Abstract

Thai Jasmine rice, a high-quality variety of rice, can further be enhanced for the economic values through organic cultivation using arbuscular mycorrhizae fungi. Therefore, a study was conducted during 2017 to 2019 at Chiang Mai University and Tin Nee Yom Farm in Chiang Mai province, Thailand. This study investigated the optimum substrate formulas and the host plants for inoculum production of arbuscular mycorrhizal (AM) fungi, and to evaluate the efficiency of the inoculum of AM fungi for the growth and yield of Thai Jasmine rice in paddy fields of organic farming. The substrates used for in oculum production were soil, sand, leaf compost and vermiculite. AM fungi were cultured in pots of eight substrate formulas and used Brachiaria ruziziensis and Crotalaria juncea as the host plants. The results showed that the best formula which had the highest AM spore density was the formula containing compost mixed with vermiculite (1:2 v/v) and used B. ruziziensis as the host plant. For using C. juncea as the host plant, the optimum formula for spore production of AM fungi the formula containing soil mixed with vermiculite at the ratio of 2:1 (v/v). The dominant species of AM fungi associated with B. ruziziensis in the optimum formula were found to be four species of Aaulospora scrobiculata, A. tuberculata, Funnelifomis coronatum and Rhizophagus intreradices. Whereas C. juncea was used as the host plant in the optimum formula, there were also found to be three species of the AM fungi except R. intreradices. Using of AM fungi from the highest inoculum product as a biofertilizer in the organic farming in Chiang Dao district, Chiang Mai province in northern Thailand, increased growth of Thai Jasmine rice by about 12% in the paddy field without compost application and about 13% with compost application to the rice plants. N, P and K contents in the rice grains were about 1.3, 1.5 and 6.9 times higher than those of the uninoculated treatment. Therefore, the AM inoculum product of this study can be used as an efficient biofertilizer for increasing grain yields of Thai Jasmine rice in organic paddy fields. Both of optimum formulas can be used for commercial inoculum production of AM fungi for using as biofertilizer in organic farming.