Nonsuberized Roots Research Articles

Rootstocks influence ‘Hass’ avocado fruit quality and fruit minerals

SummaryTo determine the potential for rootstocks to improve avocado quality, ‘Hass’ fruit from trees on seedling ‘Velvick’ (SV), clonal ‘Velvick’ (CV) or clonal ‘Duke 7’ (CD) rootstocks were harvested in 1999 and 2000, ripened at 20°C immediately after harvest (non-stored) or stored at 5°C for four weeks (stored), and then fruit quality and mineral concentrations determined. In 2000, non-stored CV fruit had lower severity of body rots (5% of flesh volume affected, caused mainly by Colletotrichum gloeosporioides) than CD fruit (20%), while body rots severity in stored CV fruit was 20% compared with 38% in stored CD fruit. Stored CV fruit had less severe diffuse discoloration (3% and 9% in 1999 and 2000, respectively) than CD fruit (7% and 20%, respectively). Stored CV fruit also had less severe vascular browning (19%) than CD fruit (33%) in 2000. In both seasons, CV fruit had 15–19% higher flesh calcium concentrations, 17–22% higher flesh boron concentrations, and 14–15% lower flesh nitrogen concentrations than CD fruit. In 2000, CV fruit also had 27% more skin calcium and 14% less skin nitrogen than CD fruit. There were no effects of rootstock on yield, canopy volume, measured length of non-suberized roots, average fruit weight, fruit length: width ratio, skin thickness, dry matter, proportion of the fruit skin purple-black when ripe, or seed mass: fruit weight ratio. These results suggest that there is potential to improve ‘Hass’ avocado quality through rootstock selection, and that tree and fruit mineral concentrations have a role in this relationship.

Cellular interaction between the saprotroph Phlebiopsis gigantea and non-suberized roots of Picea abies

Non-suberized seedling roots of Norway spruce (Picea abies) were challenged in vitro under sterile conditions with oidiospores from the saprotrophic basidiomycete Phlebiopsis gigantea. The root surface supported spore germination and mycelial growth. Samples were taken at defined time intervals for histochemical, SEM and TEM observations. Infective structures developed 24–48 h post inoculation (p.i). Appressoria appeared to be induced by ridges or groove-like structures on the root surface and by similar structures created by mycelial mats. Penetration into epidermal cells occurred 3 d p.i. with cortical and meristematic colonization observed 4–5 d p.i. Browning reactions of the root surface occurred within 5 d p.i. at high spore concentrations but were delayed at lower inoculum concentrations. The inoculum threshold for penetration of epidermal cells and colonization within 5 d p.i. was 104 spores ml−1. Invasion and disruption of root vascular regions were not observed with any inoculum. At the TEM level, tissue colonization was primarily intercellular by cell to cell hyphal development within middle lamellae. The presence of a translucent layer ahead of fungal hyphae during cell wall penetration was probably caused by the action of hydrolytic enzymes secreted by the invading fungi. Host responses were mostly marked by encasing of hyphae within an electron dense layer, formation of reaction zones and retraction of the plasmalemma of cortical cells. However, the majority of inoculated seedling roots examined were not rotted in contrast to spruce roots inoculated with a common pathogenic basidiomycete (Heterobasidion annosum).

GROWTH, ROOT ALTERATION, AND NUTRIENT UPTAKE OF NEEM TREE (Azadirachta indicaA. Juss) SEEDLINGS IN RESPONSE TO VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGI AND PHOSPHORUS NUTRITION

SUMMARY Growth and nutrient uptake of neem tree (Azadirachta indica A. Juss) seedlings were studied in response to vesicular-arbuscular mycorrhizal (VAM) fungi Glomus intraradices Schenck and Smith, and 2 levels of phosphorus (P). Extensive VAM colonization in neem roots occurred at both P levels: 0.65 and 1.30 mM P. Growth of VAM plants at both P levels was similar, while growth of noncolonized (Non-VAM) plants increased with increasing P supply. At the low P level, VAM plants had greater leaf area, shoot, root and leaf dry weight, and a greater root: shoot ratio than Non-VAM plants. Low P, VAM plants had a greater leaf area and root dry weight and a comparable leaf and shoot dry weight and root: shoot ratio, when compared with high P, Non-VAM plants. VAM inoculation also altered dry mass partitioning to root systems resulting in greater root length and dry weight of suberized roots in VAM plants. The length of nonsuberized roots increased with increasing P supply regardless of VAM inoculation. VAM inocu...

