Phytophthora cryptogea root rot of tomato in rockwool nutrient culture. I. Analysis of root infection

The spatial and temporal colonisation of tomato plants by Phytophthora cryptogea was studied in rockwool nutrient culture. Root growth and the distribution and progress of infection were measured on dissected root fragments obtained from a detailed destructive sampling of the substrate. Dissected fragments of root or roots and fibres were plated on BNPRA agar, a selective Phytophthora medium. Roots colonised all parts of the rockwool substrate 60 days after planting with the exception of surface marginal and central areas of the slab which had a lower solution content. Most root biomass occurred in and immediately beneath the original growing block. The distribution of P. cryptogea closely followed the pattern of root colonisation. An alternative, novel method for root analysis involved the dissolution of the mineral fibre and its formate bonding resin by digestion in 1 m H₃PO₄ for 45 min. Comparative recoveries of P. cryptogea from plated fragments of dissected root and fibre or comminuted samples of acid-released or dissected root showed that the acid treatment initially reduced the number of Phytophthora colonies in block and slab roots by 67% and 61% respectively. After 28 days, colony recovery from acid-released roots in the rockwool slab increased and was between 4% and 13% lower than from other plating methods. Since 1 m H₃PO₄ was lethal to zoospores and surface sporangia, the colonies recovered were interpreted as originating exclusively from root lesions. Root fresh weight of healthy and inoculated plants declined during the initial period of fruit formation. P. cryptogea infection led to a progressive reduction in root weight in the growing block and main slab and 28 days after inoculation, was approximately 50% of the controls. The acid digestion of rockwool fibre is proposed as a new approach to the problem of root and pathogen analysis in this substrate.     

Phytophthora cryptogea root rot of tomato in rock woo] nutrient culture. II. Effect of root zone temperature on infection, sporulation and symptom development

The effect of root-zone temperature on Phytophthora cryptogea root rot was studied in tomato cv. Counter grown under winter and summer conditions in rockwool culture. A nutrient temperature of 25°C resulted in increased root initiation and growth, higher in winter-grown than in summer-grown plants. Rhizosphere zoospore populations were greatly reduced at 25°C and above. Growth of P. cryptogea in vitro was optimal between 20°C and 25°C and completely suppressed at 30°C. Encystment was enhanced by increased temperatures above 20°C. Zoospore release in vitro occurred in cultures maintained at constant temperatures in the absence of the normal chilling stimulus. Optimal release was at 10°C; no zoospores were released at 30°C. Inoculated, winter-grown tomato plants maintained at 15°C developed acute aerial symptoms and died after 21 days. Comparable plants grown at a root-zone temperature of 25°C remained symptomless for the 3-months duration of the experiment. Summer-grown infected plants at the higher root temperature wilted but did not die. Enhanced temperature was ineffective as a curative treatment in summer-grown plants with established infection. Aerial symptoms of Phytophthora infection are seen as a function of the net amount of available healthy root. With high root zone temperatures this is determined by new root production and decreased inoculum and infection.     

大豆种质对疫霉根腐病抗性特点研究

对1027份中国和国外引进的大豆种质进行了大豆疫霉(Phytophthora sojae)根腐病的抗病性鉴定评价.结果表明,中国大豆种质的抗病性高于国外引进种质;中国南方的大豆种质抗病性较北方种质强,长江流域大豆中抗病种质比率最高,其次为黄淮海流域种质,而东北地区抗病种质较少;不同省份大豆种质的总体抗病性差异明显;育成品系的抗性好于改良品种和农家种,但不同省份来源的农家种、品系和品种抗性存在差异,黑龙江材料抗病性最低,这也是该省大豆疫霉根腐病严重发生的重要原因之一;在大豆籽粒脐色为黄色和褐色的材料中,抗病种质较多.     

