Effects of systemic fungicidal seed dressings on the incidence of Phytophthora megasperma, nodulation, and nitrogen fixation in two soybean cultivars

1983 ◽  
Vol 23 (120) ◽  
pp. 87 ◽  
Author(s):  
A Diatloff ◽  
JAG Irwin ◽  
JL Rose
Keyword(s):  
Nitrogen Fixation ◽  
Root Rot ◽  
Disease Incidence ◽  
Resistance Mechanisms ◽  
Field Resistance ◽  
Nitrogen Fixing ◽  
Phytophthora Megasperma ◽  
Phytophthora Root Rot ◽  
High Level ◽  
Root Health

Two cultivars of soybeans, Davis and Ross, resistant and susceptible to Phytophthora root rot, respectively, were grown in a field trial where there was a moderately high level of Phytophthora megasperma f. sp. glycinea. The efficacy of metalaxyl and Dowco 444 as fungicidal seed dressings, their interaction with host resistance and the effect of plant health on nodulation and nitrogen fixing activity (acetylene reduction) were assessed. The cultivar Davis showed a relatively high level of field resistance in the absence of fungicidal protection; this was manifest in increased emergence and a lower incidence of disease in the surviving plants. In contrast cv. Ross had virtually no field resistance. In both cultivars, disease incidence was lower where fungicides were used. Metalaxyl was more effective than Dowco 444 on cv. Ross but not on cv. Davis. This suggests that the better performance of Dowco 444 on Davis was through an enhancement of existing resistance mechanisms of the host. Nitrogen fixing activity was generally higher in Davis than in Ross with a positive correlation between nitrogen fixing activity and nodule number. Disease incidence was negatively correlated with nitrogen fixing activity indicating the dependence of nitrogen fixation on root health. Neither fungicides suppressed nitrogen fixing activity at the rates used.

Glasshouse and field screening of chickpea cultivars for resistance to Phytophthora megasperma f.sp. medicaginis

1991 ◽  
Vol 31 (5) ◽  
pp. 663 ◽  
Author(s):  
ML Dale ◽  
JAG Irwin
Keyword(s):  
Disease Incidence ◽  
Field Trials ◽  
Field Resistance ◽  
Phytophthora Megasperma ◽  
Phytophthora Root Rot ◽  
Progress Curve ◽  
Susceptible Control ◽  
Epidemic Development ◽  
Compound Interest ◽  
Chickpea Cultivars

The resistance expressed by a range of chickpea cultivars to phytophthora root rot in glasshouse and field trials was examined. Van der Plank's compound interest equation was the most suitable transformation for providing parameters to describe epidemic development for most of the cultivars when compared to the simple interest equation by plotting residuals and coefficients of determination. The area under the disease progress curve (AUDPC) was significantly correlated with the final disease incidence (FDI), which was also significantly correlated with the apparent infection rate (r), but r and AUDPC were not significantly correlated. The AUDPC proved to be relatively indiscriminate in this study for selecting resistant cultivars, since the value for the susceptible control cultivar was high, and many cultivars therefore had statistically lower AUDPC values. Several cultivars (i.e. CQ1591, ICC7568 and 232-4) were resistant on the basis of both the FDI and r parameters in the field trial and considered worthy of further investigation. When the parameters FDI or r were used to categorise the disease reactions of cultivars in the field, only half of the 30 cultivars assessed showed similar responses in both the glasshouse and field trials. The glasshouse assay used here does not allow the detection of all potentially useful forms of field resistance, and further work is needed in the development of a glasshouse assay which gives an accurate representation of field response to Phytophthora megasperma Drechs. f. sp. medicaginis Kuan and Erwin.

Factors contributing to poor lucerne persistence in southern Queensland

1977 ◽  
Vol 17 (89) ◽  
pp. 998 ◽  
Author(s):  
JAG Irwin
Keyword(s):  
Bacterial Wilt ◽  
Root Rot ◽  
Crown Rot ◽  
Wide Spread ◽  
Phytophthora Megasperma ◽  
Phytophthora Root Rot ◽  
Colletotrichum Trifolii ◽  
Disease Survey ◽  
Disease Surveys ◽  
Made In

Lucerne disease surveys made in southern Queensland have shown the presence of seven fungal root and crown diseases. The two most wide spread and serious diseases are Phytophthora root rot (Phytophthora megasperma) and Colletotrichum crown rot (Colletotrichum trifolii). The general disease survey did not reveal the presence of bacterial wilt (Corynebacterium insidiosum) in Queensland. Studies made on the survival of lucerne populations for 2.5 years at three sites in Queensland have shown that disease was the major cause of all detected plant deaths.

