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Assam Agricultural University, Jorhat
Assam Agricultural University is the first institution of its kind in the whole of North-Eastern Region of India. The main goal of this institution is to produce globally competitive human resources in farm sectorand to carry out research in both conventional and frontier areas for production optimization as well as to disseminate the generated technologies as public good for benefitting the food growers/produces and traders involved in the sector while emphasizing on sustainability, equity and overall food security at household level.
Genesis of AAU -
The embryo of the agricultural research in the state of Assam was formed as early as 1897 with the establishment of the Upper Shillong Experimental Farm (now in Meghalaya) just after about a decade of creation of the agricultural department in 1882. However, the seeds of agricultural research in today’s Assam were sown in the dawn of the twentieth century with the establishment of two Rice Experimental Stations, one at Karimganj in Barak valley in 1913 and the other at Titabor in Brahmaputra valley in 1923. Subsequent to these research stations, a number of research stations were established to conduct research on important crops, more specifically, jute, pulses, oilseeds etc. The Assam Agricultural University was established on April 1, 1969 under The Assam Agricultural University Act, 1968’ with the mandate of imparting farm education, conduct research in agriculture and allied sciences and to effectively disseminate technologies so generated. Before establishment of the University, there were altogether 17 research schemes/projects in the state under the Department of Agriculture. By July 1973, all the research projects and 10 experimental farms were transferred by the Government of Assam to the AAU which already inherited the College of Agriculture and its farm at Barbheta, Jorhat and College of Veterinary Sciences at Khanapara, Guwahati.
Subsequently, College of Community Science at Jorhat (1969), College of Fisheries at Raha (1988), Biswanath College of Agriculture at Biswanath Chariali (1988) and Lakhimpur College of Veterinary Science at Joyhing, North Lakhimpur (1988) were established. Presently, the University has three more colleges under its jurisdiction, viz., Sarat Chandra Singha College of Agriculture, Chapar, College of Horticulture, Nalbari & College of Sericulture, Titabar. Similarly, few more regional research stations at Shillongani, Diphu, Gossaigaon, Lakhimpur; and commodity research stations at Kahikuchi, Buralikson, Tinsukia, Kharua, Burnihat and Mandira were added to generate location and crop specific agricultural production packages.
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ThesisItem Open Access STUDY ON INTEGRATED MANAGEMENT OF THE VIRAL DISEASE COMPLEX IN BHUT JOLOKIA (Capsicum chinense Jacq.)(2021) Khaidem, Princy; Kalita, Manoj KumarBhut (Capsicum chinense Jacq.) is one of the important spice crops which is mainly cultivated in the Northeastern region of India. Owing to its traditional importance, pharmaceutical applications, and high commercial value, Bhut Jolokiais getting importance but the production of the crop has been hindering attributable particularly due the infection of a number of viruses. With the growing need for proper management approaches for managing the viruses infecting the crop, a number of management strategies have been studied in the present investigations to manage the viral diseases in Bhut Jolokia. Hot water treatment was given to CMV-infected Bhut Jolokia seeds under different temperature regimes and periods. Thermotherapy was observed to be highly significant in reducing the virus infectivity. Bhut jolokia seeds treated at 50°C for 120 minutes was observed to be the best treatment with minimum disease incidence (26.08%), followed by 55°C for 60 minutes and 55°C for 120 minutes. It was recorded that the virus infectivity gradually reduced at higher temperature with longer exposure period, but, the germination rate was declined. The effect of SAR activating chemicals viz., Salicylic acid (SA), a key signalling molecule triggering plant resistance, and Benzothiadiazole (BTH), an analogue of SA were tested on CMV-infected Bhut Jolokiaseeds to see their effect in the disease incidence. Foliar application of Salicylic acid and Benzothiadiazole at three different concentrations @200, 300 and 400 ppm each was tested where BTH @ 400ppm and SA @ 300 and 400ppm were recorded to be the best among all the treatments displaying less severe symptoms with 55.56 per cent disease reduction over control. Field