Maximum Yield Loss Research Articles

Common cocklebur (Xanthium strumarium L.) interference in grain sorghum [Sorghum bicolor (L.) Moench]: the influence of weed and crop density.

The common cocklebur (Xanthium strumarium L.) is an invasive weed species in the Asteraceae family that probably originated in Central or South America but has now spread worldwide, where it infests numerous crop fields, including sorghum. It is also a significant invasive weed in various parts of Ethiopia, including the eastern region. In this study field experiments were conducted to investigate the effect of various densities of sorghum and X. strumarium on their growth and reproductive output at Haramaya and Babile Research Stations of Haramaya University in Eastern Ethiopia during the 2022/2023 growing seasons. Sorghum yield loss was greatly affected by X. strumarium density, reaching maximum yield losses of 79.2% and 93.1% at the maximum weed density at Haramaya and Babile, respectively. The presence of X. strumarium in sorghum resulted in reduced aboveground dry matter and leaf area index (LAI). The extent of this reduction depended on the density of X. strumarium. As crop density increased, X. strumarium dry matter, LAI, and bur production m-2 decreased. The highest bur production per unit area for X. strumarium was observed at its highest density (16 plants m-2) with 1097 and 869 burs per unit area at Haramaya and Babile, respectively. These results indicated that higher densities of sorghum were effective in suppressing the bur production of this weed, leading to reduced yield loss. Therefore, sorghum competitiveness against X. strumarium can be improved using higher crop densities. This could play a key role in weed management by reducing the use of herbicides and mechanical controls, thereby forming an important part of integrated weed management. © 2024 Society of Chemical Industry.

Integrating Maize Yield and Agricultural Drought Analysis for Sustainable Food Security: A Provincial Study in South Africa (1993–2022)

ABSTRACTExtreme climatic events, such as droughts, hinder progress toward achieving the sustainable development goal of food security. South Africa is vulnerable to drought‐related agricultural losses, which have led to food insecurity. However, few studies have focused on the long‐term impacts of drought on crop production at a regional scale. Therefore, we aimed to examine the intensity, magnitude, and trend of rainfall‐based short‐term agricultural drought at the provincial scale in South Africa based on the Standardized Precipitation Index (SPI). Additionally, we analyzed the impact of agricultural drought on maize yield by calculating the Standardized Yield Residual Series (SYRS) and Crop Drought‐Resilience Factor (CDRF). To this end, we collected rainfall data from 29 stations across nine provinces along with maize yield data for the period of 1993–2022. Agricultural drought analyses based on the three‐month (SPI‐3) and six‐month (SPI‐6) SPIs demonstrated dynamic variations in occurrence, with Sen's slope indicating that 10 stations exhibited a significant increase in drought events across South Africa. Notably, SPI‐6 analysis showed that Gauteng, Free State, and North West provinces experienced the highest percentages of severe to extreme drought events during the study period, at 4.17%, 3.89%, and 3.61%, respectively. Furthermore, the majority of provinces in South Africa experienced an extreme SPI‐6 magnitude ranging from −46.03 in Western Cape Province to −61.6 in Free State Province. The dynamic effects of agricultural drought on maize yield revealed that the maximum yield loss of 13% occurred in 1993 in Eastern Cape Province, while some provinces experienced no yield loss during certain years. However, CDRF analyses identified Western Cape (CDRF [SPI‐3] = 0.52, CDRF [SPI‐6] = 0.62) and Mpumalanga (CDRF [SPI‐6] = 0.7) provinces as the most vulnerable to food insecurity due to the severe non‐resilience of maize to drought in these regions. This study reveals the complex interplay between climatic extremes and maize yield variability, providing valuable insights for managing regional food production systems and ensuring future food security in South Africa.

