Extent Of Root Colonization Research Articles

Response of soybean and tomato plants under dual inoculation with Glomus sp. and root-knot nematode Meloidogyne incognita

The arbuscular mycorrhiza fungus Glomus can increase plant’s water and nutrient uptake and provide protection against plant parasitic nematodes. This study aimed to determine the response of soybean and tomato plants under inoculation with Glomus sp. and root-knot nematode Meloidogyne incognita at different application times in pot experiments. On soybean, Glomus sp. alone or in combination with M. incognita significantly increased plant height, while simultaneous inoculation of both microorganisms significantly increased the root dry weight. The total leaf P content of soybean however, significantly decreased in response to all inoculation methods. On tomato plants, Glomus alone significantly increased tomato shoot dry weight, total plant dry weight, and the total leaf P content. The final nematode population, the number of nematodes penetrating the root, and the root gall scores were not significantly impacted by either Glomus or M. incognita inoculation The inconsistent effect of Glomus inoculation on plant growth and total leaf P content as well as the inability of Glomus to reduce M. incognita infestation may be contributed by the extent of root colonization by Glomus and variability in the species of Glomus.

VBA-AMF: A VBA Program Based on the Magnified Intersections Method for Quantitative Recording of Root Colonization by Arbuscular Mycorrhizal Fungi.

The extent of mycorrhizal fungi colonization is an important factor for determining the function of mycorrhizal fungi in fungi-host interaction, and quantifying the extent of mycorrhizal fungi colonization is a fundamental and essential task for researchers engaged in mycorrhizal studies. Intersect methods, such as the gridline intersect and magnified intersections methods, are accurate and objective, and are widely used to assess the colonization status of arbuscular mycorrhizal (AM) fungus. However, no convenient procedures or add-ins for Excel spreadsheets have been developed to simplify these methods. Here, we propose a procedure using the Visual Basic for Application (VBA) program in Excel that is based on the magnified intersections method, which we refer to as VBA-AMF (arbuscular mycorrhizal fungi). Time-saving and convenience are the two most prominent advantages of the VBA-AMF procedure, as it enables researchers to compute the colonization rate of AM fungi in roots, and consequently the extent of root colonization by AM fungi. VBA-AMF can also be modified to measure the status of other fungal colonizations in plant roots following the same strategy.

Evaluation of AMF formulations on growth, root colonization and biophysical parameters of maize (Zea mays L.)

Mycorrhizal formulations are becoming increasingly popular in many countries and for many crops, but less studies on their effect on plant parameter and mycorrhizal studies. There for we have evaluated different AMF formulations under green house studies. In this study soil samples from the UAS, Dharwad experimental plots were collected, sterilized and used in a pot experiment. The maize Hybrid (GPMH-1101) was grown in the pots upto 45 days. The plant dry weight, root length, bio physical parameters, P concentrations in plant tissues was measured and the extent of root colonization by arbuscular mycorrhizal fungi (AMF) was determined. AMF formulations have shown significant influence on the growth and biophysical parameters of plants that could be related to differences in the infective propagules in formulations. The inoculum potential and efficacy of the AMF formulations can promote P uptake and benefit plant growth.

Physiological Responses of Basil (Ocimum Basilicum L.) Cultivars to Rhizophagus Irregularis Inoculation under Low Phosphorus Availability.

Arbuscular mycorrhizas (AM) can improve phosphorus (P) nutrition and could serve as an environmentally friendly approach for sustainable crop production under P-limiting conditions. The objectives of this study were to assess the effect of AM on different physiological traits and to quantify the responsiveness of different basil (Ocimum basilicum L.) cultivars to AM under low P availability. The basil cultivars ‘Genovese’, ‘Sweet Basil’, ‘Dark Opal’, and ‘Erevanskii’ were inoculated (AMI) using Rhizophagus irregularis. Photochemical efficiency and gas exchange were measured on AMI and non-inoculated (AMC) plants and, at harvest, the shoot biomass, shoot P concentration, root morphological traits, frequency of mycorrhizas in the roots (F%), and extent of root colonization (M%) were determined. Significant differences in F% and M% were found among the examined cultivars, with the highest found in ‘Dark Opal‘ and the lowest in ‘Erevanskii‘. AMI reduced the shoot biomass and increased the shoot P concentration as well as other examined root traits in ‘Genovese’ and ‘Erevanskii’, whereas it did not affect those traits in ‘Dark Opal’ and ‘Sweet Basil’, indicating differences in responsiveness to AM. AMI positively affected the gas-exchange parameters in all examined cultivars, probably due to the increased sink capacity of a bigger root system and/or AM structures within the roots.

