Diagrammatic scale for severity evaluation of the Eremanthus erythropappus–Puccinia velata pathosystem

Candeia (Eremanthus erythropappus (DC.) MacLeish), a native forest species from South America, has garnered commercial interest due to its production of essential oil that contains alpha-bisabolol. This compound is widely used in the pharmaceutical and cosmetics industry, with approximately 80% of Brazilian production being exported. Since candeia rust (Puccinia velata) has only been reported in Brazil, little is known about its epidemiology and control. There is no methodology to quantify rust severity in candeia, justifying the elaboration and validation of a diagrammatic scale containing eight levels of disease severity based on leaf area coverage (0.25%, 0.5%, 1%, 2%, 4%, 8%, 16% and 32%). In a natural sampling of disease in the field, 95% of the leaves showed severity below 16%, with the remaining 5% showing severities between 16% and 32% of leaf area. Validation of the proposed diagrammatic scale was performed by assessing the results from 10 inexperienced evaluators, performing evaluations of three leaves with different severity levels. The evaluations were performed at 7-day intervals; in the first instance, severity values were assigned without the diagrammatic scale, and for the second attempt, the scale proposed in this study was used. The accuracy and precision of the severity estimates produced by each evaluator compared to the real severity was analysed by linear regression and by Lin's statistics. The reproducibility of the estimates was evaluated by analysing the coefficient of determination of linear regressions by pairs of evaluators. The scale provided adequate levels of accuracy, precision, repeatability and reproducibility, indicating the proposed scale was a suitable method for quantifying the severity of candeia rust.     

Methodology to Improve the Efficiency of Evaluation of the Severity of Angular Leaf Spot in Common Bean

Disease severity assessment by means of a scoring scale, especially for angular leaf spot (Pseudocercospora griseola) in common bean, is hindered in experiments for assessment of progenies and/or breeding lines due to lack of uniformity of occurrence of the pathogens and segregation within progenies. The purpose of this study was to estimate the efficiency of the use of one plant per plot in assessing the severity of angular leaf spot in experiments for assessment of progenies and/or breeding lines in the common bean crop. To that end, two experimental strategies were used – one of them using one plant per plot and another using a standard size plot (SPP) (2–4‐m length rows). The experiments were conducted in the period from November 2011 to May 2012 in the municipalities of Lavras and Lambari, state of Minas Gerais, Brazil. Forty‐one lines from the breeding programme of the Universidade Federal de Lavras (UFLA) and from other research institutions were assessed, which differed in regard to their degree of susceptibility to P. griseola. The lines were assessed in regard to the severity of said disease using a five‐degree diagrammatic scale. In all the one plant per plot experiments, severity scores of angular leaf spot from the beginning of its occurrence, and later in intervals ranging from 7 to 12 days, were obtained. In the experiment with the SPP, assessment was made a few days prior to grain harvest. Estimates of the correlations between severity scores and grain yield (GY) were mostly of small magnitude. There was good coincidence between the lines classified as more resistant or more susceptible to the pathogen under the two conditions.     

Efficacy of some plant extracts in the management of cercospora leaf spot of groundnut in the Sudan savanna of Nigeria