Genetic Improvement of Drought Tolerance in a Mega-Rice Variety Improved White Ponni through Marker-Assisted Backcross Breeding

In the ever-changing climatic conditions, it has become important to enhance rice productivity to ensure global food security. Drought is one of the major limiting factors in rice pro- duction. Drought during the reproductive stage results in maximum or complete yield loss. Efforts have been taken to develop drought-tolerant rice lines by introgressing three major drought-effect QTLs, viz. qDTY1.1, qDTY2.1, and qDTY3.1, from Apo into a susceptible popular rice variety, Improved White Ponni (IWP). Backcross inbred lines of IWP × Apo were developed through the marker-assisted backcross breeding approach. Foreground analysis using linked markers resulted in the identification of 17 progenies carrying two or more QTLs, and the recurrent parent genome recoveries of these lines were >95.6% using 72 genome-wide SSR markers distributed throughout all chromosomes. Upon phenotypic evaluation of 17 IWP BILs, the water limited condition resulted in the identification of improved lines by recording the yield and the yield-related parameters. The promising performance of IWP BILs in terms of spikelet fertility (63.3%) and grain yield per plant (>10 g) under drought stress indicated the positive effects of introgressed qDTYs, while IWP recorded complete yield loss (94.2%). Out of the cultivars considered, the best-performing lines which truly exhibited drought tolerance, with more increased yield than the recurrent parent under water-limited conditions, and the effects of these QTLs and their interactions were examined in this research work.

Pumpkin Injury and Yield Response to Low Rates of 2,4-D Choline and Dicamba

The recent release of 2,4-D- and dicamba-tolerant soybean traits has increased the risk of off-target herbicide injury and yield loss for specialty crop growers in the midwestern United States. Most dicotyledonous plants, including many specialty crops like pumpkin (Cucurbita pepo), are susceptible to synthetic auxin herbicides; however, the relationship between off-target herbicide rate, visible crop injury, and eventual yield loss is not well documented. The objective of this 2-year field study in 2019 and 2020 was to determine the effect of sublethal herbicide rates of 2,4-D and dicamba on visible injury and crop yield loss in pumpkin when applied at the vegetative and flowering growth stages. Herbicides included 2,4-D choline salt (1066 g ae·ha−1 labeled rate) and dicamba diglycolamine salt (560 g ae·ha−1 labeled rate) ranging from 1/500 to 1/4 of the labeled rate. Visible injury ratings were recorded every 7 d after application and pumpkins were harvested and weighed when ripe. Injury and yield data were fit to a four-parameter log-logistic regression model to estimate effective doses (ED) required for 5% to 50% visible injury or yield loss. Pumpkin treated with the 1/10 and 1/4 rates of 2,4-D at both growth stages had visible injury (± 1 SE) ranging from 8% (± 3%) to 55% (± 3%), but injury did not always result in yield loss. Maximum yield loss from 2,4-D was 32% (± 2%), observed following the 1/4 rate at the vegetative growth stage in 2020 (estimated ED for 20% yield loss was ∼1/50). Pumpkin treated at the vegetative growth stage with the 1/10 and 1/4 rates of dicamba resulted in 65% (± 6%) to 82% (± 1%) visible injury and 33% (± 2%) to 86% (± 14%) yield loss (estimated ED for 20% yield loss was ∼1/10 in 2019 and ∼1/15 in 2020). At the flowering stage, dicamba rates of 1/10 and 1/4 caused visible injury of 31% (± 2%) to 74% (± 5%) and yield loss of 26% (± 10%) to 60% (± 14%) (estimated ED for 20% yield loss was ∼1/20 in 2019 and ∼1/5 in 2020). Susceptibility of pumpkin to 2,4-D and dicamba suggests herbicide applicators and pumpkin growers should consider strategies that mitigate off-target movement, including using nozzles that increase droplet size, shielded sprayers, thorough tank cleanout, buffer zones, and programs that facilitate communication between applicators and growers.

Effects of waterlogging at different growth stages on the photosynthetic characteristics and grain yield of sorghum (Sorghum bicolor L.)

