Root Rot Fungus Research Articles

Glomus intraradices, Pseudomonas alcaligenes, and Bacillus pumilus: effective agents for the control of root-rot disease complex of chickpea (Cicer arietinum L.)

The effects of Glomus intraradices, Pseudomonas alcaligenes and Bacillus pumilus on the root-rot disease complex caused by the root-knot nematode Meloidogyne incognita and the root-rot fungus Macrophomina phaseolina in chickpea was assessed by quantifying differences in the shoot dry mass, pod number, nodulation, and shoot content of chlorophyll, nitrogen, phosphorus and potassium. Inoculation of plants with G. intraradices, P. alcaligenes and B. pumilus alone and in combination significantly increased shoot dry mass, pod number, and content of chlorophyll, nitrogen, phosphorus and potassium in plants inoculated with pathogens over that in the uninoculated control plants. P. alcaligenes caused a greater increase in shoot dry mass, pod number, chlorophyll, nitrogen, phosphorus and potassium in plants with pathogens than did G. intraradices or B. pumilus. Combined application of G. intraradices, P. alcaligenes and B. pumilus to plants inoculated with pathogens caused a greater increase in shoot dry mass, pod number, nitrogen, phosphorus, and potassium than did an application of P. alcaligenes plus B. pumilus or of G. intraradices plus B. pumilus. Root colonization by G. intrardices was high when used alone, while inoculation with the pathogens reduced root colonization by G. intraradices. In the presence of P. alcaligenes and B. pumilus, root colonization by G. intraradices increased. In plants inoculated with just one antagonist, P. alcaligenes reduced galling and nematode multiplication the most, followed by G. intraradices, then B. pumilus. The greatest reduction in galling, nematode multiplication and root-rot was observed when both bacterial species and G. intraradices were applied together.

Rhizotron studies on Zea mays L. to evaluate biocontrol activity of Bacillus subtilis

The effect of Bacillus as a biocontrol agent against some root-rot fungi was tested using maize (Zea mays L.) in rhizotrons placed in a growth chamber with relative humidity 60% with a 12 h photoperiod and day and night temperatures of 24 and 18°C respectively. Rhizoctonia solani Kuhn caused pre-emergence damping-off in the untreated maize seeds showing weak and soft roots as observed through the perspex rhizotrons. Image analysis was used to quantify the effects of Bacillus treatment on seedlings infected with Pythium sp. Bacillus B77 and B81 were most effective in the control of the pathogen, R. solani which achieved a biocontrol activity of 24 and 35% respectively with regard to shoot dry biomass while B81 achieved 48% biocontrol with reference to root dry biomass. There was no effect on the root area. For root dry biomass, B81, B69, B11 and B77 showed higher biocontrol activity in comparison to the control. Pythium sp. caused pre- and post emergence damping- off in the untreated seeds. Root rot of the maize seedlings caused by Pythium sp. was slightly controlled by Bacillus B69 and B81 which achieved biocontrol activity of 18 and 11% respectively. For the biocontrol of Fusarium solani, Bacillus B77, B69, B81 achieved biocontrol activity of 50, 48 and 33% respectively with reference to root dry biomass.

Artificial Infection of Rosellinia necatrix with Purified Viral Particles of a Member of the Genus Mycoreovirus Reveals Its Uneven Distribution in Single Colonies

