Himmelstein J, Maul J E, Balci Y, Everts K L
Department of Plant Science and Landscape Architecture, University of Maryland, College Park 20742.
United States Department of Agriculture-Agricultural Research Service, Beltsville, MD 20705.
Plant Dis. 2016 Sep;100(9):1910-1920. doi: 10.1094/PDIS-08-15-0956-RE. Epub 2016 Jul 7.
Fall-planted Vicia villosa or Trifolium incarnatum cover crops, incorporated in spring as a green manure, can suppress Fusarium wilt (Fusarium oxysporum f. sp. niveum) of watermelon. During cover crop growth, termination, and incorporation into the soil, many factors such as arbuscular mycorrhizae colonization, leachate, and soil respiration differ. How these cover-crop-associated factors affect Fusarium wilt suppression is not fully understood. Experiments were conducted to evaluate how leachate, soil respiration, and other green-manure-associated changes affected Fusarium wilt suppression, and to evaluate the efficacy of the biocontrol product Actinovate AG (Streptomyces lydicus WYEC 108). General and specific suppression was examined in the field by assessing the effects of cover crop green manures (V. villosa, T. incarnatum, Secale cereale, and Brassica juncea) on soil respiration, presence of F. oxysporum spp., and arbuscular mycorrhizal colonization of watermelon. Cover crop treatments V. villosa, T. incarnatum, and S. cereale and no cover crop were evaluated both alone and in combination with Actinovate AG in the greenhouse. Additionally, in vitro experiments were conducted to measure the effects of cover crop leachate on the mycelial growth rates of F. oxysporum f. sp. niveum race 1 and Trichoderma harzianum. Soil microbial respiration was significantly elevated in V. villosa and Trifolium incarnatum treatments both preceding and following green manure incorporation, and was significantly negatively correlated with Fusarium wilt, suggesting that microbial activity was higher under the legumes, indicative of general suppression. Parallel to this, in vitro growth rates of F. oxysporum f. sp. niveum and Trichoderma harzianum on V. villosa leachate amended media were 66 and 213% greater, respectively, than on nonamended plates. The F. oxysporum spp. population (based on CFU and not differentiated into formae specialis or races) significantly increased in V. villosa-amended field plots. Additionally, the percentage of watermelon roots colonized by arbuscular mycorrhizae following V. villosa and Trifolium incarnatum green manures was significantly higher than in watermelon following bare ground (58 and 44% higher, respectively). In greenhouse trials where cover crops were amended to soil, Actinovate AG did not consistently reduce Fusarium wilt. Both general and specific disease suppression play a role in reducing Fusarium wilt on watermelon.
秋季种植的毛叶苕子或绛车轴草覆盖作物，在春季作为绿肥翻耕入土，可抑制西瓜枯萎病（尖孢镰刀菌西瓜专化型）。在覆盖作物生长、刈割及翻耕入土过程中，许多因素如丛枝菌根定殖、渗滤液和土壤呼吸等存在差异。这些与覆盖作物相关的因素如何影响枯萎病抑制作用尚不完全清楚。开展试验以评估渗滤液、土壤呼吸及其他与绿肥相关的变化如何影响枯萎病抑制作用，并评估生物防治产品Actinovate AG（利迪链霉菌WYEC 108）的功效。通过评估覆盖作物绿肥（毛叶苕子、绛车轴草、黑麦和芥菜）对土壤呼吸、尖孢镰刀菌种类的存在情况以及西瓜丛枝菌根定殖的影响，在田间检测一般抑制和特异性抑制作用。在温室中，对毛叶苕子、绛车轴草和黑麦覆盖作物处理以及无覆盖作物处理进行了单独评估，并与Actinovate AG组合评估。此外，进行了体外试验，以测量覆盖作物渗滤液对尖孢镰刀菌西瓜专化型1号生理小种和哈茨木霉菌丝生长速率的影响。在毛叶苕子和绛车轴草处理中，绿肥翻耕前后土壤微生物呼吸均显著升高，且与枯萎病呈显著负相关，这表明豆科植物下微生物活性较高，显示出一般抑制作用。与此平行的是，在添加毛叶苕子渗滤液的培养基上，尖孢镰刀菌西瓜专化型和哈茨木霉的体外生长速率分别比未添加渗滤液的平板高66%和213%。在添加毛叶苕子的田间小区中，尖孢镰刀菌种群数量（基于菌落形成单位，未区分专化型或生理小种）显著增加。此外，毛叶苕子和绛车轴草绿肥处理后，西瓜根被丛枝菌根定殖的百分比显著高于裸地种植的西瓜（分别高出58%和44%）。在温室试验中，向土壤添加覆盖作物后，Actinovate AG并未持续降低枯萎病发病率。一般病害抑制和特异性病害抑制在降低西瓜枯萎病发病率方面均发挥作用。