study was conducted to evaluate the integrated effect of management practices like nursery net cover of seedlings, Benzothiadiazole @ 300 ppm with Biometa @ 5% and neem oil @ 5ml/L; Salicylic acid @ 300 ppm with Biometa @ 5% and neem oil @ 5ml/L; Biometa @ 5% and neem oil @ 5ml/L; Biometa @ 5% and Nuvan @ 1ml/L and sticky traps in different treatment combinations in the management of the viral disease infecting Bhut Jolokia. The plants were observed to be naturally infected by CMV and PVY, ChLCV forming a viral disease complex. DAS-ELISA, RT-PCR, and PCR were used for molecular detection of the viruses. The infected plants exhibited a wide range of symptoms such as severe mosaic, filiform, curling, and crinkling of leaves with a reduction in size, stunted plant growth with bushy appearance, fewer flowers, and deformed fruits were exhibited at later stages of plant growth. Incidence of the viral disease complex of CMV, PVY, and ChLCV ranged from 20.80 to 47.23 percent different treatments. The treatment combination T1 with Net cover of seedlings + Sticky trap +Benzothiadiazole @ 300 ppm at 2-3 leaf stage at 3 days interval for 3 times + Bio-Meta @ 5% at 60, 90 and 120 DAT+ Foliar spray with neem oil @5ml/L at 10 days interval from 30 DAG for 5 times was found to be the most effective treatment by delaying the number of days to the first appearance of symptoms with the lowest disease incidence of 20.80 per cent, maximum yield of 3.22 kg/4.5 m2, and highest benefit-cost ratio of 8.56:1.ThesisItem Open Access Organic management of Pest and Diseases in Potato(2021) Patowary, Debarshi; Saikia, M. K.In the present investigation, efforts have been made to evaluate the comparative efficacy of two different forms of copper fungicides viz., copper oxychloride and copper hydroxide against late blight of potato incited by Phytophthora infestans (Mont.) de Bary under the different spray schedule (10 numbers of sprays at 4 days interval and 8 numbers of sprays at 5 days interval) with a view to select the most effective one for management of the disease. Field experiment performed revealed that both the fungicides could control late blight to a varying extent. Among the fungicides, copper hydroxide proved to be the best in reducing late blight severity. The fungicide could provide highest protection (73.74%) to moderately late blight resistant variety (Kufri Himalini) and 47.23% protection to the susceptible variety (Kufri Jyoti) when applied 10 numbers spray of copper hydroxide @0.2% at 4 days interval. This treatment gave maximum tuber yield 15.73 and 10.26 t/ha in K. Himalini and K. Jyoti respectively. Although maximum net return Rs. 54,200 with a corresponding incremental benefit-cost ratio of 2.25 was recorded in this treatment (10 numbers spray with copper hydroxide @0.2% at 4 days interval) but at the same rate of application the highest B:C ratio (2.41) obtained in the treatment of copper oxy-chloride with a net return of Rs. 43,500. An another study on comparative efficacy of four microbial bioformulations viz., Biometa, Biosona, Biollium and Biogreen against Red ant (Dorylus orientalis Westwood) on potato was evaluated during 2018-2019 and 2019-2020. The formulation, Biosona (combined tuber treatment @6g/kg tuber and soil application with enriched compost @ 2 t/ha) gave highest tuber yield of 11.23 t/ha with a minimum nfestation rate of 15.71% tuber damage and maximum protection (47.02%) against red ant and also gave a satisfactory profit of Rs. 19,700 with a B:C ratio of 1.48. The third investigation was carried out during 2018-2019 and 2019-2020 to evaluate the comparative efficacy of four microbial bio-formulations viz., Biometa, Biosona, Biolium and Biogreen against Aphid (Myzus persicae and Aphis gossypii) on potato. Biolium (Verticilium lecani) @0.5% spray gave highest tuber yield of 10.27 t/ha with a highest protection 33-66 % against aphid. This treatment gave a satisfactory profit of Rs. 10,400 with a B:C ratio of 1.44.ThesisItem Open Access MICROBE BASED MANAGEMENT OF CITRUS CANKER DISEASE vis a vis PREVAILING WEED FLORA(AAU, Jorhat, 2021) Bokotial, Pinkumoni; Nath, Bharat Ch.Citrus canker disease as well the weed flora of citrus grove decrease the quality and quantity of the citrus fruit. An eco-friendly approach for management of Citrus canker disease vis a vis prevailing weed flora was attempted using bioactive microorganisms, Pseudomonas fluorescens and weed pathogens. In the assessment of weed composition, two weeds, Alternanthera philoxeroides and Commelina benghalensis were found to have highest population density of 83% and 25% in the field condition with visible disease