Various plants, including sorghum (Sorghum bicolor L.), are exposed to waterlogging; however, little is known about the effects of waterlogging at different growth stages on sorghum. A pot experiment was conducted using two sorghum hybrids, Jinuoliang 01 (JN01) and Jinza 31 (JZ31), to investigate the effects of waterlogging at different growth stages on the photosynthesis enzyme activity, chlorophyll content, malondialdehyde (MDA) content, photosynthetic parameters, dry matter accumulation, and grain yield. The experiment was conducted using waterlogging treatments implemented at the five-leaf stage (T1), flowering stage (T2), and filling stage (T3), using standard management (no waterlogging) as a control (CK). The adverse effects of waterlogging on sorghum growth varied with the waterlogging timing, with the maximum impact at T1, followed by T2 and T3. JZ31 was more sensitive to waterlogging compared to JN01. Waterlogged conditions inhibited the photosynthetic enzyme activity and reduced the chlorophyll content and photosynthesis, ultimately lowering the biomass yield and grain yield. The maximum yield loss was observed with the T1 waterlogging treatment; the grain yield of JN01 and JZ31 decreased by 52.01–54.58% and 69.52–71.97%, respectively, compared with CK. Furthermore, the decline in grain yield in T1 was associated with reducing grain number per panicle. These findings indicate that sorghum is sensitive to waterlogging at the five-leaf stage and JZ31 is more sensitive to waterlogging than JN01, which may provide a basis for selecting genotypes and management measures to cope with waterlogging in sorghum.

Status and prospects of cultivation of niche crops in Ukraine

Аіm. To find out the place and role of niche crops in agricultural production in Ukraine and to identify the main risks of their cultivation technology. Methods. The general approach to the study of the problem is dialectical. The general scientific methods (induction and deduction, analysis and synthesis, scientific generalization, scientific abstraction) are used. Results.The article covers the issues of the state of cultivation of traditional and niche crops in Ukraine for the period from 2012 to 2022. The advantages of introducing niche crops into production and the reasons that hinder the growth of their acreage are presented. Conclusins. The necessity of improving the technologies of growing niche crops in order to adapt to climate change is indicated. The main components of obtaining the maximum yield and possible losses in the technological process are presented.

Population Dynamics of Digitaria sanguinalis and Effects on Soybean Crop under Different Glyphosate Application Timings

Large crabgrass (Digitaria sanguinalis) is one of the most problematic weeds in summer crops in Argentina. Emergence throughout the season of several cohorts allows the weed to escape postemergence control. Demographic models are useful tools to understand and compare the effect of different agronomic management decisions on weed population growth, as well as to identify critical functional stages that affect population growth rates. The objectives of this work were (i) to study population dynamics of D. sanguinalis in soybean, (ii) to determine the effect of glyphosate application timing on weed demographic parameters and soybean yield losses, and (iii) to evaluate the effect of weed density on soybean yield loss. A field experiment was conducted in two locations, in a completely randomized design with three replicates. Treatments included a control without glyphosate and glyphosate applied at soybean stages V4 or R1. The demographic stages (initial seedbank, seedlings, and adult plants) and parameters (establishment, survival, and fecundity) were estimated. Reproductive organs were evaluated in each cohort, including raceme per plant, spikelets per raceme, and seeds per spikelet. Weed and crop biomass and yield crop were assessed at harvest. Three cohorts were identified, the first of which emerged in November and contributed 93% of the total seedlings and 71% of the total adults. Glyphosate applied at V4 reduced the survival rate of the first cohort, as well as the total shoot biomass and the fecundity rate, increasing the biomass and crop grain yield. Both application timings affected tillers per plant, racemes per tiller, and fertile spikelets per raceme. Glyphosate at R1 did not effectively reduce weed competition, but reduced seed production as application at V4. Yield losses estimated with the model of the rectangular hyperbola according to weed density showed a yield loss at low densities (I) of 18%, and a maximum yield loss (A) of 82%. To avoid yield losses, herbicide applications targeting the first cohort are more effective than later applications targeting subsequent cohorts. However, at both times glyphosate applications reduced the number of seeds entering the seedbank, and therefore the population growth rate.

