Anisohydric behaviour in grapevines results in better performance under moderate water stress and recovery than isohydric behaviour

Aims

Arbuscular mycorrhizal fungi (AMF) can control root-knot nematode infection, but the mode of action is still unknown. We investigated the effects of AMF and mycorrhizal root exudates on the initial steps of Meloidogyne incognita infection, namely movement towards and penetration of tomato roots.

Methods

M. incognita soil migration and root penetration were evaluated in a twin-chamber set-up consisting of a control and mycorrhizal (Glomus mosseae) plant compartment (Solanum lycopersicum cv. Marmande) connected by a bridge. Penetration into control and mycorrhizal roots was also assessed when non-mycorrhizal or mycorrhizal root exudates were applied and nematode motility in the presence of the root exudates was tested in vitro.

Results

M. incognita penetration was significantly reduced in mycorrhizal roots compared to control roots. In the twin-chamber set-up, equal numbers of nematodes moved to both compartments, but the majority accumulated in the soil of the mycorrhizal plant compartment, while for the control plants the majority penetrated the roots. Application of mycorrhizal root exudates further reduced nematode penetration in mycorrhizal plants and temporarily paralyzed nematodes, compared with application of water or non-mycorrhizal root exudates.

Conclusions

Nematode penetration was reduced in mycorrhizal tomato roots and mycorrhizal root exudates probably contributed at least partially by affecting nematode motility.     

Arbuscular mycorrhizal fungi can alter some root characters and physiological status in trifoliate orange (<Emphasis Type="Italic">Poncirus trifoliata</Emphasis> L. Raf.) seedlings

Citrus plants strongly depend on mycorrhizal symbiosis because of less or no root hairs, but few reports have studied if their root traits and physiological status could be altered by different arbuscular mycorrhizal fungi (AMF). In a pot experiment we evaluated the effects of three AMF species, Glomus mosseae, G. versiforme and Paraglomus occultum on the root traits and physiological variables of the trifoliate orange (Poncirus trifoliata L. Raf.) seedlings. Root mycorrhizal colonization was 58–76% after 180 days of inoculation. AMF association significantly increased plant height, stem diameter, leaf number per plant, shoot and root biomass. Mycorrhizal seedlings also had higher total root length, total root projected area, total root surface area and total root volume but thinner root diameter. Among the three AMFs, greater positive effects on aboveground growth generally ranked as G. mosseae > P. occultum > G. versiforme, whilst on root traits as G. mosseae ≈ P. occultum > G. versiforme. Compared to the non-mycorrhizal seedlings, contents of chlorophyll, leaf glucose and sucrose, root soluble protein were significantly increased in the mycorrhizal seedlings. In contrast, root glucose and sucrose, leaf soluble protein, and activity of peroxidase (POD) in both leaves and roots were significantly decreased in the mycorrhizal seedlings. It suggested that the improvement of root traits could be dependent on AMF species and be related to the AMF-induced alteration of carbohydrates and POD.     

The effect of Meloidogyne incognita on the histopathology of Momordica charantia roots

Bitter gourd (Momordica charantia L.) was inoculated with root-knot nematode Meloidogyne incognita to investigate the anatomical abnormalities in the affected roots. Soon after inoculation the second-stage juveniles (J2) entered at or near the root caps and migrated intercellularly towards the zone of vascular differentiation. Discrete giant cells were observed after three days of inoculation. The nematode induced hypertrophy and hyperplasia near the giant cells. After six days, the juveniles moulted to their third stage (J3). At the same, time giant cell size and density of giant cell cytoplasm increased. The continuity of vascular strands remained unaffected. Between 12 and 24 days of inoculation the giant cells enlarged several times and became multinucleate and enclosed dense and granular cytoplasm. The nematodes became almost pyriform 18 days after inoculation. The orientation of vascular strands changed, due to hypertrophy, hyperplasia and enlargement of the nematode. After 30 days of inoculation the nematodes developed into mature females and started egg laying. A large amount of parenchyma transformed into abnormal xylem.     

Effect of root-rot fungus (Macrophomina phaseolina) on the life cycle of root-knot nematode (Meloidogyne javanica) Race-2 on balsam

The penetration of second stage juveniles of Meloidogyne javanica started within 12 hours after inoculation and the rate of penetration gradually increased with the passage of time up to the fifth day in the plants inoculated with root-knot nematode alone and up to the sixth day when plants were infected with root-knot nematode and root-rot fungus. Mostly, the penetration of second stage juveniles of Meloidogyne javanica took place in the meristematic region but in some cases the juveniles also penetrated into the root tips and oriented themselves near the stellar region almost parallel to the longitudinal axis of the roots. The life cycle of Meloidogyne javanica on balsam was completed within 25 days, whereas the duration of the life cycle and fecundity of females was adversely affected in the presence of fungus (Macrophomina phaseolina) and it took about 33 days to complete the life cycle, i.e. the presence of Macrophomina phaseolina delayed the life cycle of the root-knot nematode (Meloidogyne javanica) by eight days.     