Evaluation of fungicides and biocontrol products for the control of Phytophthora root rot of hydrangeas

Abstract

Phytophthora root rot is one of the most important diseases in almost all hydrangeas of nursery production. In this study, the efficacy of fungicides and biocontrol products against Phytophthora root rot of hydrangea was assessed in greenhouse and field experiments. Treatments used in field or greenhouse experiments were RootShield PLUS⁺, MBI110, IT-5103, Grotab, OxiPhos, TerraClean 5.0?+?TerraGrow program, Segovis, Pageant Intrinsic, Empress Intrinsic and Subdue Maxx. Pots/plots were inoculated with Phytophthora nicotianae grown on rice grains, sterilised rice grains were used for negative controls. After the trials, plant growth data (total plant weight, root weight, plant height, plant width) were recorded, and roots were assessed for disease severity using a scale of 0–100%. The treatments most effective in reducing Phytophthora root rot severity were Segovis, Empress Intrinsic, Subdue Maxx, TerraClean 5.0?+?TerraGrow program in both greenhouse and field experiments. This study will help nursery producers make proper management decisions by using recommended fungicides and biocontrol products of this study in a rotation or alone to manage Phytophthora root rot of hydrangea.     

The effect of chemical and biological treatment on root and crown rot disease caused by Phytophthora cryptogea Pethybr. & Lafferty in Gerbera

Phytophthora root and crown rot (Phytophthora cryptogea) on gerbera is difficult to manage because most gerbera cultivars are susceptible to P. cryptogea. This study was conducted in order to determine the in vivo (pot experiment) efficacy of some fungicides and biofungicides. In pot experiments, fungicides were applied 7 days after inoculation with P. cryptogea, while biofungicide was applied 7 days before inoculation. In this study, soil drenches of five fungicides were tested. “Ametoctradin+dimethomorph (100 ml/day),” “mandipropamid+difenoconazole (60 ml/day),” “propamocarb+fosetyl‐Al (200 ml/day),” “mancozeb+metalaxyl‐M (250 g/day)” and “azoxystrobin+difenoconazole (100 ml/day)” active substances were used. Similarly, one biofungicide Bacillus amyloliquefaciens syn. MBI 600 (50 g/100 L) was applied by soil drenching. Efficacy of treatments was assessed according to the percentage of the root system which was visibly rotten at the end of the experiment. Root and crown rot severity was rated on a scale of 0 = 0% root system necrotic, 1 = 1%‐25% necrotic, 2 = 26%‐50% necrotic, 3 = 51%‐75% necrotic and 4 = 76%‐100% necrotic from 12 to 21 days. In this experiment, “azoxystrobin 200 g/L + difenoconazole 125 g/L” exhibited the highest efficacy against P. cryptogea with a ratio of 43.75%. The other fungicides and biofungicides ametoctradin 300 g/L + dimethomorph 225 g/L, mandipropamid 250 g/L + difenoconazole 250 g/L, propamocarb 530 g/L + fosety‐Al 310 g/L, mancozeb 64%+metalaxyl‐M 4% and Bacillus amyloliquefaciens syn. MBI 600 11% were ineffective. Importance should be given to management strategies of P. cryptogea of and more experiments should be carried out for a better understanding of the use of registered fungicides and biofungicides.     

Thermal sensitivity of Phytophthora cinnamomi and long-term effectiveness of soil solarisation to control avocado root rot

Root rot caused by the fungus Phytophthora cinnamomi is a major disease of avocados worldwide. Heat sensitivity of a collection of P. cinnamomi isolates was determined by exposing agar discs containing mycelium or mycelium plus chlamydospores at various temperatures for different periods. Long‐term effectiveness of soil solarisation to control Phytophthora root rot was evaluated in two field trials. In the first, soil disinfestation by solarisation was applied in 1990 to a naturally infested plot before planting avocado (Persea americana) and viñatigo (Persea indica) seedlings. In the second trial, established avocado trees were solarised for four consecutive summers (1996–1999). Results for heat sensitivity showed that fungal mycelium was inactivated after 1–2 h at 38°C. However, 1–2 h at 40°C was needed to kill all propagules when chlamydospores were present. Fungal growth inhibition after thermal treatments was related to levels of time and temperature, and detrimental effects occurred as consequence of sublethal thermal doses. Soil solarisation presented long‐term positive effects when applied as a preplanting treatment. Five years after solarisation, disease severity (0–5 scale where 0 = healthy and 5 = dead plant) of avocado and viñatigo planted in solarised soil was 2.03 and 0.71, respectively, compared with 4.65 and 4.84 in controls. Eleven years after solarisation, the percentage of dead plants in solarised soil was 73% for avocado and 43% for viñatigo but 100% in controls. In contrast, an insufficient level of control was observed in established orchards, probably because of the lower temperature reached during solarisation under the shade of tree canopy. In this situation, maximum temperatures at 5‐cm depth were 10–13.7°C lower than under solar‐heated mulch, only exceeding 40°C in 1997.     

