병해 개요 📝: 박과 반점세균병은 오이, 호박, 멜론 등 박과 작물의 잎에 각진 모양의 반점을 형성하는 세균성 잎병입니다. 주로 원인균은 Pseudomonas syringae pv. lachrymans (오이의 각흑병균)으로 알려져 있으며, 간혹 Xanthomonas cucurbitae 등에 의해서도 유사한 증상이 나타날 수 있습니다. 감염된 잎에는 처음에 잎맥에 둘러싸인 작은 수침상(물에 젖은) 투명 반점이 생기며, 이것이 커지면 잎 뒷면에 흰 유액(세균 군집)이 맺힙니다. 병반은 잎맥에 의해 각이 진 모양으로 퍼지다가, 내부 조직이 연한 갈색~짚색으로 변하며 말라붙습니다. 습도가 높을 때 잎 뒷면 병반 위에 하얀 우윳빛의 세균 삼출물이 분비되는데, 이것이 마르면 얇은 흰 막(crust)으로 남습니다. 결국 병반 부위의 잎조직은 바스라져 구멍이 뚫리므로 잎이 누더기처럼 찢어지고, 심하면 잎이 노랗게 변하여 조기 낙엽됩니다. 줄기나 잎자루에도 유사한 갈색 반점이 생길 수 있으며, 어린 과일(오이 등)에 감염되면 원형의 함몰된 흰색 반점이 생기고 갈라져서 흰 딱지 모양으로 변합니다. 이 병은 장마철 노지재배 오이, 호박 등에 심각한 피해를 주며, 병든 과실은 내부까지 연부조직이 썩어 상품가치를 상실합니다.
병 발생 환경 🌦️: 각종 박과 작물에서 반점세균병은 온도 20~27℃, 습도 80% 이상의 조건에서 발생이 가장 심합니다
. 특히 여름 장마철과 같이 온도가 25℃ 내외로 유지되면서 며칠간 비가 이어질 때 병이 급속히 번집니다. **산성 토양(pH<6.5)**에서는 작물이 스트레스를 받아 병에 더 잘 걸리고, 이런 토양을 가지는 지역에서 피해가 크다고 알려져 있습니다. 실제로 알칼리성 토양(pH≥7.2)에서는 포자 발아와 병 발생이 크게 억제됩니다. 비 오는 날씨 외에도, 밤낮의 온도차로 잎 표면에 이슬이 맺히거나 지면 안개로 잎이 젖어 있는 시간이 길 때에도 감염이 일어납니다. 반대로 햇볕이 강하고 건조한 날씨에는 세균의 활동이 위축되어 증상이 진행되지 않을 수 있습니다. 하지만 병원균은 토양과 식물체 내부에서 살아남아 있다가, 기후가 다시 습윤해지면 곧바로 활동을 재개하기 때문에, 장마가 지난 후 *늦여름(8~9월)*에 2차 발병도 종종 나타납니다. 시설재배(비가림)에서는 빗물은 막을 수 있으나 내부 습도가 높으면 충분히 발생할 수 있어 주의해야 합니다.
감염 경로와 확산 🔄: 박과 반점세균병균은 종자에 부착하여 전염되거나, 토양 속에서 병든 뿌리, 잔사 형태로 월동하면서 1차 전염원이 됩니다. 감염된 종자를 파종하면 떡잎에 바로 작은 각진 반점이 나타나고, 이 병든 모종이 밭에 옮겨지면 장마철에 급속히 주변으로 병을 퍼뜨립니다. 세균은 빗방울의 튐을 통해 잎에서 잎으로 전파되는데, 빗물이 병든 잎의 세균을 씻어 내어 인접한 건강한 잎에 뿌려주면 그곳의 기공이나 작은 상처로 침입합니다. 잎 뒷면의 세균성 삼출물은 특히 전염성이 높아서, 사람이나 농기구가 잎을 스칠 때 묻어 다른 식물로 옮겨질 수도 있습니다. 또한 배수불량으로 인한 지표수의 흐름이나 관개수 재이용 등으로 밭 사이에 세균이 이동하기도 합니다. 한번 잎에 들어간 세균은 잎 조직 내에서 증식하며 물관을 타고 일부 줄기, 과일까지 퍼질 수 있습니다. 그러나 주로 잎에 머무르며 잎 조직을 분해하고, 잎 표면으로 다량 배출되어 확산됩니다. 병원균은 십자화과 잡초 등에는 잘 감염되지 않고, 거의 박과 식물에만 기생하므로, 윤작과 휴작을 통해 토양 내 병균 밀도를 줄일 수 있습니다. 하지만 토양 속 휴면상태의 세균(후막포자 등은 없지만 생체로)이 수년간 생존 가능하므로, 감염 토양에서는 지속적으로 주의가 필요합니다.
