Effect of foliar‐applied potassium silicate on coffee leaf infection by Hemileia vastatrix

Coffee leaf rust, caused by Hemileia vastatrix, is the most devastating disease of coffee. Since limited information is available in the literature on silicon (Si) affecting plant diseases in coffee, this study was designed to investigate foliar application of potassium silicate (PS), a source of soluble (Si), on infection process of coffee leaf rust at the microscopic level. The foliar Si concentration for plants sprayed with water and PS has no significant difference (0.24 and 0.30 dag kg^?1, respectively). X‐ray microanalysis indicated that the deposition of Si on the leaves of the plants that were sprayed with PS was greater in comparison to the leaf samples from the plants sprayed with water. Rust severity on leaves of plants sprayed with water or sprayed with PS reached 44% and 32%, respectively, at 36 days after inoculation (dai). Plates of polymerised PS were observed on the leaf surfaces of the plants sprayed with the product, in contrast to its absence on the leaf surfaces of plants sprayed with water. At 36 dai, a greater number of uredia were observed on the leaf surfaces of plants sprayed with water in comparison to the leaf surfaces of plants sprayed with PS. On fractured leaf tissues that were sprayed with PS, less fungal colonisation was observed in comparison to the leaves of plants sprayed with water. In conclusion, the results of this study suggest that the effect of foliar‐applied Si on the control of the coffee leaf rust development may be attributed to the physical role of the polymerised PS, its osmotic effect against urediniospores germination, or both.     

Physiological Responses of Rice Plants Supplied with Silicon to Monographella albescens Infection

This study investigated the effect of silicon (Si) on the resistance of rice plants of the cv. ‘Primavera’ cultivar that were grown in a nutrient solution with 0 (?Si) or 2 mm (+Si) Si to leaf scald, which is caused by Monographella albescens. The leaf Si concentration increased in the +Si plants (4.8 decag/kg) compared to the ?Si plants (0.9 decag/kg), contributing to a reduced expansion of the leaf scald lesions. The extent of the cellular damage that was caused by the oxidative burst in response to the infection by M. albescens was reduced in the +Si plants, as evidenced by the reduced concentration of malondialdehyde. Higher concentrations of total soluble phenolics and lignin‐thioglycolic acid derivatives and greater activities of peroxidases (POX), polyphenoloxidases (PPO), phenylalanine ammonia‐lyases (PAL) and lipoxygenases (LOX) in the leaves of the +Si plants also contributed to the increased rice resistance to leaf scald. In contrast, the activities of chitinases and β‐1,3‐glucanases were higher in the leaves of the ?Si plants probably due to the unlimited M. albescens growth in the leaf tissues, as indicated by the larger lesions. The results of this study highlight the potential of Si in decreasing the expansion of the leaf scald lesions concomitantly with the potentiation of phenolic and lignin production, and the greater activities of POX, PPO, PAL and LOX rather than simply acting only as a physical barrier to avoid M. albescens penetration.     

Wheat Resistance to Spot Blotch Potentiated by Silicon

Spot blotch, caused by the fungus Bipolaris sorokiniana, is one of the most important diseases on wheat. The effects of silicon (Si) on this wheat disease were studied. Plants of wheat cultivars BR‐18 and BRS‐208 were grown in plastic pots containing Si‐deficient soil amended with either calcium silicate (+Si) or calcium carbonate (?Si). The content of Si in leaf tissue was significantly increased by 90.5% for the +Si treatment. There was no significant difference between Si treatments for calcium content, so variations in Si accounted for differences in the level of resistance to spot blotch. The incubation period was significantly increased by 40% for the +Si treatment. The area under spot blotch progress curve, number of lesions per cm² of leaf area, and real disease severity significantly decreased by 62, 36 and 43.5% in +Si treatment. There was no significant effect of Si on lesion size. The role played by total soluble phenolics in the increased resistance to spot blotch of plants from both cultivars supplied with Si was not clear. Plants from cultivar BR‐18 supplied with Si showed the highest values for concentration of lignin‐thioglycolic acid derivatives during the most advanced stages of fungus infection. Chitinase activity was high at the most advanced stages of fungus infection on leaves from both cultivars supplied with Si and may have had an effect on fungus growth based on the reduction of the components of resistance evaluated. Peroxidase activity was found to be high only at 96 h after inoculation of both cultivars supplied with Si. Polyphenoloxidase activity had no apparent effect on resistance regardless of Si treatments. Results revealed that supplying Si to wheat plants can increase resistance against spot blotch.     

