Abstract: Non-chemical options for the management of Phytophthora palmivora on papaw in far northern Queensland were evaluated in pot and field experiments. In pots, sawdust (150 m3/ha) + urea (600 kg/ha) reduced root rot, increased plant growth and reduced Phytophthora inoculum to undetectable levels. The addition of filterpress (400 m3/ha) and mill ash (200 m3/ha), reduced the damage caused by P. palmivora, but amendment with chicken manure (4% v/v), MinPlus (4.5 t/ha) and Trichodry (1.0 kg/m3) plus Trichoflow (5.0 kg/ha) failed to reduce root damage. In a second pot experiment, growing brassica (Bioquire Mulch) as a green manure significantly (P < 0.05) reduced Phytophthora inoculum levels and root rot severity, whereas the incorporation and composting of soybean, brachiaria, banana and sugar-cane failed to reduce the severity of root rot in papaw compared to a bare fallow. In a field crop of papaw grown for 46 weeks on 0.75 m high mounds, the suppressive effects of sawdust (150 m3/ha) + urea (600 kg/ha), filterpress (400 kg/ha), molasses (100 L/ha/week for 20 weeks), brassica (Bioquire Mulch, 4.5 kg/ha), soybean (cv. Leichardt, 40 kg/ha) and gypsum (5 t/ha) were compared. Soil amended with sawdust + urea had the lowest incidence of root rot. Soil amended with filterpress or molasses had the highest incidence of root rot and the highest populations of P. palmivora. Cumulative totals of percentage soil moisture were greatest in soil amended with filterpress or molasses, and this was evidence of the influence soil moisture retention has on root rot development.
Abstract: The species composition of a total of 173 red clover root fungal isolates from red clover roots from two established organic fields, a field in a transitional phase to organic and from two conventional fields was investigated based on morphology and molecular methods. Fusarium avenaceum was the most common Fusarium species overall but it occurrred less frequently in older organic fields. Gliocladium spp., Trichoderma spp. and Rhizoctonia spp. isolates were more common in the established organic clover fields, which had been under organic management for more than ten years and in one conventional field, than in a field still in the transitional phase. The taxonomical status of certain Fusarium, Alternaria and Sclerotinia isolates difficult to identify by morphological traits alone could be confirmed by species-specific primers and by comparing their ITS (internal transcribed spacer region) sequences to known sequences. The fingerprinting patterns of RAPD-PCR products could be used for the identification of fungal isolates and for studying the genetic variation among the isolates. Only one of the Fusarium isolates originating from apparently healthy red clover roots was clearly pathogenic to germinated red clover seedlings. In detached leaf experiments, the cvs Jokioinen and Ilte were more susceptible to one of the Sclerotinia trifoliorum isolates than cvs Betty and Bjursele, while all of them were equally susceptible to two other S. trifoliorum isolates. In further greenhouse experiments with intact plants it was possible to slow down the development of clover rot to some extent by means of one of the biological agents tested (Bacillus subtilis 10-VIZR, commercial name Alirin B), and almost completely by chemical control.
Abstract:Fusarium head blight (FHB) caused by Gibberella zeae (anamorph = Fusarium graminearum) is a devastating disease that causes extensive yield and quality losses to wheat in humid and semi-humid regions of the world. Biological control has been demonstrated to be effective under laboratory conditions but a few biocontrol products have been effective under field conditions. The improvement in the physiological quality of biocontrol agents may improve survival under field conditions, and therefore, enhance biocontrol activity. Bacillus subtilis RC 218 and Brevibacillus sp. RC 263 were isolated from wheat anthers and showed significant effect on control of FHB under greenhouse assays. This study showed the effect of water availability measured as water activity (aW) using a growth medium modified with NaCl, glycerol and glucose on: (i) osmotic stress tolerance, (ii) viability in modified liquid medium, (iii) quantitative intracellular accumulation of betaine and ectoine and (iv) the biocontrol efficacy of the physiologically improved agents. Viability of B. subtilis RC 218 in NaCl modified media was similar to the control. ,i>Brevibacillus sp. RC 263 showed a limited adaptation to growth in osmotic stress. Betaine was detected in high levels in modified cells but ectoine accumulation was similar to the control cells. Biocontrol activity was studied in greenhouse assays on wheat inoculated at anthesis period with F. graminearum RC 276. Treatments with modified bacteria reduced disease severity from 60% for the control to below 20%. The physiological improvement of biocontrol agents could be an effective strategy to enhance stress tolerance and biocontrol activity under fluctuating environmental conditions.