symptoms. From the cultural and morphological study of these two isolates, they showed their similarity with Nimbya alternantherae and Colletotrichum siamense. The molecular characterization of these microorganisms was made to determine their distinctiveness from their close relatives through sequencing of ITS region of ribosomal DNA.Interactive action of these two weed pathogen with P. fluorescens resulted in the partial compatibility of P. fluorescens with Nimbya alternantherae and incompatibility reaction in all other possible treatment combinations in vitro. The antagonistic potential of these compatible microbes was tested in vitro singly or in combination and per cent inhibition of target pathogen, Xanthomonas citri pv. citri were recorded and analyzed. Highest inhibition (30.00 %) of X. citri pv. citri was recorded against P. fluorescens and N. alternantherae followed by P. fluorescens (18.52%) in vitro. In the field study, highest citrus canker disease reduction (21.85%) was recorded in the treatment of P. fluorescens followed by treatment comprising of P. fluorescens and N. alternantherae (14.61%). In case of management of Alternantherae philoxeroides weed in field condition, highest percent disease increase (77.49% in manual analysis and 69.98% in AI analysis) was recorded against treatment of N. alternantherae followed by treatment comprising of P. fluorescens and N. alternantherae (41.63% in manual analysis and 45.95% in AI analysis). Correlation studies revealed positive linear relationship between manually and AI analysed data.ThesisItem Open Access Biochemical, histopathological and molecular characterization of sesamum phyllody disease in Assam(2021) Gogoi, Shankar Hemanta; Nath, P. DebThe field of phytoplasma diseases witnessed a new height of systematic study and research works throughout the world. An effort was made for biochemical, histopathological and molecular characterization of the sesamum phyllody disease. Sixteen (16) different alternate hosts were identified by molecular technique and out of that 9 were characterized. Three different groups of phytoplasma viz., aster yellows (16SrI), clover proliferation (16SrVI) and stolbur phytoplasma (16Sr XII) were identified to be associated with the phytoplasma alternate host samples. By using iPhyClassifier tool Brinjal phytoplasma isolate was grouped into the subgroup level 16SrVI-D. Exitinus indicus was detected for phytoplasma presence; characterization was done and it was found that it may play a new role for sesamum phyllody phytoplasma transmission. Ten (10) sesamum cultivars were grown in the field and pot conditions to observe the disease reactions and the cultivars were found moderately resistant (MR) to moderately susceptible (MS). The sesamum phyllody disease was successfully transmitted from infected to healthy sesamum plants by graft transmission (80%). Membrane-bound, phytoplasma-like bodies were detected in Transmission electron microscopy. Total chlorophyll content was reduced by 41.02 per cent in severely infected plants, while in mildly infected plant it was reduced by 28.20 per cent. Ratio between chlorophyll “a” and chlorophyll “b” progressively reduced as a result of infection. The ratio was 1.02 in healthy plants, while it was 1.01 and 0.96 in case of mild infection and severe infection, respectively. Phyllody disease considerably increased the dry matter content in the infected plant. Increase in dry matter content was 12.41 per cent and 19.85 per cent in mildly infected and severely infected plants, respectively. However, no considerable difference in moisture content was observed in both mildly and severely infected plants compared to the healthy ones. Phyllody disease decreased the total nitrogen as well as protein content. The reduction in protein content was 8.50 per cent in mildly infected leaves and 13.29 per cent in severely infected leaves. Phenol content was increased as disease advanced from milder to severe symptoms stage from 2.24 mg/g to 2.68 mg/g, respectively, as compared to healthy leaves i.e., 1.85 mg/g. Molecular characterization of Sesamum phyllody phytoplasma was done from all the agro-climatic zones of Assam and all the phytoplasma isolates were grouped into 16SrI-B. Restriction Fragment Length Analysis (RFLP) was done with three restriction enzymes viz., BamHI, EcoRI and RsaI. Sequence analysis, iPhyClassifier and the comparison between virtual and actual RFLP pattern revealed that there is no genetic difference among the Sesamum phyllody phytoplasma isolates of Assam.ThesisItem Open Access SYNTHESIS OF NANOPARTICLE FROM BIORESOURCES FOR MANAGEMENT OF BLAST DISEASES OF RICE(2021) Kaman, Pranjal