Silicon and Triadimenol for the Management of Coffee Leaf Rust

This study documents an experiment that was undertaken in the 2006/2007, 2007/2008 and 2008/2009 growing seasons on Coffea arabica cv. ‘Catuaí Vermelho IAC 144’ that sought to evaluate the effects of various calcium silicate rates combined with the fungicide triadimenol on the incidence of coffee leaf rust. The experimental design was a randomized complete block in a split plot with five treatments (with varied calcium silicate rates and with or without triadimenol) and four replications. Each experimental unit (split plot) consisted of seven coffee plants (14 m²), which were the central five plants used for the evaluations. Calcium silicate (CS) and lime (L) were used according to the following mixtures (M): M1: 0% CS and 100% L; M2: 25% CS and 75% L; M3: 50% CS and 50% L; M4: 75% CS and 25% L; and M5: 100% CS and 0% L. The leaf Si concentration did not increase as CS rates increased in the soil. There was no reduction in the area under rust progress curve (AURPC) as the rates of CS increased in the soil. During the growing seasons 2006/2007, 2007/2008 and 2008/2009, rust incidence reached 94, 96 and 92% on plants that did not receive triadimenol, respectively, whereas the incidence did not exceed 6, 38 and 16%, respectively, for those plants that did. For yield, no interaction was observed between the calcium silicate rates and with or without triadimenol. The yield increased by 117% for plants receiving triadimenol compared with those that did not. The 3‐year experiments indicated that soil amendment with calcium silicate had no effect on either reducing coffee leaf rust incidence or increasing yield. Conversely, as expected, coffee leaf rust symptoms were dramatically reduced on plants sprayed with triadimenol, and this was accompanied by a significant gain in yield.     

Method validation for the determination of ochratoxin A in green and soluble coffee by immunoaffinity column cleanup and liquid chromatography

A method was validated for the determination of ochratoxin A (OTA) in soluble and green coffee. Performance parameters evaluated included selectivity, accuracy, intermediate precision, linearity, limit of detection, limit of quantitation, and ruggedness. The method was found to be selective for OTA in both matrices tested. Recovery rates from soluble coffee samples ranged from 73.5 to 91.2%, and from green coffee samples from 68.7 to 84.5%. The intermediate precision (RSDr) was between 9.1 and 9.4% for soluble coffee and between 14.3 and 15.5% for green coffee analysis. The linearity of the standard calibration curve (r²) was <0.999 for OTA levels of 1.0–20.0 μg/kg in coffee samples. The limit of detection was determined to be 0.01 ng of OTA on column, while the limit of quantitation was found to be 0.03 ng on column. The limit of quantitation is equivalent to 0.6 μg/kg in soluble coffee samples and 0.3 μg/kg in green coffee samples. The results of the ruggedness trial showed two factors are critical for soluble coffee analysis: the extraction method, and the flow rate of the mobile phase. For green coffee analysis two critical factors detected were the extraction method and the storage temperature of the immunoaffinity column. Five samples of soluble coffee and 42 of green coffee were analysed using the validated method. All soluble coffee samples contained OTA at levels that ranged from 8.4 to 13.9 μg/kg. Six of the 42 green coffee samples analysed (14.3%) contained OTA at levels ranging from 0.9 to 19.4 μg/kg. The validated method can be used to monitor OTA levels in Colombian coffee for export or for local consumption.     

Influence of plant silicon and sugarcane cultivar on mandibular wear in the stalk borer Eldana saccharina

1 Silicon can increase the resistance of plants to attack by herbivorous insects. The present study aimed to determine the effect of silicon and cultivar on mandibular wear in larvae of the sugarcane stalk borer Eldana saccharina Walker (Lepidoptera: Pyralidae).
2 Four sugarcane cultivars, resistant (N21, N33) and susceptible (N11, N26) to E. saccharina were grown in a pot trial in silicon deficient river sand, with (Si+) and without (Si−) calcium silicate. Individual third-instar larvae were confined on the sugarcane stalk at three known feeding sites (leaf bud, root band and internode) and left to feed for 21 days.
3  Eldana saccharina larval heads were mounted on stubs, with the mandibles oriented horizontally and photographed under a scanning electron microscope. Mandibular wear was measured from the digital images using a quantitative method.
4 Although there was a trend for increased wear in larvae that developed on Si+ cane, no significant effect of silicon, cultivar or site on mandibular wear of E. saccharina was shown.
5 This is the first study to accurately and quantitatively measure the mandibular wear of an insect fed on Si+ plants.     