Effects of a Companion Plant on the Formation of Mycorrhizal Propagules in Artemisia tridentata Seedlings

Inoculation of seedlings with arbuscular mycorrhizal fungi (AMF) can increase their establishment after outplanting. The success of this practice depends partly on the extent of root colonization and abundance of AMF propagules in the outplanted seedlings. We conducted a greenhouse experiment to investigate the effects of a companion plant, the native grass Poa secunda J Presl (Sandberg bluegrass), on the formation of spores and vesicles, AMF colonization, and AMF taxa present in the roots of the shrub Artemisia tridentata Nutt (big sagebrush). These effects were tested at two phosphorus (P) fertilization levels, 5 μM and 250 μM. Neither coplanting nor differences in P had an effect on spore density in the potting mix. In contrast, coplanting increased vesicular colonization of A. tridentata from 5% to 18%, but only at low P. Differences in P also affected vesicular colonization of P. secunda, which was 10% and 30% at high and low P, respectively. Arbuscular colonization of A. tridentata was not affected by the treatments and ranged between 12% and 20%. In P. secunda, arbuscular colonization was lower but increased from high to low P. Coplanted seedlings exposed to low P also had the highest levels of total AMF colonization, 70% for A. tridentata and 63% for P. secunda. On the basis of partial sequences of the 28S ribosomal RNA gene, coplanting did not affect the AMF taxa, which were within the Glomeraceae. In some taxa within this family, root fragments containing vesicles are the main propagules. Particularly in this situation, increases in vesicle density caused by coplanting and low P are likely to facilitate mycorrhization of A. tridentata after outplanting, resulting in higher levels of colonization than those naturally occurring in the soil. Such outcomes are critical for assessing the extent to which A. tridentata establishment is limited by insufficient AMF colonization.

Beneficial effect of arbuscular mycorrhizal fungus, Glomus fasciculatum on plant growth and nutrient uptake in tomato

In the present study arbuscular mycorrhizal fungus (AMF), Glomus fasciculatum was used as bio-inoculant in three different cultivars viz., PKM-1, Gaurav and Monarch of tomato to assess the efficacy of AMF on the extent of root colonization, plant growth parameters and plant N, P, K status in pot experiments under greenhouse conditions. The three tomato cultivars showed positive response to AM fungal inoculation. The per cent AM fungal root colonization ranged from 26.4 to 36.0% in 30 days and 40.2 to 47.0% in 60 days old plants. Per cent root colonization was maximum (47.0%) in PKM-1 and minimum 40.2% in cultivar Monarch. Glomus fasciculatum treated plants resulted in significant increase in plant height, shoot and root fresh and their dry weights over control plants recording maximum in Monarch cultivar. The shoot and root dry weights in 30 days crop of AM inoculated plants in Monarch cultivar increased to more than four and threefolds, respectively over control. In 60 days crop the shoot dry weights of AM inoculated plants were increased to 56.04% and root dry weight to 125.32% over control. Plant N, P and K content was significantly increased in G. fasciculatum inoculated plants indicating that these three elements were efficiently transported in mycorrhizal plants. Biomass, and dry matter production was maximum in cultivar Gaurav. N and K content of AM inoculated PKM-1 plants was increased to 132.54 and 26.38% respectively over control. However, P was recorded maximum in cultivar Monarch that increased to 114.68% over control. The results of our experiment proved G. fasciculatum as a biofertilizer in three cultivars of tomato.

