Arbuscular Mycorrhizal Inoculation of Peanut in Low-Fertile Tropical Soil. I. Host-Fungus Compatibility

The effects of inoculation with an indigenous Mozambican and a commercial arbuscular mycorrhizal (AM) inoculant on two peanut (Arachis hypogaea L.) cultivars, a traditional, low-yielding Mozambican landrace (Local) and a modern, high-yielding cultivar (Falcon), were tested in a non-sterile and low-fertile Mozambican soil. Host-fungus compatibility was determined as a percentage of root colonization in combination with the effects on plant-growth parameters, nodulation, and yield. Mycorrhizal colonization increased with inoculation, particularly in cultivar Falcon with the commercial inoculant. The differences in root colonization were reflected in plant growth responses as changes in leaf and root biomass, leaf-area ratio, nodulation, and yield components. The peanut landrace Local seemed to be more compatible with the indigenous AM fungi, whereas the modern cultivar Falcon responded best to the commercial inoculant. The results encourage the use of mycorrhizae as a biological tool for increasing production of peanut in low-fertile tropical soils. Inoculation may compensate for low soil fertility, particularly for cultivars that are bred for high yields, are under high fertilization, and are not adapted to the indigenous AM fungi. For peanut landraces, on the other hand, adequate management of the indigenous AM potential seems to be a more appropriate course.     

Arbuscular mycorrhizal fungi affect the growth,nutrient uptake and water status of maize (Zea mays L.) grown in two types of coal mine spoils under drought stress

Drought stress greatly affects the growth and development of plants in coal mine spoils located in the Inner Mongolia grassland ecosystem. Arbuscular mycorrhizal fungi (AMF) can increase plant tolerance to drought. However, little is known regarding the contribution of AMF to plants that are grown in different types of coal mine spoils under drought stress. To evaluate the mycorrhizal effects on the drought tolerance of maize (Zea mays L.) grown in weathered (S1) and spontaneously combusted (S2) coal mine spoils, a greenhouse pot experiment was conducted to investigate the effects of inoculation with Rhizophagus intraradices on the growth, nutrient uptake, carbon:nitrogen:phosphorus (C:N:P) stoichiometry and water status of maize under well-watered, moderate and severe drought stress conditions. The results indicated that drought stress increased mycorrhizal colonization and decreased plant dry weights, nutrient contents, leaf moisture percentage of fresh weight (LMP), water use efficiency (WUE) and rehydration rate. A high level of AMF colonization ranging from 65 to 90% was observed, and the mean root colonization rates in S1 were lower than those in S2. In both substrates, inoculation with R. intraradices significantly improved the plant growth, P contents, LMP and WUE and decreased the C:P and N:P ratios of plants under drought stress. In addition, maize grown in S1 and S2 exhibited different wilting properties in response to AMF inoculation, and plant rehydration after drought stress occurred faster in mycorrhizal plants. The results suggested that inoculation with R. intraradices played a more positive role in improving the drought stress resistance of plants grown in S2 than those grown in S1. AMF inoculation has a beneficial effect on plant tolerance to drought and effectively facilitates the development of plants in different coal mine spoils.     

Responses of phytohormones and gas exchange to mycorrhizal colonization in trifoliate orange subjected to drought stress

Phytohormones have an essential ability to adapt to abiotic stresses, including drought stress (DS), by mediating physiological and molecular processes. Arbuscular mycorrhizas (AMs) can enhance tolerance of DS, but the information regarding phytohormone changes in AM plants exposed to DS is little known. Trifoliate orange (Poncirus trifoliata) seedlings colonized by an AM fungus Funneliformis mosseae were subjected to DS and well-watered for 6 weeks. Plant growth performance, gas exchange, indole-acetic acid (IAA), gibberellins (GAs), brassinosteroids (BRs), abscisic acid (ABA), methyl jasmonate (MeJA) and zeatin riboside (ZR) were determined. The 6-week DS treatment strongly restricted root mycorrhizal colonization. Mycorrhizal inoculation significantly increased plant growth parameters under DS, as compared with non-mycorrhizal treatment. Mycorrhizal treatment also induced significantly higher leaf-relative water content, net photosynthetic rate, transpiration rate and stomatal conductance but lower intercellular CO₂ concentration and leaf temperature under DS, compared with non-mycorrhizal treatment. Mycorrhizal plants under DS condition represented significantly higher leaf ABA, IAA, GAs, BRs and ZR levels than non-mycorrhizal plants. The study, hence, suggested that mycorrhizal inoculation induced the changes of gas exchange and endogenous phytohormone levels to enhance drought tolerance in trifoliate orange.     

