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The temporal and spatial progress of sheath blight was assessed on a set of mega rice varieties of South Asia and local varieties of North India in field experiments for two consecutive years. With artificially created disease focus disease severity was recorded on five un-inoculated plants from the focus in four directions after two, four and six weeks of inoculation. The mega varieties differed in their level of susceptibility to sheath blight. The temporal progression of the disease was significantly increased in Swarna and Swarna Sub-1 followed by PR 114 and PR 121 varieties. Area under disease progress curve (AUDPC) ranged 184.92 – 683.67 in tested varieties. The disease severity decreased as the distance from the disease focus increased in all varieties, the significance of the spatial spread depended on the susceptibility level of the variety. Swarna and Swarna Sub-1 showed higher level of susceptibility. The exponential regression model explained the increased severity with time which get decreased with increase in distance from the disease focus. Relationship of week after inoculation with disease severity indicated that model explained 96.0% variability of the response data in Swarna. The morphological traits like plant height, number of tillers per hill and tiller angle of the varieties had a significant correlation with the disease severity and incidence. In the absence of genetic resistance, this study provides evidence of requirement of a six-week period for differentiating the susceptible or resistant response of rice varieties to sheath blight under field conditions. Plant morphological traits are the key factor which can be consider in disease resistant breeding programme.

Bacterial blight of rice caused by Xanthomonas oryzae pv. oryzae (Xoo) is an important disease of rice causing significant yield losses. Currently, there are ten highly diverse pathotypes of Xoo prevalent in Punjab state of India. Breeding for and deploying host plant resistance is the most economical approach for the management of this disease. But pathogen variability coupled with uncertainties in prevailing weather conditions due to climate change poses serious threat to the durability of R genes and makes the plant vulnerable to attack by the pathogen. During the current study, biochemical basis of resistance of two R genes, Xa4 and Xa7 was studied at different temperature regimes and five pathotypes of Xoo viz. PbXo-4, PbXo-7, PbXo-8, PbXo-10 and Sgr-1001. Level of resistance in Xa4 and Xa7 genes was observed to be highly correlated with the expression of three defense related enzymes viz. peroxidase, polyphenol oxidase and phenylalanine ammonia lyase. It was further observed that the expression of Xa4 and Xa7 was influenced by temperature as Xa4 showed increased effectiveness at lower temperature while Xa7 was more effective at high temperature. The differential pattern of lesion length progression on these near isogenic lines in response to different temperature regimes also suggests the level of quantitative resistance imparted by these genes.

False smut of rice caused by Ustilaginoidea virens (Cooke) Takahashi (teleomorph Villosiclava virens) has emerged as a serious concern in rice production. While variation for resistance exists in rice germplasm, most of the cultivated varieties are susceptible to false smut. A total of 125 diverse lines from global rice diversity panel were screened for resistance to false smut along with susceptible checks GSR123 and PR116, under natural hot spot for 3 years at two different locations and artificial inoculation conditions in a fourth consecutive year. False smut resistance was recorded based on infected panicles per plants (IPP), number of smut balls per plant (NSBP) and a disease score (DS). Of 125, 21 germplasm lines showed high level of resistance in all the years under natural hot spot as well as artificial inoculation conditions whereas 31 germplasm lines showed moderate resistance. Genome wide association study for false smut related traits identified significant associations on chromosomes 2, 3, 6, 9 and 11 for IPP. Similarly, significant associations for NSBP were identified on chromosomes 3 and 8 and DS on chromosomes 3, 4 and 11. Most of these QTLs were found to be associated with all the traits. The study highlights the potential donors for resistance to false smut that could be utilized in rice breeding programme. The identified QTLs could be the potential candidate regions for further studying the false smut resistance.