Inoculation of Pinus pinea seedlings with Pisolithus tinctorius and Suillus bellinii promotes plant growth in benfluralin contaminated soil

In order to develop new strategies aiming at reconverting agriculture-managed soils into forest plantations, pesticides effect on plant growth needs to be further understood. Thus, the development of Pinus pinea seedlings on soil spiked with benfluralin mimicking different application rates was evaluated, as a well as its effect on root colonisation with Pisolithus tinctorius and Suillus bellinii. P. pinea development and ectomycorrhiza colonization on soil spiked with benfluralin were assessed after 6 month growth. P. pinea seedlings inoculated with P. tinctorius showed higher plant growth and increased nutrient levels than seedlings inoculated with S. bellinii. At field application rate, benfluralin had an inhibitory effect on growth of non inoculated plants. Inoculation with P. tinctorius promoted plant development and nutrient uptake whereas inoculation with S. bellinii did not seem to confer plant protection against the toxic. Although P. tinctorius and S. bellinii were able to form ectomycorrhizae in the presence of benfluralin, the extent of root colonisation was affected by the herbicide. P. tinctorius conferred protection to P. pinea against benfluralin toxicity, overcoming the effect of the herbicide on P. pinea growth and nutrient uptake. This approach can be advantageous for plant establishment on pesticide contaminated soils.

Increasing phosphorus supply is not the mechanism by which arbuscular mycorrhiza increase attractiveness of bean (Vicia faba) to aphids.

Arbuscular mycorrhizal (AM) fungi, important plant mutualists, provide plants with nutrients such as phosphorus (P) in return for carbon. AM fungi also enhance the attractiveness of plants to aphids via effects on emissions of plant volatiles used in aphid host location. We tested whether increased P uptake by plants is the mechanism through which AM fungi alter the volatile profile of plants and aphid behavioural responses by manipulating the availability of P and AM fungi to broad beans (Vicia faba L.) in a multi-factorial design. If AM fungi affect plant volatiles only via increased P acquisition, we predicted that the emission of volatiles and the attractiveness of mycorrhizal beans to aphids would be similar to those of non-mycorrhizal beans supplied with additional P. AM fungi and P addition increased leaf P concentrations by 40 and 24%, respectively. The production of naphthalene was less in mycorrhizal plants, regardless of P addition. By contrast, production of (S)-linalool, (E)-caryophyllene and (R)-germacrene D was less in plants colonized by AM fungi but only in the absence of P additions. The attractiveness of plants to pea aphids (Acyrthosiphon pisum Harris) was positively affected by AM fungi and correlated with the extent of root colonization; however, attractiveness was neither affected by P treatment nor correlated with leaf P concentration. These findings suggest that increased P uptake is not the main mechanism by which mycorrhiza increase the attractiveness of plants to aphids. Instead, the mechanism is likely to operate via AM fungi-induced plant systemic signalling.

Arbuscular mycorrhizal symbiosis alters stomatal conductance of host plants more under drought than under amply watered conditions: a meta-analysis.

Stomata regulate rates of carbon assimilation and water loss. Arbuscular mycorrhizal (AM) symbioses often modify stomatal behavior and therefore play pivotal roles in plant productivity. The size of the AM effect on stomatal conductance to water vapor (g s ) has varied widely, has not always been apparent, and is unpredictable. We conducted a meta-analysis of 460 studies to determine the size of the AM effect under ample watering and drought and to examine how experimental conditions have influenced the AM effect. Across all host and symbiont combinations under all soil moisture conditions, AM plants have shown 24 % higher g s than nonmycorrhizal (NM) controls. The promotion of g s has been over twice as great during moderate drought than under amply watered conditions. The AM influence on g s has been even more pronounced under severe drought, with over four times the promotion observed with ample water. Members of the Claroideoglomeraceae, Glomeraceae, and other AM families stimulated g s by about the same average amount. Colonization by native AM fungi has produced the largest promotion. Among single-AM symbionts, Glomus deserticola, Claroideoglomus etunicatum, and Funneliformis mosseae have had the largest average effects on g s across studies. Dicotyledonous hosts, especially legumes, have been slightly more responsive to AM symbiosis than monocotyledonous hosts, and C3 plants have shown over twice the AM-induced promotion of C4 plants. The extent of root colonization is important, with heavily colonized plants showing ×10 the g s promotion of lightly colonized plants. AM promotion of g s has been larger in growth chambers and in the field than in greenhouse studies, almost ×3 as large when plants were grown under high light than low light, and ×2.5 as large in purely mineral soils than in soils having an organic component. When AM plants have been compared with NM controls given NM pot culture, they have shown only half the promotion of g s as NM plants not given anything at inoculation to control for associated soil organisms. The AM effect has been much greater when AM plants were larger or had more phosphorus than NM controls. These findings should assist in further investigations of predictions and mechanisms of the AM influence on host g s .

