Incidence Of Stem Rot Research Articles

BOTANICALS, BIOFUMIGANTS AND ANTAGONISTS APPLICATION IN MANAGING STEMROT DISEASE CAUSED BY RHIZOCTONIA SOLANI KUHN IN CARNATION

ABSTRACT The pathogen, Rhizoctonia solani Kuhn is a polyphagous fungus and has a vast potential of attacking a wide range of host plants causing host decay, damping –off, stem rot, crown rot ,stemcanker, root rot, fruit decay and foliage diseases. The stem rot is an emerging devastating disease incarnation rating next in importance to Fusarium wilt with a seedling mortality of 37% under optimum climatic conditions. Because of high incidence and crop importance, the present studywas carried out to manage the disease with application of different plant extracts (botanicals), biofumigant releasing crop residues and biocontrol agents both under in vitro and field conditions. Out of 11 botanicals including two commercial formulations of neem (neemgold, neemazil) testedat 5,10,20,30,40% and 1,2,3,4,5% concentrations respectively revealed that seed extracts of Meliaazedarach and leaf extract of Adhatoda vasica showed maximum inhibition in mycelial growthwithin the range of 44.38 to 44.25% followed by Murraya koenigii (37.77%) and Tagetes erecta(37.62%).The commercial formulations of neem compared to other treatments were foundstatistically superior to inhibits mycelial growth. In general, higher concentration resulted in moreinhibition of the R. solani, above 50 % inhibition was recorded at concentration of 40 per cent, maximum being in neemgold (60.53%) compared to 5% or 10%. Among different crop residues, cauliflower and cabbage were found most effective in reducing the incidence of carnation stem rot to 22.28 and 24.25% from 48.34% registered in control. The plant and flower characters such as plant height, stem length, no. of flowers/plant, flower size/plant and no. of days to first floweringget reduced to 142 compared to 157 days. The average colony forming unit of the pathogen reducedto 22.83x103 from 58.12x103 in one cropping season. Antagonists, Trichoderma viride, T. harzianum and Bacillus subtilis resulted into mycelial inhibition of 65.08, 63.70 and 55.05%. However in field the highest disease control of stem rot was achieved in integrated treatments whenthe rooted cuttings of carnation were pretreated with neemgold or neemazil for 20 minutes as diptreatment and planted in soil amended with T. viride and T. harzianum by giving disease control between 63-73%.

Monitoring of plant and airborne inoculum of Sclerotinia sclerotiorum in spring oilseed rape using real‐time PCR

Sclerotinia stem rot of spring oilseed rape (Brassica napus) is caused by Sclerotinia sclerotiorum. In Sweden, the disease leads to severe crop damage that varies from year to year. A real‐time PCR assay was developed and used to determine the incidence of S. sclerotiorum DNA on petals and leaves of spring oilseed rape as well as in air samples, with the aim of finding tools to improve precision in disease risk assessment. Five field experiments were conducted from 2008 to 2010 to detect and study pathogen development. Assessments of stem rot showed significant differences between experimental sites. The real‐time PCR assay proved fast and sensitive and the relationship between percentage of infected petals determined using a conventional agar test and the PCR assay was linear (R2 > 0·76). There were significant differences in S. sclerotiorum incidence at different stages of flowering. The incidence of S. sclerotiorum DNA on the leaves varied (0–100%), with significantly higher incidence on leaves at lower levels. In one field experiment, S. sclerotiorum DNA was not detected on petals during flowering, whereas the pathogen was detected on leaves, with a corresponding stem rot incidence of 7%. The amount of S. sclerotiorum DNA in sampled air revealed that spore release did not coincide with flowering on that experimental site. Thus, using a real‐time PCR assay to determine the incidence of S. sclerotiorum on oilseed rape leaves, rather than on petals, could potentially improve disease risk assessment.

