Defence‐Related Enzymes in Soybean Resistance to Target Spot

Target spot, caused by the fungus Corynespora cassiicola, has become a serious foliar disease in soybean production in the Brazilian Cerrado. Information in the literature regarding the biochemical defence responses of soybean to C. cassiicola infection is rare. Therefore, the objective of this study was to determine the biochemical features associated with soybean resistance to target spot. The activities of chitinases (CHI), β‐1‐3‐glucanases (GLU), phenylalanine ammonia‐lyases (PAL), peroxidases (POX), polyphenol oxidases (PPO) and lipoxygenases (LOX), as well as the concentrations of total soluble phenolics (TSP) and lignin‐thioglycolic acid (LTGA) derivatives, were determined in soybean leaves from both a resistant (FUNDACEP 59) and a susceptible (TMG 132) cultivar. The target spot severity, number of lesions per cm² of leaflet and area under the disease progress curve were significantly lower for plants from cv. FUNDACEP 59 compared to plants from cv. TMG 132. The GLU, CHI, PAL, POX and PPO activities and the concentration of LTGA derivatives increased significantly, whereas LOX activity decreased significantly on the leaves infected by C. cassiicola. Inoculated plants from cv. FUNDACEP 59 showed a higher PPO activity and concentrations of TSP and LTGA derivatives at 4 and 6 days after inoculation compared to plants from cv. TMG 132. In conclusion, the results of this study demonstrated that the defence‐related enzyme activities increased upon C. cassiicola infection, regardless of the basal level of resistance of the cultivar studied. The increases in PPO activity and concentrations of TSP and LTGA derivatives, but lower LOX activity, at early stages of C. cassiicola infection were highly associated with soybean resistance to target spot.     

Efficacy of Acibenzolar‐S‐Methyl and β‐Aminobutyric Acid for Control of Downy Mildew in Greenhouse Grown Basil and Peroxidase Activity in Response to Treatment with these Compounds

Downy mildew, caused by the oomycete pathogen Peronospora belbahrii, is a devastating foliar disease of basil in the United States and worldwide. Currently there are very few chemistries or organic choices registered to control this disease. In this study, two systemic acquired resistance (SAR) inducers, acibenzolar‐S‐methyl (ASM) and β‐aminobutyric acid (BABA), were evaluated for their in vitro effects on the pathogen, for their potential to control basil downy mildew in greenhouses, and for changes in peroxidase activity in basil plants treated with these two SAR inducers. No significant inhibition of sporangial germination was detected in water agar amended with ASM at concentrations lower than 100 mg/l or with BABA at concentrations lower than 500 mg/l. Efficacy of ASM and BABA in greenhouses varied depending on the rate, method and timing of application. The area under the disease progress curve (AUDPC) of disease severity was significantly reduced compared to the non‐treated control when ASM was sprayed (in all experiments) or drenched (in one out of two experiments) pre‐, or pre‐ + post‐inoculation at rates of 25–400 mg/l. Three weekly post‐inoculation sprays of ASM at the rate of 50 mg/l reduced AUDPC by 93.0 and 47.2% when started 3 and 7 days after inoculation (DAI), respectively. The AUDPC of disease severity was also significantly reduced when BABA was sprayed pre‐ + post‐inoculation at rates of 125–500 mg/l. According to the prediction using a log‐logistic function, 50% maximum disease protection was achieved at a concentration of 27.5 mg/l of ASM. Basil plants treated with these two SAR inducers and challenged with the pathogen showed significantly higher peroxidase activity than the non‐treated control at 8 DAI. Temporally, the highest activity of peroxidase was detected at 8 DAI, decreased at 15 DAI and waned further at 23 DAI.     