Mycorrhization, establishment and growth of outplanted Picea abies seedlings produced under different cultivation systems

In forest nurseries seedlings are commonly produced using different cultivation systems which may have a profound effect on the extent of root colonisation by ectomycorrhizal (ECM) fungi and, consequently, on subsequent performance of the outplanted seedlings under field conditions. In this study, we compare effects of bare-root and containerised cultivation systems on mycorrhization, establishment and growth of nursery-produced Picea abies. One hectare experimental plantation was established on poor fertility sandy site. In total, 1250 seedlings of each treatment were planted in rows as ten individual replicates. The results of this study showed that production of P. abies seedlings using containerised system can yield abundant ECM colonisation of seedling roots and significantly improve seedling survival in the field. Some reduction in height increment may occur during the first years as a possible cost for support of ECMs. Study demonstrated that selection of proper cultivation system might result in similar or higher mycorrhization and survival rates of outplanted seedlings than achieved by expensive and laborious artificial mycorrhization.

No tillage affects the phosphorus status, isotopic composition and crop yield of Phaseolus vulgaris in a rain-fed farming system

Conservation tillage promotes the accretion of soil organic matter and often leads to improved soil fertility and moisture availability. However, few studies have looked at the physiological response of crop plants to different tillage practices. It was therefore hypothesised that measuring the nutrient concentrations and stable isotope composition (δ(13)C, δ(18)O, δ(15)N) of shoots could help evaluate the physiological response of common bean (Phaseolus vulgaris L.) to different tillage treatments (no tillage (NT) and mouldboard ploughing (MP)) in a rain-fed farming system in northern Mexico. NT significantly enhanced shoot phosphorus concentration in bean plants. Tillage exerted a negative effect on the extent of root colonisation (%) by arbuscular mycorrhizal fungi (AMF). Lower shoot δ(18)O but unchanged δ(13)C values in plants from the NT system suggest enhanced stomatal conductance but also enhanced photosynthetic rate, which overall resulted in unchanged water use efficiency. Bean plants in the NT system showed lower shoot δ(15)N values, which suggests that a larger proportion of total plant nitrogen was obtained through atmospheric nitrogen fixation in this treatment. Greater diversity of AMF soil communities and heavier colonisation of roots by AMF in the NT compared with the MP system appeared to contribute to improved crop nutrition, water relations and yield in this rain-fed agroecosystem.

Growth response of maize plants (Zea mays L.) to wheat and lentil pre-cropping and to indigenous mycorrhizae in field soil

The presence of indigenous mycorrhizal fungi may have significant effects on the growth and on the root morphology of plants, under arid and semi arid soil conditions. Lentil and wheat are the traditional crops grown in Southeastern Turkey. In this study soil samples from the Harran plain were collected from the 0-15 cm surface layer under wheat or lentil crop residues and used in a pot experiment carried out under greenhouse conditions with four levels of P fertilization: 0, 20, 40 and 80 mg kg-1 soil as Ca(H2PO4)2. Half of the soil batches were submitted to a heating treatment (80°C, 2 h). The maize variety PX-9540 was grown in the pots for 57 days. At harvest, plant dry weight, root length, P and Zn concentrations in plant tissues were measured and the extent of root colonization by arbuscular mycorrhizal fungi (AMF) was determined. Results showed that maize plants grown in soils where lentil had been previously cultivated grew better than those grown after wheat cultivation. In both cases, P concentration in plant tissues increased with increased P fertilization. There were no significant differences in root AMF colonization between soils with different crop sequences, nor with soils submitted to high temperature. Previous crops had a significant influence on the growth of plants that could be related to differences in the indigenous mycorrhiza inoculum potential and efficacy that can promote P uptake and benefit plant growth.

