Effects of cultivar resistance and single fungicide application on rice sheath blight, yield, and quality

The increased number of sheath blight (Rhizoctonia solani)-resistant rice (Oryza sativa) cultivars available will allow producers to use less fungicide and avoid significant reductions in grain and milling yields. Among cultivars currently in cultivation in the southern United States, sheath blight resistance levels range from very susceptible to moderately resistant. A study was conducted to determine the response of cultivars, with different levels of susceptibility, to sheath blight inoculations and fungicide application and to determine the impact of sheath blight disease development on rice yield and quality. Sheath blight epidemics in field plots were initiated by inoculation at the panicle differentiation growth stage in 2006 and 2007. Azoxystrobin at 0.17 kg a.i. ha⁻¹ was applied at mid-boot. Inoculation significantly increased sheath blight severity and incidence and caused yield losses of 8% in moderately resistant cv. Jupiter to 40% in very susceptible cv. Trenasse. Milling yields were affected to a lesser extent. Fungicide treatments reduced sheath blight incidence and severity, regardless of cultivar except in Jupiter. Single azoxystrobin applications were effective in minimizing yield loss due to sheath blight in all cultivars.     

Integrating a host-resistance factor into the FAST system to forecast early blight of potato

A host resistance factor was integrated into the FAST (Forecaster ofAlternariasolani onTomatoes) system to initiate and to schedule fungicide applications for three levels of potato cultivar susceptibility while maintaining disease control and yield. Four cultivars ranging from susceptible to moderately resistant were each treated with the fungicide chlorothalonil during two field seasons. The five fungicide treatments were a 7-day schedule initiated after 50% flowering; a non-sprayed control; and three FAST application schedules based on combinations of critical levels of cumulative severity (CS, the disease severity values as a function of leaf wetness and temperature) and cumulative rating (CR, the disease rating values as a function of average temperature and hours of relative humidity greater than 90%) values. The FAST system predicted the onset of early blight and subsequent periods conducive for disease development in 1993 and 1994. There were cultivar-by-spray-schedule interactions for both disease severity and yield, suggesting that differences in early blight sus-ceptibility exist between cultivars. Use of the recommended schedules for the cultivar’s targeted level of susceptibility reduced early blight severity and minimized fungicide use while maintaining yield. These results indicate that a host-resistance factor can be incorporated into the FAST system.     

Differential effect of delayed planting on soybean cultivars varying in susceptibility to bacterial pustule and wildfire in Korea

In 2009 and 2010, the effect of delayed planting on bacterial pustule (Xanthomonas axonopodis pv. glycines) and wildfire (Pseudomonas syringae pv. tabaci) in four soybean cultivars was evaluated in fields in Suwon and Naju, Korea. Soybean was planted on 15 May as the first (traditional) planting date; then, planting was delayed at approximately 15-day intervals (three times) after the first planting. In plots planted approximately 15 or 30 days after the traditional planting date, the disease incidence in highly (Saeolkong and Taegwangkong) and moderately (Pungsannamulkong) susceptible cultivars was significantly reduced under moderate disease pressure, but disease reduction in highly susceptible cultivars was sometimes diminished especially against bacterial pustule under high disease pressure. Altered planting date had no effect on disease incidence in the least susceptible (resistant) cultivar (Cheongja-3-ho), regardless of disease pressure. Consistent differences in disease occurrence were not observed between planting locations. The results from this study indicate that delayed soybean planting reduced the bacterial disease incidence and differentially affected resistant and susceptible cultivars. Thus, planting resistant cultivars at the optimal planting date is desirable, but in the case of susceptible cultivars, delayed planting could be considered along with application of other control measures such as agrochemicals.     

