Root Contact Research Articles

Spread and effects of Armillaria luteobubalina sp. nov. in an Australian Eucalyptus regnans plantation

Trees up to 25 m tall died suddenly at the edges of a steadily extending patch of dead and dying trees in a fast-growing plantation of Eucalyptus regnans F. Muell. near Traralgon, Victoria. Measurements of tree height and stem diameter made during the 12 years since the plantation was established indicate that, prior to their death, trees at the margins of the extending patch grew as rapidly as unaffected neighbours. During May 1973 and May 1974, Armillaria luteobubalina Watling & Kile sp.nov. fruited prolifically on dead and infected trees. Few rhizomorphs have been found so that spread of infection seems to have been mainly by mycelial growth within root systems and at root contacts. Infection has spread from inoculum in a single stump of Acacia melanoxylon R. Br. at an average annual rate of 2.5 m. Untreated stumps of healthy 10-year-old trees felled in unaffected parts of the plantation during the fruiting season of 1973 have not become infected. In pathogenicity tests with an isolate from the cap of a fruiting body, E. regnans seedlings have suddenly wilted and died following penetration of the tap root-root collar zone and subsequent girdling of the stem. It is concluded that the deaths at Traralgon are due to primary attack by A. luteobubalina .

VESICULAR‐ARBUSCULAR MYCORRHIZA IN NATURAL VEGETATION SYSTEMS

SummaryThe intensity of vesicular‐arbuscular mycorrhizal infection was assessed in the major vegetation types of east‐central England. All of the most important species of grassland, scrub and woodland were mycorrhizal and each individual of any species normally carried a heavy VA infection. Members of the Gramineae were particularly heavily infected. In limestone grassland, infection extended to members of the Cyperaceae and Juncaceae. Infection levels were high throughout the year, the highest levels occurring in the most nutrient‐stressed situations.Mycorrhiza develops soon after germination, often while seedlings are still in the cotyledon stage. Since numbers of viable Glomus type spores are low, infection is thought to arise from root to root contact rather than from spores. The Ecological implications of the widespread infection are discussed.

HOE 23408, A NEW SELECTIVE HERBICIDE FOR WILD OATS AND GREEN FOXTAIL IN WHEAT AND BARLEY

A series of field, growth chamber, and laboratory experiments showed that HOE 23408 [4-(2,4-dichlorophenoxy)-phenoxy propionic acid methyl ester] as a post-emergence herbicide provided selective control of wild oats (Avena fatua L.) and green foxtail (Seteria viridis L. Beauv.) in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) equal to or better than barban (4-chloro-2-butynyl m-chlorocarbanilate) over a growth period extending from the 2- to 5-leaf stages in both weed species. Wheat was highly tolerant to HOE 23408 at all growth stages, while with barley there was some leaf mottling and suppression of both shoot and root development. The 6-row cultivars Gait, Bonanza and Conquest largely recovered from the effects, but the 2-row cultivar Betzes suffered significant yield reduction. HOE 23408 moved mainly in an acropetal direction when applied to different parts of the wild oats plant. Application made on or below the meristematic area of the stem apex caused necrosis and eventual death of the entire plant. Phytotoxicity following soil application was markedly less than with foliar application. Indications were that it was also more phytotoxic to the emerging weeds via shoot than via root contact. Although HOE 23408 is relatively insoluble in water, it leached to a limited extent in soils.

Growth characteristics of Phellinus (Poria) weirii in soil and on root and other surfaces

Growth of Phellinus (Poria) weirii (Murr.) Gilbertson from alder block inoculum into the surrounding soil to infect healthy roots was less than 10 cm. Tree-to-tree spread of this root rot fungus, beyond that which would occur as a result of root contact, may be facilitated by growth of the mycelium over roots of minor vegetation and over wood buried in soil. Ectotrophic mycelium is profuse on the bark of infected roots of Douglas fir (Pseudotsugamenziesii (Mirb.) Franco) and western hemlock (Tsugaheterophylla (Raf.) Sarg.), limited on infected roots of pine (Pinusmonticola Dougl., P. contorta Dougl, P. ponderosa Laws.), and nearly absent on infected roots of western red cedar (Thujaplicata Donn). Rate of spread of P. weirii root rot through stands with a high component of western red cedar or pine, or both, should be considerably slower than in pure stands of Douglas fir.