Effects of Co-Inoculation with Arbuscular Mycorrhizal Fungi and Rhizobia on Fungal Occupancy in Chickpea Root and Nodule Determined by Real-Time PCR

Legume roots in nature are usually colonized with rhizobia and different arbuscular mycorrhizal fungi (AMF) species. Light microscopy that visualizes the presence of AMF in roots is not able to differentiate the ratio of each AMF species in the root and nodule tissues in mixed fungal inoculation. The purpose of this study was to characterize the dominant species of mycorrhiza in roots and nodules of plants co-inoculated with mycorrhizal fungi and rhizobial strains. Glomus intraradices (GI), Glomus mosseae (GM), their mix (GI + GM), and six Mesorhizobium ciceri strains were used to inoculate chickpea. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to assess occupancy of these fungal species in roots and nodules. Results showed that GI molecular ratio and relative density were higher than GM in both roots and nodules. These differences in molecular ratio and density between GI and GM in nodules were three folds higher than roots. The results suggested that M. ciceri strains have different effects on nodulation and mycorrhizal colonization pattern. Plants with bacterial S3 and S1 strains produced the highest root nodulation and higher fungal density in both the roots and nodules.     

Interaction of vesicular arbuscular mycorrhiza with root knot nematodes in tomato

Summary The interaction between the VA mycorrhizal fungus,Glomus fasciculatus and the root-knot nematodes,Meloidogyne incognita andM. javanica, and their effects on the growth and phosphorus nutrition of tomato was studied in a red sandy loam soil of pH 6.0. Inoculation of tomato roots with root-knot nematodes enhanced infection and spore production byG. fasciculatus. Inoculation of tomato plants withG. fasciculatus significantly reduced the number and size of the root-knot galls produced byM. incognita andM. javanica. Inoculation withG. fasciculatus although improved plant growth and its total phosphorus content compared to the uninoculated plants, the difference were not statistically significant.     

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.     

Arbuscular mycorrhiza‐mediated resistance in tomato against Cladosporium fulvum‐induced mould disease

Root colonization with arbuscular mycorrhizal fungi (AMF) enhances plant resistance particularly against soil‐borne pathogenic fungi. In this study, mycorrhizal inoculation with Glomus mosseae (Gm) significantly alleviated tomato mould disease caused by the air‐borne fungal pathogen, Cladosporium fulvum (Cf). The disease index (DI) in local leaves (receiving pathogen inoculation) and systemic leaves (just above the local leaf without pathogen inoculation) was 36.4% and 11.7% in mycorrhizal plants, respectively, whereas DI was 59.6% and 36.4% in the corresponding leaves of AMF non‐inoculated plants, after 50 days of Gm inoculation, corresponding to 15 days after Cf inoculation by leaf infiltration. Foliar spray inoculation with Cf also revealed that AMF pre‐inoculated plants had a higher resistance against subsequent pathogen infection, where the DI was 41.3% in mycorrhizal plants vs. 64.4% in AMF non‐inoculated plants. AMF‐inoculated plants showed significantly higher fresh and dry weight than non‐inoculated plants under both control (without pathogen) and pathogen treatments. AMF‐inoculated plants exhibited significant increases in activities of superoxide dismutase and peroxidase, along with decreases in levels of H₂O₂ and malondialdehyde, compared with non‐inoculated plants after pathogen inoculation. AMF inoculation led to increases in total chlorophyll contents and net photosynthesis rate as compared with non‐inoculated plants under control and pathogen infection. Pathogen infection on AMF non‐inoculated plants led to decreases in chlorophyll fluorescence parameters. However, pathogen infection did not affect these parameters in mycorrhizal plants. Taken together, these results indicate that AMF colonization may play an important role in plant resistance against air‐borne pathogen infection by maintaining redox poise and photosynthetic activity.     

