Field Resistance in Three Native Monocotyledon Species That Colonize Indigenous Sclerophyll Forest After Invasion by Phytophthora cinnamomi

1984 ◽  
Vol 32 (4) ◽  
pp. 339 ◽  
Author(s):  
D Phillips ◽  
G Weste
Keyword(s):  
Phytophthora Cinnamomi ◽  
Lateral Roots ◽  
Fungal Growth ◽  
Field Resistance ◽  
Root Production ◽  
Root Tip ◽  
Bare Ground ◽  
Rapid Reduction ◽  
Sclerophyll Forest ◽  
Disease Extension

Lepidosperma laterale (Cyperaceae), Gahnia radula (Cyperaceae) and Poa sieberana (Poaceae) colonize bare ground of dry sclerophyll forest after disease due to P. cinnamomi. To determine their resistance, plants grown in divided root boxes were inoculated with 150-200 zoospores of the pathogen. Infected roots ceased growth. In the small necrotic lesions produced, the pathogen remained viable and capable of providing a source of inoculum for disease extension. Fungal growth was usually limited to the lesion but in some cases a few hyphae were observed in adjacent tissue. Away from the lesion there was a rapid reduction of fungal material and of the associated cellular disintegration. Rates of root production and root growth were not stimulated by infection but uninfected lateral roots replaced the root tip in some plants; in others, a new root tip emerged from the necrotic zone, enabling the plant to outgrow the fungal attack.

Phytophthora cinnamomi: Population Densities in Forest Soils

1977 ◽  
Vol 25 (5) ◽  
pp. 461 ◽  
Author(s):  
G Weste ◽  
P Ruppin
Keyword(s):  
Environmental Factors ◽  
Soil Water ◽  
Phytophthora Cinnamomi ◽  
Soil Water Potential ◽  
Forest Community ◽  
Population Densities ◽  
Sclerophyll Forest ◽  
Soil Temperatures ◽  
Disease Extension ◽  
Pathogen Populations

Population densities of Phytophthora cinnamomi, associated disease and environmental factors were studied concurrently during a 2-year period in three different forest ecosystems. Pathogen populations showed seasonal variation, low values being obtained for winter months associated with soil temperatures less than 10°C. Populations increased with warmer temperatures for spring and summer, but declined during dry periods in late summer or early autumn when the soil water potential was lower than -9 bars, although at that period soil temperatures were favourable. High populations were recorded in autumn, then declined with decrease in soil temperatures during winter. Correlation coefficients indicated a highly significant relationship between pathogen populations and soil temperatures from autumn to early summer, and between soil moisture and pathogen population for summer and autumn, in the Brisbane Ranges independently of site. The same pattern was evident in wetter forests at Narbethong and savannah woodlands at Wilson's Promontory, although results were not significant. Disease was evident wherever the pathogen occurred among susceptible hosts. The savannah woodland, the dry shrubby sclerophyll forest and the wetter sclerophyll forest all contained susceptible dominants; consequently disease was associated with changes in the forest community such as early death of the understorey, later die-back and death of the trees, and an increase in sedges and in bare ground. Symptoms and deaths increased with time from invasion. The severity of disease and its rate of extension, apart from spread by free water, were associated with environmental factors such as shallow soil, poor drainage and low soil water-holding capacity. These were characteristic of the Brisbane Ranges, where destruction of the forest community was severe and the rate of disease extension rapid. In the deep krasnozem at Narbethong and the deep sands of Wilson's Promontory, destruction was confined to the most susceptible hosts, disease extension was continuous but slow, and deaths occurred in a mosaic throughout the infected zone.

Phytophthora cinnamomi in the Brisbane Ranges: Patterns of Disease Extension

1976 ◽  
Vol 24 (2) ◽  
pp. 201 ◽  
Author(s):  
G Weste ◽  
P Ruppin ◽  
K Vithanage
Keyword(s):  
Environmental Factors ◽  
Phytophthora Cinnamomi ◽  
Soil Characteristics ◽  
Drainage Water ◽  
Sclerophyll Forest ◽  
Disease Extension ◽  
Wavy Boundary ◽  
Active Disease

Three patterns of disease extension were observed in areas of uncultivated shrubby dry sclerophyll forest invaded by the pathogen Phytophthora cinnamomi. Environmental factors were found to determine which pattern developed. Where inoculum was spread downhill with drainage water, diseased areas were separated by clearly defined boundaries from unaffected vegetation. Where disease extension occurred uphill through soil or from root to root, a wavy boundary marked the active disease front. Investigations showed that absence of disease extension for 4 years in highly susceptible vegetation may be associated with differences in soil characteristics.

