Jong-Pil Chun

Optimization of substrate formulation and mineral nutrition during the production of vegetable seedling grafts

The use of seedling grafts has been increasingly popular in the production of fruit vegetables in Korea. Superior scion cultivars grafted on seedling rootstocks tolerant to soil-borne diseases often results in higher crop yield and quality. For the production of healthy grafted transplants, seedlings have to be grown under the most favorable cultural conditions. Substrate composition and property as well as mineral nutrition play an important role. Various substrates containing peatmoss, perlite, vermiculite, and coir-dust have been tested for their influence on seedling growth. In the chemical properties of substrates investigated just before grafting and after formation of grafted union, the ECs in 4 substrates rose as the pre-plant fertilizer level was elevated. The ECs in peatmoss containing substrates were lower than those in coir dust containing substrates when all substrates contained equal amount of pre-plant fertilizers. The ECs in substrates containing vermiculite were higher than those in perlite. In all substrates, the elevation of pre-plant fertilizer levels resulted in the increase in NO3−-N and K+ concentrations and decrease in Na+ concentration. The recommended EC levels of substrates for the raising of plug seedlings of bedding plants are applicable to fruit vegetables when the seedlings are grown in peatmoss + perlite (PP) substrate. But those in peatmoss + vermiculite (PV), coir-dust + perlite (CP) and coir-dust + vermiculite (CV) substrates should be altered based on the kinds and rates of substrate components. In case of crops, the water melon rootstock ‘Cham Bak’ (Lagenaria siceraria Standl), showed the stronger salt tolerance than cucumber rootstock ‘Heukjong Hobak’ (Cucurbita ficifolia) indicating that pre-or post-plant fertilizer levels should be varied based on the kinds of crops grown. The peppers grew well in PP and PV substrates rather than CP or CV substrates in before or after grafting. This also implies that the components of substrates should be changed based on the specific crops.

Effects of Pre-Drying, Delayed Cooling, and Carbon Dioxide on Skin Blackening Disorder in Asian pear ( Pyrus pyrifolia Nakai) ‘Chuhwangbae’

We examined the effects of pre-drying rates, delayed cooling, and carbon dioxide (CO2) treatment on skin blackening, a major physiological disorder during cold storage in Asian pear (Pyrus pyrifolia Nakai) ‘Chuhwangbae’. Total skin blackening incidence was calculated as the percent disorder index (PDI). PDI significantly decreased with increasing pre-drying rate: the highest PDI was 37.3 for the 1% pre-drying treatment and the lowest PDI was 5.1 for the 4% treatment. Meanwhile, the 5% pre-drying treatment did not show a statistically significant difference from the 4% treatment. A 48-h cooling delay at 20°C was the most effective treatment for preventing skin blackening. PDI after cold storage at 1°C was 6.2, 9.2, and 19.1 for 48-h delay, 24-h delay, and no delay, respectively. In the CO2 treatment, 2% CO2-treated fruit showed rapid disorder symptoms from eight days after cold storage at 1°C, and the PDI increased to 19.6 at 12 days and to 63.2 at 20, which was three times higher than the untreated fruits. A decrease in total phenolic content appeared more pronounced in the tissues treated with 2% CO2, while polyphenol oxidase (PPO) activity in untreated fruits increased with increasing skin blackening incidence. However, there was no increase in PPO activity with the 2% CO2 treatment, skin blackening appeared to be a CO2 injury rather than enzymatic oxidation. Additional key words: CO2 injury, peroxidase, polyphenol oxidase, pre-conditioning, storage