Influence of Rhizophagus spp. and Burkholderia seminalis on the Growth of Tomato (Lycopersicon esculatum) and Bell Pepper (Capsicum annuum) under Drought Stress

Beneficial interactions of arbuscular mycorrhizal fungi (AM Fungi) and plant growth promoting rhizobacteria (PGPR) have an important role in keeping agriculture sustainable. The present study reports the positive effects of AM fungi (Rhizophagus intraradices, Rhizophagus fasciculatum), Burkholderia seminalis and dual inoculation of these two strains on growth of Lycopersicon esculatum and Capsicum annuum plant under drought stress conditions. Each treatment was replicated six times and was arranged in a complete randomized block design. A significant increase in terms of biomass, root length, shoot length, and chlorophyll content was observed with the plants inoculated with these beneficial microorganisms. Accumulation of proline was found to be less in AM fungi inoculated plants suggesting the role of it in mitigating the water stress. A positive correlation between % colonization and chlorophyll content, root length, catalase activity, and guaiacol peroxidase has been observed depicting the importance of the AM fungi in drought tolerance.     

Response of neem (Azadirachta indica A. Juss) to indigenous arbuscular mycorrhizal fungi, phosphate-solubilizing and asymbiotic nitrogen-fixing bacteria under tropical nursery conditions

Neem (Azadirachta indica A. Juss) seedlings were inoculated with arbuscular mycorrhizal (AM) fungi, Glomus intraradices Schenck and Smith and G. geosporum (Nicol. and Gerd.) Walker, Azospirillum brasilense, and phosphate-solubilizing bacteria (PSB) individually or in various combinations in unsterile soil under nursery conditions. Seedlings were harvested at 60 and 120 days after transplantation. Microbial inoculation resulted in increased mycorrhizal colonization, greater plant height, leaf area and number, root collar diameter, biomass, phosphorus, nitrogen and potassium content, and seedling quality. Inoculated seedlings also had low root/shoot ratios and low nutrient utilization efficiencies. Populations of PSB declined with seedling growth; contrarily populations of A. brasilense increased. A. brasilense and PSB populations were related to each other and influenced root colonization by AM fungi. Microbial inoculation effects were greatest when seedlings were inoculated with a combination of microbes rather than individually. This clearly indicates that these microorganisms act synergistically when inoculated simultaneously, with maximum response being when both AM fungi were coinoculated with A. brasilense and PSB. The results emphasize the importance of microbial inoculations for the production of robust, rapidly growing seedlings in nurseries and illustrate the advantage of inoculating soils of a low microbial population with indigenous microbes.     

The impact of biological pesticides on arbuscular mycorrhizal fungi

Arbuscular mycorrhizal (AM) fungi have a key role for plant nutrition in organic farming systems where crop protection relies on biopesticides. Although these are considered safe, their effects on non-target organisms, such as AM fungi, are not known and should be evaluated. A pot and a field experiment were employed to investigate the impact of biological pesticides (azadirachtin, spinosad, pyrethrum and terpens) on exogenous AM fungal inoculum (pots) and on indigenous AM fungi (field). The synthetic fungicide carbendazim and non-pesticide treated controls with or without mycorrhizal inoculation were also included. Plant growth and root colonization were measured 20 and 40 days post inoculation (dpi) in the pot experiment, or 40 and 90 dpi in the field study. Pesticide effects on the structure of the intraradical AM fungal community were determined via DGGE and cloning. Spinosad, pyrethrum and terpenes did not affect the colonization ability and the structure of the AM fungal community. On the contrary, pot application of azadirachtin resulted in a selective inhibition of the Glomus etunicatum strain of the inoculum. DGGE analysis showed that the field application of azadirachtin induced significant and persistent shifts in the AM fungal community. Carbendazim completely hampered mycorrhizal colonization in pots, compared to its field application which had a transitory effect on the colonization ability and the community structure of indigenous AM fungi. Our study provides first evidence for the effects of biological pesticides on the diversity of AM fungi.     

