Centimeter Of Root Research Articles

Arabidopsis thaliana and Pisum sativum models demonstrate that root colonization is an intrinsic trait of Burkholderia cepacia complex bacteria.

Burkholderia cepacia complex (Bcc) bacteria possess biotechnologically useful properties that contrast with their opportunistic pathogenicity. The rhizosphere fitness of Bcc bacteria is central to their biocontrol and bioremediation activities. However, it is not known whether this differs between species or between environmental and clinical strains. We investigated the ability of 26 Bcc strains representing nine different species to colonize the roots of Arabidopsis thaliana and Pisum sativum (pea). Viable counts, scanning electron microscopy and bioluminescence imaging were used to assess root colonization, with Bcc bacteria achieving mean (±sem) levels of 2.49±0.23×10(6) and 5.16±1.87×10(6) c.f.u. per centimetre of root on the A. thaliana and P. sativum models, respectively. The A. thaliana rhizocompetence model was able to reveal loss of colonization phenotypes in Burkholderia vietnamiensis G4 transposon mutants that had only previously been observed in competition experiments on the P. sativum model. Different Bcc species colonized each plant model at different rates, and no statistical difference in root colonization was observed between isolates of clinical or environmental origin. Loss of the virulence-associated third chromosomal replicon (>1 Mb DNA) did not alter Bcc root colonization on A. thaliana. In summary, Bcc bacteria possess intrinsic root colonization abilities irrespective of their species or source. As Bcc rhizocompetence does not require their third chromosomal replicon, the possibility of using synthetic biology approaches to engineer virulence-attenuated biotechnological strains is tractable.

EVALUATION OF MEXICAN GUAVA GERMPLASM AGAINST ROOT KNOT NEMATODES

Root knot nematodes (Meloidogyne spp.) are one of the main phytosanitary problems of guava orchards in Mexico. At Calvillo, Aguascalientes, almost 90% of the seven-thousand hectares cultivated with guava are infested with nematodes. Although there are chemical and biological strategies to manage this problem, genetic resistance of native guava germplasm under cultivation has never been studied. The purpose of the present study was to determine the degree of susceptibility of a group of guava selections included at the germplasm bank of INIFAP as well as other guava accessions. Air-layering plants of the selections 10, 12, 20, 45, 46, 48, 106, 115, 117, and 118 were obtained, and then placed in pots of 12 kg of capacity. Plants were inoculated with 12 ml J2 plus nematode eggs collected at infested guava orchards of Aguascalientes, Michoacan, and Zacatecas. Results using air-layering plants showed that selections 46, 106, and 45 were more tolerant with 26, 35, and 35% of root damaged, respectively, while the most susceptible was selection 48 with 70% of the roots showing galls. In the group of guava seedlings, four accessions (51, 58, Boyaca, and Brazil) showed the highest gall numbers per centimeter of root, whereas the least affected were selection 42 and a Psidium spp. This study provides evidence that guava genetic resistance to nematodes could be present in the germplasm under study, and could be used as rootstocks or hybridization in future works.

Local and Systemic Effects of NaCl on Root Composition, Rhizobacteria, and Fusarium Crown and Root Rot of Asparagus

