Influence of cyanobacterial auxin on sprouting of taro (Colocasia esculenta var. antiquorum) and corm yield

Abstract

Cyanobacteria are widely exploited in wet land rice cultivation as biofertilizer. Apart from nitrogen fixation, cyanobacteria are capable of producing a number of plant growth promoting substances. Among this, Indole acetic acid (IAA) is of prime importance. In the present study, five strains of nitrogen fixing filamentous cyanobacteria, viz. Anabaena, Aulosira, Cylindrospermum, Nostoc and Tolypothrix were tested for IAA production. IAA production in cyanobactreia could be induced by culturing them in tryptophan supplemented BG11 media. IAA was detected and quantified using Salkowski's method. Among the five strains Aulosira, Nostoc and Tolypothrix produced significant amount of IAA. Response surface methodology (RSM) was used to optimise three parameters, viz. tryptophan, pH and culture period to improve IAA production by Nostoc. The results revealed that the selected parameters had a significant effect on IAA production. Based on the RSM results under optimum conditions, viz. tryptophan 2.75 mg/ ml, pH 7 and incubation time 14 days, Nostoc produced 8.66 μg/ml IAA. The culture filtrate of Nostoc effectively promoted sprouting of taro corm and the induction effect was ascertained on germination of cowpea seeds. The biometric parameters of taro corm and cowpea seeds exposed to Nostoc culture filtrate showed the growth promoting attribute of the cyanobacteria compared to that of synthetic IAA. This study reports for the first time the possible application of cyanobacteria as a biofertilizer to two varieties, viz. Muktakeshi and Telia of a tuber crop taro (Colocasia esculenta) adapted to waterlogged conditions.