Rainfall and temperature distinguish between Karnal bunt positive and negative years in wheat fields in Texas

A model for Tilletia indica (Karnal bunt)—Triticum aestivum (Wheat) system under changing environmental conditions

Karnal bunt (KB) of wheat incited by Tilletia indica Mitra is now gaining importance from the last few years due to its increasing incidence. Regular surveys are conducted to collect wheat grains samples from different grain markets of Punjab, India. Since weather plays a significant role in the initiation as well as the development of Karnal bunt. Thus, the variation in Karnal bunt incidence worked out and is being interpreted in relation to the prevailing environmental conditions during the most susceptible stage for the two decades (1991–92 to 2014–15) for the Punjab, India. The incidence of Karnal bunt was correlated with the weather parameters during the February and March of the corresponding year. The correlation analysis revealed the positive role of rainfall, rainy days, evening relative humidity, and Humid thermal index of March and the negative role of sunshine hours of February in the development and incidence of Karnal bunt. By using these parameters, a multiple regression model was developed and validated for forecasting the disease. The regression analysis showed a coefficient of determination of 0.77 and a D.W value of 1.88. The detailed analysis of historical data for more than two decades divulged the amount of total rainfall as well as the number of rainy days of March as the most critical factor for the Karnal bunt development.

Effects of Tilletia foetida on Microbial Communities in the Rhizosphere Soil of Wheat Seeds Coated with Different Concentrations of Jianzhuang

Tilletia foetida (syn. T. laevis) leads to wheat common bunt, a worldwide disease that can lead to 80% yield loss and even total loss of production, together with degrading the quality of grains and flour by producing a rotten fish smell. To explore the potential microbial community that may contribute to the control of soil- and seed-borne pathogens, in this study, we analyzed the effects of the plant pathogenic fungus T. foetida on rhizosphere soil microorganisms in wheat seeds coated with different concentrations of a fungicide (Jianzhuang) used to control the disease. To analyze the bacterial and fungal abundance in T. foetida-infected and mock-infected plants, the microorganisms were sequenced using high-throughput HiSeq 2500 gene sequencing. The results showed that bacterial communities, including Verrucomicrobia, Patescibacteria, Armatimonadetes, Nitrospirae, Fibrobacteres, Chlamydiae, and Hydrogenedentes, and fungal communities, including Basidiomycota and Ciliophora, were more prevalent in the mock group than in the T. foetida-infected group, which may contribute to the control of wheat common bunt. Moreover, cluster and PCoA analysis revealed that replicates of the same samples were clustered together, and these results were also found in the distance index within-group analysis for bacterial and fungal communities in the T. foetida-infected and mock groups.

The impact of Fosetyl-Aluminium application timing on Karnal bunt suppression and economic returns of bread wheat (Triticum aestivum L.)

Fungal pathogens exert severe qualitative and quantitative damages to wheat crop. Karnal bunt of wheat caused by Tilletia indica Mitra, Mundkur is a severe threat to global food security. Nonetheless, T. indica is regulated as a quarantine pest in numerous countries, which further aggravates the situation. Tolerant varieties and appropriate management practices for Karnal bunt are imperative to meet the global wheat demands. This two-year study explored the impact of fungicide [Fosetyl-Aluminium (Aliette)] application timing on allometric traits, disease suppression and economic returns of bread wheat. Four bread wheat cultivars differing in their tolerance to Karnal bunt were used in the study. Fungicide was applied as either seed treatment (ST), foliar application at heading (FAH) or ST + FAH, whereas no application (NA) was taken as control. Lasani-08 performed better than the rest of the cultivars in terms of allometric traits (plant height, leaf area, crop growth rate, photosynthesis, and chlorophyll content), yield and economic returns. Nonetheless, minimal disease severity was recorded for Lasani-08 compared to other cultivars during both years. The ST improved allometric traits of all cultivars; however, ST + FAH resulted in higher yield and economic returns. Cultivar Pasban-90 observed the highest disease severity and performed poor for allometric traits, yield and economic returns. It is concluded that ST + FAH of Fosetyl-Aluminium could be a pragmatic option to cope Karnal bunt of wheat. Nonetheless, Pasban-90 must not be used for cultivation to avoid yield and quality losses.

Remote sensing and spatial statistical techniques for modelling Ommatissus lybicus (Hemiptera: Tropiduchidae) habitat and population densities

In order to understand the distribution and prevalence of Ommatissus lybicus (Hemiptera: Tropiduchidae) as well as analyse their current biographical patterns and predict their future spread, comprehensive and detailed information on the environmental, climatic, and agricultural practices are essential. The spatial analytical techniques such as Remote Sensing and Spatial Statistics Tools, can help detect and model spatial links and correlations between the presence, absence and density of O. lybicus in response to climatic, environmental, and human factors. The main objective of this paper is to review remote sensing and relevant analytical techniques that can be applied in mapping and modelling the habitat and population density of O. lybicus. An exhaustive search of related literature revealed that there are very limited studies linking location-based infestation levels of pests like the O. lybicus with climatic, environmental, and human practice related variables. This review also highlights the accumulated knowledge and addresses the gaps in this area of research. Furthermore, it makes recommendations for future studies, and gives suggestions on monitoring and surveillance methods in designing both local and regional level integrated pest management strategies of palm tree and other affected cultivated crops.