Climate change is predicted to cause adverse effects on global agricultural production by influencing spatial and temporal disease epidemics. The increase in temperature and atmospheric carbon dioxide levels causes physiological changes in plants that result in increase in intensity of crop diseases. Warming may cause shifts in agroclimatic zones in which host plants migrate into new areas resulting in the emergence of new disease complexes. The global disease scenario will be impacted by climate change as it can alter pathogen development, cause changes in host-pathogen interactions, and facilitate the emergence of new races of pathogens, which in turn break down host-plant resistance. In this chapter, we review the impact of climate change on different plant pathogens such as fungi, bacteria and viruses, development of new races of pathogens, deployment of R genes, occurrence of host-plant resistance and pathogen aggressiveness. We also review the probable strategies to mitigate the adverse effects of climate change on plant disease management practices to address future food security goals.

Twenty five isolates of Acidovorax avenae subsp. avenae causing bacterial leaf streak collected from infected maize crop grown in different geographical regions of Punjab, northern India were characterized for their molecular diversity using twenty five random amplified polymorphic DNA (RAPD) markers. All the primers showed amplification with a total of 1769 amplified fragments. Among RAPD primers, S112 was found to be highly polymorphic with PIC value of 0.95 while OPT-4 was least polymorphic. The size of amplified DNA fragments ranged from 59 bp to 3.9 kbp. Dendrogram based on molecular data generated by 25 RAPD collectively divided all 25 isolates into four groups. From 25 isolates, 20 were used for their pathological characterization and based on the multivar cluster analysis of pathogenicity data, these were divided into three groups, each producing a distinct range of disease score on particular maize inbred/hybrid used in this study. Isolate Aaa2 was found to be the most virulent with an average disease score of 8.6, whereas Aaa17 was found least virulent with average disease score of 5.1. The most virulent isolates of this pathogen were present in central Punjab. This was the first attempt to study the genetic diversity and pathogenic variation in Punjab populations of A. avenae subsp. avenae.

Sanitization of vegetables consumed raw has tremendous importance due to health risks associated with food-borne pathogens. This study elaborated the effectiveness of varied concentrations of disinfectants used for washing fresh carrot vegetable against five potential pathogens. The pathogens were identified during the course study and compared with MTCC standard cultures. It was found that induction of 50percent killing against five pathogens viz. Aeromonas hydrophila, Shigella flexneri, Staphylococcus aureus, Escherichia coli and Listeria monocytogenes required concentration (LC50) of Sodium hypochlorite upto 100ppm, Citric acid upto 1000ppm, Lactic acid 724ppm, CaO 2570ppm, Tannic acid 794ppm and Cineole 100ppm with 5minutes washing period. Of the entire chemical tested, sensory scoring for vegetable taste, acidic taste the overall appreciation of citric acid corroborates its use as an effective sanitizing agent to treat vegetables. Cineole on the other hand has high response value at 69ppm but loose appreciation due to poor odour and taste. The purpose of the study is to establish current state of intervention for maintaining the high microbial safety of fresh vegetables consumed raw as intended health benefits. Organic acids like citric and lactic acid can be used in food industry as emerging sanitation strategy with minimum contact time and consumers palatability.

Bacterial stalk rot (BSR) of maize caused by Dickeya zeae is an important disease in northwest region of India. In the current study, eighty maize lines were evaluated for resistance against this disease. Of these, 20 were moderately resistant, 25 were moderately susceptible and the rest were highly susceptible to BSR. Six lines from each set were randomly selected. Activities of three antioxidant enzymes, viz. phenylalanine ammonia lyase (PAL), peroxidase (POX) and polyphenol oxidase (PPO) were analysed from these three sets of maize lines representing different levels of resistance. A trend of elevated activity of PAL, POX and PPO was observed in all the three sets of maize lines. The results showed significantly more activity of these three enzymes in moderately resistant than highly susceptible maize lines. The activity of PAL and PPO peaked after 48 hr and of POX after 72 hr of challenge inoculation by D. zeae in all the maize lines. The activity of these enzymes further correlated negatively with disease development. Our results show that PAL, POX and PPO play an important role in contributing towards resistance in maize against BSR.

