Biological control of root-rot of Coleus forskohlii Briq. using microbial inoculants

The root-rot or wilt of Coleus forskohlii is a very serious soil-borne disease caused by Fusarium chlamydosporum. A field study was undertaken to study the possibility of controlling the disease using three biocontrol agents viz., Glomus mosseae, Pseudomonas fluorescens, Trichoderma viride, singly and in combination. Planting of coleus cutting was done in wilt sick soil. Inoculation with Trichoderma viride + Glomus mosseae gave the best result in controlling the disease. The same treatment also resulted in maximum growth, yield and root forskolin concentration of coleus. Plants treated with T. viride + G. mosseae showed a disease severity index of 33.28% compared to uninoculated control plants, which had a maximum disease severity index of 85.5%. The fungicide Emisan (0.2%) was not as effective as the biocontrol agents in controlling the pathogen.     

Plantago lanceolata and Plantago rugelii Extracts are Toxic to Meloidogyne incognita but not to Certain Microbes

Extracts from the plants Plantago lanceolata and P. rugelii were evaluated for toxicity to the root-knot nematode Meloidogyne incognita, the beneficial microbes Enterobacter cloacae, Pseudomonas fluorescens and Trichoderma virens, and the plant-pathogenic fungi Fusarium oxysporum f. sp. gladioli, Phytophthora capsici, Pythium ultimum, and Rhizoctonia solani. Wild plants were collected, roots were excised from shoots, and the plant parts were dried and ground to a powder. One set of extracts (10% w/v) was prepared in water and another in methanol. Treatments included extract concentrations of 25%, 50%, 75% and 100%, and water controls. Meloidogyne incognita egg hatch was recorded after 7-day exposure to the treatments, and second-stage juvenile (J2) activity after 48 hours. All extracts were toxic to eggs and J2, with P. lanceolata shoot extract tending to have the most activity against M. incognita. Numbers of active J2 remained the same or decreased in a 24-hour water rinse following the 48-hour extract treatment, indicating that the extracts were lethal. When data from water- and methanol-extracted roots and shoots of both plant species were combined for analysis, J2 tended to be more sensitive than eggs to the toxic compounds at lower concentrations, while the higher concentrations (75% and 100%) were equally toxic to both life stages. The effective concentrations causing 50% reduction (EC₅₀) in egg hatch and in J2 viability were 44.4% and 43.7%, respectively. No extract was toxic to any of the bacteria or fungi in our assays.     

Interaction of Vesicular-arbuscular Mycorrhizal Fungi and Phosphorus with Meloidogyne incognita on Tomato

The influence of two vesicular-arbuscular mycorrhizal fungi and phosphorus (P) nutrition on penetration, development, and reproduction by Meloidogyne incognita on Walter tomato was studied in the greenhouse. Inoculation with either Gigaspora margarita or Glomus mosseae 2 wk prior to nematode inoculation did not alter infection by M. incognita compared with nonmycorrhizal plants, regardless of soil P level (either 3 μg [low P] or 30 μg [high P] available P/g soil). At a given soil P level, nematode penetration and reproduction did not differ in mycorrhizal and nonmycorrhizal plants. However, plants grown in high P soil had greater root weights, increased nematode penetration and egg production per plant, and decreased colonization by mycorrhizal fungi, compared with plants grown in low P soil. The number of eggs per female nematode on mycorrhizal and nonmycorrhizal plants was not influenced by P treatment. Tomato plants with split root systems grown in double-compartment containers which had either low P soil in both sides or high P in one side and low P in the other, were inoculated at transplanting with G. margarita and 2 wk later one-half of the split root system of each plant was inoculated with M. incognita larvae. Although the mycoorhizal fungus increased the inorganic P content of the root to a level comparable to that in plants grown in high P soil, nematode penetration and reproduction were not altered. In a third series of experiments, the rate of nematode development was not influenced by either the presence of G. margarita or high soil P, compared with control plants grown in low P soil. These data indicate that supplemental P (30 μ/g soil) alters root-knot nematode infection of tomato more than G. mosseae and G. margarita.     

Does Inoculation with Glomus mosseae Improve Salt Tolerance in Pepper Plants?