Comparative Metabolomic Profiling of Horse Gram (Macrotyloma uniflorum (Lam.) Verdc.) Genotypes for Horse Gram Yellow Mosaic Virus Resistance.

Horse gram (Macrotyloma uniflorum (Lam.) Verdc.) is an under-utilized legume grown in India. It is a good source of protein, carbohydrates, dietary fiber, minerals, and vitamins. We screened 252 horse gram germplasm accessions for horse gram yellow mosaic virus resistance using the percent disease index and scaling techniques. The percentage values of highly resistant, moderately resistant, moderately susceptible, susceptible, and highly susceptible were 0.34, 13.89, 38.89, 46.43, and 0.34, respectively. Repetitive trials confirmed the host-plant resistance levels, and yield loss was assessed. The present disease index ranged from 1.2 to 72.0 and 1.2 to 73.0 during the kharif and rabi seasons of 2018, respectively. The maximum percent yield loss was noticed in the HS (75.0 -89.4), while HR possessed the minimum (1.2-2.0). The methanolic leaf extracts of highly resistant and highly susceptible genotypes with essential controls were subjected to gas chromatography-mass spectrometry analysis. Differential accumulation of metabolites was noticed, and a total of 81 metabolites representing 26 functional groups were identified. Both highly resistant and susceptible genotypes harbored eight unique classes, while ten biomolecules were common. The hierarchical cluster analysis indicated a distinct metabolite profile. Fold change in the common metabolites revealed an enhanced accumulation of sugars, alkanes, and carboxylic acids in the highly resistant genotype. The principal component analysis plots explained 93.7% of the variation. The metabolite profile showed a significant accumulation of three anti-viral (octadecanoic acid, diphenyl sulfone, and 2-Aminooxazole), one insecticidal (9,10-Secocholesta-5,7,10(19)-triene-3,24,25-triol), one antifeedant (cucurbitacin B), and six metabolites with unknown biological function in the highly resistant genotype.

EFFICACY OF TRICHODERMA AGAINST GREEN GRAM ROOT ROT PATHOGEN MACROPHOMINAPHASEOLINA

Green gram (Vignaradiata L.) is one of Indias most essential and widely cultivated pulse crops. Several biotic and abiotic factors cause the yield loss in green gram. Among the biotic factors, root rot is one of the devasting factors which can cause maximum yield loss under severe conditions. Ten pathogenic isolates of Macrophominaphaseolinacausing root rot in Greengramwere collected from different locations in the Perambalur District of Tamil Nadu. The isolates produced root rot symptoms under artificial inoculation to confirm the pathogenicity. Among these isolates, Macrophominaphaseolina 1 isolated from Valikandapuramwas virulent, which took for further study. To test the efficacy of fungal biocontrol agents against the Greengram root rot pathogen, ten Trichodermaviride were isolated from ten different places in the Perambalur District of Tamil Nadu and evaluated in vitro. Among the ten isolates tested against Macrophominaphaseolina, the isolate Tv- 1 isolated from the Esanai village of Perambalur District effectively arrested the mycelial growth of Macrophominaphaseolina, which recorded 61.00 per cent growth inhibition over control.