Bacterial stalk rot of maize caused by Dickeya zeae previously known as E. chrysanthemi pv. zeaehave economic importance of reduced crop yield up to 98.8%. The disease is more prevalent in rainy season in India. The bacterium prefers high temperature and moisture for their growth result is plant toppled down within week. The pathogen has wide host range (maize, rice, tomato, chilli and brinjal etc.) which help to pathogen for long survival in soil. The bacterium characterized by biochemical and molecular tactics. In present, Pel gene and rDNA specific primers are frequently used for D. zeae characterization. The pathogen significantly controls under in vitro and in vivo condition via bleaching powder (drenching of 100 ppm) and antibiotics. The present studies generated data on pathogen nomenclature, etiology, epidemiology, host range, pathogen survival, biochemical, physiological and molecular characterization, germplasm evaluation and disease management.

For the control of bacterial blight of rice caused by Xanthomonasoryzaepv. oryzae, sixty four Pseudomonas fluorescens strains were recovered from rice and wheat rhizosphere. These strains were identified on the basis of internal transcribed spacer (ITS) region. It was observed that the strains showing fluorescence in the selective media showed the amplification of the targeted P. fluorescens specific ITS region. The strains were also characterized for the production of the antibiotic 2, 4-diacetylphloroglucinol (DAPG) using phlDlocus. The characteristic 750bp region was amplified in all the DAPG producing strains. These strains were evaluated against X. oryzae in vitro by dual culture method. The P. fluorescens strains found effective in vitro were further tested in field for their antagonistic potentiality and disease suppression ability. P. fluorescens strain number Pf-4-R showed maximum inhibition i.e. of 5.5 mm against the test pathogen X. oryzaepv. oryzae. Talc based powder formulation of the effective strain Pf-4-R used for field evaluation, showed that pre-inoculation foliar sprays were effective in controlling bacterial blight of rice with disease suppression efficiency ranging from 29.6 to 65.6 percent in different treatments.

Among six fungal species viz.Aspergillus spp., Fusarium spp., Penicillum spp., Rhizopus spp., Trichoderma spp. and Alternaria spp. isolated from maize ear rot samples collected from five different districts of Punjab, the incidence of A. flavus was highest (42.15%) followed by Penicillium spp. (20.75%). The maximum frequency of A. flavus (57.10%) was found in Hoshiarpur district, closely followed by Jalandhar. In all, thirty nine isolates of Aspergillus spp. (33 isolates of A. flavus and 6 isolates of A. niger) were characterized morphologically. Twenty isolates of A. flavus producing sclerotia were of L-type strains having sclerotia diameter >400 μm. Isolates of A. flavusproduced yellowish green, dark green and light green colonies and isolates of A. niger produced dark black colonies. Sterigmata in all the isolates of Aspergillus spp. were of uniseriate type. Based on colony diameter and growth rate per day all the 39 isolates of Aspergillus spp. were grouped into fast, medium and slow growing categories. Based on multivariate cluster analysis, the isolates of A. flavus were grouped into three distinct clusters each having 13, 17 and 3 isolates respectively.In the present study, Aspergillus flavus was found predominantly associated species with the maize ear rot. Further, the morphological variation observed within Aspergillus flavus and A. niger indicated the need for proper surveillance and monitoring exclusively for the prevention of moulds in maize produce in Punjab before it reaches the consumer.

A virulent strain (M-13) of Dickeya zeae causing bacterial stalk rot of maize, isolated from Hoshiarpur district of Punjab was tested against different antimicrobial agents. Five antibacterial chemicals viz., stable bleaching powder, streptocycline, cristocycline, blitox, kocide and one bioagent (Pseudomonas fluorescens) were evaluated against D. zeae under in vitro and in vivo condition. The chemicals were tested with different concentrations i.e. 50, 100, 200, 500, and 1000 and >1000 ppm and bioagent supernatant used as such without any dilutions. All the test chemicals and bioagent (P. fluorescens strains) reduced the log cfu/ml of D. zeae. Amongst chemicals, stable bleaching powder with 100 ppm concentration showed most effective antibacterial activity which reduced the population of D. zeae with 6.35 log cfu/ml and amongst P. fluorescence strains, MPF-5 strain showed effective result with 8.07 log cfu/ml. In field condition bleaching powder also showed good result to reduce the disease severity with increased the crop yield when used as both methods (drenching and dusting). However, post inoculation drenching with 100ppm concentration showed minimum mean of disease severity (7.13%) with high yield (7.4 kg) in all three maize cultivars (Dekalb Double, Punjab Sweet Corn-1 and PMH-1). The increase yield per cent as compared to control was 52.4% in Dekalb Double, 64% in Punjab Sweet Corn-1 and 57.9 % in PMH-1 maize cultivars.