Potential of endophytic Streptomyces spp. for biocontrol of Fusarium root rot disease and growth promotion of tomato seedlings

Sixteen endophytic actinobacteria isolated from roots of native plants were evaluated for their antagonistic potential against soil-borne phytopathogenic fungi. Among them, three strong antagonistic isolates were selected and characterised for in vitro plant-growth-promoting and biocontrol traits, including production of hydrogen cyanide, indole-3-acetic acid and siderophores, chitinase and β-1,3-glucanase activities, and inorganic phosphate solubilisation. In all trials, the strain Streptomyces sp. SNL2 revealed promising features. The selected actinobacteria were investigated for the biocontrol of Fusarium oxysporum f. sp. radicis lycopersici and for growth promotion of tomato (Solanum lycopersicum L. cv. Aïcha) seedlings in autoclaved and non-autoclaved soils. All seed-bacterisation treatments significantly reduced the root rot incidence compared to a positive control (with infested soil), and the isolate SNL2 exhibiting the highest protective activity. It reduced the disease incidence from 88.5% to 13.2%, whereas chemical seed treatment with Thiram® provided 14.6% disease incidence. Furthermore, isolate SNL2 resulted in significant increases in the dry weight, shoot and root length of seedlings. 16S rDNA sequence analysis showed that isolate SNL2 was related to Streptomyces asterosporus NRRL B-24328^T (99.52% of similarity). Its interesting biocontrol potential and growth enhancement of tomato seedlings open up attractive uses of the strain SNL2 in crop improvement.     

Uneven distribution of nutrients in the root zone affects the incidence of blossom end rot and concentration of calcium and potassium in fruits of tomato

Tomato plants (Lycopersicon esculentum Mill. var. DRK) were grown hydroponically to determine the effect of an uneven distribution of nutrients in the root zone on blossom end rot (BER) and Ca and K concentrations in the fruits. The plants were grown in rockwool with their root system divided into two portions. Each portion was irrigated with nutrient solutions with either the same or the different electrical conductivity (EC) in the range 0 to 6 dS m^–1. Solutions with high EC supplied to both sides of the root system significantly increased the incidence of BER. However, when only water or a solution of low EC was supplied to one portion, BER was reduced by 80%. Fruit yields were significantly higher (P<0.01) for plants that received solutions of the uneven EC treatments (6/0 or 4.5/0 EC treatment). Plants supplied with solutions of uneven EC generally had higher leaf and fruit concentrations of Ca but lower concentrations of K than those supplied with solutions of high EC. There was no difference in Ca concentration at the distal end of young fruits of the uneven EC treatment but it was reduced in the high EC treatments. The concentration of K in the mature fruits of the uneven EC treatments was lower than that of the high EC treatments and higher or similar that of the 3/3 or 2.5/2.5 EC treatments (controls). A clear relationship was found between the incidence of BER and the exudation rate. High rate of xylem exudation was observed in the uneven EC treatments. Reduction of BER in the uneven EC treatments is most likely to be the effect of high exudation rate on Ca status in the young fruits. It was concluded that high EC of solution had positive effects on Ca concentration and incidence of BER provided that nutrient solution with low EC or water is supplied to the one portion of the root system.     

Ethylene-induced root coiling in tomato seedlings

Roots of tomato seedlings can be induced to coil by treatment with ethylene. The extent of coiling is dependent on the level of ethylene to which the seedlings are exposed and can be prevented by the incorporation of Ag ions into the growing medium. In contrast to all other tomato mutants examined, roots of the mutant diageotropica do not reorientate their growth in response to ethylene. The results of an agar penetration test indicate that roots of this mutant are agravitropic. The relationship between gravitropism and root coiling, and the origin of the ethylene modified growth pattern is discussed.     

Leaf yield loss assessment due to Macrophomina root rot disease in mulberry gardens of south India

Abstract

Leaf yield loss in mulberry due to Macrophomina root rot disease was assessed in three different states of south India at field level. The highest leaf yield loss recorded was in V-1 variety (34.74%), whereas the lowest leaf yield loss was in K-2 variety (28.54%). However, the leaf yields losses in other varieties viz., MR-2 (32.90%), S-36 (32.06%), RFS-175 (31.75%) and S-13 (29.0%) recorded were medium. The average leaf yield loss was 31.49% due to root rot disease caused by M. phaseolina in mulberry.     