The Association Between Leaf Malondialdehyde and Lignin Content and Resistance to Spot Blotch in Wheat

Spot blotch (causative pathogen Bipolaris sorokiniana (Sacc.) Shoem) is a common disease of wheat in the Eastern Gangetic Plains region of India. The association of leaf malondialdehyde and lignin contents with the severity of spot blotch disease was studied using a correlation analysis based on a population of recombinant inbred lines bred from the cross cvs. Yangmai 6 (resistant) × Sonalika (susceptible). The material was field‐tested over two consecutive years and inoculated artificially with a highly virulent strain of the pathogen. Disease severity was assessed at three growth stages around and after anthesis. Leaf lignin content tended to be higher in the more resistant RILs, while the opposite was the case for leaf malondialdehyde content. Lesion size showed a positive correlation with disease severity and leaf malondialdehyde content, while disease severity and leaf lignin content were negatively correlated with one another, as were leaf malondialdehyde and leaf lignin content. Leaf malondialdehyde and/or leaf lignin content could be informative as markers for selection for higher levels of resistance against spot blotch in wheat.     

Potassium phosphites in the protection of common bean plants against anthracnose and biochemical defence responses

The aim of this study was to investigate the effectiveness of potassium phosphites for the control of anthracnose and the mode of action of these products on common bean plants against Colletotrichum lindemuthianum, comparing it with the standard resistance inducer acibenzolar‐S‐methyl. The protection of plants against anthracnose was evaluated in greenhouse after treatment with potassium phosphites (Phosphite A and B, 5.0 ml/L), acibenzolar‐S‐methyl (0.25 g/L), or no treatment (control). Two sprayings of the treatments were performed, respectively, at V4 stage (three trifoliate leaves) and at the R5 stage (flower buds present). The inoculation with C. lindemuthianum was performed 5 days after the first spraying. Phosphite formulations A and B reduced the severity of anthracnose by 68.7% and 55.6%, respectively, and the presence of phosphites in the leaf tissues were detected at concentrations between 1 and 3 mm by 7 days after spraying. These same concentrations of phosphites reduced the mycelial growth of C. lindemuthianum in vitro by 15.0% to 25.7%. In addition, the activities of defence enzymes and the levels of phenolic compounds and lignin were assessed. Phosphite treatments enhanced the activity of various enzymes, including superoxide dismutase, peroxidase, chitinase, and β‐1,3‐glucanase, and increased the lignin and a small increase in the levels of soluble phenolics. This study provides evidence that phosphite treatments control anthracnose by acting directly on C. lindemuthianum and by inducing the production of defence responses.     

Differential physiological responses to environmental change promote woody shrub expansion

Direct and indirect effects of warming are increasingly modifying the carbon-rich vegetation and soils of the Arctic tundra, with important implications for the terrestrial carbon cycle. Understanding the biological and environmental influences on the processes that regulate foliar carbon cycling in tundra species is essential for predicting the future terrestrial carbon balance in this region. To determine the effect of climate change impacts on gas exchange in tundra, we quantified foliar photosynthesis (A_net), respiration in the dark and light (R_D and R_L, determined using the Kok method), photorespiration (PR), carbon gain efficiency (CGE, the ratio of photosynthetic CO₂ uptake to total CO₂ exchange of photosynthesis, PR, and respiration), and leaf traits of three dominant species – Betula nana, a woody shrub; Eriophorum vaginatum, a graminoid; and Rubus chamaemorus, a forb – grown under long-term warming and fertilization treatments since 1989 at Toolik Lake, Alaska. Under warming, B. nana exhibited the highest rates of A_net and strongest light inhibition of respiration, increasing CGE nearly 50% compared with leaves grown in ambient conditions, which corresponded to a 52% increase in relative abundance. Gas exchange did not shift under fertilization in B. nana despite increases in leaf N and P and near-complete dominance at the community scale, suggesting a morphological rather than physiological response. Rubus chamaemorus, exhibited minimal shifts in foliar gas exchange, and responded similarly to B. nana under treatment conditions. By contrast, E. vaginatum, did not significantly alter its gas exchange physiology under treatments and exhibited dramatic decreases in relative cover (warming: −19.7%; fertilization: −79.7%; warming with fertilization: −91.1%). Our findings suggest a foliar physiological advantage in the woody shrub B. nana that is further mediated by warming and increased soil nutrient availability, which may facilitate shrub expansion and in turn alter the terrestrial carbon cycle in future tundra environments.     

Boron fertilizers in rape – a risk for honey bees?