A pot experiment was conducted to determine the effects of Glomus mosseae inoculation on growth and some biochemical activities in roots and shoots of pepper (Capsicum annuum L. cv. Zhongjiao 105) plants subjected to four levels of NaCl [0 (control), 25 (low), 50 (medium), and 100 (high) mM] for 30 days, after 30 days of establishment under non-saline conditions. In mycorrhizal (M) plants, root colonization varied from 48 to 16 %. M plants had higher root and shoot dry weight and leaf area compared with non-mycorrhizal (NM) plants. Under salinity stress, M plants accumulated higher amounts of leaf photosynthetic pigments as well as soluble sugar, soluble protein, and total free amino acids in roots and shoots than those of NM plants. In contrast, the accumulation of proline was less intense in M plants than NM plants. Salt stress induced oxidative stress by increasing malondialdehyde (MDA) content; however, the extent of oxidative damage in M plants was less compared with NM plants due to G. mosseae-enhanced activity of superoxide dismutase (SOD) and peroxidase (POD). We concluded that inoculation with G. mosseae improved growth performance and enhanced salt tolerance of pepper plants via improving photosynthetic pigments and the accumulation of organic solutes (except proline), reducing oxidative stress, and enhancing antioxidant activities of the SOD-POD system.     

Photochemical processes, carbon assimilation and RNA accumulation of sucrose transporter genes in tomato arbuscular mycorrhiza

Arbuscular mycorrhizal fungi enhance CO₂ assimilation of their hosts which ensure the demand for carbohydrates of these obligate biotrophic microorganisms. Photosynthetic parameters were measured in tomato colonised or not by the arbuscular mycorrhizal fungus Glomus mosseae. In addition, carbohydrate contents and mRNA accumulation of three sucrose transporter genes were analysed. Mycorrhizal plants showed increased opening of stomata and assimilated significant more CO₂. A higher proportion of the absorbed light was used for photochemical processes, while non-photochemical quenching and the content of photoprotective pigments were lower. Analysis of sugar contents showed no significant differences in leaves but enhanced levels of sucrose and fructose in roots, while glucose amounts stayed constant. The three sucrose transporter encoding genes of tomato SlSUT1, SlSUT2 and SlSUT4 were up-regulated providing transport capacities to transfer sucrose into the roots. It is proposed that a significant proportion of sugars is used by the mycorrhizal fungus, because only amounts of fructose were increased, while levels of glucose, which is mainly transferred towards the fungus, were nearly constant.     

Effects of preplant inoculation of apple (Malus domestica Borkh.) with arbuscular mycorrhizal fungi on population growth of the root-lesion nematode,Pratylenchus penetrans

Six species of arbuscular mycorrhizal (AM) fungi (Glomus aggregatum, G. clarum, G. etunicatum, G. intraradices, G. mosseae and G. versiforme) were evaluated, in three greenhouse experiments, for their effects on reproduction of the root-lesion nematode, Pratylenchus penetrans, and growth of Ottawa 3 apple rootstock. Glomus mosseae increased total dry weights of nematode-inoculated and non-inoculated rootstock in all three greenhouse experiments, and G. intraradices increased dry weights in two of three greenhouse experiments. Plants inoculated with G. mosseae generally supported fewer P. penetrans per gram of root than plants inoculated with other AM fungi, but did not differ significantly from the controls in any greenhouse experiment. Colonization of roots by AM fungi was reduced by P. penetrans at initial inoculum densities greater than 250 nematodes/L soil. In field trials, preplant inoculation with either G. intraradices or G. mosseae increased rootstock growth and leaf concentrations of P, Mg, Zn and Cu in fumigated plots but not in non-fumigated plots, indicating that colonization by native AM fungi in non-fumigated plots may have been sufficient for adequate nutrient acquisition. The abundance of vesicles and arbuscules was greater in roots of plants inoculated with AM fungi before planting than in roots of non-inoculated plants, in both fumigated and non-fumigated plots. P. penetrans per gram of root and per 50 ml soil were significantly lower for G. mosseae- inoculated plants than for non-inoculated plants in fumigated soil but not in non-fumigated soil.     

Effect of <Emphasis Type="Italic">Glomus</Emphasis> species on physiology and biochemistry of <Emphasis Type="Italic">Catharanthus roseus</Emphasis>

The present study on efficacy of different Glomus species, an arbuscular mycorrhizal (AM) fungus (G. aggregatum, G. fasciculatum, G. mosseae, G. intraradices) on various growth parameters such as biomass, macro and micronutrients, chlorophyll, protein, cytokinin and alkaloid content and phosphatase activity of pink flowered Catharanthus roseus plants showed that all Glomus species except G. intraradices enhanced the chlorophyll, protein, crude alkaloid, phosphorus, sulphur, manganese and copper contents of C. roseus plants along with phosphatase activity significantly over uninoculated plants. However only G. mosseae and G. fasciculatum exhibited superior symbiotic relationship with the plant. G. mosseae was found to be the best for increasing the crude alkaloid content (8.19%) in leaf and also in increasing the quantity of important alkaloids vincristine and vinblastine.     