ABSTRACT The role of NaCl in suppression of Fusarium crown and root rot of asparagus was investigated in split root culture so the direct effects of NaCl on the root and rhizosphere could be separated from effects that were translocated to the nontreated root side. One side of the root system was exposed to 100 ml of 0, 0.5, or 1.0% NaCl, while the other side received deionized water. Both sides of the root system were inoculated with conidial suspensions of the pathogens Fusarium oxysporum and F. proliferatum. When plants were harvested and assayed, root lesions and CFUs of F. oxysporum or F. proliferatum per centimeter of root from both exposed and nonexposed roots decreased as the NaCl rate increased to 1.0%, but the reduction relative to the control was significantly greater on roots that were directly exposed to NaCl (51% reduction in root lesions) than on adjacent nonexposed roots (31% reduction in root lesions). On both sides of the root systems, disease suppression with NaCl was associated with increases in the rhizosphere densities of fluorescent pseudomonads and Mn-reducing bacteria in the rhizosphere soil. In addition, as the NaCl rate increased, root tissues had marked reductions in malic acid and amino acids while concentrations of Cl and Mn increased in equal proportions on both sides of the root system. Chloride ions were absorbed in greater amounts than Na ions, and were more mobile in the plant than Na. Plants treated with 1% NaCl (171 meq of Cl(-) per liter) had soil leachates 1 week later of 47 meq of Cl(-) per liter from pots exposed to NaCl, but in the adjacent nonexposed pots, the amount of Cl in the leachates slowly increased over the course of the study to 20 meq/liter, presumably through the root exudation. These findings suggest that suppression of Fusarium crown and root rot of asparagus with NaCl may be due to multiple mechanisms. Maximum suppression occurs when NaCl is directly applied to roots, but suppression still occurs on distal non-treated roots resulting from systemic mechanisms. The latter mechanism may be associated with a root-mediated alteration in the rhizobacteria.

Influence of Resistant Tobacco and Tobacco Cyst Nematodes on Root Infection and Secondary Inoculum ofFusarium oxysporumf. sp.nicotianae

The influence of Fusarium wilt-resistant broadleaf tobacco and Globodera tabacum tabacum on infection and secondary inoculum production by Fusarium oxysporum f. sp. nicotianae was investigated under greenhouse and field microplot conditions. Wilt severity and postharvest F. osysporum density in soil was greater for wilt-susceptible than wilt-resistant tobacco in all experiments. G. t. tabacum increased the number of F. oxysporum colonies recovered per centimeter of root for wilt-susceptible but not for resistant tobacco after 8 wk. F. oxysporum levels in soil were greater after plant infection by both F. oxysporum and G. t. tabacum than after plant infection by F. oxysporum alone. Wilt-resistant tobacco supported F. oxysporum densities that were intermediate between susceptible tobacco and fallow and significantly greater than fallow only after more than one season of production, regardless of nematode infection, under both field and greenhouse conditions

Ethylene as a Possible Mediator of Light- and Nitrate-Induced Inhibition of Nodulation of Pisum sativum L. cv Sparkle

Exposure of pea (Pisum sativum L. cv Sparkle) roots to light suppressed nodulation and induced an increase in ethylene production by roots. Dim light did not affect the number of infections per centimeter of root on the primary root, but most infections were blocked when the infection thread was in the epidermis or in the outer cortex. This is the same stage of infection on lateral roots that is blocked by exogenous ethylene. Silver, an inhibitor of ethylene action, increased nodule number on roots exposed to dim light. Exposure of pea roots to nitrate also suppressed nodulation and induced increased ethylene production by roots. However, induction of ethylene production from roots by nitrate was less than that induced by dim light. Nitrate decreased the number of infections per centimeter of lateral root. With 25 mm nitrate, about half of the infections that occurred were blocked in the epidermis or in the outer cortex. Silver did not reverse the inhibitory effects of nitrate on nodulation. Our data indicate that the inhibitory effect of light may occur via increased ethylene production, but they do not support the hypothesis that ethylene mediates nitrate control of nodule number. The possible role of ethylene in regulating nodule number should be studied in experiments in which light is excluded from the roots.

Development of vesicular-arbuscular mycorrhiza in groundnut and other hosts

A vesicular-arbuscular mycorrhizal fungus, identified asGlomus mosseae Gerdemann and Trappe, was found to occur in groundnut and some other hosts. In groundnut roots under experimental conditions, the fungus showed three phases of development-a lag phase of 3–4 weeks by the end of which formation of vesicles was noticed, a phase of gradual development upto 12 weeks, by which time an average of 6 vesicles per centimeter of root developed and a constant phase where there was no further increase of the fungus. Pigeon-pea, black gram, green gram, angular gourd, onion, maize, sorghum and pearl millet also formed mycorrhizae with this fungus, but tomato and egg-plant did not. The lag phase was longer and the average number of vesicles developed per unit root length was less in the non-leguminous hosts.

