Improved growth of salinity-stressed soybean after inoculation with salt pre-treated mycorrhizal fungi

Two sets of experiments to determine the effect of mycorrhiza on soybean (Glycine max) growth under saline conditions and to investigate the salt acclimation of mycorrhizal fungi were conducted. In the first experiment, the effect of an arbuscular mycorrhizal (AM) fungus Glomus etunicatum on mineral nutrient, proline and carbohydrate concentrations and growth of soybean. Under different NaCl concentrations (0, 50, 100, 150 and 200mM) was evaluated. Salinity decreased AM colonization. In both the M and nonAM plants shoot and root proline and shoot Na and Zn concentrations were increased under salinity. Soybean plants inoculated with the AM fungus had significantly higher fresh and dry weight, root proline, P, K and Zn but lower shoot proline and Na concentrations compared to the non inoculated plants. In the second experiment, the AM fungus was pre-treated with NaCl (salt acclimation) then was used as inoculum for soybean plants subjected to 100mM NaCl. Root colonization, fresh and dry weight, root proline, P, K and Zn concentrations were greater in soybean plants inoculated with the salt pre-treated fungus, compared to those inoculated with the nonsalt pre-treated fungus. However, for Na, the situation was the opposite. Based on these results, the AM inoculation helps the growth of soybean plants grown in saline conditions. When the AM fungus was pre-treated with NaCl with a gradual increase of concentration, and then exposed to a sudden salt stress, their efficiency was increased. This may be due to the acclimation of the AM fungus to salinity.     

Xyloglucanases in the interaction between saprobe fungi and the arbuscular mycorrhizal fungus Glomus mosseae

We studied the production of xyloglucanase enzymes of pea and lettuce roots in the presence of saprobe and arbuscular mycorrhizal (AM) fungi. The AM fungus Glomus mosseae and the saprobe fungi Fusarium graminearum, Fusarium oxysporum-126, Trichoderma harzianum, Penicillium chrysogenum, Pleurotus ostreatus and Aspergillus niger were used. G. mosseae increased the shoot and root dry weight of pea but not of lettuce. Most of the saprobe fungi increased the level of mycorrhization of pea and lettuce, but only P. chrysogenum and T. harzianum inoculated together with G. mosseae increased the dry weight of pea and lettuce respectively. The AM and saprobe fungi increased the production of xyloglucanases by plant roots. The level of xyloglucanase activities and the number of xyloglucanolytic isozymes in plants inoculated with G. mosseae and most of the saprobe fungi tested were higher than when both microorganisms were inoculated separately. The possible relationship between xylogucanase activities and the ability of AM and saprobe fungi to improve the dry weight and AM root colonization of plants was discussed.     

Seasonal variation of arbuscular mycorrhizal fungi in temperate grasslands along a wide hydrologic gradient

We studied seasonal variation in population attributes of arbuscular mycorrhizal (AM) fungi over 2 years in four sites of temperate grasslands of the Argentinean Flooding Pampas. The sites represent a wide range of soil conditions, hydrologic gradients, and floristic composition. Lotus glaber, a perennial herbaceous legume naturalised in the Flooding Pampas, was dominant at the four plant community sites. Its roots were highly colonised by AM fungi. Temporal variations in spore density, spore type, AM root colonisation, floristic composition and soil chemical characteristics occurred in each site and were different among sites. The duration of flooding had no effect on spore density but depressed AM root colonisation. Eleven different types of spores were recognized and four were identified. Two species dominated at the four sites: Glomus fasciculatum and Glomus intraradices. Spore density was highest in summer (dry season) and lowest in winter (wet season) with intermediate values in autumn and spring. Colonisation of L. glaber roots was highest in summer or spring and lowest in winter or autumn. The relative density of G. fasciculatum and G. intraradices versus Glomus sp. and Acaulospora sp. had distinctive seasonal peaks. These seasonal peaks occurred at all four sites, suggesting differences among AM fungus species with respect to the seasonality of sporulation. Spore density and AM root colonisation when measured at any one time were poorly related to each other. However, spore density was significantly correlated with root colonisation 3 months before, suggesting that high colonisation in one season precedes high sporulation in the next season.     