Field trials were conducted to evaluate the efficacy of neem seed, garlic clove, onion bulb, ginger rhizome and pawpaw leaf extracts applied as foliar spray in controlling cercospora leaf spot of groundnut in the Sudan savanna of Nigeria during the 2002 and 2003 cropping seasons. Ridomil was used as a positive check while the control was left untreated. Three spray regimes (once, twice and thrice) were evaluated. A strip plot design with three replications was used in setting up the experiments. Ex-Dakar, a cercospora leaf spot susceptible Spanish Valencia groundnut variety, was used as planting material. All the plant extracts reduced the incidence and severity of cercospora leaf spot in both seasons compared to the untreated crops. However, neem seed and garlic clove extracts significantly reduced the incidence and severity of the disease compared to the other plant extracts. Ridomil was more effective in controlling the disease than the plant extracts. Three sprays with the plant extracts gave better control of the disease than one or two sprays in the season. The highest seed yield of 3115 kg/ha and 3311 kg/ha in 2002 and 2003, respectively, were obtained with neem seed extract treatment while the lowest seed yield of 2134 kg/ha and 2334 kg/ha in 2002 and 2003, respectively, were recorded from the untreated crops. Also the highest seed yield of 3124 kg/ha and 3418 kg/ha in 2002 and 2003, respectively were obtained following three sprays compared to 2523 kg/ha and 2641 kg/ha for one spray in 2002 and 2003, respectively and 2840 kg/ha and 3085 kg/ha for two sprays in 2002 and 2003, respectively. The highest haulm yield of 4121 kg/ha and 4089 kg/ha in 2002 and 2003, respectively were also obtained following treatment with neem seed extract. The lowest haulm yield of 2951 kg/ha and 3045 kg/ha in 2002 and 2003 respectively, were recorded from the control. Three sprays gave higher haulm yield (4265 kg/ha and 4279 kg/ha in 2002 and 2003, respectively) than one and two sprays in the season. Neem seed extract could therefore be used to control cercospora leaf spot and to improve groundnut production in the Sudan savanna of Nigeria.     

Development and Validation of a Diagrammatic Scale to Assess the Severity of Black Rot of Crucifers in Kale

The aim of this study was to develop a diagrammatic scale to evaluate black rot (Xanthomonas campestris pv. compestris) severity on kale (Brassica oleraceae var. acephala) leaves. The diagrammatic scale was developed and validated with eight levels of severity, ranging from 0.19 to 48.8%. More than 95% of the leaves collected from the field showed severity levels ranging from 0.1 to 21%, and 5% of the leaves showed severities higher than 22%. The validation of the scale was performed by 10 inexperienced evaluators, and the data were analysed with two methods: linear regression and Lin's statistics. Without the scale, most evaluators overestimated disease severity, whereas the use of the scale resulted in increased precision, accuracy, repeatability, and reproducibility of the estimates according to both validation methods. In conclusion, the proposed diagrammatic scale proved to be useful for assessments of black rot severity in kale leaves. The scale may be of interest to researches performing studies on epidemiology or breeding for resistance.     

Partial replacement of local common bean mixtures by high yielding angular leaf spot resistant varieties to conserve local genetic diversity while increasing yield

The effect of replacing proportions of local farmer bean (Phaseolus vulgaris) mixtures with varieties resistant to angular leaf spot on grain yield was evaluated under local disease pressure in the Kivu region of Zaire. Local bean mixtures in on-station and in multi-locational trials containing respectively 25%, or 50% of Centro Internacional de Agricultura Tropical (CIAT) breeding lines BAT76, or A285, resistant to angular leaf spot yielded significantly more than the local mixture alone. Yields exceeded expected values in three seasons of on-station testing and in two seasons of multi-locational trials. Yield over the expected was found to be a property of new mixtures not protected with fungicide and were attributed to disease control. Relative to expected yields non-protected farmer mixture components performed 17% and 16% better than in protected plots and A285 components yielded 24% and 16% better at respectively 25% and 50% A285 supplementation levels. A285 increased yields of the local mixture components and benefitted from the local mixture when not protected by fungicide. Yield increases in multi-locational trials were largely attributed to the higher yield potential of the resistant variety A285, although angular leaf spot severity was significantly reduced. It was concluded that high yielding, resistant varieties were able to increase bean yield in the region, but probably at a substantial cost in genetic diversity in farmer bean mixtures. That said, a partial replacement strategy is preferable to strategies which encourage complete replacement of local germplasm with one or few high yielding varieties.     

