In vitro inhibitory activity of antimicrobial peptides cecropin, α-thionin DB4, and γ-thionin RsAFP1 against several pathogens of strawberry and highbush blueberry

Abstract

As part of a program to develop transgenic highbush blueberry (Vaccinium corymbosum L.) and strawberry (Fragaria 'xananassa Duchesne) cultivars with increased levels of disease resistance, we have investigated the feasibility of introducing genes for the antimicrobial peptides cecropin B and MB39, α-thionin BB4 (DB4) and γ-thionin RsAFP1 (RsAFP1) by testing the effects of these peptides on several important pathogens of these two crop species. A thin-layer plate bioassay was conducted with these peptides and the pathogens Botrytis cinerea (Pers.ex. Fr.), Botryosphaeria dothidea (Mouq.ex. Fr.) Ces & de Not., Colletotrichum acutatum Simmonds, C. gloeosporioides (Penz.) Penz.et Sacc., C. fragariae Brooks, Monilinia vaccinii-corymbosi Reade (Honey), Phytophthora fragariae Hickman and Xanthomonas fragariae Kennedy and King. The minimum lethal concentration (μM) for cecropin ranged from 0.02 for X. fragariae strains 10 and 128 to 72.8 for C. gloeosporioides isolate Akp1. For DB4, the minimum inhibitory concentration (μM) ranged from 0.03 for X. fragariae strain 6 to 87.2 for B. cinerea isolate cc. For RsAFP1, the minimum inhibitory concentration (μM) ranged from 0.13 for X. fragariae strain 6 to 61.4 for M. vaccinii-corymbosi isolate 9423-X-45. These results indicate that introducing genes for either cecropin, DB4 or RsAFP1 into strawberry may be useful for controlling bacterial angular leaf spot disease caused by X. fragariae.