Search

Bacterial fruit blotch (BFB), caused by Acidovorax citrulli, is an economically devastating disease in melon. Molecular characterization of causal strains and identification of sources of resistance are necessary to control this important disease. Many strains of BFB were identified by partial sequencing and documented in GenBank. Recently, there was an outbreak of BFB strain NIHHS15-280 in melon fields (Goksung, Jeonnam, Korea) that severely hampered melon production in Korea. For this reason, we characterized NIHHS15-280 by partially sequencing the 16S rRNA gene using PCR-based markers. The partial sequence of the 16S rRNA gene of NIHHS15-280 was much more similar to A. citrullistrains associated with melon and watermelon hosts than other cucurbit hosts. A PCR-based assay identified the strain (NIHHS15-280) as belonging to A. citrulligroup I, which predominantly infects non-watermelon cucurbits (virulent to melon). Thirty-five melon genotypes were screened against NIHHS15-280 in a detached-leaf inoculation assay. The lack of visible disease symptoms 11 days after inoculation in lines PI353814 and PI140471 indicated these to be highly resistant lines, whereas moderate resistance was observed in lines PI420145 and SCNU1154 and cultivars ME6 and ME5. Also, the most resistant lines were corroborated by a fruit inoculation assay. The characterized A. citrullistrain NIHHS15-280 (group I) and identified resistant lines will serve as a valuable resource for further genetic studies and improvement of BFB resistance in melon.

Biochar effects on legume growth and biological nitrogen fixation have been studied extensively, mostly in acidic soils with laboratory produced biochar. In the present study, a pot experiment in a full factorial experimental design was performed to examine soybean yield and nodulation of three genotypes grown with or without biochar and NPK fertilizers in an alkaline soil. We observed synergistic effects of biochar and NPK fertilizer applications on biomass and seed yields for all three soybean genotypes. Total biomass production and seed yield increased on average by 67% and 54%, respectively, with biochar and by 201% and 182% with NPK fertilizer application compared to the control. When applications of biochar and NPK fertilizer were combined, the increases were 391% and 367%, respectively. However, the biomass production in the control was very low (692 kg ha−1) due to a high soil pH (8.80). The nodulation increased with biochar and NPK fertilizer applications, and was largest with the combined application. A correlation was found between leaf chlorophyll content (single photon avalanche diode value) and nodule number. We suggested that the synergistic increase in yield was due to a decrease in soil pH caused by biochar and NPK fertilizer applications thereby increasing P availability in this alkaline soil.