野生大豆资源对大豆疫病抗病性和耐病性鉴定

大豆疫病是大豆重要病害之一,在世界范围内导致严重经济损失。防治大豆疫病最有效方法是利用抗病或耐病品种。筛选抗性资源是发掘抗性基因和抗病育种的基础。本研究鉴定了野生大豆资源对大豆疫病的抗病性和耐病性,以期发掘优异抗源。苗期用子叶贴菌块方法鉴定104份野生大豆资源对两个不同毒力的大豆疫霉分离物PSJS2(毒力型:1a,1b,1c,1d,1k,2,3a,3b,3c,4,5,6,7,8)和PS41-1(毒力型:1a,1d,2,3b,3c,4,5,6,7,8)抗性,结果表明33份资源抗PS41-1,35份资源抗PSJS2,其中18份抗两个分离物。在抗病性鉴定基础性上,用菌层接种方法对选择的82份资源进行耐病性鉴定,发现7份高耐病性资源。这些结果表明,野生大豆中可能含有新的大豆疫病抗病和(或)耐病资源,这些抗病或耐病资源可以用于未来大豆抗病育种,以丰富大豆对大豆疫病的抗性遗传基础。     

连作大豆根分泌物对根腐病病原菌的化感作用

采用砂培,水培和室内培养等试验方法研究了连作大豆根分泌物对根腐病病原菌的化感作用。结果表明,与对照相比,连作和轮作大豆根分泌物对半镰孢菌,粉红粘帚功和尖镰孢菌尤其是对半裸镰孢菌的生长有明显的化感促进作用,差异达显著或极显著水平,低浓度时,连作大豆根分泌物对半裸镰孢菌和粉红粘帚菌生长的化感促进作用明显大于轮作大豆,差异达显著水平,同一茬口,高浓度根分泌物半裸镰孢菌生长的化感促进作用小于低浓度,而且在连作大豆中差异达显著水平。与对照相比,高浓度的邻苯二甲酸和丙二酸（L5和B5）对半裸镰孢菌,粉红粘帚菌和尖镰孢菌尤其是对半裸镰孢菌的生长有化感抑制作用,差异达显著或极显著水平,而低浓诬的邻苯二甲酸和丙二酸对半裸镰孢菌,粉红粘帚菌和尖镰孢菌的生长有化感促进,部分差异达显著水平。     

黑龙江省主要栽培大豆品种(系)对大豆疫霉根腐病的多抗性评价

用下胚轴伤口接种方法接种鉴定黑龙江省60个栽培大豆品种和育成品系对5个具有不同毒力大豆疫霉菌菌株41-4、PMCl、USAR4、PSZJ6和USAR17的抗性.有50个品种(系)抗1个或1个以上茵株或表现中间类型,其中有5个、8个、16个和21个品种(系)分别对4个、3个、2个和1个菌株表现抗性或中间类型.60个品种(系)对5个菌株共产生12种反应模式,其中呈RRSSR反应类型的品种(系)可能含有Rpslα或Rpslc基因,品系农大3861可能含有Rps3c基因,呈SSSSS反应模式的品种(系)可能含有Rps7基因,或不含抗病基因;其它9种反应模式与含有已知单基因品种或单基因组合的反应模式不同,可能具有未知抗病基因.该研究结果表明,黑龙江省具有较丰富的抗大豆疫霉根腐病大豆品种(系),大部分品种(系)的抗性是有效的,可合理地用于大豆生产和抗疫霉根腐病育种.     

Effect of sub-optimal root zone temperatures at varied nutrient supply and shoot meristem temperature on growth and nutrient concentrations in maize seedlings (Zea mays L.)

