Saturday, 15 July 2006

Diagnosis of Leaf-wilt Symptom of Watermelon(Cucurbita ctrullus L.) in Protected Cultivation Caused by Different Factors.

Byoung Choon Jang, National Institute of Agricultural Science and Technology, RDA, Seodun-Dong 249, Gwonseon-Gu, Suwon-Shi, 441-707, South Korea

This study was carried out to investigate the cause of leaf-wilt of watermelon in protected cultivation at local farm lands in Haman, Kyungnam province and Kochang, Jeonbuk province. The leaf-wilt phenomena of crops in protected cultivation is usually caused by disease, nematodes and salt accumulation. However, the leaf-wilt phenomena of watermelon in Haman and Kochang surveyed were caused by different factors. The protected watermelon in Haman was transplanted at 15 January (winter season) for harvesting early. Transplanting too early induced poor root growth because of low temperature in soil, and excess growth of leaf and stem because of high air temperature in vinyl house. Leaf-wilt phenomena were displayed by unbalance of water potential between roots and leaves. Low temperature of soil could delay the nitrification in soil. If soil temperature increased rapidly, nitrate concentration in soil is high and then increasing Electronic Conductivity (EC) of soil prevents the root growth. Also, ground water table in these sites was high, and water penetration of soil was poor. The roots of wilted plants were highly distributed near the soil surface and root growth rate and root hairs were limited. The watermelon in Kochang was transplanted at 25 march (spring season). Leaf-wilt phenomena of watermelon in this land were especially prevalent next to normal plants of the same variety and growing in soil with the same properties. The cause of leaf-wilt was bad crossing skill. This inducted the poor beginning growth and prevented root growth. These conditions caused insufficient water uptake by roots at beginning fruit fleshing stage. Therefore, the root growth was poor, and water absorption rate from root was lower than transpiration rate in leaves.

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