Rape (Brassica napus L.) is foraged intensively by honey bees (Apis mellifera). Pesticide applications during bloom are sometimes combined with foliar boron fertilizer applications. Boron has insecticidal properties, and therefore, risk to honey bees cannot be excluded. This study was conducted to test whether foliar boron fertilizers could be hazardous for bees under real field conditions. Six colonies were transferred to a rape field in bloom which was treated with boron (1 kg/ha). Six control colonies were transferred to an untreated rape field approximately 7 km away. Performance parameters of the colonies were measured. Samples of honey and beebread were collected from all colonies before and after boron fertilizer application. The contents of boron and of Al, Cd, Cr, Fe, K, Mn, Ni, P, Pb, S and Zn were measured in honey by inductively coupled plasma mass spectroscopy (ICP MS) and by ICP–atomic emission spectroscopy (ICP‐OES). No significant differences were found in honey yield (P = 0.622), number of capped brood (P = 0.089), number of uncapped brood (P = 0.123) or number of bees (P = 0.87). Application of boron fertilizer did not affect the concentration of boron in honey (P = 0.656) or beebread (P = 0.665). The concentrations of other elements confirmed the suitability of rape nectar for bee nutrition. This study suggests that the application of foliar boron fertilizers in blooming rape is not hazardous for bee colonies.     

Effect of Elevated Atmospheric CO2 and Temperature Increases on the Severity of Basil Downy Mildew Caused by Peronospora belbahrii Under Phytotron Conditions

Three experimental trials have been carried out on the basil (Ocimum basilicum)–downy mildew (Peronospora belbahrii) pathosystem, under phytotron conditions, to evaluate the effect of simulated elevated atmospheric CO₂ concentrations and temperatures as well as that of their interaction. Six CO₂ and temperature combinations were tested to establish their effect on disease development. The photosynthetic efficiency (PI) and chlorophyll content index (CCI) of the basil plants were monitored throughout the trials. Average disease incidence was 43.8% under standard conditions (18–22°C and 400–450 ppm of CO₂)_, while average disease severity was 22.1%. In the same temperature regime, a doubled level of CO₂ caused a significant increase in both disease incidence and severity. When temperatures ranged between 18 and 26°C, CO₂ at 800–850 ppm increased disease incidence. At the highest temperatures tested, that is at 26–30°C, which are not favourable for downy mildew development, the increase in CO₂ had no significant effect on disease incidence. A decreasing trend of PI was observed for the PI values of the inoculated plants. This trend was particularly pronounced for high CO₂ levels at the end of the experiment. In the same way as for disease development, lower values were recorded for the inoculated plants at the end of the experiment at 18–22°C for both CO₂ concentrations and at 22–26°C for 850 ppm of CO₂. The non‐inoculated plants showed higher photosynthetic efficiency than the inoculated plants. Similar trends were also observed for the CCI, thus confirming that downy mildew incidence and severity, which in particular caused foliar damage at high CO₂ concentrations, led to a decrease in the physiological performances.     

Effect of Bursaphelenchus xylophilus infection on leaf photosynthetic characteristics and resource‐use efficiency of Pinus massoniana

Pine wilt disease (PWD ) is considered as the most destructive forest‐invasive alien species in China. We measured gas exchange parameters and foliar carbon isotope ratios (δ¹³C) of different infection phases of Masson pine in order to investigate the effect of Bursaphelenchus xylophilus infection on photosynthetic responses and resource‐use efficiency. The results showed that net photosynthetic rate (P _n), transpiration rate (T ), stomatal conductance (g _s), and internal CO ₂ concentrations (C _i) decreased in the infested trees at photosynthetic photon flux density (PPFD ) levels from 0 to 2,000 μmol m^?2 s^?1 compared with controls. The maximum net photosynthetic rate (P _max) was significantly declined in the infected trees than in controls (p  <  .05). There also exist significant differences in dark respiration rate (R _d) among different infection phases (p  <  .05), but the value is highest in the middle infection phase, followed by the control and then the terminal infection phase. This indicates that Pinus massoniana plants need to consume more photosynthetic products during the middle infection phase in order to defend against pine sawyer beetle feeding and PWD infection. Isotopic analysis revealed a significant decrease of the foliar δ¹³C (p  <  .05), as much as 2.5‰ lower in the infected trees. The mean leaf N content was about 12.94% less in the middle infection phase and 27.06% less in the terminal infection phase, causing a significant increase of the foliar C:N ratio in infested trees. Both of the net photosynthetic rates and foliar δ¹³C were linearly correlated with the foliar N content. We also found a significant decrease (p  <  .05) of resource‐use efficiency in PWD ‐induced P. massoniana plants, which can be attributed to the closure of stomatal pores and the inactivation or loss of both Rubisco and other key Calvin cycle enzymes. This study highlights the impact of photosynthetic characteristics, foliar carbon isotope ratios, and resource‐use efficiency of PWD ‐induced trees, which can help identify PWD infestations at the photosynthetic and physiological levels so as to better facilitate management actions.     