Roots and water - Transport of water to plant roots in soil

The theory of water uptake by a single root is reviewed, including infinite and finite systems, and constant and variable diffusivity. This theory predicts the water potential and content at the root surface will depend upon soil and root parameters, most of which are readily determinable, but the uptake rate of water per unit length of root is uncertain. Uptake rates averaged over whole root systems will usually be small, suggesting only very small gradients of water content around roots, but it is likely that local rates may, on occasion, be much larger than the averages, and the possibility of large gradients cannot then be dismissed. Certain special effects may alter these conclusions, particularly salt accumulation around roots and no contact or partial contact of roots with soil. Both demand a fast uptake rate of water before they become important, and salt accumulation is unlikely to be important except in saline soils. Methods of dealing with whole root systems are briefly considered. Differing root density can be dealt with by subdividing the root volume into compartments, or by regarding the problem as one of dispersion pattern. Further advance requires better information about local boundary conditions imposed by roots on the surrounding soil.

Ganoderma philippii . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Ganoderma philippii . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Recorded from a wide range of phanerogams. Cause of lethal root disease ('root rot') of rubber, tea, coffee, cacao and cinchona; being particularly important on the first two crops. DISEASE: Red root rot, causing the death of the host, accompanied by rhizomorphic encrustation of the roots described above. This is accompanied by a decay of the roots which, in its early stages, is pale brown and firm and becomes pale buff, water-soaked and spongy later on. The distribution of the disease in plantation is typically patchy. In a similar African disease, sometimes attributed to G. philippii (= G. pseudaferreum ), the advancing rhimomorphs are separate for 2-3 feet before forming the root sheath (R.A. Fox, pers. comm.). GEOGRAPHICAL DISTRIBUTION: South East Asia, from Burma through Malaysia and Vietnam in the north; Sri Lanka, Southern India through Indonesia to Papua New Guinea in the south (CMI Distribution Map No. 98, ed. 2. 1965: records in Africa are based on vegetative characters only and not confirmed by corresponding sporophore collections). TRANSMISSION: By root contact with neighbouring infected trees or with infected woody material in the soil. Where sporophores are formed, spread by air-borne basidiospores is possible, although attempts to infect stumps with these have been unsuccessful (49, 1467).

Polyporus baudonii . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Polyporus baudonii . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Celtis rhomnifolia, Cassia siamea, Eucalyptus spp., Gmelina arborea, Pinus spp. DISEASE: Death of host and decay of roots and crown. Pale brown rot. GEOGRAPHICAL DISTRIBUTION: Africa (Angola, Congo, Ghana, Ivory Coast, Kenya, Malagasy, Mozambique, Republic of South Africa, Tanzania, Upper Volta, Zaire). TRANSMISSION: Through soil by root contact; by air-borue spores.

Ganoderma zonatum . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Ganoderma zonatum . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Elaeis guineensis, Cocos nucifera, Borassus aethiopum ; has been recorded on Sebal palmetto in Northern America. On Dicots it has only been recorded for Eucalyptus but it can develop on dead wood. DISEASE: Like G. boninense causes a base rot on palms in Africa. GEOGRAPHICAL DISTRIBUTION: Throughout tropical Africa on palms. In America it is recorded from Florida, but is probably distributed in South America. No specimen, however, has been available from there. TRANSMISSION: As no rhizomorphs have so far been detected and, moreover, considering that spore production is abundant the latter appear to be the only means of transmission with the leaf stalk bases as the port of entry into the base of the trees. The possibility of transmission by root contact with infected residues in the soil or diseased plants cannot be excluded.

Ganoderma tornatum . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Ganoderma tornatum . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: pleurivorous DISEASE: Heart and butt rot. GEOGRAPHICAL DISTRIBUTON Occurs throughout the tropics, to the extreme tip of South Africa and to the shores of the Pacific Ocean in Canada. The area of distribution overlaps that of G. applanatum in the north west of India and Pakistan (CMI Descript. 443) but does not extend north of the Sahara in Africa. It is not found in southern Europe. Its distribution in South America is still uncertain as few specimens have been available from that continent. In the Pacific it extends from the Philippines to New Caledonia and Papua. This appears to be the commonest species of Ganoderma in the tropics, with G. chalcrum (Cooke) Stey. coming second. TRANSMISSION: No rhizomorphs have been observed in relation to G. tornatum . Thus, the only likely means of transmission is by air-borne spores or root contact with infected plant material in the soil.

