Department of Plant Pathology, North Carolina State University, Raleigh, NC, USA.
Phytopathology. 2011 Feb;101(2):223-30. doi: 10.1094/PHYTO-04-10-0125.
Wood-based mulches are used in avocado production and are being tested on Fraser fir for reduction of Phytophthora root rot, caused by Phytophthora cinnamomi. Research with avocado has suggested a role of microbial cellulase enzymes in pathogen suppression through effects on the cellulosic cell walls of Phytophthora. This work was conducted to determine whether cellulase activity could account for disease suppression in mulch systems. A standard curve was developed to correlate cellulase activity in mulches with concentrations of a cellulase product. Based on this curve, cellulase activity in mulch samples was equivalent to a cellulase enzyme concentration of 25 U ml(-1) or greater of product. Sustained exposure of P. cinnamomi to cellulase at 10 to 50 U ml(-1) significantly reduced sporangia production, but biomass was only reduced with concentrations over 100 U ml(-1). In a lupine bioassay, cellulase was applied to infested soil at 100 or 1,000 U ml(-1) with three timings. Cellulase activity diminished by 47% between 1 and 15 days after application. Cellulase applied at 100 U ml(-1) 2 weeks before planting yielded activity of 20.08 μmol glucose equivalents per gram of soil water (GE g(-1) aq) at planting, a level equivalent to mulch samples. Cellulase activity at planting ranged from 3.35 to 48.67 μmol GE g(-1) aq, but no treatment significantly affected disease progress. Based on in vitro assays, cellulase activity in mulch was sufficient to impair sporangia production of P. cinnamomi, but not always sufficient to impact vegetative biomass.
木质覆盖物被用于鳄梨生产中，并正在对湿地冷杉进行测试，以减少由可可疫霉引起的疫霉根腐病。对鳄梨的研究表明，微生物纤维素酶通过对可可疫霉的纤维素细胞壁产生影响，在抑制病原体方面发挥作用。这项工作旨在确定纤维素酶活性是否可以解释覆盖物系统中的疾病抑制作用。建立了一条标准曲线，将覆盖物中的纤维素酶活性与纤维素酶产品的浓度相关联。基于该曲线，覆盖物样品中的纤维素酶活性相当于产品中 25U/ml 或更高的纤维素酶酶浓度。可可疫霉持续暴露于 10 至 50U/ml 的纤维素酶中显著减少了游动孢子的产生，但仅在浓度超过 100U/ml 时才减少生物量。在羽扇豆生物测定中，将纤维素酶以 100 或 1000U/ml 的浓度在受感染的土壤中应用于三个时间点。在施用后 1 至 15 天之间，纤维素酶活性下降了 47%。在种植前 2 周以 100U/ml 的浓度施用纤维素酶，在种植时产生的土壤水（GE g(-1) aq）中每克土壤的葡萄糖当量活性为 20.08μmol，与覆盖物样品相当。种植时的纤维素酶活性范围为 3.35 至 48.67μmol GE g(-1) aq，但没有一种处理方法显著影响疾病进展。基于体外测定，覆盖物中的纤维素酶活性足以损害可可疫霉游动孢子的产生，但并不总是足以影响营养生物量。