Abstract: In this study, a total of 17 Plant Growth Promoting Rhizobacteria (PGPR) strains, consisting of eight different species (Bacillus subtilis, Bacillus pumilus, Burkholderia cepacia, Pseudomonas putida, Bacillus amyloliquefaciens, Bacillus atrophaeus, Bacillus macerans and Flavobacter balastinium), were tested for antifungal activity in in vitro (on Petri plate) and in vivo (on potato tuber) conditions against Fusarium sambucinum, Fusarium oxysporum and Fusarium culmorum cause of dry rot disease of potato. All PGPR strains had inhibitory effects on the development of at least one or more fungal species on Petri plates. The strongest antagonism was observed in B. cepacia strain OSU-7 with inhibition zones ranging from 35.33 to 47.37 mm. All PGPR strains were also tested on tubers of two potato cultivars ‘Agria’ and ‘Granola’ under storage conditions. Only B. cepacia strain OSU-7 had significant effects on controlling potato dry rot caused by three different fungi species on the two potato cultivars. There were no significant differences in rot diameters among the treatments in comparison to the negative control (with water). This is the first study showing that B. cepacia has great potential to be used as effective biocontrol agent of Fusarium dry rot of potatoes (F. oxysporum and F. culmorum) under storage conditions.
Abstract:Fusarium wilt is now a major disease of carnation crops worldwide. Methyl bromide, which is used to remedy it, is environmentally unsafe. An alternative approach integrated into biological control is to grow crops in suppressive media. Suppressiveness of seven plant growth media to Fusarium oxysporum f. sp. dianthi was evaluated in bioassays with carnation (Dianthus cariophyllus) cv. Medea. These media were: (1) grape marc compost, (2) cork compost, (3) olive oil husk + cotton gin trash composted and mixed with rice husk, (4) spent mushroom compost mixed with peat, (5) coir fibre, (6) light peat and (7) vermiculite. In order to look for carnation Fusarium wilt suppressiveness indicators, growth medium pH and β-glucosidase activity were evaluated. Furthermore, F. oxysporum populations were measured in plant growth media at the beginning and end of bioassays. The compost media showed a range of suppressiveness in comparison with peat. Grape marc compost was the most effective plant growth medium in suppressing carnation Fusarium wilt. On the other hand coir fibre, peat and vermiculite were conducive for this disease. β-glucosidase activity and pH were positively correlated with disease severity as in other reports for tomato. Therefore, these two parameters are good indicators for carnation Fusarium wilt suppressiveness, and possibly for other F. oxysporum pathosystems. All composts showed similar F. oxysporum populations at the end of the bioassays to peat and vermiculite.
Abstract: Sequence comparisons of ABC transporter genes from two strains of Fusarium oxysporum (one biocontrol and one phytopathogenic (f. sp. lycopersici Race 1) isolates) to 16 sequences from other fungi among those deposited in GenBank indicated that these genes are well conserved. However, sequences of promoter and 5′ UTR regions of a previously characterized ABC transporter gene FoABC1 differed between 8 phytopathogenic and 11 biocontrol strains of F. oxysporum. A phylogenetic analysis of promoter sequences indicated that pathogenic strains were grouped in a single clade, clearly distinct from clades with biocontrol agents. Although sequencing of promoter regions was done on only 20 strains, results suggest that FoABC1 may be regulated differently between phytopathogenic and biocontrol strains of the fungus. In studies on the activity (RNA) of FoABC1 in the presence of the fungicide thiram, one pathogen was down regulated to undetectable levels by a brief exposure to thiram, the other pathogenic strain was not affected, while the one of the two biocontrol strains was up regulated and expression of FoABC1 in the other biocontrol strain was not changed. After a 1 h exposure to thiram, the level of expression of one pathogen remained down regulated to undetectable levels, while the other pathogen and both biocontrol agents were up regulated compared to the time zero control. Additional research is needed to further understand the significance of the genetic difference in promoter regions between phytopathogenic and biocontrol strains for FoABC1.