Influence of arbuscular mycorrhizae on root colonization,growth and productivity of two wheat cultivars under salt stress

Two pot experiments were conducted in the greenhouse of the National Research Center, Egypt during 2003/2004 and 2004/2005 to investigate the efficacy of arbuscular mycorrhizae (AM) on root colonization, growth and productivity in two wheat cultivars, Sakha 8 and Giza 167, under salt stress. The extent of the AM effect on wheat development varied with plant cultivar and salinity level. Maximum root colonization and spore production were observed with the Sakha 8 cultivar, which resulted in greater plant growth and productivity at all salinity levels. AM and plant development were adversely affected by increasing salinity. However, the presence of mycorrhizal fungi protected wheat against the detrimental effect of salinity, and stimulated growth, productivity, total crude protein concentration and nitrate reductase activity. The average enhancement in grain yield due to AM inoculation was 76 and 68% at 0.15 mS cm^?1, 93 and 84% at 3.13 mS cm^?1, 130 and 115% at 6.25 mS cm^?1, and 154 and 120% at 9.38 mS cm^?1 salinity for Sakha 8 and Giza 167, respectively. In general, mycorrhizal inoculation enhanced the ability of wheat to cope with saline conditions and using AM inoculants can help plants to thrive in degraded arid/semi-arid areas.     

AM真菌和水分条件对稀土尾矿堆中植物生长的影响

通过温室盆栽试验研究了不同水分处理下接种3种丛枝菌根（AM）真菌（Diversispora spurcum、Glomus aggre gatum和Glomus constrictum）后对稀土矿砂中黑麦草（Lolium perenneL.）和狗牙根（Cynodon dactylon（L.）Pers.）植物株高、地上和地下部分干重及植株内Pb和Zn含量的影响。结果表明：不同水分处理下黑麦草和狗牙根与AM真菌均有一定的结合。在干旱胁迫（W1和W2）下,接种3种AM真菌均提高了黑麦草的株高、地上和地下部分干重,其中,接种Glomus aggregatum促进作用最为显著,重度干旱胁迫（W1）处理下接种后黑麦草株高、地上和地下部分干重比对照分别提高了76.16%、202.86%和481.82%;接种Glomus constrictum显著提高了狗牙根的株高、地上和地下部分干重,W1处理下狗牙根接种后的株高、地上和地下部分干重比对照分别提高了119.17%、290.63%和247.37%。接种AM真菌的植株内Pb和Zn含量与AM真菌种类、植物品种、水分处理及重金属性质等相关,在W1处理下接种Glomus constrictum显著降低了黑麦草植株内Pb的含量,而对Zn的含量影响不大;而对于狗牙根,在W1处理下接种Glomus constrictum显著增加了其Pb和Zn的含量。此外,还测定了植物叶片丙二醛和脯氨酸含量,结果显示接种AM真菌明显降低了干旱处理下黑麦草和狗牙根叶片丙二醛和脯氨酸含量,表明接种AM真菌能有效提高植物的抗逆性。     

Influence of arbuscular mycorrhizal fungi and salinity on growth,biomass, and mineral nutrition of<Emphasis Type="Italic"> Acacia auriculiformis</Emphasis>

The effect of salinity on the efficacy of two arbuscular mycorrhizal fungi, Glomus fasciculatum and G. macrocarpum, alone and in combination was investigated on growth, development and nutrition of Acacia auriculiformis. Plants were grown under different salinity levels imposed by 0.3, 0.5 and 1.0 S m^-1 solutions of 1 M NaCl. Both mycorrhizal fungi protected the host plant against the detrimental effect of salinity. The extent of AM response on growth as well as root colonization varied with fungal species, and with the level of salinity. Maximum root colonization and spore production was observed with combined inoculation, which resulted in greater plant growth at all salinity levels. AM fungal inoculated plants showed significantly higher root and shoot weights. Greater nutrient acquisition, changes in root morphology, and electrical conductivity of soil in response to AM colonization was observed, and may be possible mechanisms to protect plants from salt stress.     

Effects of mycorrhizal fungi on root-hair growth and hormone levels of taproot and lateral roots in trifoliate orange under drought stress

