瓜類作物淹水逆境枯萎及預防之研究

Abstract

西瓜(Citrullus lanatus (Thumb.) Matsum. & Nakai.)及甜瓜類(Cucumis melo L.)為臺灣重要的蔬果作物，但在生長季時經常遭受到豪雨或淹水浸害的威脅，每年損失慘重。本研究探討造成瓜類淹水逆境的主要病因或機制，首先整理近兩年有關豪雨造成農作物淹水災情報告，發現豪雨造成瓜類死亡災情中以西瓜最為嚴重。而經由訪談農民得知瓜類淹水死亡情形非常迅速，而淹水是否淹過植株可能為影響瓜類淹水死亡的重要因子。研究以微生物喜好、供一般進行生化需氧量( BOD )測定時之標準溶液葡萄糖-麩胺酸水溶液，做為耗氧有機物，以達定量耗氧的目的，並比較添加耗氧有機物與單純使用清水造成瓜類萎凋嚴重度的差異，亦比較淹水高度對於瓜類萎凋嚴重度的影響。結果顯示僅有在水中含有耗氧有機物的情形下瓜類植株才會萎凋枯死，而淹過全株又比只淹過土面，萎凋情形才更顯著。 在品種比較方面發現西瓜品種中華光比華寶及天福更不耐淹水逆境，甜瓜類品種間則差距不大，其他瓜類部分絲瓜與扁蒲較南瓜與小胡瓜更耐淹水逆境。 本研究探討有機質肥料使用多寡是否為影響瓜類淹水逆境枯死原因之一，結果除部分植株整株枯死外整體並未有萎凋產生，推測有機質肥料使用多寡並不是造成瓜類淹水逆境死亡的主因。研究原本預期使用不同殺菌劑能有效維持水中溶氧量，並使瓜類淹水逆境萎凋情形降低。但結果顯示所選擇之殺菌劑保粒黴素丁( polyoxorim)及阿莫西林( amoxicillin )並不能有效達成預期目的，推測為水中菌相複雜即使殺死部分耗氧菌仍會有其他耗氧菌生存耗盡水中氧氣。 在水中進行打氣處理為本研究測試中最有效預防瓜類淹水逆境的措施，可維持水中溶氧量，對於預防香瓜及洋香瓜受淹水逆境萎凋死亡的效果良好，瓜類植株幾乎無萎凋情形產生。對於預防西瓜受淹水逆境萎凋死亡的效果較差，但仍比僅用耗氧有機物水溶液所造成的萎凋輕微。

高畦栽種瓜類亦為有效預防瓜類淹水逆境的方法，本研究模擬田間情形，比較不同畦面高度栽種瓜類在同高度淹水一天下瓜類萎凋程度是否不同。兩批次實驗結果皆顯示僅有淹水高度高於畦面，瓜類植株才會出現萎凋枯死情形。 綜合以上結果推測淹水逆境中造成瓜類萎凋死亡的原因為水中含有耗氧物質消耗氧氣使植株缺氧而萎凋枯死，且淹過植株者造成瓜類萎凋情形更嚴重。田間做高畦及打氣處理維持水中溶氧量為最有效能預防瓜類淹水逆境之方法，但打氣設備田間成本較高，是否能以其他能在水中產生氧氣維持水中溶氧量的物質來替代仍需進一步研究。

Watermelon ( Citrullus lanatus ( Thumb.) Matsum. & Nakai. ) and melons ( Cucumis melo L. ) are important fruit or vegetable crops in Taiwan, but are often threatened by heavy rain or flooding during the growing season and suffer great losses every year. In this study we investigate the causal factors and mechanisms of the flooding stress on cucurbit crops. Firstly we surveyed the agricultural damage reports of flooding caused by heavy rain in the past two years, and found that watermelons suffered the greatest losses in the episodes caused by heavy rain. Through interviews with related farmers, it was learned that cucurbit crops died very quickly after flooding, and the overhead flooding type may be an important factor causing the death of cucurbit crops. In this study a glucose-glutamate solution, also a standard solution for determining the biochemical oxygen demand (BOD), was used as oxygen-consuming organic compounds to treat the cucurbit seedlings. It can be decomposed by microorganisms around the rhizosphere to simulate the oxygen-deficient environment quantitatively. The experiment using glucose-glutamate solution to irrigate the cucurbit seedlings in pots showed that only at very high concentration the watermelon seedlings were affected as compared with the clean water control. However when the cucurbit seedlings were dipped and flooded in 2500 ppm of glucose-glutamate solution, most of the cucurbit seedling showed wilt symptoms quickly. A series of experiment showed the results that the cucurbit crops will suffer and die only in the presence of oxygen-consuming organic compounds in the water, and that flooding over the whole plant is also more dangerous than that only flooding over the soil surface.

The sensitivity of watermelon varieties toward the oxygen-consuming flooding was determined using the same experiment. Results showed that the watermelon variety Huaguang exhibits higher sensitivity toward the oxygen-consuming flooding than Huabao or Tianfu variety. The sensitivity of sweet melon varieties was also determined and showed little difference among the varieties. While the loofah and bottle gourds were more tolerant to flooding stress than the pumpkins and cucumbers species. In this study we also use organic fertilizers at different ratio to treat the cucurbit seedlings under flooding with clean water. Results showed that it is not the crucial factor causing the wilt of crops. The addition with anti-biotic chemicals in the flooding solution showed that they can not stop the wilting of cucurbit seedlings, indicating that oxygen deficient situation was not improved enough to save the crops. Both microbicides including the polyoxorim and amoxicillin, can not overcome the low dissolved oxygen situation, indicating that they may only kill parts of oxygen-consuming microorganism in the complicated microflora in the rhizosphere. Air-pumping treatment in water is tested out to be the most effective method to prevent cucurbit crops from flooding stress in this study. It can maintain dissolved oxygen content in the water and effectively prevent the melons from flooding stress. The efficacy of air-pumping for preventing watermelons from flooding wilt is not as good as that in melons, but it can mitigate the wilting severity of watermelon seedlings. Making high soil bed for the crops was also tested out as an effective method to prevent cucurbit crops from flooding wilt. In this study different soil bed with different height and different flooding levels were setup and used to grow the cucurbit seedlings upon the beds. Results of two replicates of experiment showed that only when the water is flooding over the whole seedlings it can cause the death of seedlings. Based on the above results, it is concluded that the main causal factor of the withering of the cucurbit crops in the flooding stress is the oxygen-consuming organic compounds in the water or rhizosphere. The oxygen-consuming materials make the plants in hypoxia circumstance and make them die quickly. So the severity of wilting by flooding over the whole plant is greater than that only flooding over the soil surface. Making higher soil beds for the crops in the field and air-pumping treatment are the two most effective methods to prevent cucurbit crops from flooding wilt. However, the cost of air-pumping in field is too high, and may be replaced by some other substances that can generate oxygen and maintain dissolved oxygen content in water in the future.