ABSTRACT Rosellinia necatrix mycoreovirus 3 (W370) (RnMYRV-3/W370, described as RnMYRV-3 in this paper), a member of the newly established genus Mycoreovirus within the family Reoviridae, is the hypovirulence factor of the white root rot fungus, Rosellinia necatrix. Two virus-free fungal isolates (W37 and W97) that were somatically incompatible with the virus-harboring field isolate (W370) were transfected with purified RnMYRV-3 particles. Virus infection was confirmed by electrophoresis and northern hybridization of viral double-stranded RNA. RnMYRV-3 was transmissible from transfected strains to their respective, virus-free counterparts via hyphal anastomosis. Virus-transfected strains produced smaller lesions on apple fruits than did their virus-free counterparts. Virus-cured strains were indistinguishable from wild-type strains in culture morphology and displayed approximately the same virulence level on apples. Virus-transfected strains had "mosaic" colony portions consisting of thin, fast-growing and dense, slow-growing mycelia, and grew more slowly as a whole than their virus-free, parental strains. The level of virus accumulation varied among virus-transfected subcultures and within its single colonies. Virus-transfected strains were occasionally cured, as was W370. Such a phenomenon may be ascribed to uneven viral distribution in single colonies and the difficulty in viral transmission to virus-free hyphae.

British Columbia Regional Meeting, 2006 The Canadian Phytopathological Society

British Columbia Regional Meeting, 2006 The Canadian Phytopathological Society

Diversity and dynamics of dsRNA in root rot fungi

Diversity and dynamics of dsRNA in root rot fungi

Influence of subsoiling on direct-seeded cereals in southeastern Idaho

The influence of shallow (20 cm deep) subsoil tillage on cereals planted with a no-till planter was investigated for 3 years at two locations in southeastern Idaho. Among Fusarium spp., F. culmorum was the primary fungus isolated from diffuse brown-black root lesions in the wetter location (Ririe), while F. semitectum, F. reticulatum, F. equiseti, and F. acuminatum were the dominant species isolated at the drier location (Arbon Valley). Increased yields resulting from methyl bromide fumigation indicated that biological factors were limiting the yield. However, subsoiling did not influence nematode populations or fungal root rots. The primary parasitic nematode found at both locations was Pratylenchus neglectus. Subsoiling had a tendency to increase soil moisture at depths between 61 and 90 cm, to increase organic matter, and to decrease nitrogen. Yield increased by 8% or more with subsoil tillage at both locations the first year. Yield increases were not significant in other years, when moisture was particularly limiting or abundant. Subsoiling may prove favorable for cereals planted in a soil-conservation tillage system, but the risk of fungal root rots may increase with such a practice. Additional study is warranted, as subsoil-tillage practices may increase yield and desirable soil parameters without compromising the benefits associated with cereal production in a soil-conservation tillage system.

Impact of root-rot pathogens on forest succession in unmanaged Pinus mugo stands in the Central Alps

In the mountain pine (Pinus mugo subsp. uncinata (DC.) Domin) forests of the Swiss National Park in the Central Alps, disease centers associated with the root-rot fungi Heterobasidion annosum (Fr.) Bref. and Armillaria spp. are characteristic elements. We assessed the impact of these pathogens on forest dynamics by studying transects running across disease centers into the adjacent forest. Overall, mountain pine was the most abundant regenerating tree species and accounted for 84% of all seedlings (<20 cm high) and 93% of all saplings (20–130 cm high), whereas Swiss stone pine (Pinus cembra L.) was less frequent (15% seedlings : 7% saplings). The density of mountain pine seedlings did not differ significantly between the disease centers and the adjacent forest, whereas mountain pine saplings were more frequent within the disease centers, indicating that growth from the seedling to the sapling stage was favoured in disease centers. There was significantly more dead wood and a greater diversity of plant species in the disease centers than in the adjacent forest. The results suggest that root-rot fungi slow down succession towards stands with a higher proportion of P. cembra by causing premature mortality of mountain pines and creating disease centers with dense mountain pine regeneration.