Interactions between vesicular-arbuscular mycorrhizal fungi and asparagus

Summary The vesicular-arbuscular mycorrhizal (VAM) fungus,Glomus versiforme increased significantly the growth ofAsparagus officinalis under controlled conditions using Turface as the growth medium. The growth responses, including increases in root fresh weight, numbers of shoots, shoot dry weight, and shoot height follow a pattern similar to other mycorrhizal systems. Indigenous VAM fungi appeared to have negative effects on average shoot fresh and dry weight, number of shoots per pot and average shoot height on one year oldA. officinalis seedlings obtained from the field and grown under controlled conditions. These results may be due either to the high levels of soluble phosphate present in the soil or the ineffectiveness of the particular indigenous fungi as mycorrhizal fungi in asparagus. Indigenous mycorrhizal fungi overwinter in asparagus root crown as vesicles and as external and internal hyphae. Soil obtained from the same fields as the one year old crowns was a good source of mycorrhizal inoculum for sterile seedlings.     

The impact of arbuscular mycorrhizal fungi on plant growth following herbivory: A search for pattern

Arbuscular mycorrhizal (AM) fungi can facilitate nutrient uptake and increase host plant growth but also place constraints on the host's carbon budget. When plants are stressed by herbivory the net effect of the symbiosis may be altered tolerance. Individual experiments manipulating AM fungi and herbivory have demonstrated increased, decreased, and no effect on tolerance but patterns with respect to plant, herbivore, or fungus characteristics have not emerged. Meta-analysis of published results from factorial experiments was used to describe the size of the effects of herbivory and of AM fungi on host growth when factors such as cause of damage, inoculum, and host characteristics are considered, and to determine whether AM fungi alter the effects of herbivory. Also, the correlation between the effect of AM fungi on tolerance and resistance was tested with data from studies that examined insect performance. Herbivory strongly and consistently reduced shoot and root growth, especially in perennial plants and crops. AM fungi increased shoot growth of perennials but not annuals, and when insects caused damage but not when artificial defoliation was applied. Root growth was consistently greater with AM fungi. The interaction of AM fungi and herbivory, which indicates whether AM fungi alter the effects of herbivory, was variable and never significant overall but homogeneity tests indicated underlying structure. In experiments that used single species inoculum, Glomus intraradices increased, whereas Glomus mosseae reduced, effects of herbivory on shoot growth. Multispecies inocula magnified effects of herbivory on root growth whereas single species inocula ameliorated effects. The impact of AM fungi on resistance to herbivory was positively correlated with the impact on tolerance; however AM fungi reduced both tolerance and resistance in many cases. Review of these results with respect to the types of systems studied suggests directions for future investigation.     

Community of arbuscular mycorrhizal fungi in drought-resistant plants, <Emphasis Type="Italic">Moringa</Emphasis> spp., in semiarid regions in Madagascar and Uganda

The community structure of arbuscular mycorrhizal (AM) fungi in the roots of drought-resistant trees, Moringa spp., was examined in semiarid regions in Madagascar and Uganda. Root samples were collected from 8 individuals of M. hildebrandtii and 2 individuals of M. drouhardii in Madagascar and from 21 individuals of M. oleifera in Uganda. Total DNA was extracted from the root samples, and partial nSSU rDNA of AM fungi was amplified using a universal eukaryotic primer NS31 and an AM fungalspecific primer AM1. The PCR products were cloned and divided by restriction fragment length polymorphism (RFLP) analysis with HinfI and RsaI. Some representatives in each RFLP types were sequenced, and a neighbor-joining phylogenetic analysis was conducted for the obtained sequences with analogous sequences of AM fungi. The RFLP and phylogenetic analyses showed that AM fungi closely related to Glomus intraradices or G. sinuosum were detected in many samples. The AM fungal groups frequently detected in the Moringa spp. might be widely distributed species in semiarid environments.     

Arbuscular mycorrhizal fungi associated with common pteridophytes in Dujiangyan,southwest China

The colonization and diversity of arbuscular mycorrhizal (AM) fungi associated with common pteridophytes were investigated in Dujiangyan, southwest China. Of the 34 species of ferns from 16 families collected, 31 were colonized by AM fungi. The mean percentage root length colonized was 15%, ranging from 0 to 47%. Nineteen species formed Paris-type and 10 intermediate-type AM. In two ferns, only rare intercellular non-septate hyphae or vesicles were observed in the roots and AM type could not be determined. Of the 40 AM fungal taxa belonging to five genera isolated from rooting-zone soils, 32 belonged to Glomus, five to Acaulospora, one to Archaeospora, one to Entrophospora, and one to Gigaspora. Acaulospora and Glomus were the dominant genera and Glomus versiforme was the most common species. The average AM spore density was 213 per 100 g air-dried soil and the average species richness was 3.7 AM species per soil sample. There was no correlation between spore density and percentage root length colonized by AM fungi.     