Physiological and biochemical changes in tomato cultivar PT-3 with dual inoculation of mycorrhiza and PGPR against root-knot nematode

Arbuscular mycorrhizal fungi (AMF) and plant growth promoting rhizobacteria (PGPR) have potential to control soil-borne diseases including plant-parasitic nematodes. First, the effects of dual inoculation of mycorrhiza (Rhizophagus irregularis) and two stains of pseudomonads (Pseudomonas jessenii strain R62 and Pseudomonas synxantha strain R81) on tomato (Solanum lycopersicum cv. PT-3) growth were tested. Further, the physiological and biochemical changes caused by these beneficial organisms during infection by the root-knot nematode Meloidogyne incognita were studied. The experiment was conducted under glass house conditions and carried out up to one month after nematode inoculation. Plants treated with dual or individual inoculation of AMF and PGPR showed significantly enhanced plant growth and reduced nematode infection. In addition, they exhibited potent activity of phenolics (28 %) and defensive enzymes i.e. peroxidase (PO; 1.26 fold), polyphenyloxidase (PPO; 1.35 fold) and superoxide dismutase (SOD; 1.09 fold) while a significant reduction in malondialdehyde (MDA; 1.63 fold) and hydrogen peroxide (H₂O₂; 1.30 fold) content was recorded when compared to the nematode-infected plants. These findings indicate the feasibility of AMF and PGPR individually or in combinations as potential biocontrol agents for the management of root-knot nematodes.     

Relative mycorrhizal dependency and mycorrhiza-nematode interaction in banana cultivars (Musa spp.) differing in nematode susceptibility

Four Musa cultivars, differing in nematode susceptibility, were selected to study their relative mycorrhizal dependency and to study the interaction between the arbuscular mycorrhizal fungus (AMF), Glomus mosseae, and two migratory endoparasitic nematodes, Radopholus similis and Pratylenchus coffeae. Mycorrhization with G. mosseae resulted in significantly better plant growth, even in the presence of R. similis and P. coffeae. No differences in relative mycorrhizal dependency (RMD) were observed among the four cultivars. G. mosseae suppressed nematode population build-up in Grande Naine and Pisang Jari Buaya. Only in the case of R. similis (Indonesian population) in Pisang Jari Buaya, no significant suppression was observed. In the case of P. coffeae, the AMF reduced the damage in the roots, caused by the nematodes. For R. similis, no reduction of damage was observed. In all, except one experiment, the frequency of the mycorrhizal colonisation was negatively affected by the nematodes.     

Suppression of the root-knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood] on tomato by dual inoculation with arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria

Arbuscular mycorrhizal (AM) fungi and plant growth-promoting rhizobacteria (PGPR) have potential for the biocontrol of soil-borne diseases. The objectives of this study were to quantify the interactions between AM fungi [Glomus versiforme (Karsten) Berch and Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe] and PGPR [Bacillus polymyxa (Prazmowski) Mace and Bacillus sp.] during colonization of roots and rhizosphere of tomato (Lycopersicon esculentum Mill) plants (cultivar Jinguan), and to determine their combined effects on the root-knot nematode, Meloidogyne incognita, and on tomato growth. Three greenhouse experiments were conducted. PGPR increased colonization of roots by AM fungi, and AM fungi increased numbers of PGPR in the rhizosphere. Dual inoculations of AM fungi plus PGPR provided greater control of M. incognita and greater promotion of plant growth than single inoculations, and the best combination was G. mosseae plus Bacillus sp. The results indicate that specific AM fungi and PGPR can stimulate each other and that specific combinations of AM fungi and PGPR can interact to suppress M. incognita and disease development.     

Utilization of noxious weeds for the management of plant-parasitic nematodes infesting some vegetable crops: Einsatz von schädlichen unkräutern zur bekämpfung von pflanzenparasitären nematoden auf verschiedenen gëmusekulturen

Significant reduction was observed in the population of plant-parasitic nematodes, Meloidogyne incognita, Rotylenchulus reniformis and Tylenchorhynchus brassicae infesting eggplant and cauliflower when given root-dip treatment in the leaf extracts of Argemone maxicana and Solanum xanthocarpum at different concentrations and dip durations. The root-knot development and larval penetration of second stage juveniles of M. incognita were also inhibited, may be due to bare-root dip treatment in leaf extracts of both the weed plants. Leaf extracts of S. xanthocarpum caused more inhibition in root-knot development, nematode multiplication of reniform and stunt nematodes than that of A. maxicana. Plant growth improvement was noted which seems to be due to dip treatment and reduction in the population of parasitic nematodes. The efficacy of root-dip treatment with respect to improvement in plant growth of eggplant and cauliflower and reduction in root-knot development and nematode population, increased with increasing the concentration of leaf extracts and dip durations.     