Incidence and distribution of Heterobasidion and Armillaria and their influence on canopy gap formation in unmanaged mountain pine forests in the Swiss Alps

Various disturbance factors on different spatial scales can lead to the creation of canopy gaps in forest ecosystems. In this study, we investigated the role of root rot fungi in the formation of canopy gaps in the Swiss National Park in the Central Alps. Dying or recently dead mountain pine (Pinus mugo subsp. uncinata trees (n = 172) and saplings (n = 192) from 42 canopy gaps were assessed for Armillaria and Annosum root rot. Heterobasidion annosum s.str. proved to be the dominant pathogen and was isolated from 49% of the trees and 64% of the saplings. Armillaria was found on 13% of the trees and 20% of the saplings. Three Armillaria species, A. borealis, A. cepistipes, and A. ostoyae, were identified. Armillaria ostoyae was the most frequent species, accounting for 72% of all Armillaria isolates. A total of 31 (74%) gaps were associated with H. annosum, and six (14%) with A. ostoyae. The remaining gaps were either associated with both pathogens (7%) or with other, unknown, factors (5%). Our findings suggest that the two pathogenic fungi, H. annosum s.str. and A. ostoyae, are the main reason for the large-scale mortality of mountain pines and the creation of canopy gaps in high elevation forests of the Swiss National Park.

Observations on the Biology ofDryocoetes betulae(Coleoptera: Curculionidae) in Paper Birch in Northern Idaho

We describe the biology and life stages of the birch bark beetle, Dryocoetes betulae Hopkins, and report its second known occurrence in Idaho. One annual generation was observed with broods overwintering as larvae and sexually immature adults. The species is polygamous with a ratio of 1.8 females per male. Two females (rarely three) joined a male after he entered the bark, and each female created a 3- to 4-cm-long egg gallery with short lateral spurs. Eggs were laid in niches along each side of the main gallery. Larvae have three instars. No hymenopterous parasitoid was found; however, two apparent predators, Rhizophagus dimidiatus Mannerheim, and a clerid, Thanasimus undatulus (Say), were present in galleries. Two mites, Histiostoma sp. and Proctolaelaps n. sp., also occurred in galleries, and a nematode of the Order Rhabditida occurred in the midgut of larvae and adult D. betulae. An ambrosia beetle, Trypodendron betulae Swaine, also infested the basal stems apart from D. betulae. Stems of infested trees were infected with a root rot fungus, Armillaria ostoyae (Romagnesi) Herink. Several generations of beetles infested the basal portion of stems of either decadent or recently dead paper birch. This behavior preserves a scarce host resource and is enhanced by a relatively low fecundity and ability to establish new galleries without flight dispersal.

Heterobasidion abietinum on Abies species in western Turkey

SummaryForty‐five basidiocarp specimens of Heterobasidion were collected from native Abies species in three locations in western Turkey: A. nordmanniana ssp. bornmülleriana in Bolu province, A. nordmanniana ssp. equi‐trojani in Balikesir province and A. cilicica in Antalya province. Pure cultures were isolated from the basidiocarps and identified to the species level with the aid of mating tests. All the specimens proved to belong to the species Heterobasidion abietinum. This root rot fungus is common in the forests investigated and appears to be relatively virulent on Abies in Turkey. This is the first report of H. abietinum outside Europe.

Radial growth responses of singleleaf pinyon ( Pinus monophylla) to wildfire

Dendroecological methods for quantifying and dating historical canopy disturbance events have been widely applied for temperate forests, but may not be useful for semi-arid woodlands, where growth is more strongly influenced by drought cycles. Our study focuses on the potential utility of dendroecological methods for reconstructing historical fire in woodlands of the Nevada Great Basin, USA, which are dominated by singleleaf pinyon pine ( Pinus monophylla Torr. and Frem.). We assess growth responses to a historical fire of known date, and compare different analytical methods involving radial-growth averaging approaches. Despite the strong influence of climate on radial growth of trees growing in semi-arid woodlands, most pinyon pines sampled in this study exhibited profound growth releases in response to fire. The growth releases could be detected using radial-growth averaging criteria, even given thresholds of percent growth change that effectively eliminated responses to climatic variability. The most conservative dendroecological method was radial-growth averaging with a 10 yr moving window and a percent growth change (PGC) threshold of at least 125%. This method detected the known fire for nearly one in three surviving trees, with very minimal occurrence of false positives in control trees or in the historical record. Results suggest that such approaches may be useful for identifying and approximately dating historical fires that burned adjacent to living pinyon trees. However, these methods will likely not be able to separate historical wildfire from other disturbance types, such as pinyon ips ( Ips confusus) or root rot fungi, which could be expected to cause growth releases in surviving trees. Also, the year of growth release following the known burn was delayed until years of good precipitation, resulting in a lagged response that can confound the ability of growth release methods to accurately pinpoint the year of disturbance.