Effect of planting date on severity of frogeye leaf spot and grain yield of soybeans

The influence of soybean (Glycine max) planting date on seasonal epidemics of frogeye leaf spot caused by Cercospora sojina and on grain yield, was evaluated during the 1991 and 1992 cropping seasons. Two susceptible (Samsoy 1 and TGx 849-313D) and one resistant (TGx 996-26E) soybean cultivars were used in field trials at Zonkwa, in the southern Kaduna state of Nigeria. Four field plantings were made at 14-day intervals from late May to mid0July. For each planting date, half the plots received foliar applications of benomyl at R₁ and R₃ growth stages, and the other half was untreated. Frogeye disease severity ratings were taken for all plots at R₄ to R₅ growth stages, and grain yield for each plot was measured at harvest. There was a significant (p < 0.05) increase in disease severity between the first and third plantings on the two susceptible cultivars in 1991, and on TGx 849-313D only in 1992. Corresponding yield reductions for the two susceptible cultivars averaged 13 and 31% for the treated and untreated plots, respectively, with each 2-week delay beyond the first planting date in 1991, and 5 and 6%, respectively, in 1992. There was no significant difference in disease among all treatments on the resistant cultivar, TGx 996-26E. Under Nigerian conditions, an increase in frogeye leaf spot severity can be expected with delayed planting of soybean after 1 June, and this can result in a corresponding loss of crop yield.     

Cropping calendar options for rice-wheat production systems at high-altitudes

The onset of rains during dry to wet transition fallow periods in rice-wheat production systems in Nepal cause substantial losses of soil nitrogen if the system is improperly managed. To make use of available nutrients and water, this transition period can either be shortened by early rice planting, or be extended by late planting, allowing a third crop to be grown. Shifting planting dates would require rice genotypes adapted to the different environments. Crop duration is influenced by both vegetative and reproductive development, which in turn is influenced by the photo-thermal environment and genotypic responses to it. An experiment was conducted to derive genotypic photo-thermal constants from phenological observations on diverse rice cultivars, which were then applied to the concept of the phenological model RIDEV to design cropping calendar options. Environmental effects on variation of crop duration were determined by planting at different dates. The risk of yield losses to sterility caused by low temperatures was estimated by simulation. Thirty-one different genotypes of rice were planted at 8 dates in 15-day intervals starting 27 April 2004 at the experimental field of the Regional Agriculture Research Station, Lumle, Nepal. The shortest duration to flowering was observed for planting dates in late May and early June. Simulation of flowering dates with RIDEV yielded correct results only for the early planting dates. For later planting dates simulated flowering dates showed an increasing deviation from the observed. In most cultivars, minimum air temperature below 18 °C during booting to heading stages caused near-total spikelet sterility and a specific delay in flowering. However, the chilling tolerant cultivars Chomrong and Machhapuchre-3 cultivated at high altitude showed less than 30% spikelet sterility even at 15 °C. Simulating crop durations with the derived thermal constants allowed evaluating the different calendar options for high altitude systems.     

Effect of planting date and inoculum level on incidence and severity of powdery scab on potato

Summary Powdery scab incidence and severity was examined on six potato cultivars planted at two different dates in a naturally infested field. There were two sub-plots; one where seed was exposed prior to planting to spores ofSpongospora subterranea from scabby peels, which were then added to the furrow at planting, and another where seed was exposed only to natural inoculum within the field. The later planting data reduced incidence and severity, but there were no differences between sub-plots. All cultivars became infected, but ‘Rosa’ was the most susceptible and ‘Katahdin’ the most resistant. Contribution No. 1720, Department of Plant Pathology, The Pennsylvania Agricultural Experiment Station. Authorized for publication September 22, 1988 as Journal Series Paper No. 8007.     

