Trichoderma conidia production using wheat straw and growth promoting effect of its bio-organic fertilizer on cucumber

ObjectivesTrichoderma species are important plant growth promotion fungi in rhizosphere of plants, whereas it is insufficient for using them to produce bio-fertilizers. This study tried to use wheat straw powder as substrate for conidia production of T. harzianum T-E5 in solid state fermentation (SSF), aimed to optimize process conditions of the fermentation as well as to check the plant growth promoting effect of the ferment produce as a bio-organic fertilizer on cucumber in greenhouse.

MethodsIn laboratory conditions, wheat straw was used as solid fermentation substrate, and numbers of conidia spores were compared under a series of single factors, including different fermenting containers, temperatures, acid concentration, acid species, amounts of inoculum, moisture contents, and forms of exogenous carbon and nitrogen resources. An orthogonal experiment was then designed to optimize fermentation conditions of temperature, acid concentration, water content, inoculation amount, and external nitrogen and carbon sources. In addition, two seasons of greenhouse pot experiments were conducted with five fertilization treatments, including chemical fertilizer, organic fertilizer, ferment product and its combinations with the chemical fertilizer or the organic fertilizer. The above ground biomass, plant heights and leaf areas of cucumber were measured, The number of total fungi and Trichoderma species in the rhizosphere soil of cucumber were counted using the diluted spread plate.

ResultsThe solid state fermentation of T-E5 in tray with wheat straw powder was suitable for production of conidial spores. The wheat straw powder was prepared by inoculation with 3% (v/w) of 1 × 10⁷ spores/mL T-E5 spore suspension prior to acidification with nitric acid solution (0.1 mol/L) and then water was added to reach an initial moisture content of 75%. Under those conditions, fermentation with addition of exogenous urea and corn powder at 28℃ for 8 days yielded the maximum number of T-E5 conidial spores of 8.87 × 10⁹ spores/g. By the orthogonal optimization, when 18.3 mL 0.05 mol/L of nitric acid, 9% (v/w) inoculation amount, and 1% (w/w) of urea were added to every 10 g of wheat straw with 70% (wet basis) of water content, at 30℃ shallow dish and fermented for 8 days, the amount of Trichoderma conidia reached to 1.1 × 10¹⁰ spores/g. The results of the first season pot experiment showed that the treatment of ferment product with chemical fertilizers (CT) increased cucumber above ground biomass, plant height and leave area by 14.97%, 16.75% and 14.64%, respectively, compared with the treatment of chemical fertilizers (CCK). Compared with the treatment of the organic fertilizer (OCK), the treatment of ferment product with the organic fertilizer (OT) increased the above ground biomass, plant height and leave area by 10.62%, 26.06% and 9.53%, respectively. The results of the second season pot experiment showed similar promoting effects, i.e. compared with CCK, CT increased the above items by 12.83%, 11.49% and 26.93% respectively, and compared with OCK, OT increased above items by 5.96%, 34.29% and 18.01%, respectively. Compared with CCK, OCK and CK, the CT and OT treatments increased the numbers of total fungi and Trichoderma species in the rhizosphere soil of cucumber by more than one order of magnitude.

ConclusionsThe bio-agent and bio-organic fertilizer with high content of T. harzianum conidial spores can be produced using wheat straw as main substrates in SSF process. This suggests it is feasible that using agricultural wastes with SSF process to produce high value added Trichoderma bio-agent and its bio-organic fertilizers. But the amount of spores is largely dependent on the fermentation conditions, and the technological parameters of SSF for producing Trichoderma spores in the pilot and factory levels need to be further studied.