Maize seedlings were grown for 10 to 20 days in either nutrient solution or in soils with or without fertilizer supply. Air temperature was kept uniform for all treatments, while root zone temperature (RZT) was varied between 12 and 24°C. In some treatments the basal part of the shoot (with apical shoot meristem and zone of leaf elongation) was lifted up to separate the indirect effects of root zone temperature on shoot growth from the direct effects of temperature on the shoot meristem.Shoot and root growth were decreased by low RZT to a similar extent irrespective of the growth medium (i.e. nutrient solution, fertilized or unfertilized soil). In all culture media Ca concentration was similar or even higher in plants grown at 12 as compared to 24°. At lower RZT concentrations of N, P and K in the shoot dry matter decreased in unfertilized soil, whereas in nutrient solution and fertilized soil only the K concentration decreased.When direct temperature effects on the shoot meristem were reduced by lifting the basal part of the shoot above the temperature-controlled root zone, shoot growth at low RZT was significantly increased in nutrient solution and fertilized soil, but not in unfertilized soil. In fertilized soil and nutrient solution at low RZT the uptake of K increased to a similar extent as plant growth, and thus shoot K concentration was not reduced by increasing shoot growth rates. In contrast, uptake of N and P was not increased, resulting in significantly decreased shoot concentrations.It is concluded that shoot growth at suboptimal RZT was limited both by a direct temperature effect on shoot activity and by a reduced nutrient supply through the roots. Nutrient concentrations in the shoot tissue at low RZT were not only influenced by availability in the substrate and dilution by growth, but also by the internal demand for growth.     

Importance of the cap in maize root growth

A large population of primary roots of Zea mays (cv. LG 11) was selected for uniform length at zero time. Their individual growth rates were measured over an 8-h period in the vertical position (in humid air, darkness). Three groups of these roots with significantly different growth rates were then chosen and their cap length was measured. It was found that slowly growing roots had long caps whereas rapidly growing roots had short caps. The production by the cap cells of basipetally transported growth inhibitors was tested (biologically by the curvature of half-decapped roots) and found to be significantly higher for longer root caps than that for shorter ones.     

Comparison of tomato root distributions by minirhizotron and destructive sampling

Calibration of minirhizotron data against root length density (RLD) was carried out in a field trial where three drip irrigation depths: surface (R0) and subsurface, 0.20 m (RI) and 0.40 m depth (RII) and two processing tomato cultivars: `Brigade' (CI) and `H3044' (CII) were imposed. For each treatment three minirhizotron tubes were located at 10, 37.5 and 75 cm of the way from one plant row to the next. Roots intersecting the minirizotrons walls were expressed as root length intensity (L _a) and number of roots per unit of minirhizotron wall area (N _ra). Root length density (RLD) was calculated from core samples taken for each minirhizotron tube at two locations: near the top of the minirhizotron (BI) and 15 cm apart from it, facing the minirhizotron wall opposite the plant row (BII). Minirhizotron data were regressed against RLD obtained at BI and BII and with their respective means. The results show that for all the situations studied, better correlations were obtained when RLD was regressed with L _a than with N _ra. Also was evident that the relationship between L _a and RLD was strongly influenced by the location of soil coring. RLD was correlated with L _a trough linear and cubic equations, having the last ones higher determination coefficients. For instance at 10 cm from the plant row when values from the top layer (0–40 cm) were analysed separately, L _a was significantly regressed with RLD measured at BII and described by the equations: RLD = 0.5448 + 0.0071 L _a (R ² = 0.51) and RLD = 0.4823 + 0.0074L _a + 8×10^–5 L _a ² – 5×10^–7 L _a ³ (R ² = 0.61). Under the 40 cm depth the highest coefficients of determination for the linear and cubic equations were respectively 0.47 and 0.88, found when L _a was regressed with RLD measured at BI. For minirhizotrons located at 75 cm from the plant row and for location BI it was possible to analyse jointly data from all depths with coefficients of determination of 0.45 and 0.59 for the linear and cubic equations respectively.     

Interactions of soil pH,nutrients and moisture on phytophthora root rot of avocado

Summary This experiment employed a factorial design combining 4 soil pH levels, 3 soil moisture levels, with and without the addition ofPhytophthora cinnamomi to the soil to evaluate the conditions that lead to Phytophthora root rot of avocado.An inverse relation between soil pH and leaf production (and root-weight) was observed in nondiseased plants. In soil infested withP. cinnamomi, plant growth and root weights were much depressed by low soil pH, and especially by low soil pH coupled with high soil moisture contents. These interactions were statistically highly significant. Root weights in pots withP. cinnamomi were closely related to the incidence of disease. A disease index was used to visually assess the conditions of roots. Isolation of the pathogen from diseased plant roots confirmed the accuracy of the disease index.A process of elimination suggsts that favorable soil Ca level and not high pHper se was responsible for disease suppression and that the devastating effects of low soil pH was produced by high Mn (and possibly Al) and associated low levels of Ca and P in soil solutions, which led to breakdown of biological control mechanisms.Journal Series No. 2801, Hawaii Institute of Tropical Agriculture and Human Resources.