Relationship of Maize Yield to Climatic and Environmental Factors under Deficit Irrigation: A Quantitative Review

There is evidence that freshwater resources available for agriculture are decreasing with an unprecedented record. New irrigation strategies are developed and tested on crops that feed the world, such as maize, to improve water productivity. Deficit irrigation is one of these strategies that can improve water productivity without a significant impact on crop production. Here, the authors review the factors that affect the response of maize yield and irrigation water productivity to water stress induced by deficit irrigation using a quantitative approach. Data were collected from peer-reviewed publications worldwide that respond to predefined criteria. The authors defined grain yield variation (GYv) and variation of irrigation water use efficiency (IWUEv) as response variables and used simple and multiple linear regression models for data analysis. Overall, maize response to deficit irrigation is significantly correlated to the water stress level (WD). Mild stress below 20% of optimal irrigation led to 0.5% to 17.45% of yield loss in the vegetative stage (VS) but resulted in 46% yield loss at the reproductive stage (RS). Water stress (20–40%) applied at both vegetative and reproductive stages (VRSs) can reduce yield by 44%. The maximum yield loss was 90% in the RS. The multiple linear regression revealed that 62% of the grain yield variability was explained by both WD and nitrogen rates in the VS, while 54% and 13% of this variability was explained in the RS and VRS, respectively. The authors also found that the WD and the climate explained the best the GYv and the IWUEv under deficit irrigation. These results suggest that regarding the climatic characteristics of site location and the complexity of maize production systems, site-specific levels of deficit irrigation should be recommended to limit yield loss and increase water productivity.

A Review on the Management of Country Bean (<em>Lablab purpureus</em> L.) Diseases in Bangladesh

Purpose: Country bean (Lablab purpureus L.) is an important pulse crop consumed as a vegetable in the central and south-western regions of Bangladesh after eggplant and taro. It promises to ameliorate nutritional demand from vegetables and has an excellent possibility for the world market. But the production is hampered due to infection of several diseases in field conditions. Research method: This study was undertaken based on secondary data of existing literature from Bangladesh and other parts of the world. So far, many research works were done on this issue but those were not available to the policy makers, extension workers, and public in a systematic manner to date. Findings: In this paper, we tried to bring forth different aspects of phytopathological problems of country bean. It usually undergoes stresses from different soilborne to seed-borne pathogens and expresses symptoms from the seedling stage to maturity. Crop protection largely depends on the integration of host plants, seeds, agronomic practices, environmental footprints, and the use of appropriate agrochemicals based on the epidemiology of target pathogens. Here, we also described effective management strategies against respective pathogens of the diverse category. These microorganisms attack at different stages of crop growth and can affect the host plants enormously to cause maximum yield loss. Research limitations: The study focused on the management of country bean diseases based on biological and chemical approaches. It presents limited information on specific technologies in different agroecological zones. Originality/Value: This study identified research gaps among Bangladesh and other countries. It also provides information to combat country bean diseases to the economic threshold level for ensuring sustainable crop yield.

Using the Taguchi experimental design for assessing within-field variability of surface run-off and soil erosion risk

Water erosion is one of the soil degradation processes driven by environmental and field factors such as rainfall intensity, slope gradient, dynamics of vegetation cover, soil characteristics, and management practices. Most of the studies assess the separate contribution of these factors under controlled conditions. However, there is a lack of adequate knowledge regarding the complex interactions between prevailing factors and soil erosion processes under heterogeneous field conditions. This study investigated 16 combinations of 5 factors at 4 levels of each factor on the soil erosion process using Taguchi's fractional factorial experiment design, identifying the factor combinations resulting in maximum sediment yield, runoff, organic carbon, and nitrogen losses. We considered the factors: Soil organic matter and silt content (SiltOM), vegetation cover (VC), slope steepness (SS), rainfall intensity (RI), and depth to a loamy layer (DLL). The interactive effects of these factors and their combinations were visualized from the analysis of signal-to-noise (S/N) responses. Results indicated that interactions between the selected factors and soil erosion processes exist and multiple linear regression models were developed to predict sediment yields, runoff, carbon, and nitrogen losses at the sub-field scale. Results revealed that 1) RI with 40.6% showed the highest contribution to sediment yield followed by SS (23.8%), VC (17.74%), SiltOM (14.77%), and DLL (3.17%), indicating a strong rainfall-erosion relationship; 2) the combination of levels of factors generating highest sediment yield was determined; 3) A simple multiple linear regression model developed for predicting local sediment yield showed the highest agreement with field observations (R2 = 82.5%). The findings suggest that Taguchi design could be used reliably for modeling soil erosion at field and sub-field scales. Using local calibration data such models have great potential for soil erosion risk assessments at the field scale, especially in areas where contributing factors and factor levels change at small spatial scales.