Association of Criconemella xenoplax and Fusarium spp. with Root Necrosis and Growth of Peach

Criconemella xenoplax, Fusarium solani, and F. oxysporum caused necrosis of Nemaguard peach feeder roots in greenhouse tests. Root necrosis was more extensive in the presence of either fungus than wtih C. xenoplax alone. Shoot growth and plant height were less for plants inoculated with F. oxysporum or F. solani than for plants inoculated with the fungi plus C. xenoplax. Neither synergistic nor additive effects on root necrosis or plant growth occurred between C. xenoplax and the fungal pathogens.     

Mycorrhizal colonization impacts on phenolic content and antioxidant properties of artichoke leaves and flower heads two years after field transplant

Greenhouse and field experiments were carried out in order to investigate the influence of mycorrhizal inoculation on total phenolic content (TPC) and antioxidant activity, expressed as antiradical power (ARP), of artichoke (Cynara cardunculus L. var. scolymus F.) leaves and flower heads extracts. The establishment of mycorrhizal symbiosis was monitored in pot and field grown plants, and the persistence of the inoculated AMF in roots after 2 years’ growth in the field was assessed by fungal ITS sequencing. Both in the greenhouse and in the field, marked increases in TPC and ARP were detected in leaves and flower heads of artichoke plants inoculated with the AM fungal species Glomus intraradices, either alone or in mixture with Glomus mosseae. In the field, plants inoculated with Glomus mix showed flower heads ARP content increases of 52.7 and 30.0% in the first and second year, respectively, compared with uninoculated plants. After 2 years’ growth in the field ITS rDNA sequences clustering with those of G. mosseae and G. intraradices were retrieved only from inoculated plant roots. Our data show that mycorrhizal inoculation may represent an efficient and sustainable strategy to improve productivity and enhance plant biosynthesis of secondary metabolites with health promoting activities.     

The Influence of Trichoderma harzianum on the Root-knot Fusarium Wilt Complex in Cotton

Wilt-susceptible cultivar ''Rowden'' cotton was inoculated wilh Meloidogyne incognita (N), Trichoderma harzianum (T), and Fusarium oxysporum f. sp. vasinfectum (F) alone and in all combinations in various time sequences. Plants inoculated with F alone or in combination with T did not develop wilt, Simultaneous inoculation of 7-day-old seedlings with all three organisms (NTF) produced earliest wilt. However, plants receiving nematodes at 7 days and Fusarium and Trichoderma at 2 or 4 weeks later (N-T-F, N-TF) developed the greatest wilt between 49-84 days after initial nematode inoculation. During the same period, Fusarium added 4 weeks after initial nematode inoculation (N-F) and Fusarium added 4 weeks after initial simultaneous inoculation of nematode and Trichoderma (NT-F) produced the least wilt. The addition of Fusarium inhibited nematode reproduction. Simultaneous inoculation with nematodes and Trichoderma (NT-) resulted in the greatest root gall development, whereas nematodes alone produced the greatest number of larvae. In comparison with noninoculated controls (CK), treatments involving all three organisms inhibited plant growth, plants inoculated with the nematode alone (N-) or with nematodes and Trichoderma (NT-) simultaneously had greatest root weight. Any treatment involving the nematode resulted in fewer bolls per plant and greater necrosis on roots than the noninoculated checks.     

Overlapping expression patterns and differential transcript levels of phosphate transporter genes in arbuscular mycorrhizal,P<Subscript>i</Subscript>-fertilised and phytohormone-treated <Emphasis Type="Italic">Medicago truncatula</Emphasis> roots