Differential Expression of Defense Related Genes in Brassica napus Infected by Sclerotinia sclerotiorum

Sclerotinia stem rot is the main disease of rapeseed. Up to date, genes involved in defending Sclerotinia sclerotiorum have not been found in rapeseed and some other related plants. In order to reveal the disease resistance mechanism, we inoculated Sclerotinia sclerotiorum on the stems of resistant variety Ning RS-1 and susceptible one APL01, and compared eleven defensive related genes' expression profiles between two varieties during the period of inoculation by using fluorescence quantitative PCR. Results showed that four genes(PGIP, Cu/ZnSOD, OXO, and GLP) were highly expressed both in Ning RS-1 and APL01, and the expression in Ning RS-1 was much higher than that in APL01. Especially, PGIP's expression at 24 hours after inoculation(hai) with Sclerotinia sclerotiorum was 170.4 times as high as that at 0 hai in Ning RS-1, while it was only 3.5 times in APL01, and PGIP's expression in Ning RS-1 was 1299.4 times as high as that at 24 hai in APL01. Two genes(LOX2 and PDF1.2) were expressed low both in Ning RS-1 and APL01, but with significant difference between two varieties. Five genes(FeSOD, PAL, EDS1, PR1, and EIN3) were also expressed low in Ning RS-1 and APL01, and without significant difference between two varieties. We inferred that the reason of resistance against Sclerotinia sclerotiorum in Ning RS-1 is related to the up-regulated expression of PGIP, which prevents the PG protein in pathogen from degrading the cell wall of infected host tissues, resulting in the inhibition of incidence and spread of sclerotinia stem rot in rapeseed.

Efficacy ofBacillus subtilisG-1 in suppression of stem rot caused bySclerotium rolfsiiand growth promotion of groundnut

A total of seven biocontrol agents with known antifungal activity against other soilborne fungal pathogens were screened for their antagonistic potential against Sclerotium rolfsii Sacc, the causal agent of stem rot disease of groundnut (Arachis hypogaea L.) by dual culture assay. Among the various biocontrol agents tested Bacillus subtilis strain G-1 was the most effective in inhibiting the mycelial growth of S. rolfsii and recorded an inhibition of 28%. Groundnut seeds when treated with B. subtilis G-1 showed significant increases in root length, shoot length and seedling vigour. A talc-based powder formulation of the highly effective strain, B. subtilis G-1, was developed and its efficacy in controlling groundnut stem rot was determined under greenhouse conditions. The results indicated that seed treatment with the powder formulation of B. subtilis G-1 alone effectively reduced the incidence of stem rot and increased the pod yield; but combined application through seed and soil increased the efficacy. Seed treatment and soil application with B. subtilis G-1 reduced the stem rot incidence from 80 per cent (with non-bacterized seeds) to 5 per cent. When the treated seeds were sown in soil, the antagonist moved to the rhizosphere and multiplied well in it. These results suggest that B. subtilis G-1 is an effective bioagent against stem rot of groundnut. Further studies are required to assess its efficacy in controlling stem rot of groundnut under field conditions.

Biological control of oilseed rape Sclerotinia stem rot by Bacillus subtilis strain Em7

In the present study, the endophytic bacterium Bacillus subtilis strain Em7 (GU258545.1) was evaluated as a biological control agent for Sclerotinia sclerotiorum on oilseed rape. In petri dish, strain Em7 not only strongly inhibited pathogen mycelium growth but also germination of sclerotia at concentrations between 109 and 1011 colony forming unit (CFU)·ml−1. Scanning electron microscopy and transmission electron microscopy studies revealed that in the presence of strain Em7, hyphae of S. sclerotiorum showed leakage and disintegration of hyphal cytoplasm. Furthermore, the strain Em7 showed a broad antifungal spectrum on mycelium growth of numerous important plant pathogenic fungi. Light microscopic observations revealed that strain Em7 caused morphological alterations including increased branching, swelling and collapse of cytoplasm. In the greenhouse, spray treatments of cell suspensions of strain Em7 (1×109 CFU·ml−1) reduced leaf and stem rot incidence and severity in the seedling and blossom stage. The control efficacy was higher when strain Em7 cell suspension was applied one day prior to inoculation of the pathogen than after inoculation. Three-year field trials showed that two applications of strain Em7 cell suspension at blossom stage significantly reduced disease incidence and severity by 50–70%. There was no significant difference in control efficacy among treatments with strain Em7 cell suspension and the fungicides containing carbendazim or tebuconazole (P = 0.05). Thus, our results strongly suggest that B. subtilis strain Em7 is a promising biological control agent for control of oilseed rape Sclerotinia stem rot.