Wheat Resistance to Bacterial Leaf Streak Mediated by Silicon

Leaf streak, caused by Xanthomonas translucens pv. undulosa, is the major bacterial disease of wheat in Brazil and other countries worldwide. This study aimed to evaluate the effect of silicon (Si) on disease development and the biochemical mechanisms possibly involved in resistance potentialized by this element. Plants of cv. BR‐18, susceptible to leaf streak, were grown in plastic pots containing Si‐deficient soil amended with either calcium silicate (+Si) or calcium carbonate (?Si). The content of Si increased (P ≤ 0.05) by 96.5% for the +Si when compared with ?Si treatment. There was no difference (P ≥ 0.05) between Si treatments for calcium content on leaf tissue, so variations in Si accounted for differences in the level of resistance to leaf streak. There was no difference (P ≥ 0.05) between Si treatments for incubation period, latent period, necrotic leaf area, and severity estimated by the software quant . However, chlorotic leaf area was reduced (P ≤ 0.05) by 50.2% for the +Si when compared with ?Si treatment. There was no difference (P ≥ 0.05) between Si treatments for the bacteria population on leaf tissue; however, the values seemed to be somewhat lower in the +Si treatment from 4 to 8 days after inoculation (d.a.i.) on leaves from plants supplied with Si. There was no difference (P ≥ 0.05) between Si treatments for electrolyte leakage. The concentration of total soluble phenolics and lignin‐thioglycolic acid (LTGA) derivatives did not show any apparent signs of increase during the course of infection and seemed to be slightly higher on plants not supplied with Si at the most advanced stages of bacterial infection. Chitinase activity was high at the most advanced stages of bacterial infection on leaves from +Si treatment and probably affected bacterial growth on leaf tissue. Peroxidase activity following bacterial infection was not increased by Si, but can be linked with the highest concentration of LTGA derivatives at 12 d.a.i. of plants supplied with Si. Polyphenoloxidase activity did not affect wheat resistance to leaf streak regarding of the Si treatments. The results clearly suggest that supplying Si to wheat plants can increase resistance to leaf streak possibly through an increase in tissue lignification and the participation of chitinases and peroxidases.     

Silicon-mediated resistance of sugarcane to Eldana saccharina Walker (Lepidoptera: Pyralidae): effects of silicon source and cultivar

Abstract:  The effects of four silicon sources – a USA calcium silicate, a local (South African) calcium silicate, Slagment^® and fly ash – on the resistance of sugarcane cultivars (two resistant and two susceptible) to Eldana saccharina Walker (Lepidoptera: Pyralidae) were studied in a potted sugarcane trial. Silicon sources were applied at 5000 or 10 000 kg/ha for the calcium silicates and Slagment; fly ash was applied at 15 000 or 30 000 kg/ha. The greatest increase in plant silicon content (particularly in stalks) was recorded for plants treated with local calcium silicate. Silicon uptake did not vary significantly between the susceptible and resistant cultivars, although the resistant cultivars had inherently higher silicon content than the susceptible ones. Treatment with silicon significantly reduced borer damage and borer performance at the higher treatment level. In general, borer damage and performance decreased with increasing rates of applied silicon and both variables were inversely related with per cent stalk silicon. On average, the higher silicon rate reduced damage by 34% in the susceptible cultivars and by 26% in the resistant cultivars, supporting the argument that susceptible cultivars benefit more from silicon treatments than resistant ones. We propose that calcium silicate amendments could be employed in the integrated, area-wide management of E. saccharina and in the management of soil acidity, both of which are widespread problems in the South African sugar industry.     