Kumar; Bhattacharyya, AshokDevelopment of reliable and eco-friendly process for synthesis of metallic nanoparticle is an important steps in the field of nanotechnology. An effort was made for biosynthesis of gold nanoparticles from bioresources like microbes Aspergillus niger, Metarhizium anisopliae, Lecanicillium lecannii, Purpeurocillium lilacinus and botanicals like Ocimum gratissimum, Acorus calamus, Aloe barbadensis and Azadirachta indica. Chloroauric acid was added as precursor for the synthesis of gold nanoparticles. Study on in vitro efficacy of biosynthesized gold nanoparticle from bioresources was tested at hundred percent concentration against Magnaporthe grisea and effective source was found to be Metarhizium anisopliae and Ocimum gratissimum. Further efficacy of biosynthesized gold nanoparticle from Metarhizium anisopliae and Ocimum gratissimum. was tested against Magnaporthe grisea at three different concentrations (50, 100 and 150ppm) comparison was made with Tryclozole @ 600 ppm. The result showed that the gold nanoparticles at 150 ppm significantly inhibit the mycelia growth of the pathogens as compared to the Tryclozole @ 600 ppm. The effective biosynthesized gold nanoparticles was characterized by UV-Vis spectrophotometer, Dynamic Light Scattering (DLS), Fourier transform infrared spectrometer (FTIR), Zeta Sizer and Transmission Electron Microscope (TEM). Formation of gold nanoparticles were confirmed by UV-VIS spectroscopy study with absorption peaks at 550 nm. FTIR study showed that synthesized gold nanoparticle has all the required functional groups like OH, N-H, C-H and COO-. Study on surface properties of nanoparticles by using zetasizer resulted that gold nanoparticle from Metarhizium anisopliae was found to be negative and were stable in nature with zeta potential value of -20.7 mV. DLS analysis showed that the average size of the biosynthesized gold nanoparticles is 32.54 nm with polydispersity index of 0.560. TEM study showed that shape of the biosynthesized nanoparticle is from triangular to quasihedral and the size range from 9-54nm. Again, a pot experiment was conducted for studying its effect on morphophysiology as well as soil physico chemical and biological properties by different methods of application like seedling dip treatment, foliar spray and soil application. A positive effect was found on the morphology, soil physico chemical and biological properties when rice seedling was treated as seedling dip treatmen + foliar spray + Soil application @ 150ppm.ThesisItem Open Access Development of mapping population and use of SSR markers for breeding disease resistance against Tomato leaf curl virus (ToLCV)(2021) Oladokun, John Oladeji; Nath, P. D.Tomato leaf curl disease (ToLCD) caused by the tomato leaf curl virus (ToLCV) has been a serious threat to tomato crops for decades and breeding genotypes resistant to ToLCD is a sustainable management option. An open field screening was conducted in an augmented design between 2018 and 2019 which was aimed at identifying resistance in 39 tomato genotypes, and developing mapping populations for genetic and inheritance trait analysis in the population. Symptoms associated with ToLCV were recorded, importantly leaf curls incidence alone accounted for 53% (in single infection). The highly resistant genotypes are EC164563, 171, EC520078-B, EC165690, IIHR 2904, H24, S. pimpinellifolium, IIHR 2871, IIHR 2862, EC157568, EC521067-B, and IIHR 2867 with incidence ranging between 8.3-18.2% ± 12.3. The S. pimpinellifolium was selected for further studies. There was a significant relationship between whitefly population × minimum temperature (r = -0.973, P=0.05), whitefly population × relative humidity (r = -0.996, P=0.05) and whitefly population × average disease incidence (r =0.996, P=0.05). Out of 60 symptomatic and asymptomatic bulked leaf samples tested by PCR with six different primers targeting different components of the genome, only 32 (53.3%) were confirmed to be ToLCV infected. The nucleotides of sequence Jorhat isolates of the DNA-β satellite component of ToLCV (accession number: MZ2962423, MZ2962424, MZ2962425) similarity identity falls between 99.4 to 99.5 % with ToLCBDB (accession number AJ542489) and a closed cluster with two ToLCBDB isolates (AJ542489 – tomato, MN985116 – country bean) in the phylogenetic tree. One hundred and twenty (120) SSR markers were screened for parental polymorphism check between Pusa Ruby (susceptible) and S. pimpinellifolium AAU2019 (resistant), only 11/120 were polymorphic while 109 /120 were monomorphic. In the cross of Pusa Ruby × S. pimpinellifolium AAU2019 and other generations F2 (self-pollinated F1), and B1F1 or BCs, developed and screened for ToLCV infection in the field, disease incidence was lowest in S. pimpinellifolium AAU2019 (7.3 %) followed by F2 (33.3%) but higher in Pusa Ruby (91.3%) when genetic control in S. pimpinellifolium AAU2019 was studied. Using a co-dominant marker (SSR 63), the inheritance and genetic analysis study of resistance to ToLCV in an interspecific cross (Pusa Ruby × S. pimpinellifolium AAU2019) in different mapping populations by SSR63 molecular marker revealed a monogenic recessive (best-fit ratios 3:1, 1:1) nature of ToLCV resistance. Progenies of F2, and B1F1 or BCs generations tested for ToLCV DNA varied in terms of the intensity on resolve in gel electrophoresis using the same DNA concentration and compared to Pusa Ruby with higher intensity and not in S. pimpinellifolium AAU2019. However, the type of resistance derived and inherited from S. pimpinellifolium AAU2019 is assumed to be controlled by a single gene in a recessive state and it is neither fixed nor dominant. This is based on the genotypic segregating pattern, responses of the generations developed to ToLCV infection. Hence, this study provides the potential of S. pimpinellifolium AAU2019 as an alternative breeding source for developing resistant cultivars against ToLCV.ThesisItem Open Access IDENTIFICATION, CHARACTERIZATION AND MANAGEMENT OF PUMPKIN MOSAIC DISEASE(AAU, Jorhat, 2021) Gogoi, Kulumanali; Mishra, RanimaThe present investigation was conducted for identification, characterization and management of pumpkin mosaic disease in Assam. A roving survey was conducted during 2019-2021 in Jorhat, Golaghat, Karbi Anglong, Biswanath Chariali and Charaideo to determine the disease incidence through symptomatology, vector population count and detection of the viruses associated with mosaic disease of pumpkin through serodiagnostic (DAS-ELISA) and molecular assay (PCR and RT-PCR). Symptomatology revealed various degrees of mosaic, mottling, vein clearing, vein banding, chlorosis, leaf distortion, small, crinkled, deformed leaves and malformed fruits with mosaic and chlorotic spots resulting in reduced yield and production. Serological detection through DAS-ELISA confirmed the association of Cucumber mosaic virus (CMV) in CMV suspected pumpkin samples. The DAS-ELISA assay revealed disease incidence of 52.38 per cent in Golaghat district and 35.71 per cent in Jorhat district. Two different types of aphid vectors viz., Aphis gossypii and Myzus persicae were observed in all the surveyed locations. Total genomic RNA extracted from symptomatic and asymptomatic pumpkin plants were subjected to RT-PCR assays using CMV, zucchini yellow mosaic virus (ZYMV) and watermelon mosaic virus (WMV) specific primers and Deng universal primer for detection of begomovirus viz., pumpkin yellow vein mosaic virus (PYVMV). RT-PCR assay revealed the presence of CMV in the samples which yielded the desired amplicon size of 593 bp. No amplification was obtained from the samples for ZYMV and WMV. PCR product of CMV infected sample from Jorhat district viz., CMV-CP Jorhat isolate was sequenced and compared with the known CMV isolates worldwide using nucleotide BLAST programme at National Centre for Bio Informatics (NCBI) and Mega X software. The sequence similarity of CMV-CP Jorhat isolate ranged from 93.11 per cent to 99.16 per cent with worldwide CMV isolates. A field experiment was conducted for management of pumpkin mosaic disease through integrated approach. It was evident from the field experiment that there was low disease incidence with low vector population as well as high yield in the treatments of hot water seed treatment at 50⁰C for 10 minutes and spraying of neem formulation @3ml/lit at 15, 30, 45 and 60 days after transplanting (T1) followed by hot water seed treatment at 50⁰C for 10 minutes and spraying of Imidacloprid @2ml/lit at 15, 30, 45 and 60 days after transplanting (T6) than the other treatments with the highest yield (80.00 q/ha) recorded for the treatment T1 with highest per cent reduction of disease over control (53.22 per cent).ThesisItem Open Access EVALUATION OF CITRUS CULTIVARS/GERMPLASMS OF ASSAM AGAINST CITRUS CANKER DISEASE(AAU, Jorhat, 2021) Kaushik, Snata; Nath, Bharat Ch.Evaluation of different citrus cultivars/germplasms against citrus canker disease in artificially inoculated conditions and their assessment for defense-related secondary metabolites, viz., total phenol, flavonoid, alkaloid content was attempted in the present study. For artificial inoculation, bacterial pathogen associated with diseased citrus canker leaf was isolated, purified, and further confirmed as