Induced defence responses and protective effects on tomato against Xanthomonas vesicatoria by an aqueous extract from Solanum lycocarpum infected with Crinipellis perniciosa

This study investigated the induced defence responses and protective effects on susceptible tomato (Lycopersicon esculentum Mill.) against Xanthomonas vesicatoria (Doidge) by a heat-treated aqueous extract (VLA) from dry necrotic tissue of ‘Lobeira’ (Solanum lycocarpum St. Hil.) branches infected with the fungus Crinipellis perniciosa (Stahel) compared with acibenzolar-S-methyl (ASM), a commercial inducer of resistance. Plantlets were sprayed with VLA and ASM and challenged 4 days later with a virulent strain of X. vesicatoria, under greenhouse conditions. The disease severity, fresh weight of shoots, the activities of phenol peroxidase (POX), polyphenol oxidase (PPO), chitinase (CHI), phenylalanine ammonia-lyase (PAL), lignin deposition, and soluble phenolic contents were evaluated in the leaf tissues. Reduction of the bacterial spot severity was observed in plantlets treated with VLA which conferred 63% of the ASM protection. This protective effect and lesion reduction promoted by VLA were probably associated particularly with POX and PAL activities, lignin deposition on leaf tissues and, to a less extent, CHI activity.     

Impacts of nano- and non-nanofertilizers on potato quality and productivity

Today, to achieve sustainable agriculture with maximum yield and minimum environmental risks, the use of nanofertilizers has riveted ample consideration. Field experiments were conducted during binary season of 2016 and 2017 at Research Farm, Faculty of Agriculture, Minia University, Egypt to estimate whether NPK nanofertilizers applied in equivalent or lower rates could replace recommended levels of NPK chemical fertilizers in potato farming systems without retrograde effects upon yield production or quality. Impacts of recommended rates of NPK chemical fertilizers (control treatments) compared to NPK nanofertilizers in equivalent or lower rates (100%, 50% and 25%), foliar or soil applied on potato productivity and quality were studied.Compared with control treatments, plots receiving foliar application of NPK nanofertilizers at 50% or 25% of recommended level showed higher values of economic yield (23.59-ton ha⁻¹), starch rates (79.62%), NPK nutrient use efficiency (67.74, 278.92, 118.54 kg potato/kg nutrient), harvest index (59.24%) and only lower potato nitrate content (1.15 g kg⁻¹) as a harmful indicator. Among all treatments, foliar application of NPK nanofertilizers at 50% rate was found to be the most economical treatment as it gave highest potato yield and quality plus highest profit: cost ratio of potato production. This research recommends foliar application of nanofertilizers in potato production to increase production and quality compared to soil applications. As yet, using lower rates of nanofertilizers as foliar application in the present study proved to be an eco-friendly environmental and economic alternative to recommended rates of chemical fertilizers with significant increase in potato productivity and quality.     