Effects of Epoxiconozale and Pyraclostrobin Fungicides in the Infection Process of Hemileia vastatrix on Coffee Leaves as Determined by Chlorophyll a Fluorescence Imaging

Coffee is the most traded commodity in the world, and Brazil is its largest producer. Coffee leaf rust, caused by the biotrophic fungus Hemileia vastatrix, is the most important coffee disease, reducing coffee yield by 35–50%. This study aimed to use the ratio of variable and maximum fluorescence of dark‐adapted tissue (F_v/F_m) as a parameter to differentiate presymptomatic tissue from healthy tissue during disease development in plants sprayed with pyraclostrobin and epoxiconazole after 4 days postinoculation. Visual severity was considered as an indicative of apparent disease and true severity as an indicative of both apparent and non‐apparent disease. There was a significant linear relationship between the areas of true severity and visual severity, and for each additional unit in the visual severity, there was an increase of 1.53 units on the true severity. For the epoxiconazole and pyraclostrobin treatments, coffee leaf rust symptoms decreased according to both visual and F_v/F_m images. Pustules on the leaves sprayed with epoxiconazole were smaller in size than those on the leaves of non‐sprayed plants but bigger than those sprayed with pyraclostrobin. The reduction in F_v/F_m values at the pustule epicentres present on the leaves of plants sprayed with epoxiconazole, and pyraclostrobin was greater than those of the non‐sprayed plants. This finding was expected and reflects the importance of these fungicides in prohibiting the progress of coffee leaf rust. The photosynthetic capacity of Coffea arabica was affected by H. vastatrix infection, and the F_v/F_m parameter was able to show this effect before the visual symptoms were noticed.     

Why is it better to produce coffee seedlings in full sunlight than in the shade? A morphophysiological approach

The coffee plant is native to shaded environments and its seedlings are often produced in shaded nurseries. However, some nursery managers, in an effort to improve the acclimation of seedlings to field conditions after transplantation, produce seedlings in full sun exposure. In this study, the morphological and physiological parameters of arabica coffee (Coffea arabica) seedlings produced in full sun (T1) and in shade (T2) were examined. The biomass accumulation and relative growth rate of T1 and T2 seedlings were similar. The T1 seedlings had less biomass allocation to shoots, a lower leaf mass ratio and a lower leaf area ratio; however, they had a greater net assimilation rate (rate of increase in plant mass per unit leaf area), which was associated with a greater net photosynthetic rate. There were no alterations in the concentrations of total chlorophylls or in the chlorophyll a/b ratio when comparing T1 and T2 seedlings. No indications of photoinhibition or photooxidative damage were observed in the T1 plants, which were shown to have a more robust antioxidant system than the T2 plants. Seedlings transferred from shade to full sun (T3) were not capable of utilising the incident extra light to fix CO₂. These seedlings showed a remarkable nocturnal retention of zeaxanthin and a significantly increased deepoxidation state of the xanthophyll cycle, even at predawn, but the activity of antioxidant enzymes was lower than in the T1 and T2 plants. Despite the acclimation capacity of T3 seedlings to the new light environment, they exhibited chronic photoinhibition and considerable photooxidative damage throughout the seven days following the transfer to full sun exposure. We further discuss the practical implications of producing coffee seedlings in full sunlight and under shade.     

Resistance inducers applied alone or in association with fungicide for the management of leaf rust and brown eye spot of coffee under field conditions

The use of resistance inducers is a promising development in the management of plant diseases, owing to their ability to control a broad spectrum of pathogens and improve the efficacy of fungicides. This study evaluates different sources of phosphonates (potassium, manganese, copper), a formulation prepared from the by‐products of the coffee industry (Greenforce CuCa), as well as the effects of their application, alone or in association with fungicide, in the management of two important coffee fungal diseases in Brazil: leaf rust and brown eye spot, caused by Hemileia vastatrix and Cercospora coffeicola, respectively. The effect of these products on defoliation, productivity and chemical composition of coffee beans (content of trigonelline, chlorogenic acid, caffeine and total soluble solids) was evaluated. Among all the alternative products tested individually, potassium phosphonate (P₂O₅—33.6% + K₂O—29%) stood out, particularly for rust control, which was similar to the results of fungicide treatments. Treatments with fungicide, Greenforce CuCa and cuprous oxide, individually, caused less plant defoliation. Regarding the chemical composition of the coffee beans, the manganese phosphonate treatment showed the highest values for trigonelline, chlorogenic acid, caffeine and total soluble solid content. The results of this study show that resistance inducers can be useful in disease management, may come to eventually replace traditional fungicides and can also contribute to the beverage quality.     

