Variable Selection Pressure for Different Levels of Resistance to Rhizoctonia Root Rot in Sugarbeet

1988 ◽  
Vol 25 (1) ◽  
pp. 63-69 ◽  
Author(s):  
E.G. Ruppel ◽  
R.J. Hecker
Keyword(s):  
Variable Selection ◽  
Root Rot ◽  
Selection Pressure ◽  
Rhizoctonia Root Rot ◽  
Different Levels

Registration of Rhizoctonia Root Rot Resistant Sugarbeet Germplasm FC 709

Crop Science ◽  
1988 ◽  
Vol 28 (6) ◽  
pp. 1039-1040 ◽  
Author(s):  
R. J. Hecker ◽  
E. G. Ruppel
Keyword(s):  
Root Rot ◽  
Rhizoctonia Root Rot

Registration of Rhizoctonia Root Rot Resistant Sugarbeet Germplasm FC 712

Crop Science ◽  
1986 ◽  
Vol 26 (1) ◽  
pp. 213-214 ◽  
Author(s):  
R. J. Hecker ◽  
E. G. Ruppel
Keyword(s):  
Root Rot ◽  
Rhizoctonia Root Rot

scholarly journals Sensitivity of Rhizoctonia Isolates to Phenazine-1-Carboxylic Acid and Biological Control by Phenazine-Producing Pseudomonas spp.

2017 ◽  
Vol 107 (6) ◽  
pp. 692-703 ◽  
Author(s):  
Ahmad Kamil Mohd Jaaffar ◽  
James A. Parejko ◽  
Timothy C. Paulitz ◽  
David M. Weller ◽  
Linda S. Thomashow
Keyword(s):  
Carboxylic Acid ◽  
Geographic Distribution ◽  
Root Rot ◽  
Cropping Systems ◽  
Annual Precipitation ◽  
Columbia Plateau ◽  
Pseudomonas Spp ◽  
Rhizoctonia Root Rot ◽  
Precipitation Zone ◽  
Low Precipitation

Rhizoctonia solani anastomosis groups (AG)-8 and AG-2-1 and R. oryzae are ubiquitous in cereal-based cropping systems of the Columbia Plateau of the Inland Pacific Northwest and commonly infect wheat. AG-8 and R. oryzae, causal agents of Rhizoctonia root rot and bare patch, are most commonly found in fields in the low-precipitation zone, whereas R. solani AG-2-1 is much less virulent on wheat and is distributed in fields throughout the low-, intermediate-, and high-precipitation zones. Fluorescent Pseudomonas spp. that produce the antibiotic phenazine-1-carboxylic acid (PCA) also are abundant in the rhizosphere of crops grown in the low-precipitation zone but their broader geographic distribution and effect on populations of Rhizoctonia is unknown. To address these questions, we surveyed the distribution of PCA producers (Phz+) in 59 fields in cereal-based cropping systems throughout the Columbia Plateau. Phz+ Pseudomonas spp. were detected in 37 of 59 samples and comprised from 0 to 12.5% of the total culturable heterotrophic aerobic rhizosphere bacteria. The frequency with which individual plants were colonized by Phz+ pseudomonads ranged from 0 to 100%. High and moderate colonization frequencies of Phz+ pseudomonads were associated with roots from fields located in the driest areas whereas only moderate and low colonization frequencies were associated with crops where higher annual precipitation occurs. Thus, the geographic distribution of Phz+ pseudomonads overlaps closely with the distribution of R. solani AG-8 but not with that of R. oryzae or R. solani AG-2-1. Moreover, linear regression analysis demonstrated a highly significant inverse relationship between annual precipitation and the frequency of rhizospheres colonized by Phz+ pseudomonads. Phz+ pseudomonads representative of the four major indigenous species (P. aridus, P. cerealis, P. orientalis, and P. synxantha) suppressed Rhizoctonia root rot of wheat when applied as seed treatments. In vitro, mean 50% effective dose values for isolates of AG-8 and AG-2-1 from fields with high and low frequencies of phenazine producers did not differ significantly, nor was there a correlation between virulence of an isolate and sensitivity to PCA, resulting in rejection of the hypothesis that tolerance in Rhizoctonia spp. to PCA develops in nature upon exposure to Phz+ pseudomonads.

scholarly journals Trait evolution under multiple selection pressures: Prey responses to predictable and unpredictable variation

2019 ◽  
Author(s):  
Manvi Sharma ◽  
Kavita Isvaran
Keyword(s):  
Variable Selection ◽  
Predation Risk ◽  
Selection Pressure ◽  
Spatial And Temporal Variation ◽  
Rock Pools ◽  
Selection Pressures ◽  
Space And Time ◽  
Natural Settings ◽  
Oviposition Sites ◽  
Desiccation Risk

