The Ralstonia solanacearum species complex (RSSC) is a major plant pathogen causing bacterial wilt in solanaceous vegetables and many economically important crop plants. In this study, nine bacterial isolates from wilt-affected eggplant and tomato plants in Tamil Nadu were characterised by a polyphasic approach. All isolates induced complete wilting of test eggplant and tomato plants within 3-4 days post-inoculation, indicating high virulence. Molecular identification via 16S rRNA sequencing and species-specific primers confirmed them as R. pseudosolanacearum; multiplex PCR assigned them to Phylotype I. Multilocus sequence typing (MLST) of five housekeeping (adk, gapA, gyrB, ppsA, gdhA) and two virulence genes (egl, fliC) revealed a high degree of genetic conservation, with most alleles identical across strains. Minor variations in ppsA and egl suggested novel alleles in three isolates. MLST analysis grouped the isolates into six clusters; Cluster I showed high similarity, Clusters III and IV exhibited allelic variation. Sequence polymorphism analysis across four phylotypes showed moderate genetic diversity within Phylotype I, indicating a genetically stable but clonally diverse population. Phylotype II exhibited slightly higher nucleotide diversity but reduced haplotype diversity, suggesting population contraction or selective constraints. Phylotype III, despite being represented by only five isolates, showed the highest nucleotide diversity and frequent recombination, reflecting a dynamic and evolving lineage. Phylotype IV displayed intermediate levels of diversity with fewer recombination events, indicating a more stable population structure. These findings emphasise the clonal structure, regional adaptation and evolutionary patterns of RSSC strains, highlighting the need for continued genomic surveillance to inform disease management strategies.

Rhizosphere bacteria based biological control strategy is an eco-friendly approach to protect crops from various plant diseases. Among these, spore-forming Bacillus, abundant in the rhizosphere, provide unique advantages for plant health. This study focused on characterising two tomato rhizosphere-associated Bacillus amyloliquefaciens strains (Trb7 and Trb11), highly effective against the bacterial wilt pathogen Ralstonia pseudosolanacearum in vitro. Species identification was based on partial 16S rRNA gene sequencing, supported by phylogenetic analysis. Five antimicrobial peptide (AMP) genes (surfactin, fengycin, bacilysin, subtilin, and spore protein) were detected in both the isolates of B. amyloliquefqciens using specific molecular markers. Greenhouse trials showed that prophylactic application of these isolates led to an 83.4% reduction in tomato bacterial wilt, with only 16.6% wilt incidence compared to the 100% in the R. pseudosolanacearum-inoculated control. Moreover, these B. amyloliquefaciens isolates exhibited plant-growth-promoting traits in vitro. Interestingly, they also showed significant inhibition of mycelial growth against Sclerotium rolfsii and Alternaria alternata, major fungal pathogens in tomatoes. Overall, our findings highlight the potent bactericidal role of B. amyloliquefaciens isolates in suppressing R. pseudosolanacearum in tomatoes.

A two days old liquid formulation of B. amyloliquefaciens containing 83.67 x 10-10 cfu / 0.1 ml was used as such in different quantities for treating one kg of sesame seed i.e. 10 ml/kg, 75 ml/kg, 100 ml/kg and 120 ml/kg of seeds and stored separately at room temperature for seventy five days. Then these treated seeds from each treatment were washed with known quantity of sterile distilled water individually and assessed the spermosphere population of B. amyloliquefaciens separately. The suspension collected from the seeds stored for seventy five days after treating with liquid formulation of B. amyloliquefaciens @ 10 ml/kg recorded 2.67 x 10-9 cfu / 0.5 ml suspension at 48 hours after plating. In another experimental study when the seeds were used ninety days after seed treatment for conducting roll towel method clearly revealed that the seed treated with liquid formulation of Pseudomonas spp. @ 20 ml/kg seed recorded highest shoot and root length of ten days old seedlings by recording 12.86 and 9.92 cm, respectively and the seeds treated with liquid formulation of B. amyloliquefaciens @ 20 ml/kg was found to record increased shoot and root length of seedlings by 12.42 cm and 9.34 cm respectively. These two treatments were statistically on par with each other