Annual Meeting, Québec, Quebec, 2006, The Canadian Phytopathological Society / Réunion annuelle, Québec, Québec, 2006, La Société canadienne de phytopathologie

Annual Meeting, Québec, Quebec, 2006, The Canadian Phytopathological Society / Réunion annuelle, Québec, Québec, 2006, La Société canadienne de phytopathologie

Anatomical-based defense responses of Scots pine (Pinus sylvestris) stems to two fungal pathogens

We investigated the cellular responses of stem tissues of mature Scots pine (Pinus sylvestris L.) trees to inoculations with two fungal pathogens. The bark beetle vectored fungus, Leptographium wingfieldii Morelet, induced longer lesions in the bark, stronger swelling of polyphenolic parenchyma cells, more polyphenol accumulation and increased ray parenchyma activity compared with the root rot fungus, Heterobasidion annosum (Fr.) Bref., or mechanical wounding. Axial resin ducts in the xylem are a general feature of the preformed defenses of Scots pine, but there was no clear induction of additional traumatic axial resin ducts in response to wounding or fungal infection. The anatomical responses of Scots pine to pathogen infection were localized to the infection site and were attenuated away from bark lesions. The responses observed in Scots pine were compared with published studies on Norway spruce (Picea abies (L.) Karst.) for which anatomically based defense responses have been well characterized.

Changes in host chitinase isoforms in relation to wounding and colonization by Heterobasidion annosum: early and strong defense response in 33-year-old resistant Norway spruce clone

We studied the defense reactions of 33-year-old susceptible and resistant clones of Norway spruce (Picea abies (L.) Karst.) to the major root-rot fungus Heterobasidion annosum (Fr.) Bref. and determined if tissue cultures can be used as a model system for studying defense responses of mature trees at the molecular level. Quantitative PCR analysis of genomic DNA obtained from samples taken at different times along the lesion length in living bark indicated that the fungus was present in higher amounts and extended further into the host tissue in the susceptible clone than in the resistant clone. In protein extracts from the same lesion samples, there were differences in temporal and spatial changes in host chitinase isoform profiles between the resistant and susceptible clones. Host chitinase isoforms with pI values approximately 4.8, 4.4 and 3.7 increased more during the first 7 days after wounding and inoculation and extended further along the lesion length in the resistant clone than in the susceptible clone. These results suggest that the time from wounding and infection to induction of defense-related expression is shorter in the resistant clone indicating a more efficient host defense response than in the susceptible clone. Tissue cultures from the same clones were not resistant to H. annosum and showed no difference in the timing of the increase in chitinase isoforms in response to the pathogen. However, tissue cultures from both clones showed an increase in chitinase isoforms within 6 to 24 h past inoculation, indicating that increased chitinase expression in response to the pathogen is part of a general defense response common to both mature clones and tissue cultures.

An endornavirus from a hypovirulent strain of the violet root rot fungus, Helicobasidium mompa