Quantification of yield losses caused by leaf anthracnose on sorghum in Brazil

The leaf anthracnose disease in sorghum, caused by Colletotrichum sublineolum (Henn. ex Sacc. & Trotter), is widely distributed throughout its Brazilian cultivation areas. The disease can cause significant losses in grain yield and quality. This study aimed to quantify the effects of leaf anthracnose on grain yield of different sorghum genotypes. Two elite inbred lines of sorghum, BR009 (susceptible) and BR008 (moderately resistant), and the hybrids, BR304 and MR43 (susceptible), BRS310 and DKB599 (moderately resistant) and BRS308 and AG1060 (resistant), were planted in a complete randomized block design with three replicates. The disease severity (DS) was evaluated weekly, starting from the onset of the first foliar symptoms, and yield losses were estimated using linear regression analysis. Leaf anthracnose significantly reduced sorghum yields in the susceptible genotypes. The highest yield loss of 86% was observed in the inbred line BR009, when the disease severity reached 100%. For the hybrids, the grain yield loss varied from 35% (BRS310) to 72% (BRS308). According to the adjusted model, a grain yield reduction of 23.48 kg/ha for BR304, 14.57 kg/ha for BRS310 and 15.91 kg/ha for DKB599 was observed for every 1% increase in disease severity. We demonstrate for the first time the effect of leaf anthracnose disease on grain sorghum yields under Brazilian conditions. The results from this study provide a starting point for developing new strategies for the integrated disease management of sorghum anthracnose.     

Effect of Zinc on the Development of Brown Spot in Rice

Brown spot, caused by the fungus Bipolaris oryzae, is one of the most destructive diseases of rice. This study investigated the effect of zinc rates on the development of brown spot in rice. Rice plants (cv. ‘Metica‐1′) were grown in hydroponic culture amended with Zn rates (applied as ZnSO₄^.7H₂O) of 0, 0.5, 1, 2 and 4 μm and inoculated with B. oryzae. The foliar concentration of Zn was determined. Leaf samples were assessed for disease severity, and then, area under brown spot progress curve (AUBSPC) was calculated. The relationship between Zn concentrations on leaf tissues and the rates of this micronutrient was best described by a positive linear regression model, while the relationship between the Zn rates and the AUBSPC was best described with a positive quadratic regression model. The correlation between Zn concentrations on leaf tissues and AUBSPC was positive and significant (r = 0.68, P < 0.05). The results from this study showed that high foliar concentration of Zn was associated with increasing rice susceptibility to brown spot.     

亚精胺对黄瓜幼苗灰霉病的诱抗作用

采用根际基质注射结合叶面喷洒不同浓度亚精胺（Spd）的方法,测定了灰霉病菌侵染下黄瓜幼苗植株病情指数、防御酶活性和抗病相关物质含量等生理生化指标,以明确Spd对黄瓜幼苗抗灰霉病的诱导作用.结果表明：Spd处理黄瓜灰霉病病情指数比对照最高降低25.4%;苯丙氨酸解氨酶（PAL）、过氧化物酶（POD）和多酚氧化酶（PPO）活性最高分别比对照提高48.4%、635.9%和38.9%;总酚、类黄酮和木质素含量也明显增加.表明Spd可诱导黄瓜幼苗对灰霉病的抗性,且最佳处理浓度为150 mg·L^-1.     

Leaf gas exchange and chlorophyll a fluorescence in soybean leaves infected by Phakopsora pachyrhizi

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is one of the most important foliar diseases affecting soybean production worldwide. This study aimed to investigate the photosynthetic performance (leaf gas exchange, chlorophyll (Chl) a fluorescence images and photosynthetic pigment pools) of soybean plants sprayed with Acibenzolar‐S‐Methyl (ASM) and the fungicide epoxiconazole + pyraclostrobin (Epo+Pyr) and further inoculated with P. pachyrhizi. The ASR symptoms progressed much faster on the leaves of plants from the control treatment (water spray) in comparison with the ASM and Epo+Pyr treatments. In general, the values for the leaf gas exchange parameters net carbon assimilation rate (A), stomatal conductance to water vapour (g_s), internal CO₂ concentration (C_i) and transpiration rate (E) increased for the infected plants sprayed with ASM or Epo+Pyr in comparison with plants from the control treatment. The values for the initial fluorescence (F_o), maximal fluorescence (F_m), maximal photosystem II quantum efficiency (F_v/F_m), effective photosystem II quantum yield (Y(II)) and quantum yield of regulated energy dissipation (Y(NPQ)) were consistently higher for the ASM and Epo+Pyr treatments in comparison with the control treatment at advanced stages of fungal infection. By contrast, the values for quantum yield of non‐regulated energy dissipation (Y(NO) were significantly lower for the ASM and Epo+Pyr treatments. The concentrations of total Chl a+b and carotenoids significantly increased for infected plants sprayed with ASM and Epo+Pyr in comparison with plants from the control treatment. The results of this study demonstrated that the spray of soybean plants with either ASM or Epo+Pyr contributed to reduce the negative effect of ASR on the photosynthesis of soybean plants.     