Ganoderma boninense . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Ganoderma boninense . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Mainly palms: Elaeis guineensis, Cocos nucifera, Livistona subglobosa, Casuarina torulosa, Areca spp., and Albizia spp. DISEASE: Very frequent on palm trees. Cause of basal rot of the stipe of Elaeis guineensis and Cocos nucifera . GEOGRAPHICAL DISTRIBUTION: From Sri Lanka in the west through Malaysia and Indonesia to the Philippines and the Japanese Island of Kyushyu and Bonin in the north east, Samoa to the east, through eastern Australia to Tasmania in the south east. Apparently widespread throughout the Indonesian and Pacific Islands and at least the eastern states of Australia. TRANSMISSION: Either by air-borne basidiospores or root contact with infected debris in the soil (Turner, 1965).

Ganoderma applanatum . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Ganoderma applanatum . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: A very wide range of broad-leaved and coniferous trees. As much confusion has arisen between G. applanatum and G. adspersum earlier references must be accepted only with care as to the hosts. It is the authors observation that G. applanatum is more frequent in the woodland biotype than in orchards, garden and roadside plantations while G. adspersum seems to be more frequent in the latter. GEOGRAPHICAL DISTRIBUTION: Throughout the northern hemisphere temperate zone. The northern limit follows the tree line. The southern limit is Florida in the USA, the Mediterranean sea in Europe, Northern Iran, Northern Pakistan, southern slopes of the Himalayas, but a specimen has been obtained from Bombay in India. In Pakistan and India it overlaps slightly with the range of G. tornatum (CMI Descript. 447). TRANSMISSION: Transmission is probably confined to air-borne spores and root contact with infected plant material in the soil.

Armillariella mellea . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Armillariella mellea [Armillaria mellea] . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: The fungus has been recorded as a pathogen on an extremely wide range of dicotyledonous and coniferous trees and shrubs (Raabe, 1962; Browne, 1968). It has also been found on potato (1: 357), narcissus (11: 376), strawberry (8: 727), bamboo (40: 436), geranium (12: 5227), sugarcane and banana (25: 355), but attack of monocotyledons and herbaceous plants is rare. DISEASE: Armillaria root rot. Armillaria root disease. Honey fungus. Armillariella mellea has two roles as a plant pathogen. It may act as a lethal pathogen by invading and destroying the cambium of the root and lower stem, following which it may colonize and rot the woody tissues of the host after its death, or it may cause a butt rot without attacking the living tissues of the host. Both types of disease have a patchy distribution in the field, characteristically spreading from inoculum centres in the soil, so that the hosts which have been most recently attacked are found at the edge of the patch. Where lethal attack occurs the host dies rapidly and (in the case of conifers and certain dicotyledonous trees) the bark of the roots and stem base is cracked and covered with gum or resin exudate. Thick, creamy-white, fan-like sheets of mycelium are found under the bark and these are frequently accompanied by flattened, dark brown rhizomorphs ( forma subcorticalis ). These rhizomorphs may also be epiphytic on roots and grow out into the soil, where their form is more cylindrical ( forma subterranea ). Sporophores may be formed on the host in advanced stages of the disease. The butt rot is a typical soft white rot with pronounced black zone lines. It seldom advances more than 1-2 m up the stem. The rotten wood is often luminous. Armillariella mellea also forms balanced mycorrhizal associations with the orchids Galeola septentrionalis and Gastrodia elata . GEOGRAPHICAL DISTRIBUTION: World wide, throughout forests of the temperate and tropic regions (CMI Map 143, ed. 3, 1969). TRANSMISSION: By infection of woody debris and stumps by air-borne basidiospores, by the growth of rhizomorphs through the soil, by root contact with infected soil debris and transport of infected plant material.