In the fungal kingdom, Trichoderma is the most exploited biocontrol agent. It is known for its ability to colonize plant root, suppress many plant pathogens, and act as inducer of systemic resistance in plant and is also involved in growth promotional activities. The knowledge on rhizosphere signalling between plant root–Trichoderma interaction is highly essential to trigger the immune response and to improve plant health. There is a bidirectional perception of signal molecules for the successful establishment of its association. The interaction of Trichoderma starts with contact to the root surface, followed by attachment, penetration, and colonization. The signal molecules from root exudates and secretomes of Trichoderma are essential for successful accomplishment of a symbiotic relationship. Among the complex composition of root exudates, sucrose plays a vital role in the attraction of Trichoderma to the plant root system. The hydrophobin and swollenins and cysteine-rich proteins secreted by Trichoderma plays a role in each step towards successful plant root interaction. This review enlightens our knowledge on root–Trichoderma interaction and its ability to overcome plant’s defense mechanism to prove itself as a “true friend” to the plant system and for improvement of soil and plant health.

Leaf blight caused by Alternaria alternate is the major disease of sunflower affecting the successful cultivation across India. fungicides, biotic and abiotic inducers namely Propiconazole, Ginger, Salicylic acid, Bacillus subtilis, Pseudomonas sp, Bacillus pumilus, Pseudomonas fluorescens, Mancozeb in eight different treatment as spray and as seed treatment were evaluated against Alternaria leaf blight of sunflower at kadukanpalaym Erode district, Tamil Nadu. This experiment was carried out for 2019 during Kharif season. During 2019, the experimental results revealed that combination of seed treatment with entophytes Pseudomonas sp. 10g/kg of seed + foliar spray at 30 and 45 days after sowing recorded least per cent disease intensity with highest yield among all treatments.

A study was conducted to isolate and characterize bacterial isolates from Rhizosphere soils with potential for suppression of charcoal rot pathogen Macrophomina phaseolina causing charcoal rot maize. Out of 10 bacterial isolates collected from forest rhizosphere soils, 2 isolates were found to be antagonistic to M. phaseolina in in vitro studies. In these best two isolates were molecularly characterized by using 16s rRNA. Data for bacterial antagonists have been deposited under the following accession numbers: MN985505 (Pseudomonas aeruginosa) and MN985650 (Pseudomonas aeruginosa.).

Alternaria blight is the most common and devastating disease caused by Alternaria alternata in sunflower. This fungus grows well in Yeast Peptone Agar and Carrot + Potato agar medium under in vitro conditions. The growth of the fungus was tested using ten different media. Carrot + Potato agar medium appeared to be better than other media for the growth of A. alternata. The growth characteristics of the fungus such as colour of the colony and sporulation were also different in different culture media. The colony of the fungus was dark brown in colour. Maximum sporulation of the test fungus was found on Richards agar (RA) Walksman agar (WA), Carrot medium and Carrot+potato agar medium whereas no sporulation was seen on Czapeck’s dox agar medium. Thus the present work will be useful for further investigation on the physiology of the fungus and management of the disease.

Ralstonia solanacearum isolates collected from wilt affected tomato plants in Coimbatore district of Tamil Nadu were characterized by morphological, biochemical and race analysis. The isolates produced typical irregular, whitish fluidal single colonies along with pinkish center on 1 % TZC amended CPG agar media. Pathogenicity test revealed the representative isolates could wilt the tomato seedlings, and tobacco leaf infiltration assay confirmed its race 1 nature. Biochemical assays revealed the isolates belong to biovar 3 and species level identity was confirmed as R. solanacearum through Biolog finger printing assay.

