Brown planthopper (BPH), Nilaparvata lugens Stål, is a serious insect pest of rice. The invasion of BPH causes heavy losses in rice production, both quality and quantity. The objective of this research was to search for Metarhizium spp., a genus of entomopathogenic fungi in the Clavicipitaceae family, from forest soil in three districts of Phetchabun Province, Thailand: Khao Kho, Lom Kao and Nam Nao to control BPH. Metarhizium spp. fungi were isolated by soil dilution plate technique and determined their efficacy using conidia suspension at the concentration of 1X108 conidia/mL on BPH at the 2-3th instar nymph fed on seedlings of susceptible rice cultivars, Taichung Native 1 (TN1). The most effective Metarhizium sp. isolate was identified using the ITS region of 18S rDNA sequencing, Basic Local Alignment Search Tool (BLAST) and evolutionary history. The result showed that 126 isolates of Metarhizium spp. were found and coded as PB-01 to PB-126. All isolates infected BPH nymph with 26.7 to 100% mortality within 6 days after contacting conidia suspension. The isolate of PB-75 showed the highest efficacy (100% BPH mortality) with the lethal times of 50% mortality (LT50) within 2.9 days. The species identification showed that the DNA sequence of Metarhizium sp. isolate, PB-75, was 98.6% similar to M. anisopliae Genbank ID JQ889704.1. Evolutionary history based on phylogenetic analysis using neighbor-joining and maximum parsimony methods confirmed that PB-75 formed the same phylogenetic clade with M. anisopliae Genbank ID JQ889704.1 and M. anisopliae var. anisopliae.

Soybean rhizobia are Gram negative bacteria that fix nitrogen in root nodules of soybeans. Selection of soybean rhizobia from present and previous soybean cultivation areas is one way to obtain efficient strains for inoculant production. At present, information on the diversity of soybean rhizobia in Thailand is scarce. The experiments aimed to isolate and characterize soybean rhizobium strains in soils from 16 subdistricts in Phitsanulok province, Thailand. Host trapping method was used to isolate bacteria from root nodules of 5 soybean cultivars grown in soils from the 16 subdistricts. Identical RAPD-PCR fingerprints revealed the 202 slow-growing isolates consisted of 121 strains. Authentication tests using 5 soybean cultivars showed all the 121 slow-growing strains had nodulated soybean roots. Four types of colony morphology on yeast extract mannitol containing congo red agar plates were obtained for all the isolated strains. Bromothymol blue (BTB) reactions on BTB agar plates revealed two types of slow-growing soybean rhizobia. Type 1 secreted alkali products after 5-day incubation, and acidic products upon prolonged incubation for another 5 days. Type 2 secreted only alkali products after 5-and 10-day incubation. Results from nucleotide sequences of 16S rDNA revealed 7, 6, and 2 strains of Bradyrhizobium elkanii, B. japonicum, and B. yuanmingense, respectively. The B. elkanii and B. japonicum strains were found to be natural variants with different RAPD-PCR fingerprints. This study is the first report on the findings of B. yuanmingense as well as natural variants of slow-growing soybean rhizobia in Thailand.