A Mechanistic Model of Botrytis cinerea on Grapevines That Includes Weather, Vine Growth Stage, and the Main Infection Pathways

A mechanistic model for Botrytis cinerea on grapevine was developed. The model, which accounts for conidia production on various inoculum sources and for multiple infection pathways, considers two infection periods. During the first period ("inflorescences clearly visible" to "berries groat-sized"), the model calculates: i) infection severity on inflorescences and young clusters caused by conidia (SEV1). During the second period ("majority of berries touching" to "berries ripe for harvest"), the model calculates: ii) infection severity of ripening berries by conidia (SEV2); and iii) severity of berry-to-berry infection caused by mycelium (SEV3). The model was validated in 21 epidemics (vineyard × year combinations) between 2009 and 2014 in Italy and France. A discriminant function analysis (DFA) was used to: i) evaluate the ability of the model to predict mild, intermediate, and severe epidemics; and ii) assess how SEV1, SEV2, and SEV3 contribute to epidemics. The model correctly classified the severity of 17 of 21 epidemics. Results from DFA were also used to calculate the daily probabilities that an ongoing epidemic would be mild, intermediate, or severe. SEV1 was the most influential variable in discriminating between mild and intermediate epidemics, whereas SEV2 and SEV3 were relevant for discriminating between intermediate and severe epidemics. The model represents an improvement of previous B. cinerea models in viticulture and could be useful for making decisions about Botrytis bunch rot control.

Physiological Responses of Hard Red Winter Wheat to Infection by Wheat streak mosaic virus

Wheat streak mosaic virus (WSMV) causes significant yield loss in hard red winter wheat in the U.S. Southern High Plains. Despite the prevalence of this pathogen, little is known about the physiological response of wheat to WSMV infection. A 2-year study was initiated to (i) investigate the effect of WSMV, inoculated at different development stages, on shoot and root growth, water use, water use efficiency (WUE), and photosynthesis and (ii) understand the relationships between yield and photosynthetic parameters during WSMV infection. Two greenhouse experiments were conducted with two wheat cultivars mechanically inoculated with WSMV at different developmental stages, from three-leaf to booting. WSMV inoculated early, at three- to five-leaf stage, resulted in a significant reduction in shoot biomass, root dry weight, and yield compared with wheat infected at the jointing and booting stages. However, even when inoculated as late as jointing, WSMV still reduced grain yield by at least 53%. Reduced tillers, shoot biomass, root dry weight, water use, and WUE contributed to yield loss under WSMV infection. However, infection by WSMV did not affect rooting depth and the number of seminal roots but reduced the number of nodal roots. Leaf photosynthetic parameters (chlorophyll [SPAD], net photosynthetic rate [Pn], stomatal conductance [Gs], intercellular CO2 concentration [Ci], and transpiration rate [Tr]) were reduced when infected by WSMV, and early infection reduced parameters more than late infection. Photosynthetic parameters had a linear relationship with grain yield and shoot biomass. The reduced Pn under WSMV infection was mainly in response to decreased Gs, Ci, and SPAD. The results of this study indicated that leaf chlorophyll and gas exchange parameters can be used to quantify WSMV effects on biomass and grain yield in wheat.

Application of the Humid Thermal Index for Relating Bunted Kernel Incidence to Soilborne Tilletia indica Teliospores in an Arizona Durum Wheat Field

A study was conducted to determine the relationship between soilborne Tilletia indica teliospore density and Karnal bunt incidence in an Arizona durum wheat field in 2005 and 2006. Soil samples were collected from 507 sample points according to a grid marked in a 7.7-ha field. Approximately 500 g of soil from the top 5 cm was collected from each sample point, and teliospores were recovered from 25-g aliquots by a modified size-selective sieving, sucrose centrifugation procedure. Twenty-five and 50 wheat heads were collected from a 1-m² area around each sample point in May 2005 and June 2006, respectively. Wheat head samples from each sample point were bulked, threshed, and examined for the presence of bunted kernels. Additionally, data for soilborne teliospores and percent bunted kernels from 70 sample points in 2005 and 2006 that corresponded to sample points from a 2004 bunted kernel survey conducted by the USDA and Arizona Department of Agriculture were analyzed. Soilborne teliospore numbers ranged from 6 to 1,000 per 25-g soil sample in the 2-year study. No bunted kernels were recovered in 2005; however, two sample points yielded bunted kernels in 2006. Weather data from three time periods in 2004, 2005, and 2006 were applied to the humid thermal index model and suggested that a conducive environment for disease development existed in 2005. Based on the data from this research, we concluded that even though high numbers of soilborne teliospores were present in the field, and although a conducive environment was present for disease to develop on only one occasion, a direct relationship between soilborne teliospores and disease incidence may not exist.