Inonotus weirii . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Inonotus weirii . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Abies amabilis, A. grandis, A. lasiocarpa, Chamaecyparis spp., Larix occidentalis, Picea engelmannii, P . sitchensis, Pinus contorta, P. monticola, P. ponderosa, Pseudotsuga menziesii, Thuja plicata, Tsuga heterophylla . DISEASE: Laminated butt rot and yellow ring rot of conifers. GEOGRAPHICAL DISTRIBUTION: North America (Western Canada, Oregon, Washington); Japan. TRANSMISSION: The disease is spread by root contact with infected material in the soil; there appears to be little spread of the fungus by growth through the soil. It is likely that infection of freshly exposed wounds takes place through airborne basidiospores.

Ustulina deusta . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Ustulina deusta . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On stumps, butts and dead roots of many genera of trees and shrubs. Particularly common on Fagus sylvatica in Europe. Host genera of economic importance include Camellia, Citrus, Cocos, Coffea, Elaeis, Hevea, Nicotiana and Theabroma . Wilkins (1934) provides a host index. DISEASES: Cause of 'charcoal base rot' of Elaeis and Hevea ; 'charcoal stump rot' and root disease of Camellia ; 'collar rot' of Hevea ; butt rott of Fagus ; 'white rot' of Tilia ; etc. In Elaeis the base is affected by a hard dry rot resulting in the progressive death of the fronds leading to death (Turner, 1971). Attacks the cell walls of tracheids so that infected wood is permeated with conspicuous black lines. Reported as responsible for the death of young Tectona grandis in Tanzania (42: 224). Usually now regarded as of little economic importance but often serious locally. The pathogenic tendencies are less pronounced in temperate than subtropical and tropical regions. GEOGRAPHICAL DISTRIBUTION: Cosmopolitan (CMI Map 417, ed. 1, 1966). In every country fide Miller (1961). TRANSMISSION: In temperate regions wind-borne conidia are probably the most important cause of infection (Wilkins, 1938, 1939) and enter through wounds, including areas which have been scorched, and pruned branches (41: 479). Infection may also arise from ascospores and through the contact of lateral roots (Fetch, 1928), and nearby infected trees and shrubs of other genera (Fetch, 1923).

Regulation of Sulfate Uptake by Excised Barley Roots in the Presence of Selenate

Active transport of SO(4) (2-) and SeO(4) (2-) has been evaluated during 60-hour contact of barley roots with nutrient solutions containing either (35)SO(4) (2-) or (75)SeO(4) (2-), or both ions, at 0.1 milli-equivalent per liter. In the SO(4) (2-) solution the time course of active transport follows a straight line; if SeO(4) (2-) is also present transport is strongly inhibited after 20 to 30 hours for both ions. The S-Se uptake ratio remains 1.4 during the 60 hours; S-Se ratio shifts from 3.0 to 3.3 in proteins and falls to 0.6 in free amino acids. S-Se discrimination is mainly operating at the level of amino acid incorporation into proteins. The presence of Se-amino acids blocks this incorporation and brings about an accumulation of free amino acids; at the same time carrier activity is inhibited. The addition of methionine or Se-methionine causes a 60 to 80% inhibition of the active transport.

Establishment and spread of Polyporus tomentosus in pine and spruce plantations in Wisconsin

Polyporus tomentosus Fr. was found in the roots of stumps in a thinned red pine plantation and in roots of living and dead trees in established root rot pockets in a white spruce plantation. Infection apparently originated in the root collar or in declining roots of stumps or weakened trees. Direct stump top invasion was not evident. Localized spread of the fungus occurred through root contacts or grafts. Presence and approximate margins of root rot pockets in a white spruce plantation were indicated by sporophores. In 13 permanent plots embracing root rot pockets observed during a 4-year period, the reduction in number of living dominant trees was 2.1%, codominants 2.4%, intermediates 15.4%, and suppressed trees 48.5%. In control plots only the number of suppressed trees decreased by 29.3%. Of the remaining living dominant and codominant trees within the disease plots 26.8% probably were infected. Expansion of 10 of the infection pockets was measured showing an increase in area of 58.3%. During the 4-year period 18 new infection centers appeared in the stand.