Magnaporthe oryzae Cav. (Anamorph Pyricularia oryzae (Cooke) Sacc.) is a cause for a very serious and threatful biotic stress called rice blast. Managing the disease through PR protein was found to be an effective approach as over expression helps in antimicrobial control. An experiment was conducted using 25 rice differentials to study pathogenesis-related (PR) protein expression and activity of enzymes such as ascorbate peroxidase, guaiacol peroxidase, glutathione reductase and superoxide dismutase during pathogen attack as they are indication of defense activation. Among them, Tetep was found resistant where in HR 12 and CO 39 was found highly susceptible to rice blast. PR 11 was expressed in resistant and moderately resistant differentials but it was unnoticed in highly susceptible differentials (HR 12 and CO 39). Activity of above mentioned defense related enzyme was found higher after 48 hours of inoculation in prominent rice variety CO 39. Among other 24, RIL 10, a moderately resistant differential recorded maximum activity of ascorbate peroxidase and glutathione reductase. The higher reports of guaiacol peroxidase and superoxide dismutase activity was observed in IR 64 and Kanto 51 respectively (moderately resistant differentials). All four enzyme activity was lowest in susceptible to highly susceptible differentials.

Several species of endophytic bacteria has been reported from various plants. In the present study, samples of roots, rhizome, pseudostem, petiole and leaves of healthy Banana plant were collected from variety Yangambi km5 (AAA). In total, 38 endophytic bacteria were isolated. Amongst 16 isolates were selected based on compatibility by cross streak method. The 16 strains tested by paper disc method, Lf4, Lf5, Lf10, Pt4 and Ps7 showed inhibitory effects against Pectobaterium carotovorum subsp. carotovorum under in vitro conditions. The Lf4 and Lf5 showed similar results for the biochemical characteristics studied. The isolate Lf10 showed a slight difference with regard to oxidase test, Methyl red, Urease test and H2S production. The isolates Pt4 and Ps7 showed similar result except nitrate reduction, KOH test and Pigment production. Bacillus subtilis (Bs) strain (culture collected from Department of Plant pathology, TNAU) was used as reference culture. The total DNA extracted from selected five isolates was identified by partial sequencing of the 16S rRNA gene and phylogenetic tree was constructed using MEGA 6.0. The results confirmed that isolates Lf4 and Lf5 were Bacillus subtilis, isolate Lf10 was an Ochrobactrum daejeonense, isolate Pt4 was an Achromobacter xylosoxidans and Ps7 was a Pseudomonas aeruginosa. The study revealed that all the five strains have biocontrol potential against soft rot pathogen.

Cotton is an important crop used globally for its natural fibre and seed. Fusarium wilt, caused by the fungus Fusarium oxysporum f. sp. vasinfectum, is a major disease of cotton capable of causing significant economic loss. The fungus persists in soil as chlamydospores and in association with the roots of susceptible, resistant and non-cotton hosts as well as in seed. In the present investigation, the major cotton growing areas of Tamil Nadu were surveyed for assessing the per cent wilt incidence, the maximum disease incidence of 28.47 per cent was recorded at Coimbatore (Loamy) followed by 24.65 per cent at Salem (Clay loam) and a minimum of 7.65 per cent incidence at Madurai with silty loam soil texture. The number of micro conidia was more as compared to macro conidia. Abundant chlamydospores were observed terminally and intercalary. The size of the macro conidia, micro conidia and chlamydospores of the virulent isolate TRY (Trichy) was 26.20x6.25µm, 13.65x4.18µmand11.87x11.48µmrespectively.

The pot culture experiments were conducted under polyhouse condition to study the pathogenicity of potato cyst nematode, Globodera rostochiensis and G. pallida on potato cv. Kufri Jyoti at different inoculum levels of 0, 10, 100, 1000 and 10,000 J2 per plant. The results revealed that, the potato cyst nematode Index was 4.0 at inoculum level of 10,000 J2/plant and 1.75 at 10 J2 per plant. However, the reproduction factor was highest 215.61 with the lowest inoculum level of 10 J2/ plant where as 118.42, 47.71 and 22.02 respectively with the initial inoculum levels of 100, 1000 and 10,000 J2 / plant. A gradual increase in the nematode inoculum levels declined the plant growth parameters progressively from 100 to 10,000 second stage juveniles (J2) per plant. The highest reduction in plant growth was recorded at a level of 10,000 J2/plant and the minimum was recorded at a level of 100J2/plant, where as 1000 J2/plant recorded as an Economic Threshold Level. Inoculation of 1000 J2/plant showed 40.60, 32.00, 40.07 and 70.20 per cent reduction in plant height, fresh weight, dry weight and yield per plant compared to uninoculated control. The maximum of 87.35 % yield reduction was recorded, at an inoculum level of 10,000 J2/plant followed by 70.20 and 27.00 % at a levels of 1000 and 100 J2/plant respectively.

