Detached Leaf Test for Evaluation of Resistance to Powdery Mildew in Pepper

Abstract

Powdery mildew caused by Leveillula taurica (Lév) G. Arn. is a quite serious disease of pepper varieties (Capsicum spp.) worldwide. The use of resistant genotypes can control the disease. Tests of resistance against powdery mildew during pepper breeding studies have been carried out by directly brushing the conidia or spraying a conidia suspension on whole potted plants grown in the greenhouse. High amounts of inoculum, labour and large experimental areas are needed for these tests. The aim of this study was to investigate the possibility of using detached leaves for resistance evaluation. Detached leaves of a sensitive cultivar (Moonset F1) were placed on two different media (water agar and moistened filter paper) in petri dishes, were inoculated using three different methods (direct brushing conidia, spraying conidia suspension in distilled water, and in sterile distilled water). Inoculated leaves were incubated under two different conditions (16 °C for 24h in dark, then 22 °C for 14 h light/10 h dark, and 21 °C for 12 h light/12h dark) in a climatically controlled room. The methods were combined with each other. The combination of water agar and moistened filter paper with inoculation by brushing conidia and spraying conidia suspension in distilled water at the second incubation condition gave infected leaf areas of 50% or more with powdery mildew at 25 day after inoculation. The authors suggest that detached leaves might be very practical to assess the resistance of pepper lines against to powdery mildew disease for breeding programmes.

Novel sources of resistance to powdery mildew (Leveillula taurica (Lév.) Arnaud) in pepper

“…For instance, some C. annuum L. commercial accessions have showed better responses against the infection in young plants (de Souza and Café-Filho, 2003). Three main inoculation techniques are commonly used: i) natural infection, ii) artificial inoculation by directly brushing conidia on leaves; iii) spraying conidia suspensions of variable concentration (10 5 -2.5 × 10 4 ml -1 ) with Triton X 100 1µl ml -1 (Molot et al, 1990;Daubeze et al, 1995;Zheng et al, 2013;Albert et al, 2017;Özer et al, 2018;McCoy and Bosland, 2019). Controlled screenings have been performed using a wide range of temperatures (16-27 °C, Molot et al, 1987;Zheng et al, 2013), humidity (30-70% ± 15 RH, Bai et al, 2003;Zheng et al, 2012) and photoperiod (12-14 h light and 12-10 h dark, Molot et al, 1987;Özer et al, 2018).…”