Infection of Tobacco Plant with Cucumber Mosaic Virus through Roots

When the roots of young tobacco seedlings raised in soil or in culture solution were inoculated with extracted juice of tobacco leaves infected with cucumber mosaic virus ordinary strain (CMV-O), 25-100 percent of seedlings showed systemic symptoms within 7-40 days after inoculation, while with CMV yellow strain (CMV-Y) about 5-20 percent of inoculated plants showed systemic symptoms. The rate of plants which showed systemic symptoms was lower than in the case of inoculation on leaves. The period required for the appearance of systemic symptoms was also longer. The difference in the rate of appearance of systemic symptoms between CMV-O and CMV-Y might be due partly to seasonal variation in susceptibility of tobacco roots and partly to the difference in the virus strains. Multiplication of CMV in the inoculated roots showed a similar pattern as in the roots of plants inoculated on leaves.Tobacco seedlings were raised in the pots (diameter 12cm) with soil, two plants per pot, and the leaves of one of the plants were inoculated with CMV-O. The other plant was covered with polyethylene bag to avoid infection by leaf contact. From more than 50 percent of root samples from uninoculated and appearently healthy tobacco plants, CMV was recovered within 31 days after inoculation on the donor host. In an experiment using tobacco plants grown in wooden-frame, and inoculated with CMV-Y, a similar result was obtained. In a test of field grown tobacco plants, growing in the vicinity of CMV infected plants, CMV was recovered from the roots of 5 plants out of 7 plants tested, even though the tested plants were showing no symptoms and no virus was detected from the leaves. The transmission of the virus may have been caused by root contact, because transmission occured more frequently in abundantly rooted plants than in poorly rooted ones, and no virus was detected from root-samples collected from root parts on the other side of neighbouring infected plant.Contact transmission has been thought to be negligible in the case of comparatively labile viruses such as CMV. From the results reported here, however, transmission by root contact may not be neglected in natural occurrences of CMV in tobaccoo plants.

Verticillium tricorpus . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Verticillium tricorpus . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Lycopersicon esculentum . Also reported on Antirrhinum . DISEASE: Wilt of tomato. GEOGRAPHICAL DISTRIBUTION: Britain, especially in the south; India TRANSMISSION: Little appreciable spread by root contact between infected plants (Isaac, 1953).

Modes of Infection and Spread of Fomes Annosus

The root and butt rot caused by Fomes annosus is one of the most eco­ nomically important diseases of conifers in the north temperate zone of the world. Sinclair (112) lists almost 150 species of trees, including some an­ giosperms, on which F. annosus has been reported. Species of Abies, Juni­ perus, Larix, Picea, Pinus, Pseudotsuga, and Tsuga are the major hosts. On most species of Pinus and Juniperus, F. annosus causes primarily a root rot and kills trees within several months to years after infection. The major exception is Pinus strobus, which is subject to typical butt rot as well as root rot, and trees usually remain alive for several years after infection un­ less windthrown. Spruces, true firs, larches, hemlocks, and Douglas fir may be killed by F. annosus when young, but later are primarily damaged by butt rot which may extend for several meters up the stem. Koenigs' (59) bibliography lists 438 references on F. annosus. Since then, more than 300 additional papers have been published. This review will not attempt to evaluate all aspects of the F. annosus problem. Instead, at­ tention will be focused only on the aspects of spread and infection which are important in devising controls for this disease. Regardless of host and type of disease produced, spread of F. a nnosus is accomplished in two major ways: (a) by spores, and (b) by growth of my­ celium across contacts between healthy and infected roots. Spores are re­ sponsible for initiation of new infection centers in previously uninfected stands whereas growth of mycelium at points of root contacts or grafts re­ sults in the enlargement of established infection centers. Factors relating to these two types of spread will be discussed separately.

Survival of Fomes annosus in Infected Roots in Soil

VARIOUS species of Fomes are known to cause considerable root damage to a variety of perennial crops including rubber and several conifer species. In most cases it has been shown that infected root tissue forms a significant source of inoculum for the infection of newly planted crops. Rishbeth1 has given detailed descriptions of the field symptoms caused by Fomes annosus in the Breckland conifer plantations of East Anglia, pointing out that the disease usually appears in patches. By exposing root systems at different stages in the development of the disease, Rishbeth found that lateral spread within such a patch is primarily due to root contact, and that Fomes annosus has only a limited competitive saprophytic ability. The disease does, however, sometimes appear in areas not previously planted with conifers, and Rishbeth2 later established that stump infections are of the greatest significance to the initiation of such new centres of infection.