Glyphosate and mycorrhization induce changes in plant growth and in root morphology and architecture in pepper plants (Capsicum annuum L.)

SummaryMycorrhizal symbiosis is the mutually beneficial association between the roots of most land plants and many soil fungi. Glyphosate is the most commonly used herbicide for effective control of weeds. This broad-spectrum herbicide is exuded by the roots of treated crops and by senescing weeds, and absorbed by new crops, affecting their growth. We therefore examined the effects of glyphosate residues in the soil, and mycorrhization, on plant growth and root morphology in Capsicum annuum L. Plants were either non-inoculated or inoculated with Glomus mosseae, and grown with different concentrations of glyphosate in soil. Pepper plants grown without glyphosate behaved as mycotrophic species. At high doses, glyphosate (6.32 µM) reduced the extent of root colonisation (to 34%) and the percentage of arbuscule formation (to 50%), and inhibited vesicle formation. Alkaline phosphatase activity was not affected by the herbicide. Inoculated plants had a higher biomass, total height, and leaf area. At the highest concentrations, glyphosate-inoculated plants had double the biomass of non-inoculated plants. Chlorophyll and leaf protein contents were higher in inoculated than in non-inoculated plants at all glyphosate concentrations tested. Inoculated plants increased their root area by approx. 50% with or without glyphosate. The interaction of mycorrhization and glyphosate reduced the mitotic index, mitotic activity, and cell length in the root apices. The highest concentration of herbicide inhibited root branching, modified root morphology and root architecture, and affected growth parameters. Pepper plants tolerate high concentrations of glyphosate in the soil. Mycorrhization benefits plant growth and increases the root area, with a high number of lateral roots, regardless of herbicide concentration. Mycorrhization would be a favourable strategy to allow plants to cope with this abiotic stress condition.

Interaction dynamics between saprobic lignicolous fungi and Armillaria in controlled environments: Exploring the potential for competitive exclusion of Armillaria on peach

Armillaria root rot, caused by Armillaria tabescens and Armillaria mellea, is a major cause of premature tree death in peach orchards in the southeastern United States. The root systems of infected trees can become entirely colonized by Armillaria, serving as an inoculum source for adjacent trees and providing massive inoculum levels in replant situations. If dead or dying trees could be colonized by an effective competitor of Armillaria before their removal, the extent of root colonization by the pathogen could be reduced, thus decreasing the threat to adjacent trees and/or subsequent plantings. Interactions between five species of saprobic lignicolous fungi (Ganoderma lucidum, Hypholoma fasciculare, Phanerochaete velutina, Schizophyllum commune, and Xylaria hypoxylon) and the two Armillaria species were examined in controlled conditions to provide proof of concept for competitive exclusion of Armillaria from peach roots. On agar-coated glass slides, all five potential antagonists induced detrimental reactions in >58% of the Armillaria hyphae observed, with the majority resulting in hyphal swelling or granulation. On poplar wood blocks, all antagonists consistently either overgrew Armillaria colonies or—in the case of S. commune—engaged in deadlock reactions; in all cases, the viability of Armillaria colonies was reduced to <30% of that of unchallenged controls. When inoculated simultaneously onto opposite ends of peach root segments, all antagonists consistently reduced growth and viability of Armillaria on and under the bark, whereby reduction of pathogen growth underneath the bark, Armillaria’s primary ecological niche, was most pronounced for G. lucidum, S. commune, and X. hypoxylon. When root segments were allowed to be colonized entirely by Armillaria before being inoculated with the antagonists, the latter were able to overgrow the pathogen on the root surface but unable to pre-empt it from underneath the bark. In summary,G. lucidum, S. commune, and X. hypoxylon caused strong hyphal and mycelial interference reactions and the most pronounced reductions in growth of Armillaria above and below the bark, indicating that they would be the most promising candidates for field-scale evaluations to restrict colonization of dead or dying peach trees by Armillaria in the orchard.