Severity Evaluation Methods in Common Bean Recurrent Selection Programme for Resistance to Angular Leaf Spot

The objectives of this study were to identify which method and period of evaluation of angular leaf spot (ALS) of common bean, caused by the fungal pathogen Pseudocercospora griseola, allow better discrimination among common bean lines derived from seven cycles of recurrent selection for resistance to this pathogen. For that reason, 35 lines of the first seven cycles of the programme were assessed for disease severity on leaves and pods using a rating scale. For leaves, the methods used were severity in field plots (SF), severity in sampled leaflets (SS) and percentage of the sampled leaf area with symptoms (%LAS). Leaf assessments were performed at 7, 14, 21, 28, 33 and 41 days after flowering (DAF), and area under the disease progress curve (AUDPC) was calculated. On pods, severity was evaluated at 41 DAF. It was observed that the SF using a rating scale is the most efficient method for selection of resistant lines, and the best time period for evaluating the disease is around 33 DAF.     

Fungal foliar diseases of Rauwolfia serpentina in wild,its seasonal occurrence,seed transmission and disease management

Rauwolfia serpentina is an important medicinal herb. Studies were conducted to determine causal organisms of foliar diseases in R. serpentina in Bhadra Wildlife Sanctuary during 2006–2009. The foliar disease incidence and its distribution and disease severity in nine state forest regions of the sanctuary were determined. The seedborne nature and transmission of the causal organism was also determined. The management of seedborne inoculum was done by seed dressing with fungicides. The effect of foliage infection on secondary metabolite content was also determined. Results of the present study indicated that Cercospora rauwolfiae is major leaf spot disease causing pathogen. The disease is homogeneously distributed through the study area. The foliar disease severity was high in Kagemanegiri forest during October–November. The minor leaf spot disease caused by Alternaria alternata occurred occasionally. Alternaria alternata is seedborne and seed transmitted and could be managed by seed treatment with Captra or Hyzeb. The secondary metabolites like alkaloids and steroids decreased with increase in foliar infection by C. rauwolfiae, while phenol and flavonoid contents increased. The study suggested that R. serpentina is affected in wild by C. rauwolfiae and A. alternata. The latter pathogen is seedborne and seed transmitted and controlled by seed treatment.     

Evaluation of indigenous bacterial strains for biocontrol of the frogeye leaf spot of soya bean caused by Cercospora sojina

Aims: Assessment of biological control of Cercospora sojina, causal agent of frogeye leaf spot (FLS) of soya bean, using three indigenous bacterial strains, BNM297 (Pseudomonas fluorescens), BNM340 and BNM122 (Bacillus amyloliquefaciens). Methods and Results: From cultures of each bacterial strain, cell suspensions and cell‐free supernatants were obtained and assayed to determine their antifungal activity against C. sojina. Both mycelial growth and spore germination in vitro were more strongly inhibited by bacterial cell suspensions than by cell‐free supernatants. The Bacillus strains BNM122 and BNM340 inhibited the fungal growth to a similar degree (I～52–53%), while cells from P. fluorescens BNM297 caused a lesser reduction (I～32–34%) in the fungus colony diameter. The foliar application of the two Bacillus strains on soya bean seedlings, under greenhouse conditions, significantly reduced the disease severity with respect to control soya bean seedlings and those sprayed with BNM297. This last bacterial strain was not effective in controlling FLS in vivo. Conclusions: Our data demonstrate that the application of antagonistic bacteria may be a promising and environmentally friendly alternative to control the FLS of soya bean. Significance and Impact of the Study: To our knowledge, this is the first report of biological control of C. sojina by using native Bacillus strains.     

Studies of the incidence, severity and distribution of false rust (Synchytrium psophocarpi), leaf spot (Pseudocercospora psophocarpi) and powdery mildew (Oidium sp.) on winged bean (Psophocarpus tetragonolobus) in Papua New Guinea