Infection and disintegration of vascular tissues of non-suberized roots of spruce byHeterobasidion annosum and use of antibodies for characterizing infection

Vascular disintegration mainly of medulla rays of spruce roots is of major significance in root rot disease of spruce caused byH. annosum. Using seedling roots as an experimental model, the possible routes and initial host reactions preceding invasion of vascular tissues was investigated. Transmission electron microscopy showed that penetration through the endodermis was an obvious route but not without host resistance. Using antibodies againstH. annosum hyphal materials, some labelling of vascular tissues remote from sites of fungal colonization suggest the release of fungal secretory products partly active in tissue disintegration. Similarly, intense labelling was also observed in severely colonized host tissues at late stages of infection. Strong labelling recorded at 3 d p.i. mainly on fungal hyphae and scant gold particles on invaded host tissues could imply that induction of host antifungal metabolites may have been a late event. A correlation was found between total antigenic material in root homogenates measured by ELISA, density of tissue labelling by immunocytochemistry and severity of disease symptoms. The importance of this in relation to diagnosis of biotic root rot diseases in the field is discussed.

Interactions between Norway spruce (Picea abies) and Heterobasidion annosum. I. Infection of nonsuberized and young suberized roots

Nonsuberized and young suberized roots of Norway spruce (Picea abies) were inoculated with an S-strain of Heterobasidion annosum for 2–20 days. The roots were sectioned for light microscopy and transmission electron microscopy. They were susceptible to infection at both stages of development. The host reaction to delimit the infection was the formation of a necrotic ring barrier in the outer cortex. In cases where the inner cortex also became infected, fungal hyphae accumulated just before the endodermis, which acted as a new barrier. Only in nonsuberized roots did the hyphae succeed in penetrating the stele, and within 3 days after inoculation the stele was almost completely digested. Other resistance reactions included accumulation of phenolic deposits, secondary thickening of cell walls, and formation of papillae. The hyphae were able to grow within and across cell walls. The presence of translucent areas around penetrating hyphae possibly reflected the digestive action of fungal enzymes. The hyphae showed signs of degeneration when entrapped in encompassing cellular deposits. Key words: Norway spruce, Heterobasidion annosum, root infection, nonsuberized roots, young suberized roots, microscopy.

435 PB 206 EFFECT OF MYCORRHIZAL FUNGI AND PHOSPHORUS ON GROWTH AND NUTRIENT UPTAKE OF NEEM TREE SEEDLINGS (AZADIRACHTA INDICA A. JUSS)

Growth and nutrient content of neem tree seedlings (Azadirachta indica A. Juss) were studied in response to the mycorrhial fungi Glomus intraradices Schenck & Smith and Long Ashton Nutrient Solution (LANS) modified to supply phosphorus (P) at 0.65 and 1.30 mM P. Three months after inoculation, an extensive mycorrhizal colonization was observed in mycorrhizal plants at both P levels. Shoot growth of mycorrhizal plants was similar at both P levels while the growth of nonmycorrhizal plants increased with increasing P supply. Mycorrhizal plants had greater leaf area, shoot dry weight and root to shoot ratio than nonmycorrhizal plants at the same P level. The length of nonsuberized roots increased with increasing P supply regardless of mycorrhizal colonization while the length of suberized roots was significantly increased by mycorrhiza. Mycorrhiza altered dry mass partitioning to root systems resulting in greater length and dry weight of suberized roots in mycorrhizal plants. Mycorrhiza also improved nitrogen, phosphorus, calcium and sulfur uptake but did not affect micronutrient uptake, except for enhancing boron.