AbstractWhen a strong selection pressure, such as predation risk, varies widely in space and time, how should prey respond? When risk varies predictably, prey are hypothesized to respond in a risk-sensitive manner. It is less clear how prey should respond when risk varies unpredictably.Additionally, prey response may also depend on how predation risk interacts with other selection pressures. Our understanding of the complex action of multiple and variable selection pressures on prey traits is still comparatively poor. Here, we examine how predictable and unpredictable aspects of predation risk act together with another important selection pressure to influence prey behaviour in the rock pool breeding mosquito, Aedes vexans. Through the selection of sites for oviposition, female mosquitoes can influence the predation risk faced by their offspring. We tested how females select oviposition sites, when encountering pools that vary in larval predation risk and desiccation risk. We comprehensively quantified spatial and temporal variation in predation risk by measuring densities of predatory dragonfly nymphs in rock pools of different sizes, along the mosquito breeding season. We also measured hydroperiod length. We next conducted manipulative experiments in rock pools and measured female oviposition responses to variation in predation and desiccation risks. Predation risk varied widely in space and time. Desiccation risk only appeared important for the small pools. Ovipositing females appeared to respond to these multiple aspects of variation in selection pressures. Females seemed to respond to predictable variation by avoiding large pools that permanently harboured predators in natural settings. Female responses were more variable to medium-sized pools with naturally stochastic predator densities, highlighting the role of unpredictability in predation risk in shaping behaviour. Females did not clearly prefer small pools that were naturally devoid of predators but carried high desiccation risk, suggesting that they balance multiple risks – predation versus desiccation – when choosing oviposition sites. Our study suggests that wild populations may commonly experience multiple and variable selection pressures that can favour seemingly puzzling trait variation. We highlight the need to quantify variation in selection pressures and investigate how such variation, especially the unpredictable aspects, shapes prey traits.

scholarly journals Characterizing and Mapping Resistance in Synthetic-Derived Wheat to Rhizoctonia Root Rot in a Green Bridge Environment

2016 ◽  
Vol 106 (10) ◽  
pp. 1170-1176 ◽  
Author(s):  
A. K. Mahoney ◽  
E. M. Babiker ◽  
T. C. Paulitz ◽  
D. See ◽  
P. A. Okubara ◽  
...  
Keyword(s):  
Pacific Northwest ◽  
Root Rot ◽  
Recombinant Inbred Lines ◽  
Genetic Resistance ◽  
Genotyping By Sequencing ◽  
Interval Mapping ◽  
Environmentally Sustainable ◽  
Soilborne Disease ◽  
Rhizoctonia Root Rot ◽  
Green Bridge

Root rot caused by Rhizoctonia spp. is an economically important soilborne disease of spring-planted wheat in growing regions of the Pacific Northwest (PNW). The main method of controlling the disease currently is through tillage, which deters farmers from adopting the benefits of minimal tillage. Genetic resistance to this disease would provide an economic and environmentally sustainable resource for farmers. In this study, a collection of synthetic-derived genotypes was screened in high-inoculum and low-inoculum field environments. Six genotypes were found to have varying levels of resistance and tolerance to Rhizoctonia root rot. One of the lines, SPBC-3104 (‘Vorobey’), exhibited good tolerance in the field and was crossed to susceptible PNW-adapted ‘Louise’ to examine the inheritance of the trait. A population of 190 BC1-derived recombinant inbred lines was assessed in two field green bridge environments and in soils artificially infested with Rhizoctonia solani AG8. Genotyping by sequencing and composite interval mapping identified three quantitative trait loci (QTL) controlling tolerance. Beneficial alleles of all three QTL were contributed by the synthetic-derived genotype SPCB-3104.

Effects of cultivation on Rhizoctonia root rot, cereal cyst nematode, common root rot and yield of wheat in the Victorian Mallee

1991 ◽  
Vol 31 (3) ◽  
pp. 367 ◽  
Author(s):  
RFde Boer ◽  
JF Kollmorgen ◽  
BJ Macauley ◽  
PR Franz ◽  
Boer RF De
Keyword(s):  
Grain Yield ◽  
Root Rot ◽  
Dry Weight ◽  
Cyst Nematode ◽  
Cereal Cyst Nematode ◽  
Common Root ◽  
Common Root Rot ◽  
Root Diseases ◽  
Rhizoctonia Root Rot ◽  
Direct Drilling

The effects of method, time and number of cultivations on root diseases and yield of wheat were studied in a field experiment, in 1985, on a calcareous sandy loam in the Victorian Mallee. The incidence and severity of rhizoctonia root rot (Rhizoctonia solani) were higher in direct-drilled wheat than in wheat sown after cultivation. Compared with direct drilling, the severity of rhizoctonia root rot in seedlings was reduced by 40% with cultivation 20 weeks before sowing; by 70% with cultivation 1 day before sowing; and by 90% with 2 cultivations, the first at 16 weeks and the second 1 day before sowing. Cultivation generally increased the incidence of common root rot (Bipolaris sorokiniana) but had no significant effects on the severity of damage by the cereal cyst nematode (Heterodera avenae) or the number of nematode cysts produced, compared with direct drilling. The incidence and severity of root diseases, and the number of H. avenae cysts produced, were not significantly different in wheat sown after rotary hoeing than in wheat sown after scarifying. The severity of damage by H. avenae, the number of nematode cysts and the incidence of common root rot were higher (45, 70 and 36%, respectively) when scarifying was done 1 day before sowing, compared with scarifying 20 weeks earlier. Differences in sowing depth probably caused this effect since seed was sown deeper (as indicated by subcrown internode lengths) and plant emergence was less in the latter treatment. The timing and number of cultivations with a rotary hoe, however, did not significantly affect the severity of damage by H. avenae, the number of nematode cysts or the incidence of common root rot. The incidence of common root rot was correlated (r = 0.71) with the subcrown internode lengths, indicating that the deeper the seed was sown the greater the proportion of plants with the disease. Dry weight of seedlings and grain yield were negatively correlated (r = -0.79 and -0.66) with the severity of damage caused by H. avenae. Plant dry weight and grain yield were, however, not correlated with the severity of rhizoctonia root rot or the incidence of common root rot.

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