병원체의 생활사 ♻️: 원인균 P. syringae pv. lachrymans는 그람음성 막대모양 세균으로, 편모를 가져 물속을 헤엄칠 수 있습니다. 이 세균은 식물체 밖 토양에서도 휴면 세포 상태로 비교적 오래 생존할 수 있지만, 주로 감염 숙주(박과 작물) 없이는 증식하지 못합니다. 봄철 토양에 잔존한 세균이 있거나 감염된 종자를 파종하면, 발아한 어린 싹의 뿌리나 떡잎에 1차 감염하여 작은 병반을 형성합니다. 이후 장마 등의 조건에서 잎의 병반으로부터 세균이 잎 표면으로 분출되고, 빗물과 함께 퍼져나가 2차 감염을 일으킵니다. 세균은 잎 조직에 정착하여 세포벽 분해효소(셀룰레이스, 펙틴 분해효소 등)를 분비하여 조직을 녹입니다. 이 과정에서 잎 뒷면에 하얀 유액(“lachrymans”는 라틴어로 눈물 흘리는이라는 뜻으로, 병반에 맺힌 세균 액체를 가리킴)을 형성하는데, 여기에는 수억 마리의 세균이 들어 있어 전염원이 됩니다. 습도가 낮아 건조해지면 이 액체가 마르면서 하얀 얇은 막(크러스트)이 생기며 일시적으로 세균의 활동이 멈추지만, 다시 습기가 차면 그 막이 녹으면서 세균이 활성을 되찾습니다. 가을로 접어들면 온도가 떨어져 잎에서의 병 증세는 멈추지만, 이때 일부 세균은 뿌리나 줄기 표면, 낙엽 등에서 살아남아 토양에 섞여 월동합니다. 포자 형태로 겨울을 나는 것이 아니라, 영양세포 상태로 살아남기 때문에 온도가 영하로 내려가는 야외 조건에서는 많은 수가 죽지만, 눈이나 흙에 보호된 일부 세균은 겨울을 견디고 다음 해에 다시 감염원을 제공할 수 있습니다.
방제 방법 🛡️: 예방적 조치로는 무엇보다도 건전 종자를 사용하는 것이 중요합니다. 각종 박과 작물의 종자를 채종할 때 병든 포장에서 받은 종자는 사용하지 말고, 종자는 파종 전에 염소계 소독제 (예: 차아염소산나트륨 1% 용액 30분 침지)나 온탕처리 (50℃에서 20분) 등을 통해 표면 세균을 제거합니다. 또한 가능한 저항성 품종을 재배합니다. 오이의 경우 각종 반점세균병에 강한 내병성 계통들이 개발되어 있으므로 활용합니다. 재배 환경 관리: 포장의 배수를 개선하여 빗물이 고이지 않게 하고, 가능한 포장 산도를 교정(석회 시용 등으로 pH 7 근처로)하여 토양을 미생물 활동에 불리하게 만듭니다. 재배 중 초기에는 구리 함유 살균제나 스트렙토마이신 등의 예방 살포를 통해 세균 밀도를 억제할 수 있습니다. 예를 들어, 잎에 작은 물무늬가 보이기 시작하면 곧바로 농용 황산구리제나 옥사테트라사이클린 등을 살포하여 주변 건강 잎으로의 확산을 차단합니다. 이미 잎 곳곳에 병반이 많아진 상태에서는 약제 효과가 떨어지므로 초기 대응이 중요합니다. 윤작: 반점세균병이 발생한 포장에서는 최소 3년 이상 박과 작물을 재배하지 않고, 벼나 콩, 옥수수 등 비기주 작물로 돌려짓기를 합니다. 발병 잔재물이 완전히 분해되도록 깊이 갈아엎고, 유기물을 너무 많이 주입하지 않습니다 (유기물 과다 시 토양 병원균 활력이 유지될 수 있음). 위생 관리: 병든 식물은 가능한 빨리 제거하여 밭 밖으로 치우거나 땅에 묻습니다. 수확 후에는 남은 줄기와 잎을 모아서 소각하거나 깊게 매립하여, 토양 표면에 세균이 남아 월동하지 않도록 합니다. 농작업 도중에도 밭을 이동할 때 흙이 묻은 농기구, 작업자 신발 등을 세척하여 세균이 다른 밭으로 옮겨가는 것을 막습니다. 이런 조치를 종합적으로 실시하면, 박과 반점세균병으로 인한 피해를 크게 경감시킬 수 있습니다. 특히 장마철 직후 신속한 약제 살포와 병든 잎 제거, 그리고 발생 전 예방 소독이 성공적인 방제의 열쇠입니다.
