Effects of arbuscular mycorrhizal fungi on severity of root rot of bananas caused by Cylindrocladium spathiphylli

The interaction between four arbuscular mycorrhizal (AM) fungi, Glomus sp., G. proliferum , G. intraradices and G. versiforme , and the root-rot fungus Cylindrocladium spathiphylli , and subsequent effects on growth and phosphorus nutrition of banana ( Musa acuminata , AAA, cv. Grande Naine) were investigated under glasshouse conditions. Overall, root infection by C. spathiphylli reduced the growth of banana plants, but preinoculation with AM fungi significantly attenuated this detrimental effect. Lower disease severity, stimulation of growth and increase of shoot P content were observed for the plants inoculated with one of the four AM fungi. Glomus sp. and G. proliferum induced the largest increase in growth parameters and shoot P content as compared to G. intraradices and G. versiforme , in the presence as well as in the absence of C. spathiphylli . Root damage caused by C. spathiphylli was decreased in the presence of AM fungi, but the inoculation of mycorrhizal plants with C. spathiphylli also decreased the intensity of AM fungal root colonization, indicating a clear interaction between the two organisms.     

Biocontrol of the pathogen Phytophthora parasitica by arbuscular mycorrhizal fungi is a consequence of effects on infection loci

The impact of colonization by the arbuscular mycorrhizal fungus (AMF) Glomus mosseae on tomato root necrosis caused by the soil-borne pathogen Phytophthora parasitica was investigated. Studies in situ permitted infection loci to be identified and the effects of the AMF on numbers to be elucidated. Effects were significant and, 7 and 16 days after inoculation with zoospores of the pathogen, roots of plants colonized by the AMF had 39% and 30%, respectively, fewer infection loci than those that were not. Concurrent studies of the rate of spread of necrosis within roots showed no changes caused by the AMF. At harvest, 26 days following inoculation with the pathogen, 61% of roots of noncolonized plants were necrotic compared with only 31% in AMF-colonized plants. It is concluded that effects on numbers of infection loci are one mechanism via which AMF achieve biocontrol of this pathogen in tomato. Measures of the effects of the AMF on root system architecture suggest that no significant changes occur and are thus not the reasons for the reduction in infection loci. The implications of these data for agricultural practice and biocontrol research are discussed.     

Suppression of Meloidogyne hapla by arbuscular mycorrhiza fungi (AMF) on pyrethrum in Kenya

Two arbuscular mycorrhiza fungi (AMF) isolated from a pyrethrum-growing region in Kenya were screened for efficacy against a nematode, Meloidogyne hapla, in greenhouses. The fungi were identified at INVAM (International Culture Collection of Vesicular Arbuscular Mycorrhizal Fungi) as Glomus etunicatum (Isolate KS18) and Glomus sp. (Isolate KS14). Isolate KS14 (Glomus sp.) significantly suppressed nematode population, growth and development by up to 54%, egg production by up to 75% and disease severity by up to 71%. Glomus etunicatum (Isolate KS18) suppressed nematode growth and development by up to 50%, egg production by up to 75% and disease severity by up to 57%. In addition, G. etunicatum and Isolate KS14, significantly improved top dry biomass of pyrethrum by up to 33% and 47%, respectively. Glomus etunicatum and M. hapla were mutually inhibitory as root colonization by G. etunicatum was significantly reduced (up to 24%) by the presence of the nematode. The presence of the nematodes, on the other hand, did not significantly affect root colonization by Isolate KS14.     

Effect of inorganic phosphatic fertilizers on the efficacy of an arbuscular mycorrhiza fungus against a root-knot nematode on pyrethrum

Effects of triple super phosphate (TSP) and single super phosphate (SSP) fertilizers on efficacy of a Glomus sp. (isolate KS 14) against Meloidogyne hapla were determined. The fertilizers were applied at 150 and 300 kg ha -1 at the time of fungus inoculation. Two months later, plants were inoculated with the nematodes. Plant growth and nematode disease parameters were determined 2 months after nematode inoculation. The fertilizers at both levels improved plant growth in all treatments. In general, the fungus improved plant growth on its own or in the presence of nematodes, but not in the presence of fertilizers. Both fertilizers at both levels were more effective in improving plant growth than the fungus. The fungus showed sensitivity to inorganic P fertilizers in that the fertilizers significantly reduced fungal root colonization and its pyrethrum growth stimulative effects. The fungus suppressed nematode disease severity unlike the fertilizers. The suppressive effects of the fungus on the nematodes were in most cases reduced by the fertilizers. The nematodes, unlike the fertilizers, did not have any significant effects on root colonization by the fungus or on its ability to improve pyrethrum growth. The presence of nematodes in fertilizer or fertilizer-fungus-treated plants, however, significantly reduced pyrethrum growth.     