Soft rot disease of Banana caused by Pectobacterium carotovorum subsp. Carotovorum is found to be a serious disease and cause considerable yield loss. Common cultivars viz., Grand Naine, Rasthali and Nendran are extremely prone to this disease. Understanding the disease diagnosis and pathogen virulence is important in management programs. The pathogen was isolated from infected rhizomes from five locations of Theni district of Tamil Nadu. Pathogenicity of all isolates was confirmed by in vitro inoculation in rhizome bits and in vivo inoculation in pseudostems of three months old tissue cultured plants of cv. Grand Naine. The virulent isolates Icb4 and Ikg2 were characterized according to the morphological and microscopic characteristics, along with the physiological and biochemical assays; which indicates that the bacteria are gram negative, rod shaped, peritrichously flagellated. The colonies form characteristic deep cavities or pits in Crystal violet pectate medium (CVP). Results of biochemical tests showed that isolates Icb4 and Ikg2 have a positive reaction for catalase, H2S production and nitrate reductase and a negative reaction for oxidase test, Indole test and gelatin liquefaction. The results determining the optimal temperature for the growth of isolates Icb4, and Ikg2 have revealed that the temperature at 30 ºC - 37 ºC were suitable to obtain profuse growth of Pectobacterium. Total DNA extracted from the isolates Icb4, and Ikg2 were subjected to PCR analysis of 16S-23S intergenic transcribed spacer region. PCR amplified 1.5 kb amplicons were sequenced. Sequence Homology and phylogeny analyses had shown that the isolates Icb4 and Ikg2 were belonged to Pectobacterium carotovorum subsp. carotovorum.

The biocontrol agent Chaetomium globosum is widely prevalent in soil and other cellulose containing substrates. Fifteen isolates of C. globosum was isolated from different microhabitats of Tamil Nadu using baiting, direct isolation from decomposed materials and through serial dilution technique. All the fifteen isolates were phenotypically identified by their colony growth and perithecia. The colour of the colony varied from greenish white to yellowish white with radial and fluffy mycelial growth pattern. The pycnidia of different Chaetomium isolates varied in their shapes like ovoid, lemoniform, elliptical or slightly elliptical with an apical germ pore. The size of ascomata varied from 105.1 – 593.45 x 51.21 - 387.41 µm dia. Comparison of perithecial production between the C.globosum isolates indicated that the number of perithecia was more in TNAU-Cg 101 and TNAU-Cg 105 isolates. Ascospores were brown in colour and size varied from 8 - 14 µm dia. The sporulation was higher in TNAU-Cg101, TNAU-Cg 102 and TNAU-Cg105 isolates. Besides, all fifteen isolates were confirmed as C.globosum, by amplification through internal transcribed spacer rDNA sequences bearing the accession numbers MK587669, MK590290, MK592857, MK603862, MK592858, MK828135, MK821416, MK823129, MK828197, MK603941, MK828136, MK757844, MK820066, MK828133 and MK828134. Phylogenetic analysis of the fifteen C. globosum isolates, indicated that all the isolates were clustered into a single group.

High incidence of wilt disease (35–45%) of tomato (Solanum lycopersicum L.) was recently observed in two different locations of Tamil Nadu state of India. Infected plants showed typical wilt symptoms which include sudden green wilting of foliage followed by drooping of leaves downwards. The characteristic white milky ooze observed on the cut end of infected stem indicated bacterial etiology. Upon isolation, bacterium produced white fluidal irregular colonies with characteristic pink center on 2, 3, 5 triphenyl tetrazolium chloride amended nutrient medium. The bacterium caused typical green wilting 4–5 days post inoculation (dpi) on one month old tomato plants. The identity of bacterium was confirmed as Ralstonia solanacearum using 16S rRNA gene sequences as well as by R. solanacearum specific PCR. Further studies confirmed that the bacterium belonged to race 1 and biovar 3. In depth genetic characterization using multilocus sequence typing (MLST) revealed that the wilt outbreaks in Tamil Nadu were caused by genetically distinct race 1 strains of R. solanacearum. While the isolate, TRsR found clustered with R. solanacearum isolates previously reported from Andaman and Nicobar Islands-India, TRsP is clustered with isolates reported from Kerala, India. The results of our MLST based genetic analysis clearly indicated horizontal spread of bacterial wilt disease of tomato as a consequence of pathogen migration with the expansion of cultivation in India.