참고문헌 및 링크 📖 :
- Virginia Tech Extension Angular Leaf Spot of Cucumber : https://www.pubs.ext.vt.edu/450/450-700/450-700.html#:~:text=The%20bacterium%20attacks%20the%20leaves%2C,occur%20on%20petioles%20and%20stems
https://extension.usu.edu/planthealth/ipm/notes_ag/veg-angular-leaf-spot
태그 🏷️: #오이 #호박 #멜론 #각흑병 #세균성반점병 #박과작물
Disease Overview 📋: Cucurbit angular leaf spot is a bacterial leaf disease of cucurbit crops (cucumber, melon, squash, etc.) characterized by small, angular leaf spots. It is primarily caused by the bacterium Pseudomonas syringae pv. lachrymans (responsible for angular leaf spot of cucumber). Initially, tiny water-soaked spots appear on the underside of leaves, delimited by leaf veins, giving them an angular shape. Under humid conditions, these lesions exude a milky white bacterial ooze on the underside of the leaf. As lesions enlarge, they turn gray or tan and may develop a yellow halo on the upper surface. The affected tissue then dries out and often cracks or falls away, leaving irregular holes and a tattered appearance in the leaf. If you hold an infected cucumber leaf up to the light, it may look like “shot-holes” scattered across it. In severe cases, entire leaves turn yellow-brown, wither, and drop prematurely, which can reduce plant vigor. The disease can also infect petioles and stems, causing elongated, water-soaked streaks that later become dark and sunken. On fruits (like cucumber or zucchini), infection causes circular, sunken spots; initially these spots are water-soaked, then they crack open and turn white and crusty. Such fruit lesions may allow secondary soft rot organisms to enter, leading to slimy decay of the fruit’s interior. Angular leaf spot is particularly destructive in warm, wet seasons, often leading to significant yield loss and fruit quality reduction in cucurbit crops if not managed.
Occurrence Environment 🌦️: Angular leaf spot thrives in warm (approximately 24–28 °C) and humid or wet conditions. The disease is notorious for flaring up during rainy periods and warm nights, such as during summer thunderstorms or extended rainy spells. Prolonged leaf wetness is a key driver: if leaves remain wet for 24 hours or more (due to rain, dew, or overhead irrigation), infection likelihood is high. Consequently, regions or seasons with frequent rain, overhead watering, or heavy dew foster outbreaks. The bacterium also favors slightly acidic soil conditions; research has shown that soils below pH 6.5 can exacerbate clubroot disease in crucifers, and similarly, acidic soils tend to worsen many bacterial diseases by stressing the plants and possibly enhancing bacterial survival. In practice, fields with low pH or nutrient imbalances often see more severe angular leaf spot. The disease commonly appears in late spring or early summer when day temperatures are warm and nights remain above ~15 °C (which allows bacteria to multiply overnight). During monsoon or rainy season, angular leaf spot can spread explosively through a cucumber field. If hot, dry weather follows, the disease may slow or even seem to stop as lesions dry out and new infections are suppressed. However, the bacteria can survive latent in plant tissue or debris and then flare up again when cool, wet weather returns – for instance, an outbreak often occurs in early summer, subsides in mid-summer heat, then resurges with cooler, wet late summer conditions. In protected culture (greenhouses or high tunnels), the lack of rain helps, but high humidity or condensation can still allow the disease to cycle. Optimum conditions for infection are roughly 75–82 °F (24–28 °C) with RH above 80%. Under these conditions, symptoms can develop in a few days of infection.