A microarray carrying 5,648 probes of Medicago truncatula root-expressed genes was screened in order to identify those that are specifically regulated by the arbuscular mycorrhizal (AM) fungus Gigaspora rosea, by P_i fertilisation or by the phytohormones abscisic acid and jasmonic acid. Amongst the identified genes, 21% showed a common induction and 31% a common repression between roots fertilised with P_i or inoculated with the AM fungus G. rosea, while there was no obvious overlap in the expression patterns between mycorrhizal and phytohormone-treated roots. Expression patterns were further studied by comparing the results with published data obtained from roots colonised by the AM fungi Glomus mosseae and Glomus intraradices, but only very few genes were identified as being commonly regulated by all three AM fungi. Analysis of P_i concentrations in plants colonised by either of the three AM fungi revealed that this could be due to the higher P_i levels in plants inoculated by G. rosea compared with the other two fungi, explaining that numerous genes are commonly regulated by the interaction with G. rosea and by phosphate. Differential gene expression in roots inoculated with the three AM fungi was further studied by expression analyses of six genes from the phosphate transporter gene family in M. truncatula. While MtPT4 was induced by all three fungi, the other five genes showed different degrees of repression mirroring the functional differences in phosphate nutrition by G. rosea, G. mosseae and G. intraradices. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Flavonoids in roots of white clover: interaction of arbuscular mycorrhizal fungi and a pathogenic fungus

The effects of two arbuscular mycorrhizal fungi (AMF) (Glomus mosseae and G. claroideum) and a pathogenic fungus (Pythium ultimum) on the production of eight flavonoids in roots of two white clover (Trifolium repens L.) cultivars were evaluated. Quantification of AM and pathogenic fungi in the roots showed that the AM symbiosis significantly reduced P. ultimum biomass and in some cases prevented infection. The flavonoid productions in clover roots varied depending on the presence of beneficial and/or pathogenic fungi, fungal isolate or plant cultivar. Only plants colonized with G. claroideum showed detectable concentrations of either coumestrol or kaempferol (cultivar-dependant). In addition, inoculation with G. claroideum resulted in significantly higher concentrations of coumestrol in cv. Sonja and medicarpin in cv. Milo. A low production of coumestrol and kaempferol in mycorrhizal plants may be G. mosseae-specific. Only the concentrations of formononetin and daidzein increased in clover roots in response to infection with P. ultimum. These flavonoids are supposedly stress metabolites, synthesized or produced from glycosides in response to pathogen infection. However, the presence of one or both AMF significantly lowered the formononetin and daidzein concentrations, and overruled the inductive effect of P. ultimum. Therefore the antagonistic action of AM against the pathogen must take place through another mechanism.     

Arbuscular mycorrhizal fungi and Trichoderma viride mediated Fusarium wilt control in tomato

The biocontrol potential of two arbuscular mycorrhizal fungi (AMF) (Funneliformis mosseae and Acaulospora laevis) and Trichoderma viride was assessed against tomato wilt caused by Fusarium oxysporum Schlecht. f. sp. lycopersici under pot condition. All the bioagent showed appreciable results in increasing plant growth. Combined inoculation of F. mosseae, A. laevis and T. viride showed maximum increases in plant height, shoot fresh weight, root dry weight, number of leaves and number of branches per plant while dual inoculation of F. mosseae and T. viride increased rest of the growth parameters like shoot dry weight, root fresh weight, root length and leaf area. AM colonisation and spore number was found highest in single inoculation of AMF, which decreases with the addition of T. viride. But, this decrease has no effect on biocontrol efficiency of bioagents. Photosynthesis, chlorophyll content and nutrient content were markedly decreased by pathogen infection. Bioagent application overcomes this effect and a remarkable increase in the plant phosphorus and nitrogen content was recorded. Among both the AMF, F. mosseae proved to be more effective strain compared to A. laevis for tomato. Maximum reduction in disease incidence and severity was recorded in combined inoculation of F. mosseae, A. laevis and T. viride. Whereas control plants without any bioagent showed maximum occurrence of disease. The findings of this study concludes that soil inoculation with F. mosseae along with root inoculation with conidial suspension of T. viride before transplantation offered better survival and resistance to tomato seedlings against Fusarium wilt.     

Direct and indirect influences of arbuscular mycorrhizal fungi on phosphorus uptake by two root hemiparasitic Pedicularis species: do the fungal partners matter at low colonization levels?

Background and Aims

Because most parasitic plants do not form mycorrhizal associations, the nutritional roles of arbuscular mycorrhizal (AM) fungi in them have hardly been tested. Some facultative root hemiparasitic Pedicularis species form AM associations and hence are ideal for testing both direct and indirect effects of AM fungi on their nutrient acquisition. The aim of this study was to test the influence of AM inoculation on phosphorus (P) uptake by Pedicularis rex and P. tricolor.

