Effect of nitrogen, phosphorus and potassium nutrition on incidence and intensity of grey blight of coconut

Abstract

The investigation on the "Effect of nitrogen, phosphorus and potassium on incidence and intensity of grey blight of coconut" was conducted during 2001-2002 at the Coconut Research Station, Balararnapuram, Thiruvananthapurarn, Kerala. The coconut palms cultivated in the Permanent Manurial Trial experimental plot of the station was used for the studies. The pathogen was isolated from the infected leaf tissue by the standard tissue isolation technique. Cultural and morphological studies confirmed the identify of the pathogen as Pestalotiopsis palmarum (Cooke) Stey. Among the different artificial media tried potato dextrose and sucrose were the best for growth and sporulation of the pathogen. Conidial morphology of fungus was studied on six media. The fungus produced largest conidia and appendages on PDA and PSA, while those produced on PDA had the maximum breadth. The maximum incidence and intensity of grey blight was observed in the month of August. During the subsequent months it declined and the least was observed in February . . The incidence and intensity of the disease was correlated with different levels of NPK fertilizer application and nutrition status of palms. Higher rate of nitrogen, phosphorus and potash application in soil resulted in higher rate of these nutrients in the leaf samples and higher rate of the disease. The disease intensity was maximum In palms supplied with the treatment combination N )P2K2 and minimum in N2P2Ko. The highest disease incidence and intensity were observed when the relative humidity was above 83 per cent. The maximum temperature at this period was 29.7oC and the minimum temperature 20.7()C. The rainfall

during this period was 243.3 mm. These weather parameters were observed during the month of August. The lowest disease incidence and intensity was observed when the relative humidity was 77.2 per cent. The maximum temperature was 31.4°C and minimum temperature 22.3°C. Rainfall during this period was 15 mm. These weather parameters were recorded during the month of February. There was a positive correlation on the incidence and intensity of grey blight with rainfall, relative humidity and wind speed where as a negative correlation was observed with temperature. Nutrient composition of the healthy leaf tissue indicated that with an increase in the nitrogen level, there was a corresponding increase in the nutrient status of major, secondary and micronutrients. A similar trend was noticed with phosphorus and potassium also. However, with increase in potassium level there was a corresponding decrease in the magnesium content. Similarly with an increase in phosphorus a decrease in zinc and boron content was observed both in healthy and diseased leaf tissues. Both in two way and three way interactions, involving NP, NK, PK and NPK the composition of nutrients of healthy as well as in diseased leaves increased with increase in the levels of nitrogen, phosphorus and potassium. Chlorophyll, total sugar, amino acid and phenol contents in healthy tissues were found to be high with higher levels of fertilizer application.