Microbial processes in the rhizosphere soil of a heavy metals-contaminated Mediterranean salt marsh: A facilitating role of AM fungi

We investigated the relationship of the zonal pattern followed by the vegetation in a polluted Mediterranean salt marsh, in semiarid south-eastern Spain, with the microbiological and biochemical properties (labile C fractions, oxidoreductases and hydrolases) of the rhizosphere soil of two halophyte species, Arthrocnemum macrostachyum and Sarcocornia fruticosa, and with the degree of arbuscular mycorrhizal (AM) colonisation in their rhizospheres. Levels of plant biomass and cover were inversely related to heavy metal contents and salinity. The concentrations of Fe, Cu, Mn and Pb extracted with DTPA hardly varied among the different zones of the salt marsh. The dehydrogenase and phosphatase activities, the soluble C and water-soluble carbohydrates concentrations and the extent of root colonisation were greater in the salt marsh zones of lower soil salinity and lower metal concentration. Urease and β-glucosidase activities were not detected in the salt marsh. Plant biomass and cover showed positive relationships with mycorrhizal colonisation ( R = 0.773, P < 0.001; R = 0.874, P < 0.001, respectively). Mycorrhizal colonisation was negatively correlated with the contents of Pb and Zn in plant tissues. This work supports the view that reduced plant uptake of toxic metals, particularly lead, could be involved in the beneficial effects of AM fungi on plant development in Mediterranean salt marshes contaminated with mining wastes.

Arbuscular-mycorrhizal fungi alleviate transplantation shock in micropropagated grapevine (Vitis vinifera L.)

SummaryThe effects of root inoculation with seven different arbuscular-mycorrhizal fungi (AMF) (Acaulospora laevis, A. scorbiculata, Entrophospora colombiana, Gigaspora gigantea, Glomus manihotis, Scutellospora heterograma) and a commercial mixed inoculum (consisting of Glomus moessae, G. manihotis and Gigaspora gigantea) on tissue culture-derived grapevine plantlets were studied during the hardening stage, under glasshouse conditions. Sixty days after inoculation, the percentages of plantlet survival, vine lengths, plant fresh and dry weights, leaf areas, photosynthetic rates, total chlorophyll contents, proline concentrations, nitrate reductase activities and nutrient status were determined. AMF-treated plantlets were superior to control plantlets for all parameters measured. Ex vitro survival rates of micropropagated grapevine plantlets were almost doubled as a result of AMF-inoculation. Correlations were calculated between the extent of root colonisation by AMF and the different parameters.Among the physiological and growth parameters, the highest positive correlation (r = 0.852) was noted for photosynthetic rate, followed by leaf area (r = 0.839). Among the biochemical parameters, the highest correlation was with proline content (r = 0.979) followed by nitrate reductase activity (r = 0.865). For nutrient status, the maximum correlation was between with AMF-colonisation and Zn (r = 0.880), followed by P (r = 0.835). With respect to the different parameters studied, A. laevis, G. manihotis and the mixed inoculum were identified as the most effective inocula. Our results indicated that AMF-colonisation could be an efficient technique to reduce the shock of transplantation for in vitro-raised grapevine plantlets for commercial use.

Impact of Arbuscular-Mycorrhizal Fungi on Phosphorus Efficiency of Wheat, Rye, and Triticale

ABSTRACT Genotypic variation and mycorrhiza play an important role in plant uptake of phosphorus (P). A pot experiment was conducted with three cereals, wheat (Triticum aestivum L. cv. PBW-34), rye (Secale cereale L. cv. R-308), and triticale (Triticale octoploide L. cv. DT-46), a hybrid of wheat and rye, to examine the genetic variation in the degree of arbuscular-mycorrhizal (AM) infection and its inheritability from parents (wheat and rye) to their progeny (triticale). The soil used for pot culture was low in available P (7.8 mg P kg−1soil). Inoculation with AM fungi showed a significant increase in extent of root colonization for all three cereals (average 70%) compared with their performance without AM (average 19.1%). However, among the three cereals, this increase was significantly greater in rye than in the other two crops, while wheat and triticale did not differ significantly. Mycorrhizal infection resulted in 1.6, 1.7, and 1.8-fold increases in shoot, root, and total plant dry matter, respectively, compared with the un-inoculated treatment. Among the three cereals, rye recorded maximum shoot, root, and total plant dry mass and P content with AM inoculation. The P uptake by wheat, rye, and triticale was 10%, 64%, and 35%, respectively, higher with rather than without mycorrhizal infection. Rye was most responsive to AM inoculation, with mycorrhizal dependency of 193%; here again, triticale followed wheat, with similar mycorrhizal dependency. Rye showed an increase in P utilization efficiency (PUE) without AM inoculation while the PUE of triticale was intermediate between wheat and rye. High efficiency of AM symbiosis in terms of P uptake exists in rye and most of these traits in triticale seem to be inherited from wheat rather than rye.