A pot experiment was used to evaluate the effects of an arbuscular mycorrhizal fungus (AMF) Funneliformis mosseae on plant growth performance, root-hair growth, and root hormone levels in trifoliate orange (Poncirus trifoliata) seedlings under well-watered (WW) and drought stress (DS). A 9-week mild DS treatment significantly reduced mycorrhizal colonization of 2nd- and 3rd-order lateral roots. Root mycorrhizal colonization was relatively higher in the 2nd- and 3rd-order lateral roots than in the taproot and the 1st-order lateral root under WW and DS. AMF seedlings exhibited significantly higher root-hair density, length (except for the taproot) and diameter in taproot and 1st-, 2nd-, and 3rd-order lateral roots under WW, and considerably higher root-hair density (except for 1st-order lateral root), length (except for 2nd-order lateral root) and diameter under DS. Mycorrhizal inoculation remarkably increased root abscisic acid (ABA), indole-3-acetic acid (IAA), methyl jasmonate, and brassinosteroids (BRs) concentrations under DS, in company with the decrease in root zeatin riboside and gibberellins levels and root IAA effluxes. Root-hair traits were significantly positively correlated with root colonization and root ABA and BRs levels. It is concluded that mycorrhizal plants possessed better root-hair growth to adapt mild DS, which is associated with mycorrhizal colonization and endogenous hormone changes.     

AM真菌和施氮量对烟叶生长和部分矿质元素含量的影响

采用土培试验研究了不同施N水平下接种AM真菌摩西球囊霉(Glomus mosseae)对烤烟不同叶位烟叶生长和部分矿质元素含量的影响。结果表明,接种AM真菌提高了烟草根系菌根侵染率,增加了烟叶总干重,其中对下位烟叶效果明显。在低N水平下,接种AM真菌提高了烟叶中N、K、Fe含量,在下位叶表现尤为显著。较高N水平下,提高了P含量,在3个叶位都有体现。Mg含量随施N量增加而提高,但处理与对照间差异不明显。施氮量为0.05~0.2g/kg土时,AM真菌接种效果最佳。     

Brassinosteroid (BR) and arbuscular mycorrhizal (AM) fungi alleviate salinity in wheat

This study was conducted to assess the impacts of brassinosteroide (BR), arbuscular mycorrhizal (AM) fungi, Glomus mosseae and their interactions on salt stress tolerance in Triticum aestivum L. After foliar spraying of mycorrhizal and non-mycorrhizal plants by 5 µM epibrassinolide, they were subjected to 0 and 150 mM sodium chloride (NaCl) for 2 weeks. The experiment was conducted in a randomized complete block design, replicated 4 times. Our results showed a probable potential of BR and/or AM fungi in improving salt tolerance of plants. Total phenol and proline content increased in BR and/ or AM treatments. AM fungi promoted plant growth, including leaf area, shoot and root dry weights, and lengths under saline condition. Moreover, BR improved growth parameters except root dry weights and lengths. This study indicated that BR and/or AM fungi may contribute to improve salt tolerance of the plant.     

Arbuscular mycorrhizas improve plant growth and soil structure in trifoliate orange under salt stress

Arbuscular mycorrhizal fungi (AMF) as a biostimulant enhance salt tolerance in plants, while the informations regarding AMF-induced changes in soil structure are only available to a limited degree. In this study, trifoliate orange (Poncirus trifoliata) seedlings were inoculated with Diversispora versiformis under 100 mM NaCl for 85 days. The salt stress considerably inhibited mycorrhizal colonization by 26%, compared with non-salt stress. Mycorrhizal inoculation significantly increased plant height, stem diameter, leaf number, shoot biomass, and root biomass, length, surface area, and volume in comparison to non-mycorrhizal inoculation under salt stress or non-salt stress. Mycorrhization induced significantly higher production of easily extractable glomalin-related soil protein (EE-GRSP), and total glomalin-related soil protein (T-GRSP), higher percentage of water-stable aggregates (WSAs) in 0.25–0.50, 0.50–1.00, and 1.00–2.00 mm size, and lower in 2.00–4.00 mm size, regardless of non-salt stress or salt stress. Mycorrhizal soils represented higher aggregate stability (in terms of mean weight diameter) under salt and non-salt stress, which was related with root colonization, root surface area, root volume, EE-GRSP, and T-GRSP. The better soil structure by mycorrhization provided higher leaf water potential under salt stress. It suggests that mycorrhizas had a positive contribution to improve plant growth and soil structure, thereby enhancing salt tolerance.     