Agroforestry management affects coffee pests contingent on season and developmental stage

1 Management of vegetational diversity in agroecosystems is a potentially regulating factor of pest population dynamics and may affect developmental stages in different ways.
2 We investigated the population dynamics of red spider mites, coffee leaf miners, and coffee berry borers in three management types of coffee agroforests: increasing plant diversity from a few shade tree species (simple-shade agroforests), intermediate-shade tree species (complex-shade agroforests) to high-shade tree species (abandoned coffee agroforests) in Ecuador. Furthermore, we studied how changes in agroforestry management affect population stage structure of each coffee pest.
3 Our results show that agroforestry management affected seasonal patterns of coffee pests in that higher densities of red spider mites were observed from August to December, coffee leaf miners from December to February, and coffee berry borers from May to July. Moreover, specific developmental stages of red spider mites, coffee leaf miners, and coffee berry borers differed in their responses to agroforestry management. During all stages, red spider mite reached higher densities in simple-shade agroforests compared with complex-shade and abandoned agroforests. Meanwhile, coffee leaf miner densities decreased from simple-shade to complex-shade and abandoned agroforests, but only for larvae, not pupae. Similarly, only coffee berry borer adults (but not eggs, larvae and pupae) demonstrated a response to agroforestry management. Environmental variables characterizing each agroforestry type proved to be important drivers of pest population densities in the field.
4 We emphasize the importance of considering seasonal differences and population structure while investigating arthropod responses to different habitat types because responses change with time and developmental stages.     

Silicon Suppresses Fusarium Wilt Development in Banana Plants

This study aimed to determine the effect of silicon (Si) in reducing the symptoms of Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (Foc), on banana plants. Banana seedlings of Grand Nain (resistant) and Maçã (susceptible) were grown in plastic trays amended with 0 (?Si) or 0.39 g Si (+Si) per kg of soil and inoculated with Foc at 60 days after transplanting. The Si concentration in the roots and rhizome‐pseudostem significantly increased by 30.26 and 58.82%, respectively, for the +Si treatment compared with ?Si treatment. The Si concentration in the roots and rhizome‐pseudostem of Grand Nain plants was, respectively, 11.57 and 37.04% greater than that found in Maçã. The +Si plants showed a reduction of 12.37, 49.81, 51.87 and 20.39%, respectively, for the area under reflex leaf symptoms progress curve, the area under root symptoms progress curve, the area under disease progress curve and the area under asymptomatic fungal colonization of tissue progress curve compared with ‐Si plants. The area under darkening of rhizome‐pseudostem progress curve (AUDRPPC) of Maçã significantly increased by 15.98% for the ?Si treatment in comparison with the +Si treatment. For the +Si treatment, the AUDRPPC of the plants from the Maçã cultivar significantly decreased by 20.59% in comparison with the plants from the Grand Nain cultivar. The area under relative lesion length progress curve (AURLLPC) of the plants from the Maçã cultivar significantly decreased by 41.54% for the +Si treatment in comparison with the ?Si treatment. There was no significant difference between the ‐Si and +Si treatments in the AUDRPPC and AURLLPC of Grand Nain. For the +Si treatment, the AURLLPC of Grand Nain significantly decreased by 9.23% in comparison with Maçã. There was no significant difference between the Grand Nain and Maçã for the AUDRPPC and AURLLPC in the ?Si treatment. The findings of this study show that supplying Si to banana plants, especially to a susceptible cultivar to Foc, had a great potential in reducing the intensity of Fusarium wilt and may play a key role in disease management when banana plants are cultivated in Si‐deficient soils infested by this pathogen.     

