EPIDEMIOLOGY AND MANAGEMENT OF CERCOSPORA LEAF SPOT OF PEANUT (ARACHIS HYPOGAEA L.) IN PUNJAB

Abstract

Cercospora leaf spot (CLS) of peanut caused by Cercosporidium personatum (Berk. & M. A. Curtis) Deighton and Cercospora arachidicola Hori is the most important disease in Pakistan. It frequently inflicts colossal yield losses of more than 50% on unsprayed peanuts. CLS of peanut is a potential threat in early monsoon areas of Pothowar region. Keeping in view the economic importance of this disease, the current studies emphasized upon Infection percentage and distribution of the disease in Punjab, influence of weather variables on CLS epidemic on peanut genotypes and management strategies to mitigate the losses caused by the disease. Disease Infection percentage was greater in high rainfall zones of district Attock 87.17 -94.2% and Rawalpindi 74.00 to 82.25%. Early summer rains in low rainfall zones resulted in higher disease Infection percentage (71.62%) when these coincided with early sown crop. Studies on pathogen-environment interaction indicated that higher amount of rainfall, rainfall events and relative humidity in Rawalpindi zone favoured CLS Infection percentage while in Talagang zone these weather variables were less conducive for the disease development. Determination of pathogen species shows Cercosporidum personatum is more significant then Cercospora arachidicola in rainfed regions of Punjab. Cercosporidum personatum isolates have variation for AUDPC, epidemic rate, final severity and sporulation under different environments. Isolates of Cercospora arachidicola and Cercosporidum personatum from Hafizabad in general are more aggressive then isolates from other locations. The variation observed indicates some physiological strains of CLS may be present in the peanut ecosystem. xviInfluence of weather variables on CLS epidemic revealed that monsoon rains making humid thermal ratios (HTR) quite favourable for disease development resulted in significantly higher infection percentage on all genotypes. It was suggested that six fortnight periods from last week of June to mid of September are most critical for the crop as HTR values are likely to remain the most suitable for significant increase in CLS Infection percentage. The model based on days with HTR>3.1 gave a good fit to the data In this model, the onset point of the epidemic was reached 3.5 days with HTR>3.1. Cercospora leaf spot incidence in Chakwal varies from year to year due to environmental conditions. In our model HTR explains most of the observed variation in peanut leaf spot epidemics. HTR>3.1 was best humidity and temperature based weather variable describing peanut leaf spot epidemics. Generally higher disease scores were recorded at late crop growth stages. Peanut genotypes evaluated against CLS under different ecological conditions exhibited variable reaction at different locations and periods depending upon fluctuations of environments. More than 80% germplasm available in the country was Virginia type and late maturing. The germplasm, 20-70% fell under moderately resistant group at flowering stages while at pod development stage 50-80% germplasm became susceptible to CLS. Valencia type plants had lower spots per leaf, sporulation values and reaction indices of spots per leaf X sporulation, spots per leaf X diseased area per leaf and defoliation X spots per leaf, than Virginia and Spanish botanical type plants. Reaction indices of spots per leaf X sporulation can be used for CLS resistance determination for Virginia, Valencia and Spanish botanical peanut types. Crop rotation with non host crops delayed CLS initiation for xvii25-34 and 89-108 days in residual and fallow plots, respectively. 46- 90% variation in peanut yield (Kg/ha) was described by days to disease initiation influenced by change in date of sowing. CLS mitigation by Carbendazim, Benomyl, Mancozeb, Thiophanatemethyl and Mancozeb + Benomyl fungicides significantly reduced CLS Infection percentage at final assessment stage. Peanut genotype BARD-699 was better responsive under protective disease conditions with higher yields than Accession No. 334.