL205 and the 3 indigenous isolates of fungal antagonists (A003, A018 and A019) was noted on disease control efficacy. However, synergistic effect on plant growth was significantly noted in T2 (KUKL205 and antagonistic fungus A003). The beneficial indigenous rhizosphere microorganisms obtained from this research are as follow: KUKL205 indentified as Bacillus sp. (base on biochemical and 16S rRNAPCR characterization), antagonistic fungi A003, A018 and A019 indentified as 2 isolates of Trichoderma harzianum and 1 isolate of Gliocladium sp.