Evaluation of fungicides applied to soil to control naturally-occurring take-all using a balanced-incomplete-block design and very small plots

Six sterol biosynthesis-inhibiting fungicides representing several combinations of properties were applied to soil to control naturally-occurring take-all (caused by Gaeumannomyces graminis var. tritici) in winter wheat in field experiments in two successive years. The average take-all severity category was never more than moderate in the different clay-loam and sandy loam sites used in each year. At each site in each year there were six treatments and an untreated control in an arrangement based on a balanced-incomplete-block design for six treatments in 10 blocks each with three treatments. Each block had three treated plots and a control plot and was paired with the complementary block of three treatments (plus control) to form a complete replicate, of which there were 30 per site. Take-all assessments in June or July showed that after incorporation into the seed bed (at 2 kg ha“¹and sometimes at 1 kg ha”¹) in autumn, two non-volatile, strongly lipophilic compounds, nuarimol and triadimenol, with good intrinsic toxicity to the take-all fungus and slow rates of degradation, partially controlled take-all. However, another compound, flutriafol, with similar properties to nuarimol and triadimenol, controlled take-all less. Two slightly volatile, strongly lipophilic compounds, flusilazole and penconazole, with good intrinsic activity, were less effective (at 2 kg ha^-1). A volatile, less lipophilic compound, PP 969, with less intrinsic activity, also partially controlled take-all, but only after application as a drench in the spring (2 kg ha^-1). The most effective treatments were generally more effective the greater the level of disease (as indicated by assessments of disease in control plots), especially in spring assessments of disease. Although flutriafol did not perform as expected, it still seems reasonable to conclude that the requirements for a soil-applied fungicide to control take-all are likely to be: (i) good intrinsic fungitoxicity, (ii) some mobility in soil water (i.e. not strongly lipophilic), and (iii) season-long persistence.     

小麦全蚀病菌原生质体制备的条件及再生菌株的致病性

分别利用崩溃酶、溶壁酶、纤维素酶和蜗牛酶酶解小麦全蚀病菌,进行原生质体的制备试验。结果显示,4种酶均能消化该菌细胞壁,获得一定数量的原生质体;产生原生质体效率最高的是溶壁酶,该酶在浓度为16 mg/mL时产生的原生质体数量最多,最佳的酶解时间为2~3 h,最适作用温度为28℃。制备的原生质体可以再生并与原始出发菌株具有相同的致病能力。     

Field tests of bacteria and soil-applied fungicides as control agents for take-all in winter wheat

Putative biological and chemical treatments for controlling take-all were used in each of three consecutive years at two locations where winter wheat crops were grown in naturally-infested fields. The chemical treatments more often decreased take-all than the biological treatments, but no treatment consistently and significantly decreased take-all, nor did any cause a significant increase in yield. An isolate of Bacillus cereus var. mycoides and one of B. pumilis, applied as soil drenches in autumn or spring, or in the seed furrows, were usually ineffective. Of the few significant effects on disease, half were associated with increases and half with decreases, and most occurred in April and did not persist to late June. Two strains of Pseudomonas pluorescens applied to the seed were ineffective. The fungicide benomyl, applied as a drench in autumn and spring at 20 kg/ha was ineffective, while nuarimol, applied as a drench in autumn at 2 kg/ha was sometimes effective. Nuarimol incorporated into the seed bed at 2 kg/ha was the most effective treatment. In analyses using a functional relationship model for data from treated and untreated plots 12% of 176 data sets for biological treatments, 38% of 96 data sets for chemical treatments and 81% of 16 data sets for combined treatments showed increasing efficiency of the treatment with increasing disease intensity. These findings also demonstrate an additional advantage of the experimental design, namely that treatments are tested at different disease intensity levels within fields.     