Biological Control of Stem Rot Disease of Carnation Caused by Rhizoctonia solani Kuhn

Five fungal antagonists viz., Trichoderma harzianum, T. hamatum, T. viride, T. polysporum and T. virens and two bacterial antagonistic species namely Bacillus subtilis and Pseudomonas fluorescens were evaluated under in vitro and field condition against stem rot of carnation variety Rubesco during 2009 and 2010. Under in vitro conditions biocontrol agents significantly inhibited the growth of Rhizoctonia solani upto 65.08 per cent in case of Trichoderma viride and under field conditions they caused significant reduction in stem rot incidence, increase plant growth and quality parameters as compared to untreated control.

Assessment of plant secondary metabolites in oil palm seedlings after being treated with calcium, copper ions and salicylic acid

The effect of calcium, copper ions and salicylic acid (SA) amendment on the incidence of basal stem rot and activity of secondary metabolites in oil palm seedlings were investigated in glasshouse study. Disease incidence (DI) in positive control (T8) was 75% at nine months after inoculation (9 MAI). However, weekly pre-immunisation with Ca2+ + Cu2+ + SA prior to inoculation significantly suppressed DI and delayed disease onset as noted in T7. In the present study, the lowest %DI was observed in T7 (15%) followed by T1, T5, T6, T3, T4 and T2. The Ca2+, Cu2+ and SA amendments were resulted in earlier and higher accumulation of plant secondary metabolites as noted in leaves, stems and root tissues in response to invasion by Ganoderma boninense. High total phenolic content concentration was detected in T7 (leaf: 233.38 ± 0.12 mg/g; stem: 132.78 ± 0.04 mg/g and root: 86.98 ± 0.28 mg/g). Similar trend was obtained in peroxidase activity, total lignin content and hydrogen peroxide scavenging activity. These results suggested that it could be due to the accumulation of phenolics, peroxidase activities, lignin content and hydrogen peroxide scavenging activities in oil palm seedling tissues which might have collectively contributed to induce resistance against G. boninense.

Role of Endomycorrhizae on Controlling Stem- and Root-Rot of Pepper Caused by Sclerotium rolfsii

This study was designed to investigate the effect of inoculation time with vesicular arbuscular mycorrhizal (VAM) fungi, Glomus spp., on the interaction between root-rot and stem-rot of pepper caused by Sclerotium rolfsii Sacc. as well as its growth. The results indicated that addition of Glomus spp. significantly increased the shoot and root fresh and dry weight with significant decrease to the disease severity (59-89%). Effect of the mycorrhizal inoculation using five species of Glomus by two different inoculation treatments on incidence of Sclerotium stem-rot as well as crop parameters of pepper plants inoculated with the tested fungus was investigated. Generally, mycorrhizal inoculation increased pepper shoot and root fresh and dry weight compared with uninoculated plants. Meanwhile, seedlings arose from seeds treated with Glomus spp. increased growth parameters and yield. G. coronatum and G. luteum were the best mycorrhizae to increase crop parameters. On the other hand, G. etunicatum, G. diaphanum and G. luteum were the best to protect pepper plants against S. rolfsii.

Biological control of stem rot of groundnut (Arachis hypogaea L.) caused by Sclerotium rolfsii Sacc. with actinomycetes

A total of 30 isolates of actinomycetes were isolated from the rhizosphere soils of groundnut collected from different parts of Tamil Nadu, India and tested for their inhibitory activity against Sclerotium rolfsii Sacc., the stem rot pathogen of groundnut. Among the various isolates tested in vitro, five isolates (CBE, MDU, PDK, ANR and SA) were found effective in inhibiting the mycelial growth of S. rolfsii in dual culture assay. These isolates were identified as Streptomyces sp. on the basis of standard bacteriological tests and 16S ribosomal RNA gene sequence analysis. Groundnut seeds when treated with Streptomyces sp. strains showed significant increases in root length, shoot length and seedling vigour. Talc-based powder formulations of the Streptomyces sp. strains, CBE, MDU and PDK selected on the basis of their in vitro antagonism on dual plate technique and plant-growth promoting activity were prepared and tested for their efficacy in controlling stem rot of groundnut under greenhouse and field conditions. Seed treatment and soil application of Streptomyces sp. strains CBE, MDU and PDK significantly reduced the incidence of stem rot under greenhouse and field conditions. The highest pod yield was recorded in plots treated with Streptomyces sp. strain CBE when compared to other strains.