Corky Root Disease: Population Fluctuations of Xiphinemabakeri Nematodes, and Disease Severity in Forest Nursery Soil Cropped with Different Seedling Species

Buildup and fluctuations of Xiphinemabakeri Williams nematode populations and disease severity were determined in seedbeds of Sitka (Piceasitchensis (Bong.) Carr.), and white (P. glauca (Moench) Voss) spruces and western hemlock (Tsugaheterophylla (Raf.) Sarg.) and Douglas-fir(Pseudotsugamenziesii (Mirb.) Franco). Population levels were the same on spruces and hemlock, and on coastal and interior forms of Douglas-fir. Numbers of total and female nematodes, and gravid females peaked in September, and May to June, respectively, then declined in late winter and early spring. No post-oviposition increase occurred in early developmental stage nematodes and the nematode overwintered primarily as eggs and juveniles. Total and gravid female population peaks correlated positively with higher ambient temperatures, and the September peak in total nematode numbers coincided with new root-growth of Douglas-fir. Soil moisture had no direct effect on nematode populations.Root disease severity of all seedling species was related to numbers of nematodes per seedling root system throughout the first and second growing seasons, but soil nematode populations for previous and current sampling dates were not correlated with current disease severity. A negative correlation was obtained between nematode numbers per cubic centimetre of root and shoot growth of Douglas-fir.

Nitrate Uptake Effectiveness of Four Plant Species

AbstractLittle information is available on the characteristics of plant roots that determine their effectiveness in nitrate uptake. The effectiveness of nitrate uptake of corn (Zea mays L.), soybeans (Glycine max L.), sorghum (Sorghum bicolor L.), and bromegrass (Bromus inermus L.) intact roots were investigated in nutrient solution culture. The maximum uptake rate per centimeter of root for corn occurred at 10 mM, for sorghum at 2.4 mM, and for bromegrass at 0.8 mM. Increasing the nitrate level above 1.0 mM did not increase the growth rate during the first 3 weeks for any of these species.The minimum level to which the plant roots reduced the nitrate concentration was 1.7, 2.7, 2.4, and 1.4 µM for forage sorghum, grain sorghum, soybeans, and bromegrass, respectively. Three cultivars of corn were compared. Two reduced the nitrate level to 2 µM and the third to 4 µM.The results of this research indicate that the roots of the species investigated absorbed nitrate of maximum rates from relatively low nitrate concentrations provided the concentration was maintained. Also, the degree of reduction in nitrate level where nitrate in solution was not maintained indicated that these plant roots had the absorptive capacity to reduce solution nitrate to concentrations of 4 µM or less.

Rooting Density and Water Extraction Patterns for Corn (Zea mays L.)1

AbstractBecause they occur at greater distances from the plant stem, roots deep within the profile often are considered less effective than those near the soil surface.An experiment was conducted to compare water‐absorbing efficiency, per centimeter of root, of corn (Zea mays L.) roots deep in the profile with that of roots near the soil surface. Plants were grown in a rhizotron compartment with rainfall excluded by a metal cover over the soil. Soil water content was determined with a neutron probe; rooting density, from measurements of roots on the glass viewing surface of the compartment. Leaf area was calculated by a length‐width method and plant height was measured daily. Stomatal aperture was estimated with a pressure drop promoter twice daily.With few exceptions, soil water content decreased and rooting density increased during the experiment. For the first weeks, transpiration exceeded pan evaporation, but toward the end of the experiment it was about half as much as pan evaporation. Water uptake per centimeter of root was affected most by soil hydraulic, conductivity, and at a given conductivity, it was greater at lower root densities. This effect of root density probably occurred because the roots were younger and more permeable at low root densities than at high root densities. Thus, for the conditions of these experiments, roots deep in the profile were probably more effective per centimeter of root for water uptake than shallow roots because they were younger and were in wetter soil.