Bacterial blight disease of rice is major constraint in rice cultivation. This disease is influenced by prevailing weather conditions, rice physiology and nutrition. The experiment was carried out to assess the role of nitrogenous fertilizer on development of bacterial blight disease of rice and Xanthomonas oryzae pv. oryzae density in guttation fluid. Disease development increased with increase in nitrogen fertilizer, among four doses of nitrogen tested (control, 36, 54,72 kg urea/acre), disease severity was maximum in the plot supplied with highest dose of nitrogen i.e. 72 kg urea/acre at both seedling (19.3%) and tillering stage (32.4%) at 30 days after inoculation. The highest population density of X. oryzae pv. oryzae (6.02 log cfu/ml) was also recovered in guttation fluid collected from X.oryzaepv. oryzae inoculated plants at tillering stage, from the plots supplied with highest dose (72 kg urea/acre) of nitrogen.Scanning electron microscopic studies also revealed intense colonization by X. oryzae pv. oryzae in rice leaves supplied with high nitrogen dose.

This study was aim to identify the pathogen associated with the red stripe/top rot disease. The isolates were collected from major sugarcane growing districts of Punjab. Molecular identification of the pathogen was carried out to confirm the associated organism with this disease. Of the different sets of specific PCR based molecular markers were used, primer sets SeQ1 (Aaa) and SeQ2 (Aaa) amplified the expected 550bp of ITS (Internal Transcribed Spacer) region of the rDNA which revealed the pathogen as Acidovorax avenae pv. avenae, whereas the primer set Aaaf3 and Aaar2 are specific to strains that infect rice crop did not amplify any fragment. Our studies confirmed Acidovorax avenae pv. avenae as the causal bacterium associated with the red stripe/top rot of sugarcane in Punjab.

Rhizoctonia solani Kuhn, a highly variable pathogen, causes sheath blight of rice globally leading to serious yield losses under favourable environmental conditions. Sixty-four Rhizoctonia isolates collected from diverse rice growing agro-ecological zones of the north Indian state of Punjab were analyzed for species identification, genetic diversity, morphological features and virulence pattern. Accurate identification of the fungal species using internal transcribed spacer species-specific primers confirmed presence of R. solani (84.4 %), R. oryzae-sativae (10.9 %), R. oryzae (1.5 %) and mixed infection of these Rhizoctonia sp. Genetic structure of the isolates resolved using inter simple sequence repeat primers revealed high degree of polymorphism (PIC value ranging from 0.80 to 0.90), clustering the pathogen population into four major groups. The virulence pattern of 18 isolates representing genetically diverse groups generated by ISSR profile was quantified on seven rice genotypes/cultivars i.e., Tetep, Jasmine 85, Te-Qing, D-256, D-6766, PR108 and PAU201 with different levels of resistance to rice sheath blight. The hierarchical cluster analysis based on different disease variables classified isolates into six main groups. Reaction of individual isolate to each genotype revealed different levels of virulence pointing towards high evolutionary potential, thus enabling it to adapt to diverse geographical regions.

Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major biotic constraint in the intensive irrigated rice belt comprising Punjab and adjoining north-western states of India. Development and deployment of host resistance is the only effective means of BB management. The pathogen is highly variable, and the current Xoo population from the state could be classified into seven distinct pathotypes (PbXo-1 to PbXo-7) by inducing differential reactions on a set of near-isoganic lines in the background of IR24 and some international, national and regional cultivars. Known BB resistance genes (Xa1, Xa3, Xa10, Xa11, Xa14, Xa18) were ineffective, whereas xa13, Xa4 + xa13, xa5 + xa13, xa13 + Xa21, Xa4 + xa5 + xa13, Xa4 + xa5 + Xa21, Xa4 + xa13 + Xa21, xa5 + xa13 + Xa21 and Xa4 + xa5 + xa13 + Xa21 and rice line IET8585/Ajaya were effective against all the seven pathotypes analysed. Xa21 was effective against all the pathotypes except PbXo-3 and PbXo-4. PbXo-7, the most dominant pathotype, was found to be virulent and induced susceptible/moderately susceptible reaction on 22 of the 40 test genotypes followed by PbXo-1, PbXo-5 and PbXo-6; PbXo-2 was the least virulent pathotype. Molecular profiling of these pathotypes using random amplified polymorphic DNA (RAPD) and IS1112-based polymerase chain reaction (PCR) generated specific and reproducible fingerprint patterns. Primers S1117, S112, S109, S1106 and JEL are more informative in distinguishing pathotypes. At a similarity of 0.50, pathotypes PbXo-1 and PbXo-2 were grouped together, whereas other five pathotypes showed separate lineage. The data using RAPD-PCR and IS1112-based PCR approaches revealed their potential in generating unique DNA fragments specific for different pathotypes that may lead to the rapid assessment of genetic variation in the pathogen population. Pyramiding of two/more partially effective known Xa genes and/or search for new disease resistance genes effective against the wider Xoo population appears to be the most appropriate approach for BB management in the near future.

Pest problems are an inevitable part of modern day agriculture. They occur because agro-ecosystems have created less stable natural ecosystems which otherwise govern ecological forces that regulate potential pest species in natural ecosystems. Raising crops in a monoculture thus provides a food resource cycle that allows pest populations to achieve far higher densities than they would in natural environments. A certain cultivation practice can also make the physico-chemical environment more favourable for pest activity, for example, through irrigation or the warm conditions found in glasshouses. New cultivars or new crops introduced into a certain area or country may provide food resources for potential pests. Also, the use of broad spectrum insecticides can destroy natural predators that help keep pests under control. In these scenarios, new pest problems arise or existing pests become more serious and cause significant damage to crops, biodiversity and landscape valued at billions of dollars per annum. New strains of plant insect-pests may arise to overcome varietal resistance in crops.

International audience; Sheath blight, caused by Rhizoctonia solani, is one of the most important rice diseases worldwide especially under irrigated agro-ecosystems. To date, no rice accession with complete resistance to sheath blight has been reported. However, a number of genotypes with varying levels of resistance have been reported. Twelve genotypes (including mega varieties) viz. Tetep, Jasmine 85, Te-Qing, Duduruchi, Betichikon, Khatochalani, D-6766, D-256, Swarna, Sarju-52, MTU-1010 and Samba Mashuri were evaluated for quantitative measurement of partial physiological resistance to sheath blight under controlled conditions using detached tiller method. Three independent experiments, each involving three replications, were conducted. Seven days after inoculation, the following disease variables were measured: number of lesions, lesion length, vertical sheath colonization (VSC) on the tiller, disease severity, relative vertical sheath colonization (RVSC) and survival of the leaf blade. Variation between rice genotypes was observed for all the disease variables. Disease severity and VSC were the two most correlated variables, whereas the number of lesions and mean lesion length were the least correlated variables. The ranking of varieties often differed depending on the disease variable considered. Amongst the genotypes tested, D-256, Tetep and Jasmin-85 had the lowest number of lesions and disease severity. Similarly, Tetep and D-256 showed the lowest levels of RVSC, whilst Jasmine-85 was found to be intermediate. D-6766, Samba Mashuri and Betichikon showed the highest levels of disease variables. The fraction of dead leaves ranged from 0.00 to 0.38. No dead leaves were observed in Te-Qing, Swarna and MTU-1010. The highest fraction of dead leaves was observed for Betichikon (0.38) followed by Duduruchi and D-6766 (0.33). Our results suggest that this method in combination with other phenotyping methods could be used to quantify partial resistance to rice sheath blight.