RCAT Persian soybean

1991 ◽  
Vol 71 (1) ◽  
pp. 175-176
Author(s):  
G. R. Ablett ◽  
W. D. Beversdorf
Keyword(s):  
Glycine Max ◽  
Root Rot ◽  
Yield Potential ◽  
Maturity Group ◽  
Phytophthora Megasperma ◽  
Phytophthora Root Rot ◽  
Group I ◽  
Glycine Max L ◽  
Cultivar Description ◽  
Late Maturity

RCAT Persian is a mid-late Maturity Group I soybean [Glycine max L. (Merr.)] cultivar with excellent yield potential, good lodging tolerance and resistance to most races of phytophthora root rot caused by Phytophthora megasperma f. sp. glycinea (Pmg) found in Ontario. Key words: Soybean, cultivar description

scholarly journals Incidence of Phytophthora Root Rot of Fraser Fir in North Carolina and Sensitivity of Isolates of Phytophthora cinnamomi to Metalaxyl

Plant Disease ◽  
2000 ◽  
Vol 84 (6) ◽  
pp. 661-664 ◽  
Author(s):  
D. M. Benson ◽  
L. F. Grand
Keyword(s):  
North Carolina ◽  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Disease Incidence ◽  
The State ◽  
Systematic Sampling ◽  
Phytophthora Root Rot ◽  
Fraser Fir ◽  
Phytophthora Spp ◽  
Old Trees

A survey of Fraser fir Christmas trees in North Carolina for incidence of Phytophthora root rot was conducted during 1997 and 1998. Field sites (7- to 13-year-old trees) and nursery transplant beds (4- to 5-year-old trees) selected at random were surveyed based on foliar symptoms of Phytophthora root rot. Field sites were surveyed with a random transect method (>3,000 trees/field) or by counting all trees (<3,000 trees/field). Overall, incidence of Phytophthora root rot averaged 9% over the 58 field sites sampled, with a range of 0 to 75%. No relationship was found between number of years Fraser fir had been planted in the field site and disease incidence. Disease incidence did not increase as field sites were rotated through second or third crops of Fraser fir. Phytophthora spp. were recovered from 1.8% of asymptomatic trees sampled from 58 field sites across the state. P. cinnamomi accounted for 91% of the Phytophthora isolates recovered. In nursery transplant beds where a systematic sampling procedure was used, incidence of diseased trees averaged 2%, with a range of 0 to 12% across 16 locations. Recovery of Phytophthora spp. averaged 1.2% from root samples collected from 50 asymptomatic seedlings at each location. Isolates collected from the field and nursery transplant beds were grown on cornmeal agar incorporated with 0, 1, 1.25, 10, or 100 μg a.i. metalaxyl/ml. All 166 isolates of P. cinnamomi tested were sensitive to metalaxyl at 1 or 1.25 μg a.i. metalaxyl/ml. Although incidence of Phytophthora root rot has not increased in the state compared to a survey done in 1976 to 1977, the disease continues to limit production of Fraser fir in North Carolina.

Effect of Phytophthora root and stem rot on the response of field-grown soybean to Saturated Soil Culture

1991 ◽  
Vol 42 (5) ◽  
pp. 791 ◽  
Author(s):  
RJ Troedson ◽  
MJ Ryley ◽  
DE Byth ◽  
JAG Irwin
Keyword(s):  
Field Resistance ◽  
Saturated Soil ◽  
Stem Rot ◽  
Soil Culture ◽  
Phytophthora Megasperma ◽  
High Soil Moisture ◽  
High Level ◽  
The Impact ◽  
Extent Of Disease ◽  
Important Disease

