B. SREE LAKSHMIBANDI MOHAN VENKATA SIVAPRASAD2023-12-072023-12-072023-12-07D6439https://krishikosh.egranth.ac.in/handle/1/5810202365In the present investigation on “Characterization and management of emerging pathogen, Corynespora on cotton”, during kharif, 2019-20 & 2020-21 survey in five major cotton growing districts of A.P. revealed PDI of Corynespora target spot ranged from 26.8% to 50.9% and 19.6% to 37.5% in kharif, 2019-2020 and 2020-2021, respectively. Pure cultures of 21 isolates showed considerable variation in cultural characters such as texture, shape of the colony, colony elevation, growth habit, nature of mycelium, number of concentric rings, pigmentation on top of culture plate, pigmentation at bottom of culture plate and morphological characters such as conidial length, width and number of pseudo septa. Based on the characters studied, 21 test isolates were categorized into different groups. The incubation period varied from 4 to 6 days. Among all the isolates, CPIK-1909 isolate was found highly virulent with low incubation period (4 days) resulting in more lesions (42.40±3.34) and highest PDI (50.50). Multivariate analysis used for cultural, morphological and pathogenic characters revealed formation of six clusters based on Euclidean distance values. Characterization of 21 Corynespora cassiicola isolates was performed using ITS 1 and ITS 4 primers. PCR amplification using ITS region resulted in an amplicon of 550 bp. Sequences of six isolates (CGGL-19001, CGGG-19004, CPIK-19009, CKGV-19011, CYPP-19016 and CKDR-19018) were deposited in NCBI (MZ314930, 29, 28, 27, 25 and 26). Molecular variability was determined for the 21 test isolates using four RAPD primers which resulted in a total of 47 bands with polymorphism having band size ranged from 300 to 2500bp. Dendrogram obtained had two clusters (PL1 and PL2), PL1 consisted of single isolate (CYPG-19017) and PL2 consisted remaining 20 isolates. xx Pooled analysis of two seasons (kharif, 2019-2020 and 2020-2021) showed that PDI of Corynespora target spot was significantly and positively correlated with Tmax, Tmin, RF and WS and expressed negative correlation with SSH and Evap. Regression studies revealed that Tmax, Tmin, RHII and Rd influenced the Corynespora target spot in cotton upto 96.5%. Step up and step down regression analysis indicated that individually Tmax, Tmin, RF, SSH, WS and Evap. influenced up to 56.0, 51.6, 25.1, 48.0, 42.5 and 35.0% respectively. Pooled analysis for yield loss estimation (kharif, 2019-2020 and 2020-2021) revealed 26% of yield loss if management practices were unattended. Minimum of four sprays of propiconazole @ 0.1% were required to nullify the loss in yield (24%) due to cotton Corynespora target spot depending on weather conditions. PDC and yield showed positive correlation with number of sprays whereas PDI was negatively correlated with number of sprays. Yield and avoidable yield loss negatively correlated with number of sprays. The test pathogen, Corynespora was found to be both externally and internally seed borne. Among the externally seed borne mycoflora, Corynespora and Aspergillus spp. were associated with cotton seeds. In case of internally seed borne association, Corynespora ranged from 2 to 18% and showed higher association than other fungi. The seed mycoflora of cotton exhibited different distribution pattern among which, Corynespora and Aspergillus exhibited highest colonizing frequency (CF) and Isolation recovery (IR) in case of externally seed borne infection. In case of internally seed borne infection, CF and IR of Corynespora was found to be the highest among all the fungi observed. For externally seed borne mycoflora, the highest Simpson’s diversity index (DI=0.826), Shannon – Wiener diversity index (H’=1.846), species richness (1.219) and Species evenness (0.949) were recorded in samples of Jaadoo BG II. For internally seed borne fungi, highest DI of 0.794 was in LHDP-1 followed by NDLA-2463 (DI=0.792) having highest H’ (1.657) with Species richness (1.429) and Species evenness (0.851). Based on in vitro poisoned food technique, dual culture and detached leaf technique studies, propiconazole, carbendazim+mancozeb, four biocontrol agents (T18001, PF1, BS2 and ACT1) and salicylic acid @ 5 mM were utilized for field studies. Pooled data for management studies (kharif, 2019 and 2020) showed lowest disease severity in foliar spray with propiconazole at 0.1% (12.4 PDI), highest yield (2931.7 kg ha-1) and BC ratio 1.46 was found on par with carbendazim+mancozeb at 0.1% (13.9 PDI, 2851.1 kg ha-1 and 1.42) and significantly superior to other treatments as against control (27.3 PDI, 2265.6 kg ha-1 and 1.13) respectively.EnglishThesis