The field experiment was carried out on farmers holding at Melur block of Madurai dt using the popular brinjal variety Kallampatti local during summer 2016 to evaluate the efficacy of certain promising plant derivatives against major sucking pests of brinjal viz., aphids, brown plant hopper, thrips, whiteflies and two spotted spider mites. The overall impact of three rounds of spray revealed that basil leaf extract 10% caused maximum reduction of sucking pest population followed by Nochi leaf extract 5%, apart from this, Neem oil 3% had moderate efficacy against sucking pests followed by Rosemary oil 2%, Cashew nut shell liquid 3%, Garlic bulb extract 10%. Followed by Soap nut powder extract 10%, Fish oil rosin soap 20%.

Tomato (Solanum lycopersicum L.) is one of the most important solanaceous crops grown throughout the world, and commonly grown in Tamil Nadu. It is one of the most and popular vegetables being second after potato in terms of food value but ranks first in terms of processing value (Dutta et al., 2013). All over India vegetable cultivation reaches 9205 thousand ha and 162187 metric tonnes (Mt) of production, in which tomato is being cultivated in about 879.63 thousands ha and the production is 18226.64 Mt with a productivity of 20.7 Mt/ha (NHB, 2013). The area of tomato cultivation in Tamil Nadu is 25, 370 hectares with production of 328.2 tonnes per hectare. The major tomato growing districts in Tamil Nadu are Dharmapuri which occupies rank first followed by Krishnagiri, Salem, Theni, Dindigul and Coimbatore (Anonymus, 2009).

Erysiphe pisi , which causes pea powdery mildew, is an obligate biotrophic pathogen that can easily adapt to its host plant. Understanding the natural incidence and genetic variations of the pathogen is essential for disease control and for breeding resistant variety to pea powdery mildew. The incidence was studied in different locations of the Nilgiris district, and the disease recorded from 32.61 to 45.55 and 14.08 to 20.84 per cent in leaves and pods, respectively. A total of 10 isolates of E. pisi were obtained from the diseased samples to study the genetic variability if any, among them using internal transcribed spacer region amplification and inter-simple sequence repeats (ISSRs). PCR amplification of total genomic DNA with ISSR primers generated unique banding patterns depending upon primers and isolates. Twelve oligonucleotide primers were selected for the ISSR assays, which resulted in 742 bands for ten isolates of E. pisi . The number of bands obtained was entered into a PRIMER 7 to understand genetic relationship and Bray-Curtis coefficient for hierarchical cluster analysis. The results showed that the variability among the pathogen isolates was moderate. The above ten isolates were grouped into two major clusters and one single cluster had an average Polymorphic Information Content value (PIC) of 0.883 and Effective Multiplication Ratio (EMR) of 90. Hence, it is inferred that the E. pisi infecting peas in the Nilgiris consists of a single clonal lineage with a moderate level of genetic diversification.

Black rot, the most serious disease of crucifers especially Brassica oleracea var. capitata (Cabbage) causes huge yield losses. Black rot is a systemic vascular disease. Typical disease symptoms are V-shaped yellow lesions starting from the leaf margins and blackening of veins. The cabbage leaves were tested for Xanthomonas campestris pv. campestris infection through morphological, physiological and biochemical analysis. The aim of the study was to identify and confirmation of X. campestris pv. campestris in cabbage. The assay of detected X. campestris pv. campestris infections in diseased plants and from bacterial colonies isolated on selective media, and was more sensitive and specific. Among the ten isolates, isolate I6 produced the maximum growth, lesion size and positive growth in different organic and inorganic sources, different biochemical and morphological analysis.