Occurrence of powdery mildew disease of Gerbera in Kerala

Abstract

A purposive sampling survey on the hilly tracts of Wayanad, Kerala revealed the existence ofpowdery mildew disease in gerbera crops, grown under both protected and open field condition.Among the other fungal diseases of gerbera, powdery mildew disease causes decisive damageto the ornamental cut flower crop, thereby decline in the industrial value of the crop. Symptomof the disease include as white powdery mat on the upper surface of leaf lamina that graduallyturned pale yellow to brown. Powdery mildew existed in two locations of Wayanad viz.,Ambalavayal and Chulliyode where highest per cent disease severity (PDS) of 50.72 wasobserved at Chulliyode and 47.2 per cent was observed at Ambalavayal during November-December. In Ambalavayal, the disease was non-significant and no correlation existed betweenweather parameters and disease progress. But, in Chulliyode, correlation studies revealed thatit was significant with positive correlation to relative humidity and a reverse relation existedwith temperature and rainfall. The weather data clearly depicts that at a low rainfall of 96 mmand above average relative humidity of 80.27 per cent during November-December was thecongenial factor influencing the disease development. But during summer, decline in relativehumidity (78.37%) and rainfall (63.13 mm) caused a slight reduction in mean per cent diseaseseverity of 49.12 per cent and 33.6 per cent at Chulliyode and Ambalavayal respectively.Morohological and cultural characters of the pathogen depicts presence of two distinct organismviz., Golovinomyces cichoracearum (Erysiphe cichoracearum) and Podosphaera sp. as thecausative organism of the disease. Golovinomyces cichoracearumproduced hyaline, septatemycelia with globose conidia with irregular peripheral end formed in a chain and Podosphaerasp. produced superficial, hyaline, coenocytic mycelium with oval or ellipsoidal, catenate conidiawith dimension ranging from 22.1-30.18 x 13.36-18.08ìm formed in unbranched erectconidiophores.