Arbuscular mycorrhizal fungi from three genera induce two-phase plant growth responses on a high P-fixing soil

Plant growth enhancing effects of arbuscular mycorrhizal (AM) fungi are suitably quantified by comparisons of mycorrhizal and non-mycorrhizal plant growth responses to added phosphorus (P). The ratio between the amounts of added P required for the same yield of mycorrhizal and non-mycorrhizal plants is termed the relative effectiveness of the mycorrhiza. Variation in this relative effectiveness was examined for subterranean clover grown on a high P-fixing soil. Plants were either left non-mycorrhizal or inoculated with one of three AM fungal species with well-characterised differences in external hyphal spread. With no P added, plants from all treatments produced <10% of their maximum growth achieved at non-limiting P supply. The growth response of non-mycorrhizal plants was markedly sigmoid. Mycorrhizal growth responses were not sigmoid but their shape was two-phased. The first phase was an asymptotic approach to 25–30% of maximum growth, followed by a second asymptotic rise to maximum growth. Growth effects of Glomus invermaium and Acaulospora laevis were quite similar. Plants in these treatments produced up to four times greater shoot dry biomass than non-mycorrhizal plants. Scutellospora calospora was less effective. The relative effectiveness of AM fungi varied with the level of P application. This is expected to apply to all soils on which a sigmoid response is obtained for growth of non-mycorrhizal plants. In a simple approximation the relative effectiveness was calculated to range from 1.46 to 15.57. Shoot P contents were increased by up to 25 times by A. laevis, significantly more than by the other two fungi. The further mycelial spread of this fungus is thought to have contributed to its relatively greater effect on plant P content.     

Response of the grapevine rootstock Richter 110 to inoculation with native and selected arbuscular mycorrhizal fungi and growth performance in a replant vineyard

Two indigenous arbuscular mycorrhizal (AM) fungi from the Mediterranean wine growing area in the Northeast of Spain were isolated and classified as Glomus intraradices Schenck & Smith. Both native fungi were found to increase the growth of the vine rootstock 110 Richter under greenhouse conditions compared with G. intraradices (BEG 72) and a phosphorus (P) fertilization treatment. The effectivity of field inoculation of Cabernet Sauvignon plants grafted on Richter 110 with the former native fungi and with G. intraradices BEG 72 in a replant vineyard severely infested by the root-rot fungus Armillaria mellea (Vahl ex Fr.) Kummer was assessed. The native fungi were not effective at enhancing plant development, and only G. intraradices BEG 72, resulted in a positive response. Field inoculation with this selected fungus increased plant shoot dry weight at the end of the first growing season.     

Effects of three AM fungi on growth, distribution of glandular hairs, and essential oil production in Ocimum basilicum L. var. Genovese

The essential oils of basil are widely used in the cosmetic, pharmaceutical, food, and flavoring industries. Little is known about the potential of arbuscular mycorrhizal (AM) fungi to affect their production in this aromatic plant. The effects of colonization by three AM fungi, Glomus mosseae BEG 12, Gigaspora margarita BEG 34, and Gigaspora rosea BEG 9 on shoot and root biomass, abundance of glandular hairs, and essential oil yield of Ocimum basilicum L. var. Genovese were studied. Plant P content was analyzed in the various treatments and no differences were observed. The AM fungi induced various modifications in the considered parameters, but only Gi. rosea significantly affected all of them in comparison to control plants or the other fungal treatments. It significantly increased biomass, root branching and length, and the total amount of essential oil (especially α-terpineol). Increased oil yield was associated to a significantly larger number of peltate glandular trichomes (main sites of essential oil synthesis) in the basal and central leaf zones. Furthermore, Gi. margarita and Gi. rosea increased the percentage of eugenol and reduced linalool yield. Results showed that different fungi can induce different effects in the same plant and that the essential oil yield can be modulated according to the colonizing AM fungus.     