FALL ARMYWORM OUTBREAKS IN ASIA: ANALYZING THE STRATEGIES TO CONTROL

Fall armyworm (Spodoptera frugiperda) is a Lepidopteran moth of Noctuidae family. Due to its polyphagous characteristic with a large host range, strong migration ability, high fecundity (average egg production per female is about 1500) and lack of diapause has already contributed to its invasiveness in America and Africa. Recently it has been introduced in Asia in the year 2018. Though it has been only around three years of Fall armyworm (FAW) introduction, it has already spread into many Asian countries and on the way to cause havoc. Though it can infest many crops, its main target and maximum yield loss has occurred in case of Maize. In America and Africa, farmers are already well known to this pest and have adapted themselves to reduce crop loss to some extent by undertaking several management options. As this pest is completely new to Asia, farmers do not know much about its biology, nature of damage and control measures. And their misdiagnosis of the pest leads to panic and increased crop loss. Therefore, it is very important to increase awareness among the farmers to identify its attack on the right time to take suitable control measures as well as preventive measures for upcoming cropping seasons. Some of the cultural, mechanical, biological and chemical control measures those were effective in reducing its infestation outside Asia, has also found to be effective inside Asia. Collaboration of these control measures according to the field condition is main concern for the cultivators. But the integrated pest management option alone can also help to keep FAW population much below economic injury level and prevent its invasiveness as a tool of sustainable management for ensuring food security.

Estimation of yield loss and relationship of weather parameters on incidence of bakanae disease in rice varieties under shallow low land ecologies of Eastern India

Aim: To assess yield loss in different rice varieties due to rice bakanae disease and to understand the role of weather parameters on disease incidence and losses. Methodology: Roving survey and surveillance was carried out for three consecutive years to assess the status of rice bakanae disease among twenty popular rice varieties growing in Eastern India. Field experiment was conducted for three successive years, i.e., 2016, 2017 and 2018 at Cuttack. Highly susceptible variety Pooja was selected for the experiment. Data on disease incidence was collected daily from 10 days after transplanting to harvesting stage and data were recorded at standard meteorological week. Correlation was performed to find the effect of different weather parameters on the incidence of bakanae disease on rice. Results: Disease being seed borne caused significant reduction in yield and quality. The maximum disease incidence was recorded in Pooja with 18.25, 28.50 and 40.25 per cent in three years. The same variety showed maximum yield loss of 35.26 per cent compared all other varieties. The data on relationship of bakanae disease incidence with weather parameters showed that the rainfall (-0.444) had significant negative correlation during 2018, while RH (0.525 and 0.606) had significant positive correlation during 2017 and 2018. Interpretation: This study gives some information for formulating breeding programs to develop resistant varieties and management measures for preventing Bakanae disease.

Formulating and assessing best water and salt management practices: Lessons from non-saline and water-logged irrigated fields