Phytophthora root and stem rot, caused by Phytophthora megasperma Drechs. f. sp. Glycinea Kuan & Erwin, is an important disease of soybean in several major growing areas across the world. Susceptible genotypes can be completely devastated, but cultivars with a high level of field resistance are available. Although high soil moisture is known to predispose to infection by Phytophthora, in the absence of this disease soybean is relatively tolerant to soil waterlogging, and has been shown to respond positively to continuous watering in the Saturated Soil Culture (SSC) system. The impact of Phytophthora on plants grown in SSC was investigated at two sites in south-east Queensland. At both sites, there were no differences between plants grown in SSC and conventional furrow-irrigated treatments in the rate or ultimate extent of disease development: susceptible cultivars succumbed to the disease, while cultivars with field resistance remained free of symptoms. A fungicidal seed dressing improved emergence and reduced initial disease infection, and improved seed yield in some cultivars. It was concluded that Phytophthora root and stem rot is not a limitation to the use of Saturated Soil Culture in soybean providing resistant cultivars are available.

scholarly journals Raised Beds and Metalaxyl for Controlling Phytophthora Root Rot of Raspberry

HortScience ◽  
1993 ◽  
Vol 28 (11) ◽  
pp. 1106-1108 ◽  
Author(s):  
K.E. Maloney ◽  
W.F. Wilcox ◽  
J.C. Sanford
Keyword(s):  
Root Rot ◽  
Disease Incidence ◽  
Silt Loam ◽  
Red Raspberry ◽  
Highly Pathogenic ◽  
Phytophthora Root Rot ◽  
Respective Treatment ◽  
Phytophthora Fragariae ◽  
Raised Bed ◽  
Substantial Control

`Titan' red raspberry (Rubis idaeus L.), highly susceptible to root rot caused by Phytophthora fragariae Hickman var. rubi Wilcox & Duncan (syns. P. erythroseptica Pethyb., “highly pathogenic” P. megasperma Drechs.), was planted in June 1990 in a silt loam naturally infested with the pathogen. Raked beds (0.36 m high) dramatically reduced disease incidence and severity relative to flatbed treatments. In contrast, metalaxyl at 372 mg·m-1 of row provided little benefit when applied to flat beds and provided consistently moderate but statistically insignificant effects when applied to raised beds. Relative to the flat bed system, primocane vigor was increased in 1992 by 16%, 190%, and 224% in the flat bed plus metalaxyl, raised bed, and raised bed plus metalaxyl treatments, respectively; total yields were increased by 7%, 231%, and 272% with these same respective treatment. The results indicate that raised-bed planting systems can provide substantial control of phytophthora root rot of red raspberries even when highly susceptible varieties are grown on otherwise marginal sites. Metalaxyl appears more effective as a supplement rather than substitute for raised beds under such conditions. Chemical name used: N- (2,6-dimethylphenyl) -N- (methoxyacetyl)alanine methyl ester (metalaxyl).

scholarly journals Phytophthora Root Rot of Blueberry Increases with Frequency of Flooding

HortScience ◽  
1999 ◽  
Vol 34 (4) ◽  
pp. 693-695 ◽  
Author(s):  
Amal de Silva ◽  
Keith Patterson ◽  
Craig Rothrock ◽  
Ron McNew
Keyword(s):  
Disease Severity ◽  
Root Rot ◽  
Phytophthora Cinnamomi ◽  
Disease Incidence ◽  
Severe Disease ◽  
Vaccinium Corymbosum ◽  
Root Infection ◽  
Phytophthora Root Rot ◽  
Severity Rating ◽  
Linear Relationships

Phytophthora root rot is a severe disease on blueberry (Vaccinium corymbosum L.) in poorly drained soils. Little is known about how mulching and frequent waterlogging affect disease severity in blueberries. Phytophthora cinnamomi Rands was grown on rice hulls, which were incorporated into the soil at the rate of 10% (v:v). Waterlogging conditions were imposed for 48 hours 1 week after planting on mulched and nonmulched blueberry plants at weekly, biweekly, and monthly intervals for a total of 3 months. Control plants were not subjected to flooding. The severity of Phytophthora root rot increased with time. Significant linear relationships were found between flooding interval and disease severity rating of shoot, percentage of root infection, and shoot and root dry weights of plants. Disease symptoms were minimal in control plants, but shoot disease rating and percentage of root infection were high in mulched and nonmulched plants that were flooded every week. Shoot and root dry weights were higher in 1997 than in 1996. In 1996, mulched plants had higher shoot dry weights than did nonmulched plants. Disease incidence was higher with weekly and biweekly flooding than with monthly or no flooding. However, mulching did not affect root infection.