Evaluation of Biorational Products for Management of Phytophthora Blight of Bell Pepper Transplants

There is a critical need for pest control products that are compatible with sustainable agricultural practices, such as those based on natural antagonists or plant defense activators. Four separate, repeated experiments were conducted in which commercially available biopesticides and phosphonate-containing products were evaluated in the greenhouse for the management of Phytophthora blight of bell pepper caused by Phytophthora capsici. The phosphonate-containing product, FNX-100, applied as a soil drench, was found to be the most effective treatment for decreasing the incidence of stem and crown rot. A single soil drench of FNX-100 applied at the lowest concentration provided disease control that was as effective as multiple applications of the highest rate. Foliar applications of FNX-100 at any concentration or frequency were ineffective for disease control, and caused pronounced phytotoxicity when compared to the FNX-100 soil drench. The phosphorous acid K-Phite was found to be less effective than FNX-100, but disease symptoms were minimal in plants treated with a soil drench of that product. While the efficacy of three other phosphonate-containing products, Prophyt, Phostrol, and FNX-2500, were inconsistent, it was observed that these products were also more effective in managing disease when applied as a soil drench rather than as a foliar spray. Accepted for publication 18 December 2012. Published 26 February 2013.

First Report of Stem Rot of Papaya Caused by Fusarium solani Species Complex in Brazil.

In October 2010, 2-year-old papaya (cv. Hawaii) trees with high incidence of stem rot were observed during a survey conducted in Rio Grande do Norte state, northeastern Brazil. Stems showing reddish brown-to-dark brown symptoms were collected and small pieces (4 to 5 mm) of necrotic tissues were surface sterilized for 1 min in 1.5% NaOCl, washed twice with sterile distilled water, and plated onto potato dextrose agar (PDA) amended with 0.5 g liter-1 streptomycin sulfate. Plates were incubated at 25°C with a 12-h photopheriod for 4 days. Pure cultures with white, fluffy aerial mycelia were obtained by subculturing hyphal tips onto PDA. Identification was made using morphological characteristics and DNA based molecular techniques. Colonies grown on PDA and Spezieller Nährstoffarmer agar (SNA) for 10 days at 25°C with a 12-h photoperiod were used for morphological identification (3). The fungus produced cream sporodochia and two types of spores: microconidia were thin-walled, hyaline, ovoid, one-celled, and 6.8 to 14.6 × 2.3 to 4.2 μm; macroconidia were thick walled, hyaline, slightly curved, 3- to 5-celled, and 25.8 to 53.1 × 3.9 to 5.7 μm. Fifty spores of each type were measured. Rounded, thick-walled chlamydospores were produced, with two to four arranged together. On the basis of morphological characteristics (1), three fungal isolates (CMM-3825, CMM-3826, and CMM-3827) were identified as Fusarium solani (Mart.) Sacc. and were deposited in the Culture Collection of Phytopathogenic Fungi of the Universidade Federal Rural de Pernambuco (Recife, Brazil). Single-spore isolates were obtained and genomic DNA of the isolates was extracted and a portion of the translation elongation factor 1-alpha (EF1-α) gene of the isolates was amplified and sequenced (2). When compared with sequences available in the GenBank and Fusarium-ID databases, DNA sequences of the three isolates shared 99 to 100% sequence identity with F. solani species complex (GenBank Accession Nos. JF740784.1, DQ247523.1, and DQ247017.1). Representative sequences of the isolates were deposited in GenBank (Accession Nos. JQ808499, JQ808500, and JQ808501). Pathogenicity tests were conducted with four isolates on 3-month-old papaya (cv. Hawaii) seedlings. Mycelial plugs taken from the margin of actively growing colonies (PDA) of each isolate were applied in shallow wounds (0.4 cm in diameter) on the stem (center) of each plant. Inoculation wounds were wrapped with Parafilm. Control seedlings received sterile PDA plugs. Inoculated and control seedlings (10 each) were kept in a greenhouse at 25 to 30°C. After 2 weeks, all inoculated seedlings showed reddish brown necrotic lesions in the stems. No symptoms were observed in the control plants. The pathogen was successfully reisolated from symptomatic plants to fulfill Koch's postulates. To our knowledge, this is the first report of F. solani species complex causing papaya stem rot in Brazil. Papaya is an important fruit crop in the northeastern Brazil and the occurrence of this disease needs to be taken into account in papaya production.