全蚀病菌在玉米上的新变种

本文报道了玉米全蚀病菌禾顶囊壳菌(Gaeumannomyces graminis)的新变种——玉米变种[Gaeumannomyces graminis(Sacc.)Arx et Olivler var.maydis Yao Wang et Zhu var.nov.]。该变种在形态学、致病性、生物学及可溶性蛋白电泳谱带等方面,均不同于禾顶囊壳菌小麦变种[G.graminis var,tritici J.Walker)、水稻变种(G.graminis var.graminis Trans.)和燕麦变种[G.graminis var.avenae(Turner)Dennis]。模式标本保存在沈阳农业大学真菌标本室。     

小麦全蚀病菌致病性遗传规律研究*

利用弱致病性白化突变菌株与强致病菌株进行有性重组,研究了小麦全蚀病菌(禾顶囊壳小麦变种,Gaeumannomyces gramimis var. tritici)致病性的遗传规律。结果表明,以接种株地上部干重为致病性指标时,该菌对小麦的致病性为数量遗传性状,估计控制致病性的基因数为5 ~ 7个。弱致病菌株与强致病菌株杂交F1代致病性由弱至强呈连续分布,子代致病性的平均水平接近种亲代致病性的平均值。致病性的遗传力为54.36% ~ 71.00%,平均为62.32%。致病性表型易受环境因素的影响。菌落颜色与致病性无明显相关。     

Identification of antifungal substances secreted by Bacillus subtilis Z-14 that suppress Gaeumannomyces graminis var. tritici

Bacillus subtilis strain Z-14 has biological control activity against the take-all fungus Gaeumannomyces graminis var. tritici (Ggt). In Petri dishes, the crude extract from B. subtilis Z-14 culture filtrate reduced take-all severity in roots of wheat seedlings by 91.3% and potted plants by 69.8% compared to the Ggt-inoculated control. Treatment with the crude extract also significantly (P?<?.05) increased growth of roots’ average length, and fresh weight in comparison with those of the Ggt-inoculated control. B. subtilis Z-14 culture filtrate was relatively thermally stable with 88.2% of the antifungal activity being retained after being heated at 100°C for 30?min. Meanwhile, the antifungal activity remained almost unchanged (>95%) when the culture filtrate was exposed to a pH ranging from 3 to 8, but significantly reduced in basic conditions. This activity was not transferred to the organic solvent phase after treatment with organic extraction agents. B. subtilis Z-14 culture filtrate exhibited a broad spectrum of antifungal activities against various phytopathogenic fungi. Three homologs of iturin A (C14–16) were characterised by liquid chromatography-mass spectroscopy (LC-MS) and electrospray ionisation mass spectrometry/mass spectrometry collision-induced dissociation (ESI-MS/MS CID).     

Incidence of Gaeumannomyces graminis var. tritici and K deficiency increase rhizospheric denitrification

Wheat inoculated with the root pathogen Gaeumannomyces graminis var. tritici (Ggt) was grown in quartz silt at two levels of potassium nutrition. While in plants well supplied with K the incidence of Ggt did not affect plant growth, it reduced shoot and root weight of K deficient plants. Denitrification, measured by the acetylene inhibition technique and expressed as N₂O/mg root weight, was increased either by low K nutrition or by Ggt infection. Highest denitrification in the rhizosphere of plants was found with a combination of both, K deficiency and Ggt attack.     

宁夏灌区小麦白粉病菌子囊壳的存活力

在宁夏灌区,小麦白粉病菌（Erysiphegraminisf.sp．tritici）子囊壳的存活力可达9个月以上。在不同发育时期,以贮存于4℃冰箱里的子囊壳存活率为最高;埋在小麦种子中的次之;置于室外的最低。大气温度和湿度对子囊壳存活力有影响,而以夏季高温为重。     

Evaluation of some Iranian wheat elite lines’ reaction to Septoria tritici leaf blotch

Septoria tritici blotch is an important wheat disease in many areas of the world including Iran’s warm, humid regions. In this study, reaction of 79 lines from elite regional wheat yield trials of the Cereal Research Department from four climate zones was evaluated to S. tritici leaf blotch in adult plant stage under an artificial field inoculation in Khuzestan province in the south of Iran for two years (2008–2009 and 2009–2010). Nurseries were artificially inoculated by spreading infected plant debris (from last growing season). Taking notes was performed with a modified Saari and Prescott method in 00–99 double-digit scale. Wheat lines were classified in groups of immune (00), highly resistant (11–14), resistant (15–34), moderately resistant (35–44), moderately susceptible (45–64), susceptible (65–84) and highly susceptible (85–99). Result showed that from 79 lines, 37 lines had susceptible reaction; 2 lines had moderately susceptible; and 40 lines showed immune.