山东省主要推广品种对玉米粗缩病的抗性鉴定

2010～2011年在玉米粗缩病重发区进行3个播期下的田间自然鉴定,评价山东省主要推广品种对玉米粗缩病（MRDV）的抗性。结果表明,供试材料对粗缩病的抗性在不同品种、不同年份和不同播期间均存在极显著差异。18个供试品种中,仅青农105表现为抗病;登海3622、邦玉358、金海5号和农大108表现为感病;先玉335、农华101、蠡玉16、丹玉86、金海604、先玉688、济单7号、隆平206、登海605、郑单958、鲁单818、蠡玉37和中科11均表现为高感。播期间比较,青农105在6月5日播种感病最轻,其次为5月10日和5月25日;其他供试品种在5月10日播种感病最轻,5月25日和6月5日播种感病较重,调整播期能降低粗缩病对玉米产量的影响。回归分析表明,通过病情指数可以准确预测玉米粗缩病导致的产量损失。     

Effects of combined application of potassium phosphite and fungicide on stem and sheath disease control,yield, and quality of rice

Phosphite has been shown to suppress some diseases in different plant species but disease control in rice has not been investigated. In 2012/13 and 2013/14 potassium phosphite was sprayed at 1775 g ha⁻¹ and 3550 g ha⁻¹ in field plots of rice in Uruguay to determine if phosphite alone or in combination with label rates of a mixed strobilurin and triazole fungicide could be used to effectively control stem rot and aggregate sheath spot in irrigated rice. Six treatments consisting of different combinations of potassium phosphite alone or with a fungicide and an unsprayed control were assayed in one application at late-boot to early-heading. Phosphite alone in single and double rate slightly reduced severity and incidence of stem rot and produced a small yield increase over the unsprayed control. Fungicide at a 50% label rate with phosphite reduced stem rot severity and incidence to a similar level as the fungicide alone applied at the label rate. Disease severity was reduced by approximately 25% and incidence by 17–20% when compared with untreated control. Yield increase was 5% for both treatments over the unsprayed control. Fungicide combined with phosphite at single and double rates reduced stem rot severity by 40–45% and incidence by 34–38% when compared with untreated control, with yield increased by 10% over the unsprayed control and 5% over plots treated with a fungicide. These results indicate that a single application of potassium phosphite combined with fungicide can be used efficiently to manage of rice stem diseases.     

Parental Selection in Rice Cultivar Improvement

The evaluation of rice (Oryza sativa L.) cultivars assists breeders in identifying useful trait relationships and in selecting parents as donors of specific traits. This study was conducted to compare long-grain rice cultivars using genotype × trait (GT) biplot analysis and determine potential donors of traits related to grain yield and quality. Seventeen cultivars in the 2005 and 2006 Uniform Regional Rice Nursery in Beaumont, Texas, USA were analyzed for 20 traits using GT biplot analysis. The GT biplots showed the diversity among cultivars with regards to yield-related traits. Cultivars recommended as donor parents were: Trenasse, Spring, Presidio, and Cocodrie for high grain yield and head rice rate; Trenasse and Presidio for semi-dwarfness; Banks for tall plant height; Wells for high flag leaf area, panicle weight, and number and mass of filled grains per panicle; Hidalgo for high tiller density; Francis for high number of spikelets per panicle; Spring and Trenasse for short flowering duration; Cheniere for more days to heading and maturity and Spring for less days; and Spring and Hidalgo for high grain weight. Breeders can use these cultivars with specific traits to increase grain yield and quality.     

播期对春玉米生长发育、产量及水分利用的影响

以郑单958和鲁单984为材料,研究了两个播期条件下春玉米的生长发育、产量形成和水分利用情况。结果表明：播期对春玉米生长发育和产量影响显著,且品种间表现趋势一致。晚播春玉米生育期缩短,在各时期叶面积指数和干物质积累均显著高于早播春玉米。晚播春玉米产量(干重)提高,粒重在播期间、品种间差异均不显著。晚播春玉米穗粒数显著提高,品种间差异不显著。推迟播期后总耗水量增加,但增加幅度小于产量增加的幅度,水分利用效率略高于早播春玉米。在本试验条件下,晚播春玉米具有较优叶面积指数,有利于干物质积累并向子粒转移,增加穗粒数。因此,在春玉米播期的选择上不应单纯考虑生育期的延长,应重视早播春玉米前期营养生长受限对产量的影响。     

