Jongtae Lee

Comparison of bulb and leaf quality, and antioxidant compounds of intermediate-day onion from organic and conventional systems

This study aimed to compare bulb and leaf characteristics, leaf diseases, physiological disorder, bulb nutritional quality, and storage loss of onion from both organic and conventional farms in southeastern Korea during the 2011/2012 growing season. Soil and plant samples were collected from 8 certified organic fields managed organically for more than 5 years and 8 conventional fields adjacent to the organic fields. Onion bulb fresh weight and marketable bulb yield were significantly higher in the conventional field than in the organic field. At harvest, tops-down and leaf yellowing were 15.0 and 16.9%, respectively, lower in organic onions compared to conventional onions. Total phenolic compounds were significantly higher in conventional than organic onions, while there were no significant differences in pyruvic acid, soluble solid and flavonoids content between conventional onions and organic onions. In principal component analysis, highly weighted variables under PC1 included the number of scales, leaf yellowing, soluble solids, pyruvic acid, flavonoids, phenolics and storage loss in organic onions, but bulb weight and leaf weight in conventional onions. In organic onions, leaf yellowing correlated positively with flavonoids (p = 0.015), but negatively with soluble solids (p = 0.040); soluble solids were negatively correlated with flavonoids (p = 0.049). By contrast, conventional onions showed a positive correlation between bulb weight and leaf weight (p = 0.038), and between soluble solids and phenolics (p = 0.019), but a negative correlation between leaf weight and leaf yellowing (p = 0.016).

Effects of Solar Heating for Control of Pink Root and Other Soil-borne Diseases of Onions

These experiments were carried out to examine efficacy of soil solarization for control of pink root disease by means of mulching with transparent polyethylene sheets in the hot season. The effects of soil solarization on incidence of pink-root disease caused by Pyrenochaeta terrestris and on onion growth and on populations of soil fungi were investigated. Solarization was dramatically effective in reducing pink root incidence in onion seedling and harvested onion bulb. A 30-day and 40-day solarization treatment significantly improved seedling survival and increased yield of `Changnyeong-deago` onion while decreasing incidence of pink root. Populations of soil fungi from fields planted to onion were assayed on selective media. Solarization treatment was effective in reducing populations of P. terrestris, Pythium spp., and Rhizoctonia sp. in soil. Increase of yield of onion bulbs was associated with control of soil-borne pathogenic fungi. Soil solarization had beneficial effects on yield, bulb diameter, or incidence of pink root.

Influence of Soil Flooding on Control of Pink Root Disease in Onion Crop

Pink root disease of onion, a known worldwide constraint upon onion production, significantly reduces crop levels in the main Korea cultivation area. In order to examine the effect of flooding on incidence of pink root disease caused by Pyrenochaeta terrestris and on onion growth and on populations of soil fungi, field experiments were conducted during two seasons, 2003/04 and 2004/05 at Onion Research Institute. Populations of soil fungi from fields were assayed on selective media. Flooding treatment was effective in reducing populations of P. terrestris, Pythium spp., and Rhizoctonia sp. in soil; fungal populations in soils flooded for 90 days were reduced to 1/2 to 1/3 of those in non-flooded soils. In nursery bed, protective activities of soils flooded for over 60 days were 93.5 to 99.2% and their pink root incidences were less than 5%, which were 1/11 to 1/18 of that in control. Increased yield of onion bulbs was associated with control of soil borne pathogenic fungi by flooding treatments. As flooding period was prolonged, bulb grade showed the tendency to increase. Soil flooding for over 60 days resulted in effective disease control, facilitated accurate planning of plant population in the field, extension of the growing-season and consequently higher yields of better quality.