Tree mineral nutrition is deteriorating in Europe

The response of forest ecosystems to increased atmospheric CO₂ is constrained by nutrient availability. It is thus crucial to account for nutrient limitation when studying the forest response to climate change. The objectives of this study were to describe the nutritional status of the main European tree species, to identify growth‐limiting nutrients and to assess changes in tree nutrition during the past two decades. We analysed the foliar nutrition data collected during 1992–2009 on the intensive forest monitoring plots of the ICP Forests programme. Of the 22 significant temporal trends that were observed in foliar nutrient concentrations, 20 were decreasing and two were increasing. Some of these trends were alarming, among which the foliar P concentration in F. sylvatica, Q. Petraea and P. sylvestris that significantly deteriorated during 1992–2009. In Q. Petraea and P. sylvestris, the decrease in foliar P concentration was more pronounced on plots with low foliar P status, meaning that trees with latent P deficiency could become deficient in the near future. Increased tree productivity, possibly resulting from high N deposition and from the global increase in atmospheric CO₂, has led to higher nutrient demand by trees. As the soil nutrient supply was not always sufficient to meet the demands of faster growing trees, this could partly explain the deterioration of tree mineral nutrition. The results suggest that when evaluating forest carbon storage capacity and when planning to reduce CO₂ emissions by increasing use of wood biomass for bioenergy, it is crucial that nutrient limitations for forest growth are considered.     

Improving key enzyme activities and quality of rice under various methods of zinc application

Zinc (Zn) is an important micronutrient for the physiology of plants. It is poorly available to the plants in soil solution. A pot experiment was conducted to evaluate effectiveness of various Zn application methods on key enzyme activities and protein content of two contrasting rice genotypes viz., PD16 (Zn efficient) and NDR359 (Zn inefficient). The treatments were, control (0 mg Zn kg⁻¹ soil), soil application (5 mg Zn kg⁻¹ soil), foliar application (0.5 % ZnSO₄ + 0.25 % lime at 30, 60 and 90 days after transplanting), soil (5 mg Zn kg⁻¹ soil) + foliar application of 0.5 % ZnSO₄ + 0.25 % lime at 30, 60 and 90 days after transplanting. Among all the methods tested soil+foliar application of Zn fertilizers was found most effective in increasing superoxide dismutase (SOD) and carbonic anhydrase (CA) activities as well as chlorophyll and protein content in both the rice varieties. NDR359, showed higher enzyme activities and more chlorophyll content in leaves than PD16, when Zn was applied either through foliar spray alone or in soil along with foliar application. Regarding the protein content in grains, PD16 showed higher protein content than NDR359, thus showed better translocation of Zn from leaves to grains.     

Valuable New Leaf or Inflorescence Resistances Ensure Improved Management of White Rust (Albugo candida) in Mustard (Brassica juncea) Crops