Separation and purification of a keratinase as pesticide against root-knot nematodes

A new alkaline keratinase, which could kill Meloidogyne incognita (a root-knot nematode) was separated and purified from Bacillus sp. 50-3 in this study. The solid ammonium sulfate was selected to precipitate the enzyme and its proper adding mass was also determined. After solid ammonium sulfate precipitation and liquid chromatography on DEAE-Sephadex-A50 column, there was 17.7-fold purification with a yield of 46.5%, as determined by azokeratin as substrate. The purification effect was determined through SDS-PAGE and the molecular weight of the enzyme was found to be 27,423 Da by the MALDI-TOF-MS. When the second-stage juveniles of Meloidogyne incognita were exposed to 50 μg/ml of keratinase solution, 98.5% of Meloidogyne incognita mortality rates were obtained compared to control after 24 h. Its simple purification step and high yield from the cheap medium affords this keratinase great biotechnological potential, especially in controlling root-knot nematodes such as Meloidogyne incognita. To the best of our knowledge, this study is the first report that uses keratinase as a pesticide.     

Root-knot development in mulberry infested with Meloidogyne incognita

Healthy mulberry roots were inoculated with second stage juveniles of the root-knot nematode, Meloidogyne incognita and the sequential anatomical changes in the root concurrent with the development of the nematode were studied with light and scanning electron microscopes. Visible anatomical changes occurred four weeks post-inoculation when the pear-shaped adult female nematodes appeared in the tissues. The infected roots lost their circular outline and increased in thickness as traumatic parenchyma was induced in the root. The stele was disorganised with reduced and deformed vascular elements. Many giant cells developed in the traumatic tissue, adjacent to the adult females. Eight weeks after the inoculation, cavities developed around the adult females by tissue disintegration, and the galls became discernable on the roots. The number and size of thegalls increased in the next three weeks, corresponding to the development of more traumatic tissues and the enlargement of the adult female nematodes. The majority of the nematodes were settled towards the gall periphery, with their posterior oriented outwards for the release of their eggs into soil by the disintegration of the outer root layers. But many were settled deep inside the gall tissue without a channel to release their eggs to soil. The inner cavities enlarged in large proportions, sometimes occupying the major volume of the gall. The conductive tissues of the root were totally disorganised or were nonexistent.     

Effects of dual inoculation of mycorrhiza and endophytic,rhizospheric or parasitic bacteria on the root-knot nematode disease of tomato

The effects of mycorrhisation and inoculation with soil bacteria on the disease caused by Meloidogyne incognita on tomato were studied in pots under greenhouse conditions. Efficacy in promoting plant growth and reducing disease severity and final nematode densities were evaluated for two arbuscular mycorrhizal fungi (AMF; Funneliformis mosseae and Rhizophagus irregularis), three soil bacteria with different living strategies (the endophyte Bacillus megaterium, a rhizospheric Pseudomonas putida and the hyperparasite of nematodes Pasteuria penetrans) and combinations of the fungi and bacteria. In M. incognita-infested plants, F. mosseae increased tomato growth more than R. irregularis, and plants inoculated with B. megaterium presented higher shoot fresh weight than with P. putida or P. penetrans, but dual inoculation did not improve tomato growth more than single inoculations. Disease severity and final nematode densities were reduced by F. mosseae compared to non-mycorrhizal plants. B. megaterium and P. penetrans reduced both the root galling and the final nematode densities compared to treatments without bacteria. P. penetrans reduced final nematode densities more than B. megaterium or P. putida. Dual inoculation of AMF and P. penetrans showed the highest efficacy in reducing the final nematode densities in tomato.     

Possible utilization of weeds for the management of plant parasitic nematodes infesting some vegetable crops

Leaf extracts of noxious weeds such as Solanum xanthocarpum and Argemone maxicana were used as bare-root dip treatment for the management of three important plant-parasitic nematodes, Meloidogyne incognita, Rotylenchulus reniformis and Tylenchorhynchus brassicae infesting tomato (Lycopersicon esculantum ) and chilli (Capsicum annuum) plants. Significant reduction was observed in the root-knot development caused by M. incognita, multiplication of nematode populations of R. reniformis and T. brassicae on both the test plants. Larval penetration of second stage juveniles of M. incognita was also inhibited at various concentrations of leaf extracts and dip durations. Leaf extract of S. xanthocarpum caused relatively more inhibition in root-knot development in case of root-knot nematode, nematode multiplication of reniform and stunt nematodes than that of A. maxicana. Because of dip treatment in leaf extracts of Argemone maxicana and Solanum xanthocarpum, the plants show better growth and at the same time the populations of nematodes such as M. incognita, R. reniformis and T. brassicae significantly decreased, which naturally improved plant growth. The efficacy of root-dip treatment with respect to improvement in plant weight and reduction in root-knot development and nematode populations, increased with increasing the concentration of leaf extracts and dip durations.     

