ETIOLOGY, EPIDEMIOLOGY AND MANAGEMENT OF CHRYSANTHEMUM FLOWER BLIGHT
Acharya N G Ranga Agricultural University
The present investigation entitled “Etiology, epidemiology and management of chrysanthemum flower blight” was carried out to assess the prevalence of the disease and further characterization. Disease dynamics during 2019-21 revealed that it is an important emerging disease both under protected and open filed conditions of Andhra Pradesh. Maximum per cent disease incidence (48.40 %) and severity (28.28 %) was recorded in East Godavari followed by Chittoor and Visakhapatnam districts. Predominant pathogen was Ectophoma multirostrata along with occurrence of Stemphylium lycopersici, Botrytis cinerea, Alternaria alternata, Colletotrichum gloeosporoides and Lasiodiplodia theobroame. Pathogenicity of the six pathogens was proved on chrysanthemum cultivar New Man and twelve isolates of Ectophoma were characterized morphologically and molecularly. Ectophoma culture was greenish grey initially with floccose to felty appearance and later became dark brown or black with appressed texture on potato dextrose agar. It produced dark brown to black, globose or irregular, solitary or aggregated pycnidia that were partly or fully submerged in the media. Conidia were hyaline, single celled, mostly oblong to ellipsoid and guttulate. Pycnidial length and width of population varied between 89.67 and 132.98 μm and from 60.56 to 89.68 μm respectively. Mean conidial length of population was 4.00±0.24 μm and conidial width of population ranged between 1.00 and 2.90 μm. Pathological and morphological characters contributed significantly to study the divergence of isolates when compared to cultural characters. Incubation period (5.33 to 8.33 days) and lesion length (7.67 to 38.33 mm) among the isolates in detached xix leaf assay correlated with the incubation period and disease severity in pot experiment (1.00 to 2.67 days and 17.67 to 65.67 PDI respectively). Based on different characters studied, the multivariate analysis revealed grouping the twelve isolates in to four clusters. Simple sequence repeat (SSR) primer based diversity analysis showed that the Ectophoma isolates, VSPPM3 and VSPPM4 from Visakhapatnam were closely related with 96 per cent similarity whereas VSPPM3 from Visakhapatnam and EGPM3 from East Godavari were distantly related with only fifty per cent similarity. Isolates were grouped irrespective of their geographical region based on clustering by Tocher’s and SSR analysis. The most virulent isolate, EGPM1 was characterized molecularly by sequencing and Phylogenetic trees constructed based on ITS region and actin gene sequences showed 92 to 100 per cent similarity with Ectophoma multirostrata. The ITS sequence of EGPM1 (EGPM19-1) was submitted and obtained NCBI unique accession number, ON819852. Correlation studies between disease parameters of chrysanthemum and weather parameters during 2019-20 and 2020-21 revealed that disease incidence and severity were significantly and negatively correlated with maximum temperature, minimum temperature, morning relative humidity and evaporation during first and second dates of planting. In vitro fungicide assays were conducted with selected fungicides, against the six pathogens isolated where complete inhibition of E. multirostrata, B. cinerea, A. alternata and C. gloeosporoides was observed with difenoconazole while mancozeb completely inhibited S. lycopersici and L. theobromae. Under field conditions two years pooled data revealed that two sprays of difenoconazole @ 0.1 per cent was significantly superior over other treatments with 40.00, 76.67 % disease incidence, 2.17, 7.64 % of disease severity on flowers and 3.52, 4.28 % of disease severity on leaves respectively at five and 15 days after second spray. It was also observed with the highest yield (6.87 kg plot-1; 7.63 t ha-1), highest B: C ratio (2.06) and highest shelf life period of flowers (4.83 days, 10.33 days at room temperature and 4 0C respectively).