Role of Physiological Parameters on Growth and Sporulation of Septorla Obesa Causing Leaf Spot in Chrysanthemum

Leaf spot (Septoria obesa Synd.) is becoming a serious problem in chrysanthemum cultivation in Himachal Pradesh. The disease was recorded upto 45 per cent in Solan district in 2003–04. The pathogen induced symptoms in 10 days in injured leaves while pycnidia and conidia developed between 17–21 days. Maximum vegetative growth and sporulation occurred on potato dextrose agar in solid phase while in liquid media Sabouraud's and potato dextrose were found equally good in terms of dry mycelial weight and spore production. An optimum temperature of 25°C and 6.0–7.0 pH levels were found effective in supporting growth of the pathogen. Although no spore count were enumerated below 15°C and above 30°C temperatures. The incubation period of 21 days found optimum at temperature of 25°C. With regards to carbon and nitrogen sources dextrose, sucrose, urea and sodium nitrate found best along with three carbon and nitrogen (C:N) ratios. Two substrates glucose (69.75%) and urea (67.50%) and two vitamins thiamine hydrochloride and mesoinsotinol supported 60–61.33% conidial germination whereas in case of amino acids, glycine (72.08%) followed by casein hydroslate (52.92per cent) recorded more germination compared to L-histidine (28.83%). However, germination in both sources increased with increase in time interval.