Host suitability of Vitis rootstocks to root‐knot nematodes (Meloidogyne spp.) and the dagger nematode Xiphinema index,and plant damage caused by infections

The host suitability of commercial Vitis rootstocks commonly used in Spain (161‐49C, 41B, 1103P, 110R, 140Ru and SO4) to root‐knot nematodes (Meloidogyne arenaria, M. incognita, M. javanica) and Xiphinema index, and damage caused by nematode infection were determined under controlled conditions. The three root‐knot nematodes reproduced with a rate higher than one in all rootstocks, indicating that they are suitable hosts for these nematodes. Growth of rootstocks infected with the root‐knot nematodes was less vigorous than that of nematode‐uninfected controls in the majority of the rootstocks studied. Root infection resulted in moderate to severe root galling in all rootstocks. The shoot and main stem diameters appeared to be the most sensitive variables of damage caused by infection by Meloidogyne spp., with reduction rates from 36% and 53% in 161‐49C to 57% and 66% in 140Ru, respectively. The shoot height was not significantly affected by the root‐knot nematodes and the root fresh weight generally increased as a consequence of intensive galling. The nematode X. index caused significant root damage with a reproduction factor higher than one in all rootstocks. However, reproduction factor was significantly influenced by the rootstock and significantly decreased by about 12‐fold (5·7 to 18·1‐fold) with the increase in inoculum density from 100 to 1000 nematodes per plant. The root dry weight was reduced by X. index infections, and was the plant growth variable most affected by the nematode infection in all rootstocks at both inoculum densities. Meloidogyne arenaria, M. incognita, M. javanica and X. index, prevalent in many world vineyards, are all shown to have a damaging effect on the six tested rootstocks.     

功能型复合微生物菌剂防治黄瓜根结线虫的研究

根结线虫是一类重要的土传性病原物,对露地和温室蔬菜造成严重的经济损失。本研究通过平板亲和性试验,构建出一组(淡紫拟青霉、红灰链霉菌和苍白杆菌各1株)生物兼容性好、作用方式互补的功能型复合微生物菌群;以各功能菌株发酵菌体为活性成分,研制出一种防治黄瓜根结线虫的功能型复合微生物菌剂;对该复合菌剂对黄瓜根结线虫的防效及植株生物量和产量的影响进行了评价,大田试验结果表明,施用该复合菌剂的土壤线虫扩繁指数最低;移栽后38和105 d,该复合菌剂处理的根结级数分别为2.0和4.6,对病害防效为56.5%和42.5%,效果优于10%噻唑膦处理;施用该复合菌剂可以促进植株生长、增加黄瓜产量。本研究为蔬菜根结线虫病的生物防治提供了新思路。     

Evaluation ofAmaranthus sp. andVernonia amygdalina, and soil amendments with poultry manure for the management of root-knot nematodes on eggplant

The suppressive effect of vernonia (Vernonia amygdalina), amaranth (Amarathus sp.) and poultry manure on root-knot nematodes (RKNs) (Meloidogyne spp.) infecting eggplant (Solanum macrocarpon) was studied at two sites in southern Benin naturally infested with these nematodes. After 3 months, soil and root-inhabiting RKN populations were significantly less (P≦0.05) in the plots cropped with vernonia, amaranth, and eggplant amended with poultry manure (PM) at the rate of 40 t ha⁻¹ as compared with the rate of 20 t ha⁻¹ and with the control. Poultry manure was more effective after 2 months than after 3 months. Overall, vernonia was the most effective treatment affecting RKN populations in the roots and the soil. The use of these treatments in nematode management through rotation and co-planted crops is discussed. http://www.phytoparasitica.org posting August 6, 2008.     

Biochemical and molecular characterization of Bacillus amyloliquefaciens, B. subtilis and B. pumilus isolates with distinct antagonistic potential against Xanthomonas campestris pv. campestris

Fifty-one Bacillus isolates were characterized by fatty acid methyl ester (FAME) analysis; universal primer polymerase chain reaction (UP-PCR) fingerprinting; production of secondary metabolites and antagonistic activity against Xanthomonas campestris pv. campestris (causal agent of black rot in cabbage) in vitro and in vivo . Based on FAME analysis and/or PCR fingerprinting, the isolates were clustered into three different groups, named as Bacillus amyloliquefaciens , B . subtilis and B . pumilus . Seed treatment with Bacillus spp. generally reduced germination of seeds and incidence of black rot, but no relationship was found between the results of in vitro and in vivo experiments. The B .  amyloliquefaciens group contained isolates that were generally the most effective at reducing attack of black rot in vivo . The metabolic profiles of these isolates suggested that they produced surfactin, iturin, bacillomycine and/or azalomycin F. Isolates belonging to the B . subtilis group were mostly able to synthesize surfactin and arthrobactin. Surfactin, amphomycin, arthrobactin and valinomycin were generally found in culture extracts of isolates belonging to the B . pumilus group. No effect on growth of the pathogen was detected when the activity of filtered culture extracts and selected metabolites produced by the three different Bacillus species was tested in vitro against X . c . pv. campestris . However, inhibition was seen when bacterial liquid cultures were used. When the ability to colonize cabbage endophytically was examined for seven selected isolates with different antagonistic potential against black rot, it was found that the ability was related to the species and not to the antagonistic activity of the isolates.     