Transmission and Spread 🔄: The angular leaf spot pathogen P. syringae pv. lachrymans is primarily seed-borne. Infected cucumber seeds can carry the bacterium externally or internally; when such seeds are planted, the emerging seedlings may show tiny water-soaked lesions on cotyledons or leaves, serving as the initial infection foci. From these, bacteria spread to other plants mostly via splashing water. Rain or irrigation splash can pick up bacteria from lesions (often visible as a whitish ooze) and deposit them onto neighboring leaves. Because lesions are often angular and limited by veins, as they enlarge they eventually break, releasing bacteria in guttation droplets or rain-induced drips that fall onto lower leaves or soil. Wind-driven rain can carry bacteria further distances within a field. Human activities also contribute: workers or tools that contact the sticky bacterial exudate can mechanically transfer bacteria to healthy plants. If one touches an oozy lesion on an infected leaf and then handles a healthy plant, the bacteria can enter via stomata or minute wounds. Similarly, insects (such as cucumber beetles) can create wounds and potentially move bacteria short distances on their bodies, although they are not efficient vectors. The pathogen can also move with surface water or runoff: in heavy rain, contaminated soil water may flow from one part of a field to another or even between fields, disseminating the bacteria. Within a plant, bacteria remain largely in the intercellular spaces of leaves and do not typically invade the xylem extensively (unlike systemic vascular pathogens). Thus, angular leaf spot is mostly a foliar disease, and the pathogen does not overwinter inside seeds of the next generation except superficially or in small numbers (which is enough to start the cycle). After harvest, the bacteria survive in crop debris or in soil as free-living cells. They have no spore stage, but they can persist as dormant cells or in biofilms on plant residues. Cold winter conditions will kill many of the exposed bacterial cells, but some survive, especially if protected in plant tissue, in soil clods, or in association with decaying plant matter. Come spring, these surviving bacteria can infect volunteer cucurbits or the next cucurbit crop, completing the cycle.
Pathogen Life Cycle ♻️: P. syringae pv. lachrymans is a Gram-negative bacterium with polar flagella that allow it to swim in water films. Its life cycle is polycyclic during the growing season, meaning it can go through multiple infection cycles. Starting from a primary inoculum (infected seed or debris in soil), the bacterium infects a host plant. On the plant surface, it often enters through stomata on wet leaves. Once inside the leaf tissue, it multiplies in the substomatal space and produces cell-wall-degrading enzymes (pectinases, cellulases) that macerate leaf tissue, leading to the water-soaked lesions which then turn necrotic. The name “lachrymans” (Latin for “tear-producing”) refers to the droplets of bacterial ooze that form on lesions, as if the leaf is crying. This ooze is packed with bacterial cells and is a potent source of secondary spread. When humidity drops, the ooze dries into a thin, whitish crust. The bacteria within can survive in that dried state for a time. When the next rain or heavy dew arrives, the dried exudate rehydrates and the bacteria become active again, ready to infect or be dispersed. This adaptation allows the pathogen to endure short dry spells. The overall life cycle can be summarized as: seed or debris → seedling infection → lesion formation and ooze → dispersal by water → new lesions on other plants → repeat, until the growing season ends. At season’s end, the bacteria’s survival stage is mostly as cells in debris or soil. They do not form specialized resting spores, so over winter many will die especially in freezing climates. However, enough cells can survive in protected niches (inside partially rotted leaf pieces, in the soil under crop residue, etc.) to initiate infections the next year. If a field is rotated away from cucurbits for several years, the bacterial population gradually declines because it doesn’t have a suitable host to multiply on, but complete eradication can be uncertain as some can persist for many years albeit at low levels.