Quantitative analysis of host resistance,fungicide and weather effects on potato early and late blight using computer simulation models

Models which simulate the development of potato early blight, potato late blight and fungicide dynamics were used to analyze the effects of host resistance, fungicide and weather on individual and combined epidemics of these diseases. Fungicide and host resistance effects were based on (and accurately reflected) products and cultivars available to commercial potato growers in northeastern USA. Moderate resistance to early blight had a 2-3 fold greater effect than did moderate resistance to late blight in suppressing early and late blight, respectively. Analysis of simulation experiments indicated that replacement of an early blight susceptible cultivar with a cultivar moderately resistant to the disease would permit a reduction in the fungicide application frequency from once every week to once every two weeks without loss of disease suppression. Fungicide effect in suppressing late blight was 2-3 fold greater than in suppressing early blight. Variation in seasonal weather (typical of northeastern USA) influenced late blight development more strongly than it affected early blight development, and it affected epidemics of individual diseases more than combined epidemics.     

Fungicide and cultivar effects on the development and temporal progress of wheat blast under field conditions

The epidemiology of wheat blast, caused by the Triticum pathotype of Pyricularia oryzae, is poorly understood, making it very difficult to manage. We reported on the individual and combined effect of host resistance and fungicide application for managing wheat blast disease on spikes. Two field experiments (Exp. 1 and Exp. 2) were conducted in a region of Brazil where blast is not known to be endemic to evaluate its development as influenced by fungicide and host resistance. Plots of wheat cultivars BR-18 (partially resistant) and Guamirim (susceptible) were either treated with the fungicide epoxiconazole + pyraclostrobin or left non-treated, and then inoculated with a spore suspension of P. oryzae at mid-anthesis. Spike blast incidence and severity, quantified at regular intervals after inoculation, increased over time, and fungicide and cultivar had statistically significant effects (P < 0.005) on both measures of disease and their temporal rates of progress. Relative to Guamirim-non-treated, BR-18-non-treated (resistance alone) led to 44 and 64% control of final incidence and severity, respectively, in Exp. 1, and 3 and 49% control, respectively, in Exp. 2. Guamirim-treated (fungicide alone) led to 65% control of incidence and 77% control of severity in Exp. 1, and 64% control of incidence and 95% control of severity in Exp. 2. For both incidence and severity, fungicide and resistance alone also reduced the temporal rate of progress relative to the susceptible non-treated. However, the greatest overall efficacy was observed when resistance and fungicide were combined, with over 70 and 90% control of final incidence and severity, respectively, and over 75% reduction in the temporal rate of spike blast progress. Based on percent control, the integrated effect of resistance and fungicide was additive for incidence, severity, and their temporal rates of progress, demonstrating the value of combining the two strategies to manage spike blast.     

Economics of foliar fungicides for hard red winter wheat in the USA southern Great Plains

Grain yields of winter wheat (Triticum aestivum L.) in the southern Great Plains are often reduced by the presence of foliar diseases. This study was conducted to determine whether the application of foliar fungicides is an economically optimal management strategy. The effects of fungicide treatment on commercially available hard red winter wheat varieties with differing levels of genetic resistance (i.e., resistant, intermediate, and susceptible) to foliar diseases were investigated at two locations, Apache and Lahoma, OK, USA, for the harvest years 2005–2012. Two fungicides were rotated between the two locations and applied at approximately Feekes growth stage 9–10.5. When averaged across years, plots to which fungicide was applied generated greater average net returns than plots that did not receive fungicide for susceptible varieties at Apache, and for resistant, intermediate, and susceptible varieties at Lahoma. However, foliar fungicide application was not economical in every year at either location suggesting fungicide use should be reassessed each year given that profitability depends on year specific yield potential, prices, and foliar disease conditions. At both locations high disease incidence occurred in all but one site-year when the average March through May relative humidity exceeded 65%. Additional research would be required to determine the relationship between weather, including relative humidity, and disease incidence, and to develop an economic threshold for treatment decision aid.     