The incidence, severity and distribution of false rust, (Synchytrium psophocarpi), leaf spot (Pseudocercospora psophocarpi) and powdery mildew (Oidium sp.) on winged beans (Psophocarpus tetragonolobus) were evaluated on pure lines and mixed stands grown in Papua New Guinea between 1976 and 1978. Almost all of the 148 pure lines were susceptible to false rust and leaf spot and the incidence of these diseases increased with plant age. Standard area diagrams were superior to disease keys in evaluating disease severity. Levels of false rust on 10 promising agronomic lines differed according to the locality where the lines were grown. Two Thai lines showed resistance to false rust but P. scandens was immune to false rust and leaf spot. Surveys of 51 sites containing mixed stands of winged beans in the Eastern Highlands, Western Highlands, East New Britain, East Sepik, Madang and Morobe Provinces of Papua New Guinea indicated that leaf spot and false rust were present in both the wet and dry seasons and the apparent absence of disease was probably due to time and size of samples. The diseases appeared to be present in all the traditional winged bean growing areas of Papua New Guinea. It was difficult to obtain evidence of differences in palatability of tissues infected with false rust. The value of surveys and disease assessment in relation to evaluation of crop losses of winged bean caused by these pathogens and selection for resistance is discussed.     

Diagrammatic Scales for Assessing Brown Eye Spot (Cercospora coffeicola) in Red and Yellow Coffee Cherries

Brazil is the world's largest coffee producer. Brown eye spot (BES) (Cercospora coffeicola) is a major crop disease that can cause 15–30% production losses and decrease the coffee beverage quality. Although the influence of this disease on beverage quality has been studied, diagrammatic scales for assessment of the disease severity in berries are still unexplored. Thus, this study has developed and validated diagrammatic scales to assess the severity of BES. Two diagrammatic scales were designed to assess the disease in berries, which can be yellow or red depending on the cultivar. The scale of yellow berries had nine grades: grade 0: 0%; 1: 0.1–5.0%; 2: 5.1–10.0%; 3: 10.1–15.0%; 4: 15.1–20.0%; 5: 20.1–30.0%; 6: 30.1–40.0%; 7: 40.1–60.0%; and 8: higher than 60.0%, while the scale of red berries had eight grades: grade 0: 0%; 1: 0.1–2.5%; 2: 2.6–5.0%; 3: 5.1–10.0%; 4: 10.1–20.0%; 5: 20.1–30.0%; 6: 30.1–50.0%; and 7: higher than 50.0% severity. Using scales improved accuracy and precision with R² = 0.99 and provided good repeatability and reproducibility of assessments of disease severity. Both scales can be used because the different berry colour influenced the accuracy and precision between the scales.     

Diagrammatic Scale for Assessment of Bacterial Blight in Coffee Leaves

Due to the lack of a standardized visual method for assessing bacterial blight (Pseudomonas syringae pv. garcae) in coffee leaves, a diagrammatic scale was developed and validated to quantify the disease. Leaves were collected in crops and nursery with different intensity of symptoms, and the true severity was determined electronically. Based on the frequency distribution of severity values and according to the Weber–Fechner's law of visual stimulus, the minimum and maximum limits and the intermediate levels in the scale were determined. Validation was performed by ten evaluators who estimated the severity of 50 leaves with different intensity of symptoms. One evaluation was performed without diagrammatic scale and two evaluations with the scale at 7‐day intervals. The accuracy, precision, repeatability and reproducibility of the estimates were evaluated. The scale had nine levels: 0 (0%), 1 (0.1–0.99%), 2 (1–2%), 3 (2.01–4%), 4 (4.01–8%), 5 (8.01–16%), 6 (16.01–25%), 7 (25.01–45%) and 8 (≥45.1%). Using the scale, the evaluators were able to improve accuracy, precision, reproducibility and repeatability of estimates, compared to evaluators without scale. The scale was appropriate to visual estimation of severity of bacterial blight in coffee leaves.     