Influence of soil organic matter decomposition on arbuscular mycorrhizal fungi in terms of asymbiotic hyphal growth and root colonization

Soil organic matter is known to influence arbuscular mycorrhizal (AM) fungi, but limited information is available on the chemical components in the organic matter causing these effects. We studied the influence of decomposing organic matter (pure cellulose and alfalfa shoot and root material) on AM fungi after 30, 100, and 300 days of decomposition in nonsterile soil with and without addition of mineral N and P. Decomposing organic matter affected maize root length colonized by the AM fungus Glomus claroideum in a similar manner as other plant growth parameters. Colonized root length was slightly increased by both nitrogen and phosphorus application and plant materials, but not by application of cellulose. In vitro hyphal growth of Glomus intraradices was increased by soil extracts from the treatments with all types of organic materials independently of mineral N and P application. Pyrolysis of soil samples from the different decomposition treatments revealed in total 266 recognizable organic compounds and in vitro hyphal growth of G. intraradices in soil extract positively correlated with 33 of these compounds. The strongest correlation was found with 3,4,5-trimethoxybenzoic acid methyl ester. This compound is a typical product of pyrolysis of phenolic compounds produced by angiosperm woody plants, but in our experiment, it was produced mainly from cellulose by some components of the soil microflora. In conclusion, our results indicate that mycelia of AM fungi are influenced by organic matter decomposition both via compounds released during the decomposition process and also by secondary metabolites produced by microorganisms involved in organic matter decomposition.     

Application of in vitro methods to study carbon uptake and transport by AM fungi

Just as multi-compartmented root chambers have advantages over standard plastic pots for the study of nutrient uptake by arbuscular mycorrhizal [AM] fungi in soil, so the split-plate in vitro system has advantages over the standard dual culture system for the study of the physiology of AM fungi. We used the split-plate culture system of Ri T-DNA transformed Daucus carota L. roots and Glomus intraradices Schenck & Smith, in which only the fungus has access to the distal compartment, to study the ability of germ tubes and extraradical and intraradical hyphae to take up ¹³C-labeled substrates. Labeled substrates were added to one side of the plate divider and plates were incubated for 8 weeks while the fungus proliferated on the side from which the root was excluded. Tissues then were recovered from the plate and examined via NMR spectroscopy. Results showed that the morphological phases of the fungus differed in their ability to take up these substrates, most notably that intraradical hyphae take up hexose while extraradical hyphae cannot. In addition, NMR studies indicated that intraradical hyphae actively synthesized lipids while extraradical hyphae did not. These data show that eventual axenic culture of AM fungi is more than a matter of finding the proper substrate for growth. Genetic regulation must be overcome to make extraradical hyphae behave like intraradical hyphae in terms of C uptake and metabolism. This revised version was published online in June 2006 with corrections to the Cover Date.     

Community analysis of arbuscular mycorrhizal fungi in a warm-temperate deciduous broad-leaved forest and introduction of the fungal community into the seedlings of indigenous woody plants

A community of arbuscular mycorrhizal (AM) fungi was investigated in a warm-temperate deciduous broad-leaved forest using a molecular analysis method. Root samples were obtained from the forest, and DNA was extracted from the samples. Partial 18S rDNA of AM fungi were amplified from the extracted DNA by polymerase chain reaction using a universal eukaryotic primer NS31 and an AM fungal-specific primer AM1. After cloning the PCR products, 394 clones were obtained in total, which were divided into five types by restriction fragment length polymorphism (RFLP) with HinfI, RsaI, and Hsp92II. More than 20% of the clones were randomly selected from each RFLP type and sequenced. Phylogenetic analysis showed that all the obtained clones belonged to Glomus but could not be identified at species level. Topsoil of the forest containing plant roots was inoculated to nonmycorrhizal seedlings of indigenous woody plants, Rhus javanica var. roxburghii and Clethra barvinervis, to introduce the community of AM fungi into the seedlings. Among these five RFLP types, four types were detected from both seedlings, which indicates that the AM fungal community in the forest root samples was introduced at least partly into the seedlings. Meanwhile, an additional four types that were not found in the forest root samples were newly detected in the seedlings, these types were closely related to one another and close to G. fasciculatum or G. intraradices. It is expected that a community of indigenous diverse AM fungi could be introduced into target fields by planting these mycorrhizal seedlings.     