Xanthomonas citri pv. citri by conducting morphological, cultural, gram staining, specific biochemical tests, and molecular characterization. Altogether thirty cultivars/ germplasms were tested for their degree of resistance against citrus canker (X citri pv. citri). All these cultivars/ germplasms showed significant differences in terms of percent disease severity and disease reaction. Out of thirty, eight cultivars/germplasms namely Jora tenga (14.67%), Bonjora (15.58%), Holong tenga (15.75%), Patijora (17.75%), Birajora (18.50%), Cleopatra mandarin (20.00%), Latipes (17.34%) and Ada jamir (20.18%) exhibited resistance response (R). Moderate degree of susceptibility (MS) was observed in fourteen cultivars/germplasms viz., Trifoliate orange (25.63%), Troyer citrange (26.87%), Rubidoux (30.37%), NRCC6 (36.58%), Bhutan orange (31.06%), Galgal (38.42%), Sopai (39.70%), Rangpur lime (43.30%), Soh bitara (30.27%) Sohmyndong (46.57%), Pummelo-1(31.34%), Pummelo-2 (28.38%), Pummelo-3(38.48%), Pummelo- 7(43.31%). Seven cultivars/germplasms namely Nainty jambhiri (52.56%), Australian orange (56.32%), Rough lemon (57.54%), Volkameriana (60.34%), White pummelo (61.64%), Acid lime (62.48%) and Grape fruit (70.63%) were categorized as susceptible types (S) while Assam lemon showed the highest degree of susceptibility (HS) against citrus cankerwith 78.14% disease severity. Further study on secondary metabolites revealed that total phenol, flavonoid, alkaloid content in citrus leaves differed greatly based on the cultivars/germplasms. The highest total phenol content (TPC) was found in one of the resistant germplasm Latipes (21.26 mg/g dry weight), while the lowest was recorded in susceptible cultivar Grapefruit (7.85 mg/g dry weight). Another resistant germplasm Jora tenga (6.47 mg/g dry weight) had the highest flavonoid content and the lowest was found in susceptible germplasm White pummelo (1.89 mg/g dry weight). Similarly, the highest alkaloid percentage was found in resistant germplasm Adajamir (10.52%) and the lowest was recorded in susceptible germplasm Volkameriana (2.30%). From the correlation analysis, three negative correlation coefficient was obtained viz.,P(rxy)= -0.861 for total phenol content, F(rxy)= -0.836 for flavonoid content and A(rxy)= -0.802 for alkaloid content.ThesisItem Open Access CULTURAL, MORPHOLOGICAL AND MOLECULAR VARIABILITY AMONG ISOLATES OF Rhizoctonia solani CAUSING WEB BLIGHT OF GREEN GRAM (Vigna radiata (L.) WILCZEK)(AAU, Jorhat, 2021) Mohana, Pradeep R K; Sharma, SupriyaWeb blight of green gram is one of the major constraints which incur huge losses and hold back the production of green gram in Assam. A comprehensive study was made during 2020-21 on the variability of Rhizoctonia solani isolates based on morpho- cultural characteristics and molecular variation. Web blight infected plants were collected from different geographical locations was designated as SH-1, SH-2, AAU-1, TT-1, and MJ- 1 and identified based on a typical character with right angle branching near the distal septum of the young vegetative hyphae. A high virulence pattern for all the isolates was recorded based on pre-emergence seedling rot and complete leaf blighting appearance within 48 hours of inoculation in susceptible cultivar (SGC-16). All the five isolates showed variation in morpho-cultural characteristics such as colony growth diameter, colony texture, concentric rings on radial growth, colony color, growth pattern, hyphal width, distribution pattern of sclerotia, sclerotial initiation, maturation, color, aggregation, exudate droplets on sclerotial surface, position of sclerotia and sclerotia on lid, sclerotial diameter, number and weight in different growth media Potato Dextrose Agar (PDA), Rose Bengal Agar (RBA), Richard’s Agar (RA), Czapeck’s Dox Agar (CDA) and Sabouraud Dextrose Agar (SDA) where most of the isolates were categorized into three and four groups based on hyphal width and sclerotial initiation respectively. The size, number, and weight of sclerotia were highly variable across different isolates concerning media. They are arranged in the central, central- peripheral, sub-central, sub-central peripheral, peripheral and scattered manner on the petri- dish with respect to media. Among different media, Sabouraud Dextrose Agar medium (85.85%) is the best growth media to study morpho-cultural variability with quantitative variables like sclerotial maturation and initiation which directly correlated with virulence of our R. solani isolates based on principal component analysis. There is no evidence of molecular variability among our isolates from different geographical locations of Assam.