Control Methods 🛡️: Managing angular leaf spot involves preventing introduction, and if present, reducing spread and inoculum. Use clean seed: This is paramount. Only plant seeds tested and certified free of P. syringae pv. lachrymans. Seed treatments can reduce seedborne inoculum; for example, soaking seeds in 1% sodium hypochlorite for 1–2 minutes or in 50 °C water for 20 minutes can significantly lower bacterial load (though hot water may affect germination slightly). Some commercial seeds are vacuum-infiltration treated with bleach or acid to kill internal bacteria. Resistant varieties: Some cucurbit varieties, especially certain cucumber cultivars, have partial resistance to angular leaf spot. Using resistant or tolerant varieties (often labeled as having resistance to angular leaf spot or “Anthracnose/Angular leaf spot”) can greatly reduce disease severity and need for chemical control. Cultural practices: Employ crop rotation; avoid planting cucurbits in the same field two years in a row if angular leaf spot has occurred. A rotation of 2–3 years with non-host crops (like cereals or legumes) can help the bacteria in soil to diminish. Improve field drainage to prevent standing water and reduce splash. Avoid overhead irrigation; if irrigation is necessary, use drip lines or water at the base of plants to keep leaves dry. If overhead watering is unavoidable, do it early in the day so leaves dry quickly in the sun. Increase plant spacing or use trellising (for cucumbers) to improve airflow and leaf drying. Manage weeds that might harbor moisture around the crop. Environmental control: In greenhouses, vent to reduce humidity. In fields, some farmers use row covers early in the season to shield young plants from rain (though covers must be removed at flowering). Chemical control: The mainstay is copper-based bactericides. Copper sprays (copper hydroxide, copper oxychloride, etc.) can protect leaf surfaces from infection and slightly suppress existing lesions’ bacteria. However, copper can be phytotoxic to cucurbits in high doses and many strains of P. syringae have moderate copper tolerance. Tank-mixing copper with mancozeb (which has some bacteriostatic effect and broad fungal control) is a common practice, and indeed, fixed copper + mancozeb is often recommended on a 7-10 day schedule during wet periods. If available and legally permissible, antibiotics such as streptomycin can be very effective in reducing bacterial spot on seedlings and transplants or during bloom (for example, streptomycin sprays in tobacco transplant production virtually eliminated similar bacterial diseases). But their use in field crops is often restricted due to resistance and regulatory issues. Some countries allow streptomycin on outdoor crops like tomato/pepper but not on cucumber; always follow local regulations. Biological control: Products containing beneficial bacteria like Bacillus subtilis or Bacillus amyloliquefaciens (e.g., Serenade, Double Nickel) have shown some efficacy in suppressing leaf spot pathogens and could be integrated into the spray program. Hydrogen peroxide or peroxyacetic acid disinfectants can also be used to burn off surface bacteria on plants if applied carefully, but these can cause phytotoxicity if not properly diluted. Sanitation: Remove and destroy crop debris after harvest; do not leave infected vines on the soil surface. Deep-plow residues to speed decomposition and bury the bacteria where they are less likely to splash onto new plants. Clean any stakes, trellis wires, or tools with disinfectant (e.g., 10% bleach or quaternary ammonia solution) because the bacteria can survive on these surfaces in dried ooze. Limit working in fields when foliage is wet; workers should avoid handling healthy plants right after touching diseased ones unless they disinfect hands and tools. Also, avoid moving soil from an infected field to a clean field (e.g., on tractor wheels); wash equipment between fields. Fertility: Maintain balanced nutrition; avoid excessive nitrogen which can lead to dense canopies that dry slowly and are more prone to bacterial infection. Also, ensure adequate levels of calcium and potassium, as healthier, firmer plant tissues are a bit more resistant to maceration by bacterial enzymes. Soil pH management: If soil is very acidic, applying lime to raise the pH above ~7.0 can create conditions less favorable for the pathogen’s persistence and also improve plant health. In summary, an integrated approach combining clean seed, cultural practices to reduce leaf wetness, rotation, timely copper sprays, and rigorous sanitation can effectively control angular leaf spot of cucurbits in most cases.
References & Links 📖 :
- Virginia Tech Extension Angular Leaf Spot of Cucumber : https://www.pubs.ext.vt.edu/450/450-700/450-700.html#:~:text=The%20bacterium%20attacks%20the%20leaves%2C,occur%20on%20petioles%20and%20stems pubs.ext.vt.edu
- UC IPM Angular Leaf Spot – Cucurbits : https://ipm.ucanr.edu/agriculture/cucurbits/angular-leaf-spot/#gsc.tab=0
Angular Leaf Spot of Cucumber
Angular leaf spot of cucurbits is caused by the bacterium Pseudomonas syringae pv. lachrymans. The bacterium can attack a wide range of cucurbits including watermelon, melon, squash, cucumber, zucchini, and pumpkin.
www.pubs.ext.vt.edu
https://extension.usu.edu/planthealth/ipm/notes_ag/veg-angular-leaf-spot
Tags 🏷️: #Cucumber #Squash #Melon #AngularLeafSpot #BacterialDisease #Cucurbits
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