Effect of host extract on growth and sporulation of Cercospora lactucae-sativae Augustus Thomas 1 & Duraisamy Saravanakumar 1 Received: 22 November 2018 /Accepted: 4 July 2019 # Australasian Plant Pathology Society Inc. 2019 Abstract Cercospora lactucae-sativae is a slow growing hemibiotrophic fungus that proves difficult to isolate and sporulate on many growth media. The study focussed on the use of a simple isolation procedure for C. lactucae-sativae and examined the effect of host extract on growth and sporulation of C. lactucae-sativae on PDA and Water Agar. The mean colony diameter was significantly greater than that of the control treatment for WA + LE at 1%, 2% and 4% only, and for all of the LE concentrations on PDA. The mean conidial concentration was significantly different from the control treatment for all concentrations on WA at and above 2% LE, while on PDA there were no significant differences between any of the treatment including the control. PCR has confirmed that the leaf spot disease affecting lettuce cultivation in Trinidad is caused by C. lactucae-sativae. Keywords Cercospora lactucae-sativae . Hemibiotrophic fungus . Lettuce extract . Pure culture Lettuce is one of the most prevalent leafy vegetables produced under open and protected conditions including hydroponics in Trinidad with an annual production of 2810 tonnes (CSO 2015). The cultivation of lettuce is seriously affected by a leaf spot disease incited by Cercospora lactucae-sativae throughout the cropping period. It is prevalent during the rainy as well as dry seasons causing yield losses up to 80%. The common practice of overhead irrigation encourages the spread of conidia. The infection begins on the lower older leaves and progresses to the younger ones. Lesions are light- dark brown, surrounded by a yellow halo and further characterised by a light ash to white coloured dot about size of the pinhole (1 mm wide) in the center of the lesion (Fig. 1 ). The isolation and detection of Cercospora species is difficult due to its slow growth and poor sporulating nature on culture media (Goode and Brown 1970). A single spore technique (Choi et al. 1999) has been reported as more suitable and successful for isolation of slow growing fungi. Further, an amendment of host extract in the media was reported as one of the methods to stimulate sporulation in hemibiotrophic and biotrophic fungi (Jacome et al. 1991; Huerta-Espino et al. 2006). However, the tech- nique has not been standardised for isolation of Cercospora from lettuce. Therefore, the standardisation of isolation and sporulation techniques for Cercospora of lettuce have become necessary to our research team for the characterisation of the pathogen, screening of resistance and development of management practices. Lettuce leaves with the characteristic symptom of cercospora leaf spot were collected from the farmer ’ s field, Orange Grove, Trinidad (10 0 37′15” N, 61 0 22′ 14” W). Lesions with surrounding green tissues 10– 20 mm, were excised from the leaves and surface sterilised in 5% NaOCl for 15 s, then rinsed thoroughly in sterile water. The surface of the leaf sections were dried and transferred to sterile Petri dishes (90 mm) containing filter paper saturated with sterile water. The plates were incubated at 28°C in complete darkness. After four days of incubation, leaf tissue was transferred from the filter paper to 5 mL sterile water and agitated to dislodge conidia from the sample. A drop of the conidial suspension was examined under a microscope to confirm the sole presence of Cercospora conidia. One hundred (100) μL aliquots of the suspension were transferred onto potato dextrose agar (PDA) plates (90 mm) amended with the antibiotic chlortetracycline at 200 mg L -1 and spread evenly with a sterile L- * Duraisamy Saravanakumar duraisamy.saravanakumar@sta.uwi.edu 1 Department of Food Production, Faculty of Food and Agriculture, The University of the West Indies, St. Augustine, Trinidad and Tobago Australasian Plant Disease Notes (2019) 14:19 https://doi.org/10.1007/s13314-019-0353-6