Antioxidant activities and metal acquisition in mycorrhizal plants growing in a heavy-metal multicontaminated soil amended with treated lignocellulosic agrowaste

The plant growth, nutrient acquisition, metal translocation and antioxidant activities [ascorbate peroxidase (APX), glutatione reductase (GR), superoxide dismutase (SOD) and catalase (CAT)] were measured in plants growing in a heavy-metal (HM) multicontaminated soil inoculated with selected autochthonous microorganisms [arbuscular mycorrhizal (AM) fungus and/or plant growth promoting bacteria (PGPB)] and/or amended with an Aspergillus niger-treated agrowaste. The treated agrowaste on its own increased root growth by 296% and shoot growth by 504% compared with non-treated control plants. Both chemical and biological treatments, particularly when combined, enhanced plant shoot and root development. The stimulation effect on plant biomass was concomitant with increased AM colonization, P and K assimilation, and reduced metal translocation from soil to plant shoot. The treated residue, particularly through interactions with AM inoculation, produced the expected bioremediation effect, leading to enhanced plant development and successful rehabilitation of contaminated soil. The enhancement of CAT, APX and GR activities caused by AM inoculation suggests that AM colonization helped plants to limit oxidative damage to biomolecules in response to metal stress. The response of the plant's antioxidant activities to the amendment appears to be related to enhanced plant biomass production. The application of amendments and/or microbial inoculations to enhance plant growth and reduce metal translocation in multicontaminated soil could be a promising strategy for remediating HM pollution.     

渭北旱塬葡萄园土著AM真菌对赤霞珠葡萄促生效应研究

以筛选自渭北旱塬葡萄园的3种土著AM真菌菌株Glomus mosseae(GM)、Glomus intraradices(GI)和Glomus versiforme(GV)为试材,在盆栽条件下研究了3种AM真菌单独接种及混合接种对酿酒葡萄赤霞珠(Cabernet Sauvignon)扦插苗营养生长指标的影响。结果表明,不同接种处理的葡萄幼苗AM真菌侵染程度不同,混合接种显著高于单接种;混合接种GI+GVGM+GVGM+GI,单接种GVGIGM。接种AM真菌促进葡萄幼苗的生长,显著提高植株高度和地上、地下干重,并提高葡萄叶片净光合速率、气孔导度、胞间二氧化碳浓度和蒸腾速率,从而提高葡萄叶片的光合作用;葡萄叶片中叶绿素含量、可溶性糖含量、可溶性蛋白含量均高于未接种对照,且混合接种优于单接种。     

Response of a wild-type and modern cowpea cultivars to arbuscular mycorrhizal inoculation in sterilized and non-sterilized soil

Cowpea is an important crop that serves as a legume and vegetable source to many smallholder farmers in sub-Saharan Africa. Soil fertility is a significant limitation to its production thus; inoculation with beneficial soil biota such as arbuscular mycorrhizal fungi (AMF) could improve its performance. However, plant–AMF interaction could vary based on crop cultivar hence affecting overall crop production. The present study aimed at determining the effect of AMF inoculation and soil sterilization on root colonization and growth of a wild-type and three modern cowpea cultivars grown by smallholder farmers in Kenya. Potted cowpea plants were inoculated with a commercial AMF inoculum comprising of Rhizophagus irregularis, Funneliformis mosseae, Glomus aggregatum and Glomus etunicatum and maintained in a greenhouse for 40 days. After harvesting, mycorrhizal colonization, nodule number and dry weight, root and shoot dry weights, nitrogen (N,) phosphorus (P) and potassium (K) content were determined. Interestingly, the modern cultivars showed significantly (p < 0.001) higher root colonization, nodulation, shoot P and N compared to the wild-type cultivar. Moreover, a strong positive correlation between AMF root colonization and shoot P (r² = 0.73, 0.90, p < 0.001), AMF root colonization and shoot N (r² = 0.78; 0.89, p < 0.001) was observed in both sterilized and non-sterilized soil, respectively. Soil sterilization affected root colonization and growth parameters with plants grown in non-sterilized soil performing better than those grown in sterilized soil. This study provides major evidence that modern cowpea cultivars are still responsive to mycorrhizal inoculation suggesting that modern breeding programs are not deleterious AMF symbiosis.     

Water stress and mycorrhizal isolate effects on growth and nutrient acquisition of wheat

Arbuscular mycorrhizal (AM) colonized plants often have greater tolerance to drought than nonmycorrhizal (nonAM) plants. Wheat (Triticum durum Desf.), whose roots were colonized with Glomus mosseae (Gms) and G. monosporum (Gmn), were grown in a greenhouse to determine effects of water stress (WS) on shoot and root dry matter (DM), root length (RL), and shoot phosphorus (P), zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe) concentrations and contents. Mycorrhizal colonization was higher in well‐watered (nonWS) plants colonized with both AM isolates than WS plants, and Gms had greater colonization than Gmn under both soil moisture conditions. Shoot and root DM were higher in AM than in nonAM plants irrespective of soil moisture, and Gms plants had higher shoot but not root DM than Gmn plants grown under either soil moisture condition. Total RL of AM plants was greater than nonAM plants, but was consistently lower for plants grown with WS than with nonWS. The AM plants had similar shoot P and Mn concentrations as nonAM plants, but contents were higher in AM than in nonAM plants. The AM plants had higher shoot Zn, Cu, and Fe concentrations and contents than nonAM plants. The Gms plants grown under nonWS generally had higher nutrient contents than Gmn plants, but nutrient contents were similar for both Gms and Gmn plants grown under WS. The results demonstrated a positive relationship between enhanced growth and AM root colonization for plants grown under nonWS and WS.     