Adaptation of Oil Palm Seedlings Inoculated with Arbuscular Mycorrhizal Fungi and Mycorrhizal Endosymbiotic Bacteria Bacillus subtilis B10 towards Biotic Stress of Pathogen Ganoderma boninense Pat

The effects of mycorrhizal endosymbiotic bacteria Bacillus subtilis B10 and composite of arbuscular mycorrhizal fungal spores in green house experiment were examined in order to evaluate their effectiveness and compatibility with oil palm seedlings in the presence of a fungal pathogen Ganoderma boninense , the most serious pathogen in oil palm ( Elaeis guineensis Jacq) in Indonesia. A three factors experiment were conducted, with mycorrhizal inoculation (M0 and M1), bacterial B. subtilis B10 inoculation (B0 and B1), and G. boninense inoculation (G0 and G1) as the first, second, and third factors, respectively. The results showed that disease severity index, plant height, root dry-weight, and phosphorus uptake were affected by co-inoculation of mycorrhizal endosymbiotic bacteria B. subtilis B10 and composite of arbuscular mycorrhizal fungi. Co-inoculation of mycorrhizal endosymbiotic bacteria B. subtilis B10 and arbuscular mycorrhizal fungi did not only reduce the percentage of basal stem rot incidence, but also significantly increased plant height and phosphorus uptake by oil palm seedlings. Our results suggest that in oil palm seedlings mycorrhizal endosymbiotic bacteria B. subtilis B10 worked synergistically with arbuscular mycorrhizal fungi in increasing plant adaptation toward biotic stress of pathogen G. boninese and could be promising biocontrol agents.

Molecular diversity of Fusarium oxysporum causing rot diseases of vanilla in south India

Incidence of root, stem and beans rot of vanilla (Vanilla planifolia Andrews) caused by Fusarium oxysporum Schlecht was surveyed in vanilla growing areas of south India during December 2008. The incidence of the disease varied from 1 to 100% in different locations. A total of 60 isolates of F. oxysporum were obtained from diseased samples, and nine morphologically different isolates were taken for molecular characterization using Randomly Amplified Polymorphic DNA (RAPD) markers to study the genetic variability if any, among them. PCR amplification of total genomic DNA with random oligonucleotide primers generated unique banding patterns depending upon primers and isolates. Nine oligonucleotide primers were selected for the RAPD assays, which resulted in 384 bands for nine isolates of F. oxysporum. The number of bands obtained was entered into a NTSYS and the results showed that the variability among the pathogen isolates was moderate. The nine isolates studied were grouped into single major cluster at 0.66 similarity index. Hence, it is inferred that F. oxysporum infecting vanilla in south India consists of a single clonal lineage with a moderate level of genetic diversification.

Modelling inoculum dispersal and Sclerotinia stem rot gradients in canola fields

Dispersal of Sclerotinia sclerotiorum ascospores and sclerotinia stem rot (SSR) incidence were studied in commercial canola fields in two North Dakota locations from 2005 to 2007. Ascospores were collected on dishes containing a semi-selective medium that were placed on the soil, within plant canopies, at various distances from an area source of inoculum. SSR incidence was recorded at the end of the growing season. SSR incidence and inoculum gradients declined with distance from the area source in 2005 and 2007. In 2006, neither ascospores nor SSR were detected. The number of S. sclerotiorum colonies per dish (COL) declined between 30% and 75% within 40 m from the source, whereas SSR incidence declined by 50% within 12–17 m from the source. Ascospore dispersal and SSR gradients across years and locations were best described by Lambert's model (pseudo-R2 ≥ 0.98; P < 0.001) although the negative exponential model also provided a good fit for both (R2 ≥ 0.81; P ≤ 0.001). Every unit increase in the weekly mean COL represented an increase in SSR incidence that ranged between 0.5 and 0.75% (R2 = 0.96; P ≤ 0.0001) in 2005 and between 0.13 and 0.17% (R2 = 0.96; P ≤ 0.0001) in 2007. The existence of short distance dispersal, disease gradients, and the close association between inoculum concentration and disease incidence highlight the importance of within-field produced inoculum and provides support for the use of control tactics that emphasize reduction of sclerotia in canola fields as an effective way to reduce inoculum and control this disease.