Reaction of soybean cultivars to races of Phytophthora megasperma f.sp. glycinea present in Queensland

1982 ◽  
Vol 33 (5) ◽  
pp. 763 ◽  
Author(s):  
JL Rose ◽  
JAG Irwin ◽  
MJ Ryley ◽  
PW Langdon ◽  
LB Jenner
Keyword(s):  
Disease Incidence ◽  
Field Resistance ◽  
The Other ◽  
Stem Rot ◽  
Breeding Line ◽  
Phytophthora Megasperma ◽  
Breeding Lines ◽  
The North ◽  
Race 1 ◽  
Race 2

Phytophthora megasperma f.sp, glycinea, the cause of phytophthora root and stem rot of soybeans, was found to be widespread in southern Queensland. Race determinations on 56 isolates were made at 26�C using the North American differential set. Thirty isolates resembled race 1 (virulent only on Harosoy), while the remaining isolates killed varying proportions of the other six differentials. Two of these isolates most closely resembled race 15. When race determinations were repeated for four isolates at 31�C, each isolate was more virulent on most of the differentials. One isolate resembling race 1 at 26�C would have been classified as race 2 at 31�C. All of the cultivars grown in Queensland were susceptible to hypocotyl inoculation, indicating the absence of genes conditioning resistance to races 1 and 15. Small proportions of plants in some cultivars, including Davis and Bragg were resistant to hypocotyl inoculation. The field resistances of 21 cultivars and breeding lines were assessed in a disease nursery. Progressive assessments of disease incidence were significantly correlated with grain yield and plant height. Davis had the highest level of field resistance while Ross and Semstar had the lowest. A breeding line (HS 1115) was identified as highly resistant to the fungus, both in the field and following hypocotyl inoculation. Three F6 lines from the cross Davis x Bragg showed a range of disease reactions, with the best showing an equivalent level of resistance to that of Davis.

Lack of control of phytophthora root in lucerne (Medicago sativa) by foliar applications of phosphorus

1991 ◽  
Vol 31 (4) ◽  
pp. 503
Author(s):  
KF Lowe ◽  
MJ Ryley ◽  
TM Bowdler
Keyword(s):  
High Risk ◽  
Medicago Sativa ◽  
Root Rot ◽  
Dry Matter ◽  
Small Reduction ◽  
Phytophthora Megasperma ◽  
Phytophthora Root Rot ◽  
Resistant Cultivars ◽  
Matter Production ◽  
Lack Of Control

Application of phosphonate was investigated as a means of controlling phytophthora root rot (Phytophthora megasperma f. sp. medicaginis) in lucerne (Medicago sativa). Foliar sprays of the chemical at rates of 2, 4 and 8 g/L did not improve the persistence or dry matter production of susceptible or resistant cultivars of lucerne, despite a small reduction in the degree of damage inflicted on lucerne plants by a severe epiphytotic of the disease. Regular monthly applications gave no better control than single applications at establishment or at the time of the development of an epiphytotic. It is concluded that phosphonate is not efficacious in controlling phytophthora root rot in lucerne and will not improve the performance of susceptible cultivars in high risk situations.

Reaction of lucerne cultivars to Phytophthora megasperma, the cause of a root rot in Queensland

1974 ◽  
Vol 14 (69) ◽  
pp. 561 ◽  
Author(s):  
JAG Irwin
Keyword(s):  
Medicago Sativa ◽  
Root Rot ◽  
Controlled Environment ◽  
Field Site ◽  
Causal Organism ◽  
Phytophthora Megasperma ◽  
Phytophthora Root Rot ◽  
Disease Surveys ◽  
Infested Field ◽  
Experimental Strains

The causal organism of Phytophthora root rot of lucerne (Medicago sativa) in Queensland was identified as Phytophthora megasperma var. sojae and a brief description of the organism is included. The results of disease surveys show that Phytophthora root rot is widespread and causes serious losses in lucerne in south eastern Queensland. A collection of lucerne cultivars and strains was screened for resistance to P. megasperma var. sojae both in controlled environment chambers and in a naturally infested field site. The cultivar Lahontan and the experimental strains ESI, BDSI, ECRSI and Combined showed high levels of resistance in both situations.

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