Field resistances/susceptibilities against Albugo candida race 2V were determined for 29 Indian Brassica juncea varieties and compared with resistant varieties from China (6) and Australia (7). ‘Basanti’ (AUDPC incidence 46.7; AUDPC severity 29.2) represents the first high‐level resistance to race 2V in Indian varieties. Several others showed lower but still useful levels of resistance, including Narendra Ageti Rai‐4 (AUDPC incidence 150.6; AUDPC severity 66.8) and JM1 (AUDPC incidence 167.1; AUDPC severity 83.7). Highly susceptible Indian varieties had AUDPC incidence values >200 and severity >100. ‘Basanti’ had least stagheads/plant (0.32), while Narendra Ageti Rai‐4 had lowest % plants with stagheads (2.48). In contrast, almost half of Indian varieties had stagheads/plant >1 and % plants with stagheads >4, and >26 for ‘Kranti’. The resistance in ‘Basanti’ paves the way forward towards significantly improved white rust management in mustard in India. JM06011, JM06021, JR049 from Australia and CJB‐003 from China had zero leaf incidence. There were significant (P < 0.001) relationships between disease incidence with severity (R² 0.92), stagheads/plant (R² 0.69) and also % plants with stagheads (R² 0.60); between disease severity with stagheads/plant (R² 0.68) and also % plants with stagheads (R² 0.69); and between stagheads/plant with % plants with stagheads (R² 0.59).     

Efficacy of Boric Acid,Monopotassium Phosphate and Sodium Metabisulfite on the Control of Apple Scab

In vitro experiments indicated that boric acid, monopotassium phosphate, sodium metabisulfite and synthetic fungicide fluopyram + tebuconazole were effective in inhibiting conidia germination and germ‐tube elongation of Venturia inaequalis. Monopotassium phosphate even at the highest concentration used in the study reduced conidia germination and germ‐tube elongation of V. inaequalis by 22.1% and 28.8%, respectively; however, the difference between two compounds at lower concentrations except 0.05% (for conidia germination) and 0.1% (for germ‐tube elongation) of boric acid was statistically significant (P ≤ 0.05). Complete inhibition was achieved by 0.01% sodium metabisulfite, 0.035% fluopyram + tebuconazole and 0.2% boric acid. Two orchard trials were conducted on the highly susceptible cv. Mutsu to apple scab to ascertain the efficacy of 0.2% boric acid, 0.5% monopotassium phosphate, 0.5% sodium metabisulfite and 0.035% fluopyram + tebuconazole for the control of apple scab. In both 2013 and 2014, except for the applications of monopotassium phosphate and sodium metabisulfite, the applications of boric acid and fluopyram + tebuconazole to trees at 10‐day intervals significantly reduced disease incidence and severity on leaves and fruit compared to the water‐treated control. In both years, the efficacy of boric acid and fluopyram + tebuconazole treatments was similar in reducing both disease incidence and severity on leaves and fruit in all monthly assessments from July to September. All treatments were neither phytotoxic to leaves and fruit nor did they adversely affect quality parameters of harvested fruit. These results show that boric acid treatment may be applied as an alternative chemical for the control of apple scab.     

Evaluation of the Use of Ammonium Bicarbonate and Oregano (Origanum vulgare ssp. hirtum) Extract on the Control of Apple Scab

In vitro experiments showed that ammonium bicarbonate and aqueous extracts of oregano were effective in inhibiting conidia germination and germ‐tube elongation of Venturia inaequalis. Complete inhibition was achieved by 1% ammonium bicarbonate, 2% oregano extract and 0.01% synthetic fungicide difenoconazole. Two orchard experiments were conducted on the highly susceptible cv. Mutsu to apple scab to investigate the efficacy of ammonium bicarbonate alone or in combination with an aqueous extract of oregano for the control of apple scab. In 2008 and 2009, except for the applications of 1% aqueous extract of oregano, the applications of ammonium bicarbonate (0.5 and 1%) and difenoconazole (0.01%) to trees at 10‐day intervals significantly reduced disease incidence and severity on leaves and fruit compared to the water‐treated control. In both years, the efficacy of 0.5 and 1% ammonium bicarbonate in inhibiting both disease incidence and severity on leaves and fruit was equally effective in all monthly assessments from June to September. Combining 0.5 and 1% ammonium bicarbonate with 1% aqueous extract of oregano did not significantly improve the efficacy of stand‐alone applications of treatments in the final assessment in 2008 and 2009. All treatments were neither phytotoxic to leaves and fruit nor did they adversely affect quality parameters of fruit including physiological disorders and taste both at harvest and after storage. These results indicate that ammonium bicarbonate treatment may be applied as an alternative chemical for the control of apple scab.