Dynamic characteristics of floret primordium development in wheat

This study was undertaken to determine the time-course of floret primordium initiation and degeneration in relation to thermal time after sowing in various cultivars and tiller positions of wheat (Triticum aestivum L.). The field experiment was carried out on the experiment station of Nanjing Agricultural University of China, and included three sowing dates: early planting of 30 September, middle planting of 30 October and late planting of 2 March and two wheat cultivars: winter type ‘Jing 411’ and spring type ‘Yangmai 158’. Quadratic and linear relationships could describe floret initiation, degeneration and abortion in response to growing-degree-days after sowing for main stem and first and second tillers of middle planting plants of both cultivars. The floret development patterns on the third tillers for all treatments deviated from the basic models and were associated with poor floret fertility. The growing-degree-days from sowing to floret initiation were significantly different between the three sowing dates and between the two cultivars. These results help quantify the dynamic processes of apical development and explain the differences in floret development of wheat with different environments, cultivars and tiller positions.     

Incidence and severity of powdery scab on potatoes in Pennsylvania

Studies were conducted in Potter Co., Pennsylvania to investigate the effect of powdery scab (Spongospora subterranea) on five potato cultivars (Norchip, Rosa, Kennebec, Katahdin, and Monona) at two planting dates. Soil temperature was within the range of 15–18 C and soil moisture was within 15–19% based on dry weight throughout the season. The effect of planting date was significant at each disease assessment, except for the severity on the fourth assessment. By the end of the season, incidence of scab was 66% or more for all cultivars. Rosa, Kennebec and Katahdin had a greater scab incidence over both planting dates and a greater severity at the first planting date than Monona and Norchip.     

Integrated management of Ascochyta blight (Didymella fabae) on faba bean under Mediterranean conditions

Integrated disease management options (two sowing dates, three fungicides and 3–6 faba bean genotypes) in managing Ascochyta blight affecting faba bean were evaluated for three cropping seasons (2006/07–2008/09) in northern Syria for their effects on disease parameters, seed infection and dry seed yield. The combined results of the three seasons on disease parameters showed that sowing dates significantly affected final disease severity and area under the disease progress curve (AUDPC); faba bean genotypes significantly affected final disease severity, rate of disease development and AUDPC. The highest AUDPC (255% days) was observed in early than late planted (168% days) faba bean genotypes. The mean AUDPC of faba bean genotypes ranged from 189% days on genotype 1053–1325 to 234% days on ILB-1814. Only faba bean genotypes and fungicides showed significant interactions in affecting final disease severity and AUDPC. Fungicide sprays significantly affected mean percent pod infection and rate of disease development but not mean percent seed infection. Faba bean genotypes showed significant differences in dry seed yield and the yield ranged from 1.7 t ha⁻¹ in cv. Ascot to 2.4 t ha⁻¹ in faba bean genotype 945-105. Improved varieties with Ascochyta blight resistance are not currently released and available for farmers in northern Syria and the integration of early planting (November–December) with one foliar fungicide spray at vegetative stage can help to reduce Ascochyta blight severity, pod and seed infections. Chlorothalonil and azoxystrobin are widely used fungicides to manage Ascochyta blights on food legumes in many countries and one of them could be used depending on their availability and costs to managing faba bean Ascochyta blight in Syria and other Mediterranean type environments.     