Field superparasitism by Phymastichus coffea, a parasitoid of adult coffee berry borer, Hypothenemus hampei

Superparasitism by Phymastichus coffea LaSalle (Hymenoptera: Eulophidae), a parasitoid of adults of the coffee berry borer, Hypothenemus hampei (Ferrari) (Coleoptera: Curculionidae: Scolytinae), was recorded under field conditions in a coffee plantation in Colombia. Parasitoid adults were released 1, 5, and 9 days after artificial infestations of 90‐, 150‐, and 210‐day‐old coffee berries with H. hampei females. The position of the beetle inside the berry and the number of P. coffea larvae per female host were assessed 10 days after each parasitoid release. Under laboratory conditions, P. coffea usually lays two eggs per host, one female and one male. In our studies, we often recorded more than six P. coffea larvae in an individual host and mean numbers of larvae per host ranged from two to 4.45. Superparasitism by P. coffea under field conditions was influenced by the age of the coffee berries, which is the most important factor determining the speed of penetration by H. hampei, and therefore the time the beetles are exposed to a P. coffea attack. The number of parasitoid larvae in each H. hampei female gradually decreased with the age of the berry, and also linearly decreased with the time of parasitoid release. Age‐dependent effects of coffee berries that alter the ratio of available hosts to searching parasitoids by providing refuges to the herbivore, largely determine the extent of superparasitism of H. hampei by P. coffea under fields conditions in Colombia.     

Sampling plan for the coffee leaf miner Leucoptera coffeella with sex pheromone traps

The population density of the coffee leaf miner Leucoptera coffeella (Guérin-Méneville & Perrottet) (Lep., Lyonetiidae) can be estimated using pheromone traps in coffee fields as male capture reflects this pest damage based on previous correlational study. However, the spatial distribution of pheromone traps and their density are necessary to optimize the sampling procedure with pheromone traps. Therefore, the objectives of the present study were to determine the pheromone trap density required per hectare to sample coffee leaf miner populations and to determine the spatial distribution of the males of this pest species. The males were sampled every 8 days in 12 consecutive evaluations. Taylor's power law and frequency distributions were used to recognize the distribution of the male capture data, which followed a negative binomial distribution. A common K was obtained, allowing the establishment of a single conventional sampling plan for the 12 fields investigated. The adjusted sampling plan requires eight traps in an area of 30 ha for a 25% precision error. Kriging-generated maps allowed the simulation of male captures for 8, 12 and 20 traps per 30 ha and the results were compared with those obtained with absolute sampling resulting in R ²-values of 0.30, 0.57 and 0.60 respectively. The traps were able to identify the more highly infested areas within the field and are a precise and efficient tool for sampling populations of L. coffeella.     

Silicon Improves the Tolerance to Water-Deficit Stress Induced by Polyethylene Glycol in Wheat (Triticum aestivum L.) Seedlings

Drought stress usually causes a serious yield reduction in wheat production. Silicon (Si) has been reported to be able to alleviate drought stress damage; however, the mechanism is still poorly understood. In this article, the effects of Si (as sodium silicate) on some parameters related to oxidative damage, proline, soluble sugar, and inorganic ions in the leaves of wheat under 20% (w/v) polyethylene glycol (PEG-6000) simulative drought stress are investigated. PEG stress depressed the growth of shoot and root and decreased leaf water potential and chlorophyll concentration. Addition of 1.0 mM Si could partially improve the growth of shoot (but not root) and increase the leaf chlorophyll concentrations of stressed plants. Inclusion of Si in culture solution also maintained leaf water potential of stressed plants at the same level as that of the control plants. PEG stress induced significant accumulation of leaf hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) as well as an increase in electrolyte leakage, which were all decreased by added silicon. These results suggest that stress-induced membrane lipid peroxidation could be partly alleviated by added silicon. Moreover, the results were also supported by the observation that PEG stress-induced decrease in glutathione concentration in the leaves was reversed by added silicon. The proline concentration in the leaves was markedly increased under PEG stress, whereas added silicon partially reversed this. PEG stress decreased the leaf soluble sugar concentration. There were significant negative regressions between proline concentration and both shoot dry weight and leaf chlorophyll concentrations, whereas there were positive regressions between the proline concentration and both H₂O₂ and MDA concentrations in the leaves, supporting the view that proline accumulation is a symptom of stress damage rather than stress tolerance. Addition of Si obviously increased Si accumulation in the shoot. Analyses of Na, Mg, K, and Ca showed no accumulation of these ions in the shoot (on the basis of per tissue dry weight) under water stress, and added Si even decreased their concentrations. These results suggest that under short-term PEG-induced water stress conditions (1 week), antioxidant defense, rather than osmotic adjustment, contributed to the improved wheat growth by Si.     