Inhibition of tomato shoot growth by over‐irrigation is linked to nitrogen deficiency and ethylene

Although physiological effects of acute flooding have been well studied, chronic effects of suboptimal soil aeration caused by over‐irrigation of containerized plants have not, despite its likely commercial significance. By automatically scheduling irrigation according to soil moisture thresholds, effects of over‐irrigation on soil properties (oxygen concentration, temperature and moisture), leaf growth, gas exchange, phytohormone [abscisic acid (ABA) and ethylene] relations and nutrient status of tomato (Solanum lycopersicum Mill. cv. Ailsa Craig) were studied. Over‐irrigation slowly increased soil moisture and decreased soil oxygen concentration by 4%. Soil temperature was approximately 1°C lower in the over‐irrigated substrate. Over‐irrigating tomato plants for 2 weeks significantly reduced shoot height (by 25%) and fresh weight and total leaf area (by 60–70%) compared with well‐drained plants. Over‐irrigation did not alter stomatal conductance, leaf water potential or foliar ABA concentrations, suggesting that growth inhibition was not hydraulically regulated or dependent on stomatal closure or changes in ABA. However, over‐irrigation significantly increased foliar ethylene emission. Ethylene seemed to inhibit growth, as the partially ethylene‐insensitive genotype Never ripe (Nr) was much less sensitive to over‐irrigation than the wild type. Over‐irrigation induced significant foliar nitrogen deficiency and daily supplementation of small volumes of 10 mM Ca(NO₃)₂ to over‐irrigated soil restored foliar nitrogen concentrations, ethylene emission and shoot fresh weight of over‐irrigated plants to control levels. Thus reduced nitrogen uptake plays an important role in inhibiting growth of over‐irrigated plants, in part by stimulating foliar ethylene emission.     

Suppression of gray leaf spot (blast) of perennial ryegrass turf by Pseudomonas aeruginosa from spent mushroom substrate

Bacteria isolated from spent mushroom substrate (SMS) were evaluated for the suppression of Pyricularia grisea, the causal agent of gray leaf spot of perennial ryegrass (Lolium perenne) turf. Thirty-two of 849 bacterial isolates (3.8%) from SMS significantly inhibited the mycelial growth of P. grisea in vitro. Six bacterial isolates that afforded maximum inhibition of P. grisea were also refractory to Rhizoctonia solani, Rhizoctonia cerealis, Sclerotinia homoeocarpa, and Fusarium culmorum. Each of the six isolates was identified as Pseudomonas aeruginosa by fatty acid profile analysis. The biocontrol activity of the bacterial isolates was not compromised by a prolonged exposure to UV radiation in vitro. In controlled-environment chamber experiments, all 32 bacterial isolates were tested for suppression of gray leaf spot on Pennfine perennial ryegrass when applied as seed treatment or foliar sprays. Foliar applications of the bacteria (10⁸ cfu/ml 0.1% carboxymethylcellulose), but not the seed treatment, significantly reduced disease severity and incidence. The three most efficient isolates from foliar application treatments, which were among the six bacterial isolates identified as P. aeruginosa, were further evaluated for suppression of gray leaf spot as a function of timing of application. The three isolates of P. aeruginosa suppressed gray leaf spot in perennial ryegrass in Cone-tainers when applied at 1, 3, and 7 days prior to inoculation with P. grisea both in controlled-environment chamber experiments, and in potted ryegrass plants maintained in the field. All application intervals, regardless of the bacterial isolate, provided significant reduction of gray leaf spot severity. Suppression of gray leaf spot by isolates of P. aeruginosa under controlled-environment chamber conditions was not different from that observed in potted ryegrass plants maintained in the field. In field experiments, an isolate of P. aeruginosa provided significant suppression of gray leaf spot when applied at 1, 7, and 14 days prior to inoculation with P. grisea. The bacterium proved effective against gray leaf spot of perennial ryegrass maintained as fairway and rough heights. These results indicate that P. aeruginosa may be a potential biocontrol agent for gray leaf spot of perennial ryegrass turf.     