Production of monoclonal antibodies against surface antigens of spores from arbuscular mycorrhizal fungi by an improved immunization and screening procedure

Monoclonal antibodies (mAbs) were produced against surface antigens of chlamydospores of arbuscular mycorrhizal (AM) fungi by immunizing mice with crushed or complete spores. The intrasplenic approach proved to be superior to the intraperitoneal method of immunization with regard to the amount of antigen required for the immune response. The hybridoma technology was combined with an improved screening procedure, applying an immunogold-silver staining technique to semi-thin sections of spores. In this way, mAbs to surface antigens on the outer wall could be selected. Two mAbs were raised against Glomus etunicatum and G. scintillans spores. Cross-reactivities of the antibodies to other structures of the fungus, to other species of Glomus and to other soil-borne fungi were tested with indirect immunofluorescent labelling. The mAbs did not react with non-AM fungi. One mAb (A5B1) selectively recognized G. etunicatum, another (D12F11) exhibited limited interspecies cross-reactivities. One further mAb (H8F7), which reacted with spores of all AM fungi but not with other fungi, was shown to be specific for Bacillus mycoides. The implications are discussed.     

Influences of Arbuscular Mycorrhizal Fungus Glomus mosseae on Growth and Nutrition of Lentil Irrigated with Arsenic Contaminated Water

Arsenic (As) contamination of irrigation water represents a major constraint to Bangladesh agriculture. While arbuscular mycorrhizal (AM) fungi have their most significant effect on P uptake, they have also been shown to alleviate metal toxicity to the host plant. This study examined the effects of As and inoculation with an AM fungus, Glomus mosseae, on lentil (Lens culinaris L. cv. Titore). Plants were grown with and without AM inoculum for 9 weeks in a sand and terra green mixture 50:50 v/v and watered with five levels of As (0, 1, 2, 5, 10 mg As L⁻¹ arsenate). Inoculum of Rhizobium leguminosarum b.v. Viceae strain 3841 was applied to all plants. Plants were fed with modified Hoagland solution (1/10 N of a full-strength solution and without P). Plant height, leaf number, pod number, plant biomass and shoot and root P concentration/offtake increased significantly due to mycorrhizal infection. Plant height, leaf/ pod number, plant biomass, root length, shoot P concentration/offtake, root P offtake and mycorrhizal infection decreased significantly with increasing As concentration. However, mycorrhizal inoculation reduced As concentration in roots and shoots. This study shows that growing lentil with compatible AM inoculum can minimise As toxicity and increase growth and P uptake.     

Differences in the effects of three arbuscular mycorrhizal fungal strains on P and Pb accumulation by maize plants

The effect of arbuscular mycorrhizal (AM) fungi on the accumulation and transport of lead was studied in a pot experiment on maize plants grown in anthropogenically-polluted substrate. The plants remained uninoculated or were inoculated with different Glomus intraradices isolates, either indigenous to the polluted substrate used or reference from non-polluted soil. A considerably lower tolerance to the conditions of polluted substrate was observed for the reference isolate that showed significantly lower frequency of root colonisation as well as arbuscule and vesicule abundance. Plants inoculated with the reference isolate also had significantly lower shoot P concentrations than plants inoculated with the isolate from polluted substrate. Nevertheless, inoculation with either indigenous or reference G. intraradices isolate resulted in higher shoot and root biomass and inoculated plants showed lower Pb concentrations in their shoots than uninoculated plants, regardless of differences in root colonisation. Root biomass of maize plants was divided according to AM-induced colouration into brightly yellow segments intensively colonised by AM fungus and non-colonised or only slightly colonised whitish ones. Intensively colonised segments of the isolate from polluted substrate contained significantly higher concentrations of phosphorus and lead than non-colonised ones, which suggest significant participation of fungal structures in element accumulation. Responsible Editor: Peter Christie.     