Application of Phytohormones to Pea Roots After Removal of the Apex: Effect on Lateral Root Production

1979 ◽  
Vol 6 (2) ◽  
pp. 195 ◽  
Author(s):  
PB Goodwin ◽  
SC Morris
Keyword(s):  
Lateral Root ◽  
Lateral Roots ◽  
Primary Root ◽  
Root Production ◽  
Root Tip ◽  
Naphthaleneacetic Acid ◽  
Root Initiation ◽  
Lateral Root Initiation ◽  
Lateral Bud ◽  
Bud Growth

Removal of 2 mm of the primary root tip of Pisum sativum caused a complete halt to primary root elongation, but did not alter the total number of laterals formed. The auxins indole-3-acetic acid and 1-naphthaleneacetic acid, when applied to the stump in a lanolin emulsion, increased the number of lateral roots. High levels of abscisic acid and low levels of the cytokinins N6-benzylaminopurine and N6-(γ, γ-dimethylallylamino)purine, and of the gibberellins GA3 and GA7, resulted in decreased lateral root production. Kinetin was without effect. There appears to be an inverse relationship between auxins and cytokinins in root/shoot growth coordination. Auxins, which are produced in the shoot tip, inhibit lateral bud growth but promote lateral root initiation. Cytokinins, which are produced in the root tip, inhibit lateral root initiation, but promote lateral stem growth.

Distribution of Armillaria luteobubalina and its Impact on Community Diversity and Structure in Eucalyptus wandoo Woodland of Southern Western Australia

1997 ◽  
Vol 45 (1) ◽  
pp. 151 ◽  
Author(s):  
B. L. Shearer ◽  
A. Byrne ◽  
M. Dillon ◽  
R. Buehrig
Keyword(s):  
Host Species ◽  
Basal Area ◽  
Plant Species Richness ◽  
Community Diversity ◽  
Survival Strategies ◽  
Annual Rainfall ◽  
Bare Ground ◽  
Pathogen Population ◽  
Disease Extension ◽  
Eucalyptus Wandoo

Armillaria luteobubalina Watling & Kile is causinghigh mortality in Eucalyptus wandoo Blakely woodland that receives low annual rainfall of 500–700 mm, and it is a significantdisturbance agent affecting community structure. Discrete disease centresranged from 0.01 ha to 8 ha in size (mean 1.2 ± s.e. 0.3 ha) and had adiscontinuous distribution within the woodland. For 38 disease centres, thetotal area infested was 46.25 ha. Infection caused death of overstorey polesand veterans creating disease centres of greatly reduced biomass. Thisreduction was reflected by a negative correlation between the mortality ofoverstorey and basal area and diameter at breast height over bark (DBH). Theaverage mortality of E. wandoo trees was 47% indisease centres of intermediate impact, compared with 66% for highimpact areas. Regeneration of the host species increased following diseaseexpression, as evidenced by: significantly greater understocking oflignotubers and saplings in disease centres than in non-infested woodland,less bare ground in disease centres than in non-infested woodland, and apositive correlation between the mortality of overstorey and live understorey.By contrast, plant species richness and diversity did not differ significantlybetween infested and non-infested woodland. The severity ofA. luteobubalina infection was not strongly related tosite factors. The rate of disease extension varied considerably between yearsduring the period 1986–1994 and averaged 2.04 ± s.e. 1.05 myr-1. Of the 26 host species recorded, 23% werefrom the Proteaceae followed by a smaller percentage from the Myrtaceae andPapilionaceae (15% each). The high impact ofA. luteobubalina in E. wandoowoodland reflects the high susceptibility of the dominant host to infectionand survival strategies of the pathogen population in the harsh woodlandenvironment.

