P. ANIL KUMARDASU RAMA SRI VINEELA2023-12-072023-12-072023-12-07D6442https://krishikosh.egranth.ac.in/handle/1/5810202369The present investigation on "Role of mineral nutrition in groundnut late leaf spot disease management" was carried out at the Department of Plant Pathology and College farm, Agricultural College, Bapatla during 2019-20 and 2020-21. In the present investigation, plant and pathogen traits governing groundnut late leaf spot disease were assessed by growing susceptible cultivar (K-6) and tolerant cultivar (Kadiri Harithandhra) in sand culture and artificially inoculated with P. personata. The data obtained indicated that prolonged latent period (17 days) and less number of lesions (28.6/leaf), smaller lesion size (1.7 mm) and increased anti-oxidant enzyme activity (SOD, POD and CAT) might have resulted in decrease in turn chlorophyll senescence/ loss (28.80%) due to pathogen which accounted for tolerance in Kadiri Harithandhra compared to susceptible K-6 (latent period:14 days, lesion number: 57/leaf, lesion diameter: 2.5mm, decrease in chlorophyll content: 39.63%). Thus, these pathogenic and plant traits were used to assess role of mineral nutrition in incorporating tolerance to LLS susceptible variety i.e., K-6. Direct effect of nutrients on P. personata conidia revealed that lack of majority of nutrients except P and Ca had no direct effect on P. personata conidial germination (61.73% and 66.20%) and number of germ tubes (1.22) respectively. However, germ tube length was greatly enhanced in K and Mg deficient solutions while in Zn and N deficient solution, the same was decreased. Deficiency of nutrients especially K, Mg, S, Cu aggravated the disease by encouraging pathogen through decreased incubation (4,4,5 and 7 days respectively) and latent periods (8, 8, 7.33 and 11 days respectively), increased lesion number (22.00, 21.67, 22.33, 14.67/leaf respectively) and lesion diameter (2.83, 2.73, 3.03 and 2.70 mm) thus higher AUDPC values (19.33, 24.67, 32.00 and 10.67) compared to control (7 days incubation period, 11 days latent period, 8.33 lesions/leaf with xvi lesion diameter 2.70 mm and AUDPC value 6.67) which further impaired chlorophyll content (0.98, 0.73, 0.66, 0.74mg/g against 0.97 mg/g in control) and anti-oxidant enzyme activity which act as primary defence mechanism in scavenging reactive oxygen species during hemibiotropic pathogen infection. Visual deficiency symptoms and nutrient content in leaves further confirmed the role of nutrient deficiencies in aggravating LLS disease and hence effect of supplementation of these nutrients K, Mg, Cu and S in managing LLS were studied. CuSO4 twice the strength had similar affect as fungicidal check (6.33 and 9.67 days) in delaying incubation (6.33 days) and latent periods (8.67 days) while KNO3 thrice the strength, MgSO4 thrice the strength has similar effect as fungicidal check (2.00/ leaf and 1.00 mm) with respect to lesion number (3.00/leaf) and lesion diameter (1.00 mm) resulting in lesser AUDPC values as fungicidal check compared to absolute control (4 days incubation period, 7.33 days latent period, 10.33 lesions/leaf, 2.50 mm diameter). SOD and POD enzyme activities showed similar trend corresponding to incubation period and latent period when comparing antioxidant enzyme activity of nutrient supplemented treatments and fungicidal check with tolerant cultivar indicating that adequate amount of nutrient supplementation to plants offers tolerance to fungal infection through altered antioxidant enzyme activity. Supplementation of CuSO4 and MgSO4 were effective in reducing disease when applied through soil during initial stages by prolonging incubation (13.67 days and 13.33 days) and latent period (8.33 and 8.67 days) but with increase in age of the crop, foliar sprays were found more effective in reducing lesion number (2.67/ leaf, 4.00/leaf) with lesser diameter and AUDPC as fungicidal check (13.67 days incubation period, 9.67 days latent period, 2.00 lesions/leaf with 1.00 mm diameter). CuSO4 and combination of four nutrients were effective in delaying incubation (11.67 days, 12.33 days) and latent period (16.67 days, 17.00 days) while MgSO4 followed by combination of four nutrients were effective in reducing lesion number (17.65/leaf, 22.15/leaf) and diameter (0.20 and 0.27 mm) thereby reduction in AUDPC values. Nutrient supplementation, though inferior to fungicidal check (14 days, 18.33 days, 1.95 lesions/leaf with 0.22), was significantly superior than absolute control in reducing disease (10.33 days incubation period, 13.67 days latent period, 70.15 lesions/leaf with 0.33mm diameter). Nutrient solutions of S at 0.5%, K2SO4 at 0.5% and CuSO4 at 0.2% had inhibitory effect on conidial germination while combination of nutrients reduced germination percentage (4.53%) and germ tube length. Pooled analysis of the field experiments conducted during rabi and summer 2020-21 revealed that Cu+S and K+Cu+Mg+S were effective with least LLS incidence (54.58% and 54.97%) and were on par with fungicidal check (47.77%). Further, Cu+S supplementation results in higher pod yield (1766.67 kg/ha) with highest rate of returns (3.16) and found superior to fungicidal check (1572.22 kg/ha and 2.60).EnglishThesis