Expression Patterns of Defense-Related Genes in Different Types of Arbuscular Mycorrhizal Development in Wild-Type and Mycorrhiza-Defective Mutant Tomato

The expression of defense-related genes was analyzed in the interactions of six arbuscular mycorrhizal (AM) fungi with the roots of wild-type tomato (Lycopersicon esculentum Mill.) cv. 76R and of the near-isogenic mycorrhiza-defective mutant rmc. Depending on the fungal species, wild-type tomato forms both major morphological AM types, Arum and Paris. The mutant rmc blocks the penetration of the root surface or invasion of the root cortex by most species of AM fungi, but one fungus has been shown to develop normal mycorrhizas. In the wild-type tomato, accumulation of mRNA representing a number of defense-related genes was low in Arum-type interactions, consistent with findings for this AM morphotype in other plant species. In contrast, Paris-type colonization, particularly by members of the family Gigasporaceae, was accompanied by a substantial transient increase in expression of some defense-related genes. However, the extent of root colonization did not differ significantly in the two wild-type AM morphotypes, suggesting that accumulation of defense gene products per se does not limit mycorrhiza development. In the mutant, interactions in which the fungus failed to penetrate the root lacked significant accumulation of defense gene mRNAs. However, phenotypes in which the fungus penetrated epidermal or hypodermal cells were associated with an enhanced and more prolonged gene expression. These results are discussed in relation to the mechanisms that may underlie the specificity of the interactions between AM fungi and the rmc mutant.

INITIAL SHOOT GROWTH AND DEVELOPMENT OF MICROPROPAGATED BLUEBERRY PLANTS FOLLOWING INOCULATION WITH AN ERICOID MYCORRHIZAL ISOLATE

ISHS XXVI International Horticultural Congress: Berry Crop Breeding, Production and Utilization for a New Century INITIAL SHOOT GROWTH AND DEVELOPMENT OF MICROPROPAGATED BLUEBERRY PLANTS FOLLOWING INOCULATION WITH AN ERICOID MYCORRHIZAL ISOLATE

Reservoir and Non‐reservoir Hosts of Bean‐Wilt Pathogen, Fusarium oxysporum f. sp. phaseoli

AbstractThe capacity of Fusarium oxysporum f. sp. phaseoli to multiply in the roots of 12 non‐host plant species was determined with the objective of selecting potential candidates for crop rotation and/or green manuring in infested bean fields. The plants were inoculated at the seedling stage by a benomyl‐resistant mutant of the pathogen using the root‐dip technique and transplanted to natural soil. The number of colony forming units/g dry root tissue (CFU/g) was determined at the full bloom stage. Quantitatively, the root colonization differed greatly among the plant species. The roots and lower stem of Dolichos lablab, Phaseolus lunatus, Mucuna aterrima, Canavalia ensiforme and Vigna unguiculata were the most compatible with the pathogen and those of Sorghum bicolor, Crotalaria juncea, Oryza sativa and Zea mays were least compatible. No disease symptoms developed on any plant species. Chlamydospore germination in the rhizosphere also differed significantly among the plant species. There was no correlation between percentage chlamydospore germination in the rhizosphere and extent of root colonization. Most plant species recommended for green manuring in bean fields allowed extensive root and stem colonization by F. o. f. sp. phaseoli and were considered as reservoir hosts. All three of the gramineous species tested and C. juncea were classed as non‐reservoir host, because the pathogen did not colonize the stem and its multiplication in the roots was very low. These plant species appear to be good candidates for long‐term field evaluation to determine their usefulness in an integrated management of Fusarium bean‐wilt.