Abstract: The economic viability of the large-scale production of T. harzianum, which is effective against the soilborne disease Phytophthora foot rot (caused by Phytophthora capsici) of black pepper (Piper nigrum), was studied. The enterprise was highly profitable, with a benefit:cost ratio of 1.84, net return of 242 618 rupees/ha at 11% interest rate for a 10-year period, and an internal rate of return of 121%.
Abstract: An even economical and more frequently used method of attaining biological
control of soil borne plant pathogens is incorporating plant residues and organic amendments to the soil, which support high level of microbial activity. In the present study farm yard manure (FyM), poultry manure (PM), coffee husk (CH) and neem cake (NC) were used as soil amendments with or without Trichoderma harzianum to evaluate their eficacy in suppressing Phytophthora meadii under varying moisture conditions. the survival of Phytophthora was found higher at 50% moisture level. Neem cake with Trichoderma appeared as a suitable amendment at all moisture level and has shown 69% reduction in Phytophthora infection over control. at 75% and 100% (ield capacity), no detectable level of Phytophthora was observed in treatments where T. harzianum was fortiied with CH, PM and NC. at ield capacity, PM and FyM with Trichoderma also reduced the build up of Phytophthora. Native population of Trichoderma was found negligible in non-amended treatments. All the four amendments maintained the population and supported the growth of Trichoderma at all moisture levels. In general, organic manures with T. harzianum reduced the population level of other fungi, while crop residues supported the growth of fungi like Penicillium, Rhizopus, Aspergillus,
Mucor, etc. besides T. harzianum.
Abstract:Phytophthora infestans (Mont.) de Bary is infamous as the causal agent of the late blight epidemic contributing to the Irish potato famine of the mid 19th century and remains agriculture’s most destructive disease as new mutations and migrations confound control measures. In efforts to develop resistant varieties, a somatic hybrid (the Wisconsin J series) between potato (Solanum tuberosum) and a wild relative(Solanum bulbocastanum) has been found to convey durable resistance against the pathogen.We screened the total protein (100 µg ml–1)of somatic hybrid varieties J138, J138A12, J101K12, J103K12, and J101K9 for in vitro spore germination inhibition of P. infestans. Since J138 exhibited maximum inhibition at 150 µg ml–1 in comparison to other varieties, we purified a 40 kD protein from J138 tubers by assaying its ability to inhibit spore germination in P. infestans spores. The highly purified protein was able to inhibit P. infestans spore germination by 70% at the 2.5 µg ml–1 concentration. The N-terminal sequence of this protein was found to have exact amino acid homology to patatin, the major storage protein of potato tubers. The inhibitory protein has the same molecular weight as patatin and cross-reacts with patatin antibodies. The infection of J138 plants with spores of P. infestans under greenhouse conditions showed that patatin is expressed in stem tissue 72 h after the plant is inoculated with field isolates of P. infestans (US8). In this communication, we report the purification, characterization and antifungal activity against spores of P. infestans of patatin-J from potato tubers.
Abstract: Six strains of Pseudomonas fluorescens, which had been found efficient in root-rot suppression in black pepper (piper nigrum L.) caused by Phytophthora capsici were tested for their ability in rejuvenating Phytophthora infected black pepper cuttings. Among the treatments, which had only bacterial application, IISR-6 ensured survival of 67% of the infected cuttings where as only 22% of the untreated plants survived 3 months after treatment. The combined application of IISR-51, IISR-6+IISR-13 and IISR-51+IISR-11 with metalaxyl-Mancozeb resulted in 100% survival of the infected plants showing an additive effect. Experiments conducted for root-poliferation activity of the P. fluorescens showed that the bacterial strains helped increase the root biomass of the plants (30-135%). All the strains increased the root length and root area in the treated plants (12-127%, 40-200%, respectively). Strains were also found to produce plant growth hormones. viz. IAA & GA.
Abstract