Infection routes for Sclerotinia sclerotiorum in apetalous and fully petalled winter oilseed rape

Near‐isogenic lines (NILs) of apetalous (AP) and fully petalled (FP) winter oilseed rape were used to investigate infection by Sclerotinia sclerotiorum, which occurs mainly via infected petals adhering to leaves in FP oilseed rape. AP1 flowers had an average of 1·4 and 0·8 petals per flower in field and polytunnel experiments, respectively. In field experiments there were no significant differences between counts of FP1 petals, FP1 stamens and AP1 stamens adhered to leaves during flowering. At any one sample time, significantly more stamens tested positive for S. sclerotiorum on AP1 than FP1 NILs, e.g. in 2004, at early flowering 37·5% and 24·2% of stamens tested positive on AP1 and FP1 NILs, respectively. In polytunnel experiments, there were significantly more sclerotinia lesions per plant in the FP1 than in the AP1 NIL. The AP1 NIL did not avoid infection completely, probably because it produced some petals, and lesions were initiated from adhered stamens as well as petals. However, while 8·5% and 16·3% of petals initiated lesions in FP1 and AP1 NILs, respectively, only 2·5% and 1·0% of stamens initiated lesions in FP1 and AP1 NILs, which suggests stamens may be less infective than petals. In field experiments the AP1 NIL had significantly less incidence of sclerotinia stem rot than the FP1 NIL in 2004 (4·9% and 7·0%, respectively). However, there was no significant difference in stem rot incidence between AP and FP lines in 2005 (3·6% and 4·3%, respectively) or 2006 (5·5% and 3·9%, respectively).

Row Pattern and Seeding Rate Effects on Agronomic, Disease, and Economic Factors in Large-Seeded Runner Peanut

ABSTRACT Recent peanut cultivar releases are trending to a larger seed size, but have great resistance to tomato spotted wilt virus (TSWV). Larger-seeded cultivars cost more to plant than smaller at an equivalent population. Reduced seeding rates could save growers on seed costs and impede the spread of southern stem rot, but can reduce plant stands which can lower yields and increase TSWV incidence. Therefore, the objectives of this experiment were to compare seven peanut cultivars (Georgia Green, Georgia-06G, AT 3085RO, Florida-07, Tifguard, AP-3, and Georgia-03L) in single and twin row patterns at three seeding rates (17, 20, and 23 seed/m) on a sandy loam soil at Plains, GA for disease incidence, agronomic, and economic performance. Measured variables included yield and grade, plant height and stand, TSWV and southern stem rot incidence, and adjusted net revenue in 2008 and 2009. Twin rows outperformed single rows whenever differences occurred. The only factors consistently affected by reducing seeding rate were plant height and stand, both decreased at the lowest seeding rate. There was a trend toward lower yields (approximately 6% reduction) at the 17 seed/m rate in twin row pattern, although net returns were not diminished compared to the higher seeding rates since lower seed costs offset yield reductions. The cultivars Georgia-06G and Florida-07 had the highest yield and adjusted net revenue among the seven cultivars in both years. Tifguard and Georgia Green had lowest overall yields and would not be preferred cultivars in sandy loam soils. This study demonstrates that twin rows have higher yield, plant stands, and net revenue, plus reduced TSWV incidence than single row pattern, and a reduction in seeding rate to 17 seed/m can be made without serious risk of lost revenue. However, benefits of reducing seeding rate in twin rows were not as pronounced as they were for single rows, and exhibited a greater potential for lower yield. A grower planting in single rows would likely have the most to gain from planting fewer seed, especially under heavy southern stem rot pressure, but planting in twin rows would still be a preferred option over single rows.

KEEFEKTIVAN EKSTRAK BIOTA LAUT AGLAOPHENIA TERHADAP AKTIVITAS ENZIM EKSTRASELULER DAN KANDUNGAN PROTEIN FUSARIUM SERTA PERSENTASE BUSUK BATANG VANILI

The aim of this research was to investigate the effect of Aglaophenia extract on the activity of cellulase and pectinase, protein content of Fusarium, and percentage of vanilla stem rot. This reasearch was carried out in-vitro with concentration of extract of 2000, 1000, 500, 250, 125, 63, and 0 ppm (w/v). The treatments were also applied on vanilla plant to determine their effect on the stem rot incidence. The results exhibited that the higher the concentration of the extract given, both enzymes activity and mycelial protein content of Fusarium decreased. The decrease of enzymes activity resulted in the decrease of vanilla stem rot percentage. The effectiveness of the extract to suppress stem rot was higher than mancozeb, therefore, the extract could be used as a control agent against vanilla stem rot.

Development and Suppression of Aerial Stem Rot in Commercial Potato Fields.