水分胁迫下AM真菌对甘草生长的影响

利用盆栽试验研究了水分胁迫下接种摩西球囊霉（Glomus mosseae）对甘草（Glycyrrhiza inflata）生长和抗旱性的影响。结果表明,土壤含水量对AM真菌接种效果有显著影响;不同水分条件下,接种AM真菌显著提高了甘草菌根侵染率和全株黄酮以及氮、磷含量。水分胁迫30 d,接种株POD活性和MDA含量显著降低,而土壤含水量为60%和80%时,接种株可溶性蛋白含量显著降低;水分胁迫60d,接种株SOD活性和可溶性蛋白含量显著降低,土壤含水量为60%和80%时,接种株POD活性和可溶性糖含量显著升高,接种株叶绿素含量只在土壤含水量为60 %时显著升高。以胁迫60d土壤含水量为60 %时接种效果最佳。AM真菌可能通过提高宿主植物根系对土壤水分和矿质元素吸收以及改善植物体内生理活动、调节保护酶活性以提高其抗旱性,促进宿主植物生长。     

Modulation of the ROS‐scavenging system in salt‐stressed wheat plants inoculated with arbuscular mycorrhizal fungi

Although there is evidence for a positive involvement of the antioxidant defense system in plant response to salt stress, there is poor information regarding the influence of mycorrhizal symbiosis on enzymatic and nonenzymatic antioxidant defense in wheat under saline conditions. The present article focuses on the contribution of mycorrhizae to antioxidant defense in salt‐stressed wheat plants. Two wheat (Triticum aestivum L.) cultivars, Sids 1 and Giza 168, were grown under nonsaline or two saline conditions (4.7 and 9.4 dS m^–1) with and without arbuscular mycorrhizal fungi (AMF) inoculation. Salt stress considerably decreased root colonization and plant productivity, particularly in Giza 168. Interestingly, mycorrhizal colonization alleviated the adverse effect of salt stress and significantly enhanced plant productivity, especially in Sids 1. The concentration of glycinebetaine, the activities of antioxidative enzymes (superoxide dismutase, peroxidase, catalase, and glutathione reductase) and the concentrations of antioxidant molecules (glutathione and ascorbate) were increased under saline conditions; these increases were more significant in salt‐stressed mycorrhizal plants, especially in Sids 1. Salt stress induced oxidative damage through increased lipid peroxidation, electrolyte leakage, and hydrogen peroxide concentration, particularly in Giza 168. Mycorrhizal colonization altered plant physiology and significantly reduced oxidative damage. Elimination of reactive oxygen species (ROS) can be one of the mechanisms how AMF improve wheat adaptation to saline soils and increase its productivity.     

Comparative Study of Substrate-Based and Commercial Formulations of Arbuscular Mycorrhizal Fungi in Romaine Lettuce Subjected to Salt Stress

To compare the effect of substrate-based and commercial arbuscular mycorrhizal fungi (AMF) in salt stress tolerance of Romaine lettuce a bifactorial analysis was carried out. Under non-saline conditions, only plants inoculated with formulation 1 stimulated shoot weight but not related with greater root AMF colonization. Phosphorus and potassium concentrations in leaves were improved by mycorrhizal association. Irrigation with 100 mM sodium chloride (NaCl) did not affect leaf relative water content and we observed no osmotic adjustment in leaves from non-mycorrhizal plants. However, root dry biomass and its starch content decreased, while leaf starch and root soluble sugar concentrations were enhanced. Lettuce inoculated with formulation 2 and substrate-based Glomus intraradices showed the highest root colonization percentages. Nevertheless, none of the mycorrhizal treatments induced a significant improvement on growth of lettuce subjected to salt stress. Romaine lettuce seems to be a moderately tolerant variety to salinity and therefore, the contribution of AMF was minimized.