We determined the complete nucleotide (nt) sequence (16,614 nt) of a large double-stranded (ds) RNA (referred to as L1 dsRNA), previously identified as the hypovirulence factor from strain V670 of the violet root rot fungus, Helicobasidium mompa. The positive-strand of L1 dsRNA contained a long open reading frame (ORF) potentially encoding a protein of 5373 amino acids (molecular mass 603,080 Da) with conserved motifs characteristic of RNA-dependent RNA polymerase (RdRp) and helicase. The ORF is the longest so far reported in the fungal kingdom. The putative RdRp and helicase were shown to be related to putative RdRps and helicases of members of the genus Endornavirus. As is the case with endornaviruses , the coding (sense) strand of L1 dsRNA contained a discontinuity (nick) at nt position 2552. A region between the RdRp and helicase domains of the polyprotein also had an amino acid sequence, resembling UDP glycosyltransferases (UGTs) in Oryza sativa endornavirus and Phytophthora endornavirus 1. Regions in the L1 dsRNA-encoded protein presumed to contain putative helicase, UGT and RdRp motifs were present at comparable positions to those in other endornaviruses. L1 dsRNA of H. mompa strain V670 was assigned to the genus Endornavirus, and here, we designate it as H. mompa endornavirus 1-670 (HmEV1-670). This represents the first report of a fungal endornavirus whose complete nucleotide sequence has been determined.

Amasya İli Soğan Ekiliş Alanlarında Bulunan Fungal Kök Çürüklüğü Hastalık Etmenlerinin Belirlenmesi

Bu çalışmada, Amasya ili yemeklik soğan Allium cepae L. ekiliş alanlarında görülen fungal kök çürüklüğü hastalık etmenleri, yayılışları ve yoğunlukları belirlenmiştir. Bu amaçla, 2000 ve 2001 yıllarında toplam 110 yemeklik soğan tarlasında inceleme yapılmıştır. Çalışma sonucunda, inceleme yapılan yemeklik soğan alanlarında kök çürüklüğü hastalığının yoğun bir şekilde bulunduğu belirlenmiştir. Çalışmanın ilk yılında Amasya ili yemeklik soğan ekiliş alanlarının %95,7’sinin, 2001 yılında ise %100’ünün kök çürüklüğü hastalık etmenleriyle bulaşık olduğu ve hastalığın bitkilerde 2000 yılında %49,1, 2001 yılında ise %70,7 oranında yaygın olduğu saptanmıştır. Hastalık şiddetinin ise 2000 yılında %34,3 ve 2001 yılında da %42,4 olduğu tespit edilmiştir. Kök çürüklüğü hastalığına yakalanmış bitkilerden yapılan izolasyonlardan, %91,6 oranında Fusarium spp., %4,2 oranında Rhizoctonia spp., %1,9 oranında Sclerotium cepivorum, %1,5 oranında Pythium oligandrum ve % 0,8 oranında Trichoderma harzianum elde edilmiştir. Patojenisite denemeleri sonucunda F. oxysporum ve R. solani AG-4’ün virülenslerinin yüksek, P. oligandrum’un virülensinin ise çok düşük olduğu belirlenmiştir. S. cepivorum orta derecede virülent bulunmuştur

Kutznerides 1−4, Depsipeptides from the Actinomycete Kutzneria sp. 744 Inhabiting Mycorrhizal Roots of Picea abies Seedlings

Bioassay-guided fractionation of culture supernatants of the actinomycete Kutzneria sp. 744 resulted in the isolation of four new depsipeptides (1-4). Structure analysis revealed the general structure: cyclo[2-(1-methylcyclopropyl)-D-glycine-(2S,3aR,8aS)-6,7-dichloro-3a-hydroxy-1,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole-2-carboxylic acid-3-hydroxy-D-glutamic acid-O-methyl-L-serine-L-piperazic acid-(S)-2-hydroxy-3,3-dimethylbutanoic acid]. The 3-hydroxy-d-glutamic acid was present as its threo-isomer in 1 and 2 and as its erythro-isomer in 3 and 4. The piperazic acid was modified to its (R)-4-chloro analogue in 2 and to its C-5/N unsaturated analogue in 4. Compounds 1-4 displayed moderate spore germination inhibiting activity against several common root-rotting fungi.