The development of aerial stem rot of potato was quantified in relation to soil type, previous crop, and atmospheric temperature in the Columbia Basin. Incidence of bacterial stem rot was assessed for several weeks beginning before row closure in 18 commercial potato fields and once at the estimated peak of disease development in 38 fields over 4 years. Aerial stem rot was first observed between 25 to 36 days following row closure for 78% of the fields assessed multiple times per season. Slopes of disease progress curves initially increased very rapidly. The partial slope estimate for mean daily maximum temperature indicated an increase of disease with an increase of mean daily maximum temperature (P < 0.0001). Estimates of partial slopes for soil type (sandy loam versus silt loam) and previous crop (sweet or field corn versus other) were significant at P < 0.001 and P = 0.046, respectively, suggesting that cultivation of potato in sandy loam-type soils or following sweet or field corn as a previous crop increases the probability of aerial stem rot. Incidence of bacterial stem rot was significantly reduced in the sections of fields treated with famoxadone plus mancozeb and famoxadone plus mancozeb plus copper hydroxide mixtures.

Susceptibility of stem and root tissues of tobacco cultivars carrying or not the Ph gene to Pythium stem rot, caused by Pythium aphanidermatum

In North Carolina (NC), USA, Pythium stem rot on tobacco is caused by Pythium aphanidermatum. During the past 10 years, Pythium stem rot incidence has been reported more frequently in tobacco fields than before. Since 1997, tobacco flue-cured cultivars carrying the Ph gene that confers immunity to race 0 of Phytophthora parasitica var. nicotianae (Ppn) have also been deployed in NC. It has been questioned whether the introduction of cultivars carrying this resistance gene contributes to the increased incidence of Pythium stem rot. We used a strain of P. aphanidermatum expressing the β-glucuronidase (GUS) reporter gene to investigate the susceptibility of stem and root tissues of four flue-cured tobacco cultivars to Pythium stem rot. Cultivars NC71 (carries the Ph gene) and RJR15 (no Ph gene, but highly resistant to Ppn) were less susceptible (P < 0.05) to P. aphanidermatum than K326 and K346 cultivars that do not carry the Ph gene. Furthermore, different parts of the plant demonstrated significant differences (P < 0.0001) to P. aphanidermatum infection although the significance depended on the cultivar. That is, in K326 and NC71 the highest percent infection was in the adventitious roots, followed by the stems and lastly the true roots, whereas in K346 and RJR15 the highest percent infection was in the adventitious roots, then the true roots and last in the stems. These results do not support the hypothesis that cultivars carrying the Ph gene may be more susceptible to Pythium stem rot than cultivars without the gene. It is likely that other reasons such as the reduction or absence of mefenoxam application in fields where cultivars carrying the Ph gene are planted or reduction in competition for infection cites with Ppn have contributed to the increase of Pythium stem rot incidence in tobacco fields in NC.

Maximizing Economic Returns and Minimizing Stem Rot Incidence with Optimum Plant Stands of Peanut in Nicaragua

AbstractPeanut growers in Nicaragua use high seeding rates, often greatly in excess of the 19.7 seeds/m recommended for growers in Georgia. Significant yield loss to peanut stem rot (caused by Sclerotium rolfsii) often occurs because of rapid disease spread in high density plant stands. It was hypothesized that lower seeding rates would be beneficial, and field experiments were conducted from 2005 to 2006 in Nicaragua to determine the optimum plant stands for stem rot management, peanut yield, and maximum economic returns. The cultivar Georgia Green was planted in twin rows at seven locations with final stands of 4 to 30 plants/m. Paired plots were either treated or not treated with flutolanil to control stem rot. Stem rot incidence consistently increased with higher peanut plant populations in fields with significant levels (&amp;gt;5%) of stem rot. In fields with more than 5% stem rot incidence, peanut yield and gross income adjusted for seed cost were maximized at within row populations of 12 to 13 and 11 plants/m, respectively, when treated with flutolanil to reduce stem rot. When flutolanil was not applied, yield and gross income adjusted for seed cost were maximized at 10 to 11 and 8 to 10 plants/m, respectively. In locations with low stem rot incidence (&amp;lt;5%), maximum yield and gross income adjusted for seed cost were attained at within row populations of 13 and 12 plants/m, respectively. Nicaraguan growers may maximize their economic return by utilizing seeding rates to obtain final stand counts of 8 to 11 plants/m in fields with severe stem rot and 12 plants/m with low disease pressure.