Soybean Resistance to Phakopsora pachyrhizi as Affected by Acibenzolar‐S‐Methyl,Jasmonic Acid and Silicon

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is one of the most important diseases on soybean. At the moment, ASR is managed mainly with fungicides due to the absence of commercial cultivars with resistance to this disease. This study evaluated the effects of acibenzolar‐Smethyl (ASM), jasmonic acid (JA), potassium silicate (PS) and calcium silicate (CS) on soybean resistance to ASR. The ASM, JA and PS were sprayed to leaves 24 h prior to inoculation with P. pachyrhizi. The CS was amended to the soil. The incubation period (time from the inoculation until symptoms development) was longer for plants growing in soil amended with CS or sprayed with ASM in comparison with plants sprayed with water (control). Plants sprayed with ASM had longer latent period (time from the inoculation until signs appearance) in comparison with the control plants. Plants sprayed with PS showed fewer uredia per cm² of leaf in relation to the control plants. The ASM and PS were the most effective treatments in reducing the ASR symptoms in contrast to the JA and CS treatments. The JA served as an inducer of susceptibility to ASR.     

Effects of silicon sources on its deposition, chlorophyll content, and disease and pest resistance in rice

Rice (Oryza sativa L.) was grown in pots with pyridine N-oxide (PNO), 4-morpholino pyridine N-oxide (MNO), and sodium meta silicate as the sources for silicon. Aliquots of these were added in fortnightly intervals to seedlings through anthesis stage. The plants were monitored for plant growth characteristics, chlorophyll content (SPAD values), photosystem 2 activity (variable to maximum fluorescence ratio of dark adapted leaves), and for blast and yellow stem borer resistance. Deposition of silica in the leaves was monitored by scanning electron microscopy and silicon mapping. PNO or MNO application resulted in significant silicon accumulation in leaf bundle sheath cells. Application of PNO and MNO imparted disease and pest resistance by increasing silicon uptake of rice plants.     

Domatia reduce larval cannibalism in predatory mites

Abstract.  1. Acarodomatia are small structures on the underside of leaves of many plant species, which are mainly inhabited by carnivorous and fungivorous mites.
2. Domatia are thought to protect these mites against adverse environmental conditions and against predation. They are considered as an indirect plant defence; they provide shelter to predators and fungivores and these in turn protect the plants against herbivores and fungi.
3. We studied the possible role of domatia of coffee ( Coffea arabica L.) (Rubiaceae) and sweet pepper ( Capsicum annum L.) (Solanaceae) in reducing cannibalism in the mites inhabiting the domatia. We measured cannibalism of larvae by adults of the predatory mites Iphiseiodes zuluagai Denmark & Muma and Amblyseius herbicolus Chant on coffee leaf discs and of the predatory mite Iphiseius degenerans (Berl.) on sweet pepper leaf. Domatia were closed with glue or left open.
4. Cannibalism in all three species increased when domatia were closed. With I. degenerans , moreover, we found that the previous diet of the cannibal attenuated the effect of domatia on cannibalism.
5. We conclude that domatia can protect young predatory mites against cannibalism by adults and that the diet of cannibals affects the rate of cannibalism.     

Altitude and coffee production systems influence extent of infestation and bean damage by the coffee berry borer

The coffee berry borer (CBB), Hypothenemus hampei Ferrari (Coleoptera: Curculionidae: Scolytinae), is one of the major insect pests of coffee worldwide. The present study was designed to assess the level of infestation of coffee berries at different developmental stages across different altitudes and coffee management systems. The experiment was carried out at three locations in southwestern Ethiopia under two coffee management systems and four coffee berry development stages with three replications. Results of the study showed significantly highest proportion of damaged berries (37.5%), number of holes per berry (10.88) and number of adult CBB per berry (7.55) on dried leftover berries at low-altitude study sites. On the other hand, the lowest mean percent damaged berries, number of holes per berry and number of adults were recorded at mid- and high-altitude study sites. The study also showed that, CBB caused significantly highest damage in plantation coffee management system than garden coffee. Results of this study highlight proper harvesting at red ripe stage in order to minimise incidence of CBB. It is also important to design integrated management strategies to mitigate CBB damage especially in lowland plantation coffee production systems.