To address the on-site and off-site salt load impact associated with non-saline and water-logged irrigated fields a well-considered strategy is required. This implies minimal salt mobilisation and additions through irrigation, no crop yield losses due to excessive salt in the root zone, and minimal irrigation-induced drainage and leaching. The aim was to formulate best water and salt management practices to achieve this strategy and conduct an extensive assessment on whether they are implemented before problems appear. Weekly and seasonal data (2-years) from 19 fields (28 measuring sites) were used. Crops included barley, wheat, groundnuts, maize and lucerne grown in a semi-arid climate. Dominant soils were sandy loam, loamy sand and sandy with lateral moving shallow groundwater tables (depth>1.2 m and electrical conductivity<250mSm−1), while electrical conductivity of primary water sources is < 100mSm−1. Good decisions included the use of centre pivot compared to flood irrigation, irrigation schedules that ensured soil matric potential for maximum crop transpiration and limited yield losses due to water logging and soil salinity. Poor decisions were incorrect sprinkler design and excessive pumping pressure and limited use of rainfall and capillary rise to irrigate less. Growing season rainfall-plus-irrigation were a mean 55% more than the quota (annual water allocated to farmers), and 35%, 39%, 60%, 106% and 67% more than a “conservative” estimate of barley, wheat, groundnuts, maize and lucerne transpiration, respectively. The magnitude of variation in this oversupply were similar than the mean values. Approximately all salts applied through irrigation were leached from the root zone, while minimal re-use of drainage water was made (only 3 fields). In terms of resource use efficiency and preventing environmental degradation the evidence is overwhelming for improved decisions at field level. However, given sufficient supply of water, continuation of the status quo, might be sustainable in the long term.

Detecting the invasive fall armyworm pest incidence in farm fields of southern India using Sentinel-2A satellite data

Damage of fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) on sorghum from the farmers’ fields of southern India was assessed using space-borne data. Comparison of the Sentinel-2A satellite data of pre and post infestation periods revealed reduction in Leaf Area Index (LAI) in the infested fields. Groundtruth data confirmed that FAW infestation reduced LAI by 49.7%, biomass by 32.5% and grain yield by 51.8%. Infestation at Panicle Initiation (PI) stage caused maximum yield loss compared to flag leaf visible and boot stages. The interaction results showed FAW infestation at different crop stages had significant effect on biomass and yield, but not on LAI. Regression analysis with spectral vegetation indices revealed LAI (R2: 0.82) and NDVI (R2: 0.80) were significantly superior in identifying FAW infestation from the satellite data. This study demonstrates feasibility of site specific pest management and prevents further spread of the invasive FAW.

Effects of Irrigation Regimes and Duration of Weed Interference on Grain Yield of Wheat (Triticum aestivum L.) in Middle Egypt

TWO EXPERIMENTS were performed at Farm of Faculty of Agriculture, El-Minia University Egypt, during two consecutive winter seasons 2017-2018 and 2018-2019 to evaluate the impact of weed removal period and different irrigation regimes on weeds, critical period of weed competition and yield and its components on wheat crop. A strip-plot design with three replications was used. Four irrigation regimes were in the horizontal plots and eight treatments of weed competition (4 weed-free periods and 4 weed competition periods) were in vertical plots. Results showed that omitting two irrigation (IR4) significantly decreased total density and dry weight of weeds, wheat traits, i.e. plant height, spike length, number of grains spike-1, 1000-grain weight, number of spikes m-2, grain yield and grain ability. Weed infestation for whole season significantly decreased all studied traits compared with weed removal even once after wheat sowing (DAS). Maximum yield losses of wheat due to weed infestation in whole season were 28.52 and 28.17% compared with weed-free treatment in the 1st and 2nd seasons, respectively. Cubic model was the best model for weed-free and weed competition over all treatments of the two seasons. The critical periods for weed control were 28 to 52 and 28 to 67 DAS in the two seasons, respectively.