Control and yield loss modelling of circular leaf spot of persimmon caused by Mycosphaerella nawae

Symptoms of circular leaf spot of persimmon (CLSP), caused by Mycosphaerella nawae, consisted of necrotic spots on leaves, chlorosis and premature defoliation. Although CLSP is a foliar disease, early fruit maturation and abscission are frequently associated with the presence of lesions on leaves and defoliation, resulting in severe economic losses. Despite their importance for the design of efficient disease management programmes, quantitative relationships between CLSP incidence and yield loss are unknown. Therefore, fungicide efficacy trials were conducted during two consecutive years in Spain to induce different levels of disease severity, defoliation and yield loss. The effects of fungicide treatments on CLSP severity were analysed by ordinal logistic regression models. Relative yield loss values were regressed against the percentage of affected leaves or defoliated obtained at different evaluation dates. The disease had high negative impact and complete yield loss was observed in the absence of effective fungicide treatments. Preventive applications of pyraclostrobin, trifloxy‐strobin and mancozeb provided the best disease control and highest yields, up to 95.77 kg tree^?1. An exponential relationship of CLSP incidence and defoliation with yield loss was found. In general, model fit and predictive ability was superior when defoliation, rather than incidence, was used as explanatory variable. The impact of defoliation on yield loss was higher in earliest evaluation dates, suggesting that early leaf abscission may be the main factor contributing to premature fruit drop and subsequent yield loss. Substantial yield losses were observed even with relatively low levels of CLSP incidence and defoliation. Therefore, it was not possible to define a critical action threshold for CLSP management based on foliar symptoms.     

Foliar fertilizers for the management of phoma leaf spot on coffee seedlings

The growing demand for alternative strategies for plant disease management has sought a reduction in the use of fungicides via the employment of resistance inducers and foliar fertilizers, among others. Therefore, this study aimed at evaluating the following foliar fertilizers for the management of phoma leaf spot: a foliar fertilizer based on macro‐ and micronutrients (Fmm: 10% N, 4% S, B, 5% Fe and 5% Zn); one based on cobalt and molybdenum (Fcm: 2% Co and 3% Mo); manganese phosphite (FMn: 30% P₂O₅ and 9% Mn); and the FMn+Fmm, Fcm+Fmm and FMn+Fcm+Fmm associations compared to a boscalid fungicide and a control with no treatment. The disease severity, the chlorophyll a and b contents, the net photosynthetic rate (LPR), the phenylalanine ammonia lyase (PAL) activity and the lignin content in leaves were assessment. Based on the severity, the area under the disease severity progress curve (AUSPC) and the efficiency of disease control in relation to untreated plants were calculated. The experimental design was in randomized blocks with eight treatments and three replications. Treatments FMn+Fmm and Fcm were the most effective in reducing the AUPSC in comparison with the control and promoted an increased activity of PAL. FMn was the treatment that promoted the highest increase in the LPR. There were no effects of the treatments on the lignin content compared to the control.     

Integrated biological control of bacterial speck and spot of tomato under field conditions using foliar biological control agents and plant growth-promoting rhizobacteria

Integration of foliar bacterial biological control agents and plant growth promoting rhizobacteria (PGPR) was investigated to determine whether biological control of bacterial speck of tomato, caused by Pseudomonas syringae pv. tomato, and bacterial spot of tomato, caused by Xanthomonas campestris pv. vesicatoria and Xanthomonas vesicatoria, could be improved. Three foliar biological control agents and two selected PGPR strains were employed in pairwise combinations. The foliar biological control agents had previously demonstrated moderate control of bacterial speck or bacterial spot when applied as foliar sprays. The PGPR strains were selected in this study based on their capacity to induce resistance against bacterial speck when applied as seed and soil treatments in the greenhouse. Field trials were conducted in Alabama, Florida, and California for evaluation of the efficacy in control of bacterial speck and in Alabama and Florida for control of bacterial spot. The foliar biological control agent P. syringae strain Cit7 was the most effective of the three foliar biological control agents, providing significant suppression of bacterial speck in all field trials and bacterial spot in two out of three field trials. When applied as a seed treatment and soil drench, PGPR strain Pseudomonas fluorescens 89B-61 significantly reduced foliar severity of bacterial speck in the field trial in California and in three of six disease ratings in the field trials in Alabama. PGPR strains 89B-61 and Bacillus pumilus SE34 both provided significant suppression of bacterial spot in the two field trials conducted in Alabama. Combined use of foliar biological control agent Cit7 and PGPR strain 89B-61 provided significant control of bacterial speck and spot of tomato in each trial. In one field trial, control was enhanced significantly with combined biological control agents compared to single agent inoculations. These results suggest that some PGPR strains may induce plant resistance under field conditions, providing effective suppression of bacterial speck and spot of tomato, and that there may be some benefit to the integration of rhizosphere-applied PGPR and foliar-applied biological control agents.     