Methods

³²P labelling was used in compartmented pots to assess the contribution of the AM pathway and the influence of AM inoculation on P uptake from a host plant into the root hemiparasites. Laboratory isolates of fungal species (Glomus mosseae and G. intraradices) and the host species (Hordeum vulgare ‘Fleet’) to which the two Pedicularis species showed obvious responses in haustorium formation and growth in previous studies were used.

Key Results

The AM colonization of both Pedicularis spp. was low (<15 % root length) and only a very small proportion of total plant P (<1 %) was delivered from the soil via the AM fungus. In a separate experiment, inoculation with AM fungi strongly interfered with P acquisition by both Pedicularis species from their host barley, almost certainly because the numbers of haustoria formed by the parasite were significantly reduced in AM plants.

Conclusions

Roles of AM fungi in nutrient acquisition by root parasitic plants were quantitatively demonstrated for the first time. Evidence was obtained for a novel mechanism of preventing root parasitic plants from overexploiting host resources through AM fungal-induced suppression of the absorptive structures in the parasites.     

Increased Growth and Yield of Hydroponically Grown Greenhouse Tomato Plants Inoculated with Arbuscular Mycorrhizal Fungi and Fusarium oxysporum f. sp. radicis-lycopersici

The arbuscular mycorrhizal fungi Glomus monosporum, G. vesiculiferum, G. deserticola, G. intraradices, G. mosseae, and two unidentified species were tested to determine their effect on plant growth and fruit production of tomato (Lycopersicon esculentum Mill.) cv. Trust inoculated with Fusarium oxysporum f. sp. radicis-lycopersici (FORL) under near-commercial greenhouse conditions. Inoculation with G. monosporum and G. mosseae significantly increased fruit yield and fruit number of tomato plants grown hydroponically in sawdust. Plant height and plant dry weight increased significantly when inoculated with G. monosporum and G. mosseae. Further, plants inoculated with G. monosporum and G. mosseae showed significantly lower FORL root infection than the untreated control plants.     

Differential effects of Oroxylum indicum bark extracts: antioxidant, antimicrobial, cytotoxic and apoptotic study

Stem bark of Oroxylum indicum (L) (SBOI) is used by ethnic communities of North East India as health tonic and in treating diseases of humans and animals. The objective of this research was to carry out a detailed investigation including total phenolic and flavonoid content, antioxidant, antimicrobial, cytotoxic and apoptotic activities of different solvent extracts of SBOI and to establish correlation between some parameters. Among petroleum ether (PE), dichloromethane and methanol (MeOH) extract of SBOI, MeOH extract contained the highest amount of total phenolic (320.7 ± 34.6 mg Gallic acid equivalent/g extract) and flavonoid (346.6 ± 15.2 mg Quercetin equivalent/g extract) content. In vitro antioxidant activity (IC₅₀ 22.7 μg/ml) was highest in MeOH extract (p > 0.05) and also a significant inverse correlation was observed between phenolic (r = 0.886)/flavonoid (r = 0.764) content and corresponding DPPH IC₅₀. Only MeOH extract inhibited both bacteria and fungi. Although, individual extract showed cytotoxicity on HeLa cells with characteristic features of apoptosis, PE extract caused maximum cytotoxicity (IC₅₀ of 112.3 μg/ml, p < 0.05) and apoptotic activity (33.2 % sub-G0/G1 population) on HeLa cells. But, there was a significant non-inverse correlation of the MTT IC₅₀ with total phenolic (r = 0.812, p < 0.05)/flavonoid (r = 0.998, p < 0.05) content in the three solvent extracts. TLC analysis showed three unique compounds in PE extract which may have a role in apoptosis mediated cytotoxicity. These results called for futher chemical characterisation of MeOH and PE extract of SBOI for specific bioactivity.     

Effects of Exogenous Salicylic Acid and Nitric Oxide on Physiological Characteristics of Perennial Ryegrass Under Cadmium Stress