Efficacy of azoxystrobin for the control of cucumber downy mildew (Pseudoperonospora cubensis) and fungicide residue analysis

During a five-year trial (2007–2011), the efficacy of azoxystrobin (Quadris, 250 g a.i. L⁻¹, Syngenta) in two doses (187.5 g a.i. ha⁻¹ and 250 g a.i. ha⁻¹) and chlorothalonil (Bravo 720-SC, 720 g a.i. L⁻¹, Syngenta) at a rate of 1.44 kg a.i. ha⁻¹ was tested for the control of cucumber downy mildew (CDM). Cultivars that were susceptible or resistant to CDM (Regal and Haros, respectively) were tested for their response to fungicide applications. Differences in both disease severity and yield of the cultivars among resistance levels and fungicide treatments were observed. A highly significant and negative correlation was obtained between AUDPC and yield. Higher yields can be achieved by planting more resistant cultivars in combination with lower doses of fungicides. This is an indication that CDM contributes significantly to yield losses in cucumber production in Serbia. While monitoring the degradation of azoxystrobin residues, a decrease in residue levels to 1.0 mg kg⁻¹ below the maximum residue level (MRL) was observed at the end of the pre-harvest interval (PHI).     

Net blotch in semi arid regions of Morocco. I Epidemiology

Net blotch caused by Pyrenophora teres F. teres, is one of the important diseases in Moroccan barley fields. Contributing factors include the lack of adequate disease and crop management. Furthermore when agricultural techniques were recommended without disease control, objectives were seldom reached and resulted in adverse growers’ reaction. To sustain farmers in the Moroccan semi-arid regions and to optimize barley production, we have focused on net blotch epidemiology and the development of adequate disease management approaches. A field experiment, conducted in five locations for two consecutive years, used six cultivars with different levels of susceptibility to net blotch. These cultivars were grown under high, medium and low inoculum levels of the pathogen, and with and without disease control. Hence, a broad range of disease epidemics was generated. All the disease progress curves showed a depression in disease severity at stem elongation. The boost in biomass production coupled with the relationship between initial disease severity and area under the disease progress curve led us to recommend seed treatment and/or seedling resistance as the initial means of disease control. Although statistical differences were measured in disease severity between fungicide treated and inoculated plots during the growing season, biological differences were not substantial until all the cultivars attained boot stage. Because of this, a single application of foliar fungicide is necessary at boot stage, with a second application needed toward the end of ear emergence when weather conditions favor disease development.     

Castor yield in response to planting date at four locations in the south-central United States

Oilseed crops have potential use in the production of biodiesel. Currently, most oil going into the production of biodiesel is derived from soybean (Gylcine max L.) grown in the central U.S. Inability of the southeastern states to compete with central U.S. soybean production has lead to the search for alternative oilseeds. The high oil content and unique properties of castor (Ricinus communis L.) give it potential for use as biodiesel. However, there is limited information on potential yields, adaptation, and planting dates of adaptation of modern castor cultivars. This study was designed to determine potential yields and ideal planting dates of castor at various locations in Mississippi and Tennessee. A single castor cultivar was sequentially planted at 14 day intervals, at four locations, ranging from Memphis, TN south to Poplarville, MS. Annual planting occurred from 1 April to 1 July at all locations, except the 1 April planting date was excluded from the two northern locations. Mean yield ranged from 89 to 1954 kg ha^?1. Northern most locations and earliest plantings resulted in the greatest yields. Precocious flowering of castor immediately after 1 April planting at Shubuta, MS was associated with a lower yield. This flowering event was also observed at Poplarville, but did not significantly affect yield. The yield reductions due to southern planting coupled with precocious flowering at the southern locations seem to indicate a limited zone of adaptation for castor.     

播期和密度对高油高产大豆合丰50脂肪含量及产量的影响

以合丰50为材料,分7个播期、5个密度,研究不同播期及密度对其品质、产量及农艺性状的影响.结果表明:播期及密度对高油高产大豆品种合丰50的产量有较大的影响,随播期的延迟和密度的增加,该品种的产量呈先上升后下降的变化趋势,差异达到极显著水平;播期埘油份含量的影响较大,而且规律性极强,即随播期的延迟各密度处理合丰50的油份含量下降.不同密度处理对油份含量的影响较小,而且规律性也不强.合丰50的最佳播种时期为5月9日左右,而最适密度为25万株·hm~(-2),此时可获得最高产量和较高的含油量.