Rattail fescue (Vulpia myuros) interference and seed production as affected by sowing time and crop density in winter wheat

AbstractField experiments were conducted in the growing seasons of 2017 to 2018 and 2018 to 2019 to evaluate the competitive effects of rattail fescue [Vulpia myuros (L.) C.C. Gmel.] in winter wheat (Triticum aestivum L.) and to assess whether delayed crop sowing and increased crop density influence the emergence, competitiveness, and fecundity of V. myuros. Cumulative emergence showed the potential of V. myuros to emerge rapidly and under a wide range of climatic conditions with no effect of crop density and variable effects of sowing time between the two experiments. Grain yield and yield components were negatively affected by increasing V. myuros density. The relationship between grain yield and V. myuros density was not influenced by sowing time or by crop density, but crop–weed competition was strongly influenced by growing conditions. Due to very different weather conditions, grain yield reductions were lower in the growing season of 2017 to 2018 than in 2018 to 2019, with maximum grain yield losses of 22% and 50% in the two growing seasons, respectively. The yield components, number of crop ears per square meter, and 1,000-kernel weight were affected almost equally, reflecting that V. myuros’s competition with winter wheat occurred both early and late in the growing season. Seed production of V. myuros was suppressed by delaying sowing and increasing crop density. The impacts of delayed sowing and increasing crop density on seed production of V. myuros highlight the potential of these cultural weed control tactics in the long-term management programs of this species.

Sheath blight development and yield loss on rice in different epidemiological conditions

Rice sheath blight and its causal agent Rhizoctonia solani AG-1 IA are associated with intensive and high input production systems. To our knowledge, resistant varieties have not been introduced for this disease, thus good crop management is expected to be among viable disease control methods. The aims of the present study were to determine the effect of different rates of nitrogen fertilizer, planting spaces and inoculum densities on sheath blight incidence and severity, including grain yield loss. Additionally we aimed to identify those developmental stages that are more susceptible to the disease. Field experiments were conducted over two consecutive years, in 2017 and 2018 in the Guilan province of Iran. Results indicated that higher N rates, denser planting and higher initial inoculum density resulted in greater disease development. Among five different growth stages, inoculation of plants at booting and flowering stages, resulted in maximum disease severity and grain yield loss. Taken together, reasonable use of nitrogen fertilizer, optimum planting space and reduced inoculum density obtained by spraying fungicide at the booting and flowering stages of rice are suggested as the best options to control sheath blight epidemics in rice.

Screening of forty Indian Amaranthus hypochondriacus cultivars for tolerance and susceptibility to tropospheric ozone stress

Tropospheric ozone stress adversely affects crop cultivars growth and productivity variably. The variable response of crop cultivars raised the need for identification of ozone (O3) stress-tolerant cultivars as an adaptive option. In the present study, forty cultivars of Amaranthus hypochondriacus were screened for susceptibility and tolerance to ozone stress. The cultivars were exposed to ambient (AO3) and elevated (EO3) ozone levels in free air ozone enrichment (FAOE) facility and monitored for foliar ozone injury symptoms appearance and yield attributes response. Foliar ozone injury symptoms on Amaranthus cultivars were interveinal yellow or black spots. Foliar ozone injury was observed in almost half of the cultivars and the maximum foliar injury (> 75%) was observed in cultivar IC-5527. The maximum yield reduction (> 90%) was observed in cultivars IC-4200 (94.9%) and IC-5569 (91.4%) compared to other cultivars. The results showed that Amaranthus cultivars exhibited variable response towards ozone stress where foliar ozone injury does not always correspond with grain yield reductions. Among the indices, Relative Yield Index (RYI), Stress tolerance (TOL), Abiotic Tolerance Index (ATI), Susceptibility Index (S) and Stress Susceptibility Index (SSSI) were positively correlated with relative yield loss in all the cultivars under ozone stress. With the help of cluster analysis and principal component analysis (PCA), the cultivars were categorized into ozone tolerant, moderately ozone tolerant and ozone susceptible category. The most tolerant cultivars were IC-5527 and IC-1733 which exhibited lower yield losses whereas the most susceptible cultivars were IC-3599 and IC-7924 having high foliar injury and maximum yield losses as compared to other cultivars. The most ozone tolerant cultivars of Amaranthus identified in this study may be recommended for cultivation to farmers in the areas experiencing EO3 during the Amaranthus crop growth period.