Phytotoxic effects of phenolic compounds on Calopogonium mucunoides (Fabaceae) roots

2015 ◽  
Vol 63 (8) ◽  
pp. 679 ◽  
Author(s):  
Roberta Cristiane Ribeiro ◽  
Rodrigo Barbosa Braga Feitoza ◽  
Helena Regina Pinto Lima ◽  
Mário Geraldo de Carvalho
Keyword(s):  
Phenolic Compounds ◽  
Cinnamic Acid ◽  
Lateral Roots ◽  
Anatomical Variations ◽  
Root Diameter ◽  
Root Tip ◽  
Root Structure ◽  
Water Control ◽  
Calopogonium Mucunoides ◽  
Standard Techniques

Studies on phenols have gained attention owing to their abundance in plants and their effects on plant development. Phenols from forage grasses may exert phytotoxicity on legume crops in intercropping systems. We aimed to identify morpho-anatomical variations in Calopogonium mucunoides Desv. roots treated with phenolic compounds. Seeds of C. mucunoides were treated with (1) distilled water (control), (2) trans-cinnamic acid, (3) a mixture of the flavonoids quercetin, rutin, kaempferol and kaempferol-3-α-rhamnoside, or (4) a combination of the flavonoid mixture and trans-cinnamic acid. After 10 days of treatment, the roots were measured, described and processed according to standard techniques in plant anatomy. In general, non-control individuals showed plant lengths decreased by 40–45%, root-tip necrosis and intense lateral root ramification. Seeds germinated in cinnamic acid presented xylem poles with a greater number of cells and a greater emission of lateral roots. In the seeds treated with flavonoids, cell division was observed in the endodermis and the pericycle, and xylem fibres went through differentiation. The combination of cinnamic acid and flavonoids led to the premature formation of fibres by the phloem. The treatments with flavonoids or cinnamic acid alone were significantly greater in root diameter (868.61 µm and 810.35 µm, respectively) than was the application of both (714.98 µm) or the control (533.76 µm). The results suggest that cinnamic acid and the tested flavonoids negatively affect the development and the root structure of C. mucunoides.

Corrigendum - Factors which affects the growth of grain legumes on a solonized brown soil. I. Genotypic responses to soil physical factors

1991 ◽  
Vol 42 (1) ◽  
pp. 95
Author(s):  
BJ Atwell
Keyword(s):  
Root Growth ◽  
Water Status ◽  
Lateral Roots ◽  
Primary Root ◽  
Grain Legumes ◽  
Root Tip ◽  
Physical Factors ◽  
Brown Soil ◽  
Penetrometer Resistance ◽  
System L

Lupins (Lupinus angustifolius cvv. Yandee and 75A-258 and L. pilosus cv. P. 20957) and pea (Pisum sativum cv. Dundale) were grown in the field for 43 days on a solonized brown soil. Shoots of L. pilosus and peas grew most rapidly, while L. angustifolius cv. 75A-258 developed a relatively large root system. L. angustifolius cv. Yandee, a commercial lupin cultivar, was poorly adapted; shoot growth was restricted and roots ceased growing 36 days after sowing. The soil factors responsible for these widely differing responses were investigated. Once primary roots of L. angustifolius were 20-30 cm deep, root extension was slow or arrested. Indeed, primary root apices of Yandee were often necrotic in the soil below 20 cm. In contrast, roots proliferated rapidly in the surface 20 cm of the soil, particularly in 7SA-258, suggesting that factors in the deeper soil layers restricted root growth most severely. The vigorous growth of lateral roots of 75A-258 was reflected in a 2.6 fold greater total root length than for Yandee 43 days after sowing. Soil physical properties were not considered a likely explanation for these observations; soil water status and porosity were always favourable for root growth and root sections indicated that no cortical degradation, typical of O2 deficient roots, had occurred. Penetrometer resistance and root tip osmotic pressures suggested that poor root growth could not be ascribed simply to soil mechanical properties. The results suggest, by inference, that soil chemical factors could underlie the phenotypic responses observed.