A dynamic simulation of loblolly pine (Pinustaeda L.) seedling establishment based upon carbon and water balances

A generalized simulation model, ROOTSIMU, which utilizes dynamic carbon and water balance algorithms, was modified to simulate loblolly pine (Pinustaeda L.) seedling growth and water uptake for a 100-day transplant period. The modifications included an allowance for time-dependent changes in photosynthesis and carbon allocation. Heat sums were used to control the initiation of growth. Additional compartments were added to separate the physiological functions of suberized and nonsuberized roots and secondary woody tissues. Values used to initialize the model were largely derived from the published literature. The predicted results of a simulation run using 1985 and 1986 weather data are reported. Changes in simulated plant water potential were closely related to periods of rainfall or high evaporative demand. Midday values were occasionally less than −7 MPa when evaporative demand was high. Simulated responses to the 1986 drought indicated that initial soil water potentials at planting affected survival at values of less than −0.064 MPa in a sandy soil. Simulated growth was very sensitive to the photosynthetic rate, less sensitive to initial soluble carbohydrate concentration, and insensitive to instantaneous carbon allocation in relation to drought stress. The predicted increase in total root length for 1985 corresponded to the responses reported in several controlled environmental studies, but these were generally higher than those reported under field conditions. The results suggest that the carbon balance algorithm represents potential root growth within the constraints imposed by the model assumptions. The extreme diurnal fluctuations in plant water potential indicate that one or more important components of the plant system used to regulate short-term drought stress are not represented. Both stem tissue capacitance and the hydraulic conductance of mycorrhizal mycelia at low soil moisture contents may be important in controlling short-term water deficits. Further advances in the application of similar models depend upon an evaluation of these variables and a better theoretical and experimental determination of the effects of the geometry of the transplanted root system.

Dynamics of the Root System of Blue Grama

Highlight: Field experiments were conducted to determine dynamics of the root system of blue grama (Bouteloua gracilis) during the 19 73 growing season at the US/IBP Pawnee Site in northern Colorado. Differentiation and growth of blue grama roots were recorded in field conditions by means of windows in excavations. Roots began to grow and differentiate a short time before leaf growth was apparent. Desiccation of soil in the mid-growing season resulted in death and subsequent decomposition of 30% to 60% of the newly formed roots., Massive root growth occurred when soil water potential was high near the end of the growing season. Roots were separated into morphological categories by microscopic analysis of soil samples on May 15, near the beginning of the growing season, and on August 9, near the end of it. Young nonsuberized roots, so important in water absorption, were concentrated in regions of the soil profile where soil water potential was high. An empirical model of root growth and development in B.

A Model of the Root Biomass Dynamics of a Shortgrass Prairie Dominated by Blue Grama (Bouteloua gracilis)

This paper reports on a compartment model of the root biomass dynamics of a short-grass prairie dominated by blue grama in which fluxes between compartments are time-varying functions controlled by the donor or acceptor compartment. The objectives of the modelling were (i) to synthesize into a conceptual framework the available information on root biomass dynamics, (ii) to detect those processes which are highly sensitive, and (iii) to elicit critical lacunae in our knowledge of the system. The sensitivity analysis of the model indicated that the rate of translocation of carbon from the above-ground carbon pool to the nonsuberized roots, their rate of respiration and death, and the rate of their ageing are crucial in changing the pattern of carbon distribution in the whole system.

Root Pressure Exudation from Apical Root Segments

THE question of why some plants exhibit copious exudation and others show little or none has remained unanswered. Very few comparative investigations of variations in root pressure among species, however, have been carried out. Reports of root pressure exudation have been based on independent observations of a wide range of materials, from cut stumps of large trees1,2 to small root segments raised in sterile culture3. Assumptions about the variable root pressure exudation among species have been based on data obtained using such a wide range of plant materials and techniques. An example is the long held assumption that conifers rarely, if ever, develop root pressure. Yet, when excised apical segments of actively growing conifers roots were observed, exudation was always present4. Similarly, it was observed that fully suberized roots would exhibit significant amounts of exudation when individual roots were studied under controlled conditions4,5. In fact, suberized roots showed higher rates of exudation than non-suberized roots from the same plant. For a study of comparisons of root pressure exudation among species, it seems, therefore, that similar techniques and plant tissues must be used.