The effects of Cd, in combination with salicylic acid (SA) and sodium nitroprusside (SNP), on ryegrass seedlings were studied. Exposure of plants to 0.1 mM CdCl₂ for 2 weeks resulted in toxicity symptoms such as chlorosis and necrotic spots on leaves. The addition of 0.2 mM SA or 0.1 mM SNP slightly alleviated the toxic effects of Cd. After application of both SA and SNP, these symptoms significantly decreased. Treatment with Cd resulted in a decrease of dry weight of roots and shoots, chlorophyll content, net photosynthetic rate (P _n), transpiration rate (T _r), and the uptake and translocation of mineral elements. In Cd-treated plants, levels of lipoxygenase activity and malondialdehyde, hydrogen peroxide (H₂O₂), and proline contents significantly increased, whereas the activities of antioxidant enzymes, such as superoxide dismutase, guaiacol peroxidase, catalase, and ascorbate peroxidase, decreased in both roots and shoots. The results indicated that Cd caused physiological stresses in ryegrass plants. The Cd-stressed plants exposed to SA or SNP, especially to SA + SNP, exhibited improved growth compared with Cd-stressed plants. Application of SA or SNP, especially the combination SA + SNP, considerably reduced root-to-shoot translocation of Cd and increased the activities of antioxidant enzymes in both roots and shoots of Cd-stressed plants. The interaction of SA and SNP increased chlorophyll content, P _n and T _r in leaves, and the uptake and translocation of mineral elements, and decreased lipid peroxidation and H₂O₂ and proline accumulation in roots and shoots. These results suggest that SA or SNP, and, in particular, their combination counteracted the negative effects of Cd on ryegrass plants.     

Influence of soil pH on the soybean-endomycorrhiza symbiosis

Summary Soybean (Glycine max {L.} Merr.) cultivars were inoculated withGigaspora gigantea andGlomus mosseae to determine mycorrhizal: cultivar relationships as affected by soil pH. The specific cultivarfungal response was dependent on soil pH. Overall cultivar responses in unlimed soil (pH 5.1) were greater forG. gigantea thanG. mosseae. The Bossier —G. gigantea combination was particularly responsive in unlimed soil and showed an increase of 10% in shoot length, 35% in shoot dry weight. 75% in root dry weight, and 397% in nodule dry weight over uninoculated controls. Little cultivar response was observed withG. mosseae inoculation in unlimed soil. In limed soil (pH 6.2), the larger responses were obtained withG. mosseae inoculated plants, although inoculation with eitherG. mosseae orG. gigantea appeared effective. In general, nodulation was greater on mycorrhizal roots than on control roots.     

Inoculation with arbuscular mycorrhizal fungi suppresses initiation of haustoria in the root hemiparasite Pedicularis tricolor

Background and Aims

Plant parasitism and arbuscular mycorrhizal (AM) associations have many parallels and share a number of regulatory pathways. Despite a rapid increase in investigations addressing the roles of AM fungi in regulating interactions between parasitic plants and their hosts, few studies have tested the effect of AM fungi on the initiation and differentiation of haustoria, the parasite-specific structures exclusively responsible for host attachment and nutrient transfer. In this study, we tested the influence of AM fungi on haustorium formation in a root hemiparasitic plant.

Methods

Using a facultative root hemiparasitic species (Pedicularis tricolor) with the potential to form AM associations, the effects of inoculation were tested with two AM fungal species, Glomus mosseae and Glomus intraradices, on haustorium initiation in P. tricolor grown alone or with Hordeum vulgare ‘Fleet’ (barley) as the host plant. This study consisted of two greenhouse pot experiments.

Key Results

Both AM fungal species dramatically suppressed intraspecific haustorium initiation in P. tricolor at a very low colonization level. The suppression over-rode inductive effects of the parasite''s host plant on haustoria production and caused significant growth depression of P. tricolor.

Conclusions

AM fungi had strong and direct suppressive effects on haustorium formation in the root hemiparasite. The significant role of AM fungi in haustorium initiation of parasitic plants was demonstrated for the first time. This study provides new clues for the regulation of haustorium formation and a route to development of new biocontrol strategies in management of parasitic weeds.     

Role of the modification in root exudation induced by arbuscular mycorrhizal colonization on the intraradical growth of Phytophthora nicotianae in tomato

We studied the role of modification in root exudation induced by colonization with Glomus intraradices and Glomus mosseae in the growth of Phytophthora nicotianae in tomato roots. Plants were grown in a compartmentalized plant growth system and were either inoculated with the AM fungi or received exudates from mycorrhizal plants, with the corresponding controls. Three weeks after planting, the plants were inoculated or not with P. nicotianae growing from an adjacent compartment. At harvest, P. nicotianae biomass was significantly reduced in roots colonized with G. intraradices or G. mosseae in comparison to non-colonized roots. Conversely, pathogen biomass was similar in non-colonized roots supplied with exudates collected from mycorrhizal or non-mycorrhizal roots, or with water. We cannot rule out that a mycorrhiza-mediated modification in root exudation may take place, but our results did not support that a change in pathogen chemotactic responses to host root exudates may be involved in the inhibition of P. nicotianae.