Experiments on competitiveness of three endomycorrhizal fungi

Summary This paper examines competition between three VA endophytes places respectively as “inoculant” fungus in an inner compartment (300 ml) below the germinating seed, and as “indigenous” fungus in an outer compartment (900 ml). Previously prepared infested soil was used as source of the endophytes. Inner and outer compartment roots were harvested separately and percentage infection determined for each fungus, using diagnostic anatomical features of each fungus. Changes in colonisation patterns were followed up to 4 and 5 months. Treatments with non-infested soil in the outer compartment were used to compare infectivity and spread of the different endophytes. All three endophytes were able to invade soil already colonised by either of the other two, butGlomus fasciculatum (E₃) was more invasive thanGlomus tenue. This pattern appeared to be related to rates of spread of the fungi in the non-infested soil. The pattern was not affected by host, clover or sorghum, or by position, immediately below the seed or in the outer compartment. It seemed that the endophyte in the inner compartment had overriding and persistent effects on plant growth, unrelated to its dominance pattern or share of overall root infection at the later harvests.     

Impact of antifungals producing rhizobacteria on the performance of Vigna radiata in the presence of arbuscular mycorrhizal fungi

Plant growth-promoting rhizobacteria (PGPR) that produce antifungal metabolites are potential threats for the arbuscular mycorrhizal (AM) fungi known for their beneficial symbiosis with plants that is crucially important for low-input sustainable agriculture. To address this issue, we used a compartmented container system where test plants, Vigna radiata, could only reach a separate nutrient-rich compartment indirectly via the hyphae of AM fungi associated with their roots. In this system, where plants depended on nutrient uptake via AM symbiosis, we explored the impact of various PGPR. Plants were inoculated with or without a consortium of four species of AM fungi (Glomus coronatum, Glomus etunicatum, Glomus constrictum, and Glomus intraradices), and one or more of the following PGPR strains: phenazine producing (P⁺) and phenazine-less mutant (P⁻), diacetylphloroglucinol (DAPG) producing (G⁺) and DAPG-less mutant (G⁻) strains of Pseudomonas fluorescens, and an unknown antifungal metabolite-producing Alcaligenes faecalis strain, SLHRE425 (D). PGPR exerted only a small if any effect on the performance of AM symbiosis. G⁺ enhanced AM root colonization and had positive effects on shoot growth and nitrogen content when added alone, but not in combination with P⁺. D negatively influenced AM root colonization, but did not affect nutrient acquisition. Principal component analysis of all treatments indicated correlation between root weight, shoot weight, and nutrient uptake by AM fungus. The results indicate that antifungal metabolites producing PGPR do not necessarily interfere with AM symbiosis and may even promote it thus carefully chosen combinations of such bioinoculants could lead to better plant growth.     

亚热带草地中植物优势种与从属种对AM真菌的差异性生长反应

AM真菌能够影响植物生态系统的群落结构.以亚热带草地生态系统为研究对象,调查了两块草地中优势种和从属种的菌根,并在盆栽试验中比较了优势种和从属种对AM真菌的土著菌种和外源菌种Glomus mosseae的生长反应、养分吸收.结果表明,两块草地各自的优势种藿香蓟和两耳草对土著菌种的菌根依赖性分别是41.5%和77.4%,远远高于从属种莎草和毛蓼（16.0%和7.9%）;但是它们对Glomus mosseae的菌根依赖性有所变化,分别是79.6%、44.2%、74.1%和24.9%.这表明,土著菌种是优势种和从属种的形成机制之一,而外源菌种可能改变基于土著菌种而形成的植物群落结构.植株磷营养的分析结果表明,AM真菌对优势种和从属种生长的促进与对磷吸收的促进高度相关,表明AM真菌促进养分吸收是其影响植物群落结构的机制之一.     

New acidic chitinase isoforms induced in tobacco roots by vesicular-arbuscular mycorrhizal fungi

Summary Chitinase activities have been compared in tobacco roots (Nicotiana tabacum cv. Xanthi nc) infected by the pathogenic fungus Chalara elegans or three species of vesicular arbuscular mycorrhizal (VAM) fungi: Glomus versiforme, G. intraradix and G. fasciculatum, using native polyacrylamide gel electrophoresis (PAGE). All previously known acidic chitinase isoforms were stimulated in roots by the pathogenic fungus and by the VAM fungi, while two new acidic chitinase isoforms were specifically induced in response to the endomycorrhizal association. After separation in sodium dodecyl sulphate polyacrylamide denaturing gels (SDS-PAGE) under non-reducing conditions, the estimated apparent molecular mass for these additional acidic chitinase isoforms from VAM-colonized samples was 33 kDa, compared to 30 kDa for the main activity stimulated in C. elegans-infected root extracts.