Effects of Resistance in Phaseolus vulgaris on Development of Meloidogyne Species

Use of resistant Phaseolus vulgaris germplasm has a potential role in limiting damaging effects of Meloidogyne spp. on bean production. Effects of two genetic resistance systems in common bean germptasm on penetration and development of Meloidogyne spp. were studied under growth room conditions at 22°C to 25°C. Nemasnap (gene system 1) and G1805 (gene system 2) were inoculated with second-stage juveniles (J2) of M. incognita race 2 and M. arenaria race 1, respectively; Black Valentine was used as the susceptible control. Up to 7 days after inoculation, there were no differences in numbers of M. incognita J2 penetrating roots of Black Valentine and Nemasnap; subsequently, more nematodes were present in Black Valentine roots (P < 0.05). More nematodes reached advanced stages of development in Black Valentine than in Nemasnap roots (P < 0.05). Total numbers of M. arenaria were greater in Black Valentine than in G 1805 roots from 14 days after inoculation (P < 0.05). Advanced stages of development occurred earlier and in greater numbers in Black Valentine plants than in G1805 plants. In these studies, resistance to M. incognita race 2 and M. arenaria race 1 in bean germplasm, which contain gene system 1 and gene system 2, respectively, was expressed by delayed nematode development rather than by differential penetration compared with susceptible plants.     

Interaction of Vesicular-Arbuscular Mycorrhizae and Cultivars of Alfalfa Susceptible and Resistant to Meloidogyne hapla

The interaction between vesicular-arbuscular mycorrhizal (VAM) fungi and the root-knot nematode (Meloidogyne hapla) was investigated using both nematode-susceptible (Grasslands Wairau) and nematode-resistant (Nevada Synthetic XX) cultivars of alfalfa (Medicago sativa) at four levels of applied phosphate. Mycorrhizal inoculation improved plant growth and reduced nematode numbers and adult development in roots in dually infected cultures of the susceptible cultivar. The tolerance of plants to nematode infection and development when preinfected with mycorrhizal fungi was no greater than when they were inoculated with nematodes and mycorrhizal fungi simultaneously. Growth of plants of the resistant cultivar was unaffected by nematode inoculation but was improved by mycorrhizal inoculation. Numbers of nematode juveniles were lower in the roots of the resistant than of the susceptible cultivar and were further reduced by mycorrhizal inoculation, although no adult nematodes developed in any resistant cultivar treatment. Inoculation of alfalfa with VAM fungi increased the tolerance and resistance of a cultivar susceptible to M. hapla and improved the resistance of a resistant cultivar.     

Does the sequence of plant dominants affect mycorrhiza development in simulated succession on spoil banks?

The aim of this field study was to examine how the development of arbuscular mycorrhizal fungi (AMF) on coal mine spoil banks is affected by the presence of plants with different mycorrhizal status. A 3-year trial was conducted on the freshly created spoil bank Vršany, North-Bohemian coal basin, the Czech Republic. Three plant species – non-mycotrophic annual Atriplex sagittata, highly mycotrophic annual Tripleurospermum inodorum (both dominants of early stages of succession) and facultatively mycotrophic Arrhenatherum elatius (a perennial grass species of the later stage of succession) – were planted on 1 m² plots over 3 years in different sequences that simulated the progress of succession on spoil banks. The development of AMF populations was monitored by evaluation of mycorrhizal colonization of plant roots and by measurement of the mycorrhizal inoculation potential (MIP) of soil. These two parameters were compared between plots inoculated with the mixture of three AMF isolates – Glomus mosseae BEG95, G. claroideum BEG96 and G. intraradices BEG140 – (“inoculated plots”) and plots exposed only to natural dispersal of AMF propagules (“uninoculated plots”). Highly colonized roots of plants together with a high MIP of soil in uninoculated plots were already found at the end of the first season, indicating rapid natural dispersal of AMF propagules. Root colonization of facultatively mycotrophic and non-mycotrophic plants in later years was affected by the mycorrhizal status of the previous plant species. The MIP of soil continuously increased throughout the experiment; in uninoculated plots, the MIP was temporarily decreased if plant species of higher mycotrophy were replaced by species of lower mycotrophy. The results lead to the conclusion that AMF colonize freshly formed sites very quickly and reproduce or accumulate in the soil, which leads to increasing MIP values. However, this infective potential can be decreased if non-mycotrophic plants predominate on the site.