Vegetation Changes as a Result of Invasion of Forest on Krasnozem by Phytophthora cinnamomi

1980 ◽  
Vol 28 (2) ◽  
pp. 139 ◽  
Author(s):  
G Weste
Keyword(s):  
Pinus Radiata ◽  
Phytophthora Cinnamomi ◽  
First Year ◽  
Acacia Dealbata ◽  
Sclerophyll Forest ◽  
Lower Height ◽  
Leaf Spot Fungus ◽  
Future Status ◽  
Reduced Water ◽  
Increased Susceptibility

Disease caused by Phytophthora cinnamomi was studied for 5 years in native and planted forest growing on krasnozem in the northern foothills of the Great Dividing Range at Narbethong, 100 km northwest of Melbourne. Changes in species composition were recorded for three sites carrying mature dry sclerophyll forest of Eucalyptus obliqua and Eucalyptus radiata, young plantations of E. obliqua, and young plantations of Pinus radiata. The mature ecualypts were diseased in 1974 and now are gradually dying. The young E. obliqua showed greater resistance than the older trees to the pathogen but infected trees were characterized by lower height, small leaves with reduced water potential, and an increased susceptibility to the leaf spot fungus Aulographina eucalypti. Susceptible understorey species such as Tetratheca ciliata and Epacris impressa died, but seedling regeneration of these has since occurred on one site. No species has disappeared from all three sites but T. ciliata and Daviesia latifolia almost disappeared from site 2, and the total number of plants was reduced. Species such as Leptospermum juniperinum and Platylobium formosum developed fluctuating cycles of chlorosis and die-back followed by either recovery or death. Resistant plants such as sedges, grasses and Acacia dealbata invaded the diseased forest. During the first year of the investigation 13% of the 4-year-old Pinus radiata died, but this particular site was well drained, warmer and drier than the others and the surviving pines later grew vigorously and crowded out other species. Symptoms are no longer evident on this site. The future status of the mature forest and the probable effects of disease on the young E. obliqua plantation are discussed.

Effect of Hypocotyl Length on Morphogenesis of Explants of Cucumber (Cucumis sativus L.) in vitro

1992 ◽  
Vol 19 (2) ◽  
pp. 165
Author(s):  
RL Gambley ◽  
W Dodd
Keyword(s):  
Cucumis Sativus ◽  
Growth Regulators ◽  
Multiple Shoots ◽  
Root Production ◽  
Concomitant Increase ◽  
Hypocotyl Length ◽  
Rapid Reduction ◽  
Cucumis Sativus L ◽  
Murashige And Skoog Medium

Explants of cucumber seedlings having different lengths of hypocotyl attached were grown axenically on Murashige and Skoog medium supplemented with kinetin (2 mg L-1). Multiple shoots developed from the apical regions of all explants. In this tissue shoots may also develop at the base of the hypocotyl, but this response is strongly dependent upon the length of the hypocotyl. As the length of the hypocotyl increased beyond 5 mm, there was a rapid reduction in basal shoot numbers and a concomitant increase in root production. We suggest that these responses are related not to the ratio or concentration of endogenous growth regulators but to different regions of sensitivity to growth regulators along the hypocotyl.

scholarly journals Modelling time variations of root diameter and elongation rate as related to assimilate supply and demand

2020 ◽  
Vol 71 (12) ◽  
pp. 3524-3534
Author(s):  
Loïc Pagès ◽  
Marie Bernert ◽  
Guillaume Pagès
Keyword(s):  
Root System ◽  
Root Elongation ◽  
Lateral Roots ◽  
Supply And Demand ◽  
Root System Architecture ◽  
Elongation Rate ◽  
Growth Patterns ◽  
Root Tip ◽  
Generic Model ◽  
Maximal Diameter

Abstract In a given root system, individual roots usually exhibit a rather homogeneous tip structure although highly different diameters and growth patterns, and this diversity is of prime importance in the definition of the whole root system architecture and foraging characteristics. In order to represent and predict this diversity, we built a simple and generic model at root tip level combining structural and functional knowledge on root elongation. The tip diameter, reflecting meristem size, is used as a driving variable of elongation. It varies, in response to the fluctuations of photo-assimilate availability, between two limits (minimal and maximal diameter). The elongation rate is assumed to be dependent on the transient value of the diameter. Elongation stops when the tip reaches the minimal diameter. The model could satisfactorily reproduce patterns of root elongation and tip diameter changes observed in various species at different scales. Although continuous, the model could generate divergent root classes as classically observed within populations of lateral roots. This model should help interpret the large plasticity of root elongation patterns which can be obtained in response to different combinations of endogenous and exogenous factors. The parameters could be used in phenotyping the root system.

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