The effect of treatment of auxin producing bacterial culture supernatant in combination with organic and inorganic fertilizers

Bacteria that secret plant growth promoting substances are good candidate for field application to improve crop yield. Especially, bacteria that excrete auxin can enhance root growth and settlement of crops to help adapting new soil environment when transplanted. In this study, we applied culture supernatant of an auxin producing bacteria Ignatzschineria sp. CG20001. The bacterial culture supernatant (BCS) was applied in combination with chicken manure and liquid chemical fertilizer. The treatment of bacterial culture supernatant enhanced growth of red kohlrabi, Brassica oleraceae var. gongyloides, especially in combination with chicken manure. To understand mechanisms related higher growth, we compared photosynthetic efficiency by measuring chlorophyll fluorescence and light harvesting antenna pigments composition. The performance index PS II was higher in BCS treated plants, and recovered faster after leaf harvest. Photoprotective mechanism was also increased in BCS treated plants, however, and DTT infiltration, non-photochemical quenching (NPQ) reduced to similar level, implying higher xanthophyll cycle dependent NPQ induction mechanism in BCS treated plants. However, in liquid chemical fertilized plants, BCS treated and non-treated plants showed the opposite pattern in the change of NPQ. The chlorophyll a/b ratio was highest in no-fertilized non-treated control, and lowest in chicken manure and BCS combination, implying impact of nutrition availability between the two groups. Through these results, we conclude that the appropriate combination of organic fertilizer and plant growth promoting bacterial metabolite can improve plant growth more than chemical fertilizers. This study also provides physiological understanding for strategic fertilization regime of organic fertilizer and biofertilizer combination.