Responses of cucumber cultivars to induction of systemic resistance against anthracnose by plant growth promoting fungi

Initial experiment on the reactions of five Japanese cultivars of cucumber toColletotrichum orbiculare infection in the greenhouse revealed that cv Suyo and Gibai were susceptible and moderately susceptible, respectively, while cv Shogoin fushinari and Sagami hanjiro were resistant to infection byC. orbiculare; cv Ochiai fushinari was moderately resistant. The ability of 16 plant growth promoting fungi (some isolates belonged to species ofPhoma and some non-sporulating isolates) isolated from zoysiagrass rhizospheres to induce systemic resistance in the above five cucumber cultivars was tested by growing plants in potting medium infested with barley grain inocula of PGPF in the greenhouse. The second true leaves of 21-day-old plants were challenge inoculated withC. orbiculare and disease assessed. Nine, out of 16 isolates, caused significant reduction of disease caused byC. orbiculare in at least two cultivars.Phoma isolates (GS8-1 and GS8-2) and non-sporulating isolates (GU21-2, GU23-3, and GU24-3) significantly reduced the disease in all the five cultivars. The disease suppression in cucumber was due to the induction of systemic resistance, since the inducer(s) and the pathogen were separated spatially and that the inducer did not colonize aerial portions. The resistance induced by certain isolates in a susceptible cultivar was less than that in a resistant cultivar. Disease suppression caused by isolate GU21-2 was similar to theC. orbiculare induced control in certain cultivars. The average rate of expansion of lesion diameter on leaves due toC. orbiculare was slower due to induction with the selected plant growth promoting fungi compared to the uninduced control plants. Roots of four cultivars were colonized by only three isolates, however, roots of one cultivar (Suyo) was colonized by five isolates suggesting the cultivar-specific root colonization ability.Abbreviations cv cultivar(s) - PGPF plant growth promoting fungal isolates - PGPR plant growth promoting rhizobacteria     

Hyperparasites of Rhizoctonia solani in Dutch potato fields

Gliocladium roseum was found to be the most common and probably the most effective mycoparasite in potato fields in the northern parts of the Netherlands. It is able to parasitize and kill living hyphae at temperatures of 12°C and higher. Sclerotia ofR. solani are often infected and killed by this fungus under suitable conditions, i.e. at temperatures of 16°C and more. Killing of sclerotia by other antagonistic organisms was also observed. It is also shown by not parasitic fungi and is caused by toxins produced by the antagonist.The development of theG. roseum population was studied during the growth of a potato crop in two soils. In both soils its initial level was very low. In both a slightly acid sandy soil and a neutral sandy loam, suppression ofR. solani can occur;G. roseum accumulated in the former mainly under continuous potato crops,Colletotrichum coccodes was the main antagonist in the latter.Samenvatting In de meeste Nederlandse aardappelakkers komen schimmels voor dieRhizoctonia solani kunnen aantasten en doden. De meest algemene, en waarschijnlijk ook de meest belangrijke, die we tot nu toe vonden, isGliocladium roseum (Tabel 1). Het is bekend, dat deze schimmel stoffen produceert die voorR. solani giftig zijn. Met behulp hiervan kanG. roseum, evenals andere antibiotisch actieve micro-organismen, ook de sclerotiën doden (Tabel 2). Voor doding doorG. roseum is de temperatuur een factor van belang. Hyfen worden nog gedood bij een temperatuur van 12°C, waarbij de sclerotiën niet meer aangetast kunnen worden. Gedurende het winterseizoen worden sclerotiën door deze schimmel naar alle waarschijnlijkheid niet gedood.De ontwikkeling van de populatie vanG. roseum en andere antagonisten vanR. solani werd gevolgd in aardappelvelden op een licht zure zandgrond en op een neutrale zware zavel. Op de zandgrond werden twee proefplekken bemonsterd: één waarop voor het vierde achtereenvolgende jaar aardappelen werden geteeld en één met een vruchtwisselingsschema van graan, bieten en aardappelen.In de zandgrond nam in het groeiseizoen de populatie vanG. roseum toe. Op de proefplek waar voor het vierde jaar achtereen aardappelen stonden werdR. solani vanaf half augustus onderdrukt, evenwel niet volledig. Ook in het vruchtwisselingsstuk breiddeG. roseum zich flink uit, doch een onderdrukking vanR. solani werd niet bereikt.In de zware zavel nam de populatie vanG. roseum niet toe. Hier werdR. solani — uit besmet pootgoed — onderdrukt doorColletotrichum coccodes (zelf een pathogeen van stolonen) en antagonistische bacteriën. De resultaten zijn vermeld in Tabel 3.De besmetting van de geoogste knollen met sclerotiën, zoals die voorkwam op de zandgrond, is in Tabel 4 vermeld. Op de zavel leverde schoon pootgoed een bijna schone oogst (2% van de knollen was zeer licht bezet met sclerotiën). Besmet pootgoed leverde een oogst met 58% schone knollen, 35% met een zeer lichte en 7% met een iets zwaardere sclerotiënbezetting. Hoewel uit 100% besmet pootgoed een veel schonere oogst werd verkregen, was eerder toch een beschadiging van het gewas opgetreden. Pas tegen het eind van het groeiseizoen werdR. solani flink onderdrukt.