Infection of Rosellinia necatrix with purified viral particles of a member of Partitiviridae (RnPV1-W8)

Isolate W8 of the white root rot fungus, Rosellinia necatrix, harbors three dsRNA segments, L1-, L2- and M-dsRNAs, and showed an irregular colony margin, slow growth, and moderate virulence. The M-dsRNA was previously shown to be the genome of a partitivirus, RnPV1-W8. Here a transfection protocol was developed for RnPV1-W8. Protoplasts of two virus-free isolates of R. necatrix were inoculated with purified viral particles using a polyethylene glycol-mediated method. Virus infection was confirmed by electrophoresis and Northern analysis. RnPV1-W8 introduced into the new host isolates was transmissible via hyphal anastomosis. However, the infection had no effect on the morphology and virulence of infected isolates of R. necatrix. This is the first report on the transfection of a partitivirus for R. necatrix.

The effect of take-all disease on gas-exchange rates and biomass in two winter wheat lines with different drought response

There have been no studies of the effect of take-all on leaf gas-exchange rates, despite the fact that take-all severely restricts plant water and nutrient uptake, which results in significant biomass and grain yield reduction. Here we describe the effect of inoculation with Gaeumannomyces graminis (Sacc.) var. tritici (Ggt) on carbon assimilation rate (A) and biomass production of wheat plants grown under two water regimes. We show that the impact of Ggt inoculation on plant growth and leaf A may be through reduced photosynthetic capacity of the leaves and not water stress per se. The nature of this reduced photosynthetic capacity remains uncertain but may involve nutrient deficiency and different enzymes produced by the fungus. In each of the 3 years the experiment was conducted, Ggt significantly reduced A, i.e. at anthesis by 18% in 2000, 15% in 2001, and 12% in 2002. In agreement with other field studies, Ggt reduced tiller number and production of all plant components, mostly root dry mass and grain mass per plant. Highly significant negative correlations were found between disease rating and A in all years, showing that at disease ratings equal or higher than 3 (on a scale from 1 to 4) A could practically be zero. While A decreased, intercellular CO2 concentration increased or did not change, and stomatal conductance was relatively high. In addition, A was more reduced under high than under low soil moisture content. These results support the idea that water stress per se did not contribute to the observed reduction of A. The mechanism of photosynthetic capacity reduction due to the Ggt root-rotting fungus is of interest as it may lead to the molecular mechanisms of plant resistance and ultimately to the development of take-all resistant plants.

Horizontal transmission and host-virulence attenuation of totivirus in violet root rot fungus Helicobasidium mompa

Monokaryotic strains of Helicobasidium mompa were used as vectors of a mycovirus between various H. mompa isolates to examine the transmissibility of one of the mycoviruses, totivirus (HmTV1–17 virus) in the hypovirulent isolate V17 of H. mompa. The isolates that acquired HmTV1–17 virus were also examined for any alteration in the virulence. Twelve dikaryotic isolates of H. mompa, belonging to 11 mycelial compatibility groups (MCGs) and being mycelially incompatible with isolate V17, were used as recipients of HmTV1–17 virus. Two monokaryotic isolates that were mycelially incompatible with isolate V17 and all of the recipients were also used as vectors of HmTV1-17 virus between isolate V17 and the recipients. When isolate V17 and recipients were directly paired on plate media, HmTV1-17 virus was transmitted from isolate V17 into 2 of the 12 recipients (i.e., 2 of the 11 MCGs). Two monokaryotic strains were paired with isolate V17, and the monokaryotic strains that acquired HmTV1-17 virus were then used as new virus donors. When the monokaryotic strains containing HmTV1-17 virus were paired with the 12 recipients, HmTV1-17 virus was transmitted into 7 of the 12 recipients from the monokaryotic strains (i.e., 7 of 11 MCGs). Based on these results, we concluded that monokaryotic strains could act as vectors to transmit HmTV1-17 virus into H. mompa isolates. When four of the H. mompa isolates that acquired HmTV1-17 virus were used to inoculate apple rootstock Malus prunifolia, the virulence of all of the isolates was attenuated from that of their parental isolates. Moreover, because the DNA fingerprints of the fungal isolates that acquired HmTV1-17 virus were the same as those of their parental isolates, the infection with HmTV1-17 virus is considered the cause of virulence attenuation of H. mompa.