Effect of pollen,natural prey and factitious prey on the development of <Emphasis Type="Italic">Iphiseius degenerans</Emphasis>

The predatory mite Iphiseius degenerans (Berlese) is commercially available as a biological control agent of thrips and spider mites in greenhouse crops. Developmental duration and immature survival of I. degeneransreared on nine types of food (almond pollen, apple pollen, castor bean pollen, plum pollen, sweet pepper pollen, Tetranychus urticaeKoch, Frankliniella occidentalis(Pergande), Ephestia kuehniella Zeller eggs and Artemia franciscana Kellogg cysts) and on three substrates (Multicel, sweet pepper leaf, and bean leaf) were determined in the laboratory. All experiments were carried out at 25 °C. On Multicel, mean developmental times on pollen ranged from 6.0 to 7.1 days, with the lowest value recorded on almond pollen and the highest on sweet pepper pollen. When reared on castor bean pollen significantly longer developmental times were obtained on a sweet pepper leaf compared to a bean leaf or Multicel. Developmental duration when offered T. urticaeon Multicel ranged between 6.1 and 6.9 days, on a bean leaf development was completed in 8.0 days. The longest developmental times on Multicel were recorded on Ephestia eggs (7.0 days) and on decapsulated Artemia cysts (7.5 days). No development beyond the protonymphal stage occurred in the absence of food or when encapsulated Artemia cysts or thrips larvae were offered on Multicel. On a sweet pepper leaf and a bean leaf, respectively 6.7 and 10.0% of the eggs reached adulthood when thrips larvae were provided as food; developmental times recorded here, were 9.0 and 8.3 days. Overall, immature mortality occurred mainly in the protonymphal stage and ranged from 0.0 to 36.7%. In conclusion, I. degenerans is able to feed on a variety of natural and unnatural foods, but thrips larvae and sweet pepper pollen are unfavourable food for immature development. This could compromise the establishment of this biological control agent when used against thrips in sweet pepper crops.     

Suppression of tan spot and plant growth promotion of wheat by synthetic and biological inducers under field conditions

Tan spot of wheat caused by Pyrenophora tritici‐repentis (Ptr) is a major leaf spot disease. No single control measure is likely to be successful in controlling tan spot and a fully integrated system of disease management is more likely to achieve a long‐term solution. Research to improve control efficacy has focused on fungicide improvement, resistant cultivars, the use of biological control agents (BCAs) mixtures and combinatorial approaches involving BCAs and plant resistance stimulants with complementary modes of action. Various biotic and abiotic agents can stimulate wheat defence mechanisms and so benefit resistance to Ptr infection. Among them, Trichoderma spp. have been widely used as antagonistic fungal agents against several pathogens as well as plant growth enhancers. Also, the synthetic agents acibenzolar‐S‐methyl (ASM) and thiamethoxam (TM) have provided broad‐spectrum disease and pest control as well as enhanced plant vigour against several fungal diseases. The aim of this research was to evaluate the effectiveness of two Trichoderma harzianum strains and two substances of synthetic origin (ASM and TM) on the suppression of tan spot and plant growth promotion of wheat plants. When BCAs, ASM and TM were applied to field plots on wheat cultivar Klein Escorpion, the severity of tan spot reduced and plant height, fresh weight, dry weight of shoots and dry weight of roots increased in comparison with the control. When applied prior to Ptr inoculation, ASM, TM and the strain Th1 of T. harzianum caused a reduction in necrotic lesions >50% compared to the control treatment. Seed treatment with TM resulted in a significant enhancement of plant height. Application of ASM significantly increased foliar fresh weight by 45% as compared to the control treatment, whereas foliar fresh weight increased 29% and 50% when TM and T. harzianum strain Th1 were applied as seed coating. Acibenzolar‐S‐methyl alone or combined with Th1 increased dry weight to >60%, whereas the effects of TM and Th1 on dry mass showed an increase that ranged from 57% to 25%. Plants treated with Th1 and both synthetic compounds achieved up to sixfold increment in root dry weight over the control.     

Effect of Cercospora zeae-maydis infested maize residue on progress and spread of grey leaf spot of maize in central Uganda

The spread of grey leaf spot caused by Cercospora zeae‐maydis from infested maize residue on the soil surface and progress over time were studied under tropical conditions at two locations in central Uganda, Kabanyolo and Namulonge, using a susceptible local cultivar, LP16. Infested maize residue collected the previous season was used as the inoculum source in varying amounts; 80% coverage, 40% coverage and 0% soil coverage were used to simulate no tillage, minimum tillage and maximum tillage with complete burial of residues. In all the seasons, disease spread was adequately described by a power law model, whereas disease progress over time was equally well represented by both Gompertz and logistic models. The time factor was highly significant (P < 0.05) for disease development, indicating both increases in disease intensity over time and change in gradients with time. The amount of infested residue on the soil surface in the maize planting was highly significant (P < 0.05) for slope (b) and intercept (a) of the linearised disease gradient. The gradient parameter (b) based on the average for the four directions from the residue source ranged from ?0.96 to ?0.08 in the second cropping season of 1999, from ?2.16 to ?0.01 and from ?0.87 to ?0.03 in the first and second seasons of 2000, respectively. The distance from the infested residue significantly affected foliar disease, but the direction from the residue inoculum source did not, nor was the distance by direction interaction significant. However, interactions between amount of residue and distance were significant. Percentage leaf area affected by grey leaf spot, the areas under disease progress curves and disease intercepts decreased with distance at both locations, but rate of disease increase (r) was generally constant with distance from residue source at Kabanyolo, but not at Namulonge. The relationship between disease severity and amount of residue cover appeared to be affected by the level of background inoculum. At Kabanyolo, where little background inoculum was present, differences were detected in disease severity parameters between the no‐residue plots and residue plots, whereas at Namulonge, where high background levels existed, there was no effect of residue on disease.     

Tunisian isolates of Trichoderma spp. and Bacillus subtilis can control Botrytis fabae on faba bean

Faba bean crops worldwide are often attacked by different diseases, particularly chocolate spot caused by Botrytis fabae Sard. Fungal and bacterial isolates collected from faba bean and barley leaves in Tunisia were evaluated for their antagonistic potential against B. fabae. In a test on detached leaves, the highest rate of decrease in disease severity was scored by Trichoderma viride, followed by T. harzianum, the fungicide Carbendazim then Bacillus subtilis. Under glasshouse conditions, all tested fungi resulted in significant disease severity reduction. T. viride reduced the rate of chocolate spot infestation on leaves and stems by 35% and 31.5%, respectively, when the rate on the control was 100%. For T. harzianum, Carbendazim and B. Subtilis, the rates of infestation on the leaves were 41.7%, 43.1% and 59.7%, respectively. On the stems, T. harzianum scored the lowest rate of 54.2% followed by B. subtilis with 79.2% then Carbendazim with 87.5%. Two consecutive seasons of field trials using the Trichoderma species, B. subtilis and Carbendazim showed significant and consistent reduction in the severity of chocolate spot infestation rates. The highest protection against the disease was obtained from T. viride. Based on these results, Tunisian isolates of Trichoderma spp. can be recommended for developing commercial bio-fungicides for integrated management of chocolate spot.