Isolation and identification of substances from sweet orange Valencia (Citrus sinensis) involved in the stimulation and/or dormancy-breaking of quiescent structures of Colletotrichum acutatum, causal agent of citrus postbloom fruit drop

Author(s)

Simone Cristiane Brand

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2012-02-01

Examining board members

Sergio Florentino Pascholati; Elena Blume; Nelson Sidnei Massola Júnior

• Advisor: Sergio Florentino Pascholati

Abstract

The postbloom fruit drop of citrus (PFDC), caused by Colletotrichum acutatum, induces abscission of young fruits, and it may cause losses up to 100%. The presence of viable inoculum in the form of conidia and/or quiescent appressoria on the plant justifies the widespread occurrence of the disease. Under rain, the PFDC is increased, possibly due to substances washed from different parts of the plant, which contain metabolites that stimulate the development of the fungus. Therefore, we aimed to determine the effect of watery washing (WWs) of flowers, flower buds, old leaves (OL) and young leaves (YL) and the mixture of them on quiescent conidia and hyphae of C. acutatum (isolates 61A and 142) in vitro and in vivo and on the severity of the PFDC, and to identify substances in the WWs, exhibiting the biological activity of interest. In addition, variations in the composition of WWs were determinated. The effect of crude volatile compounds (CVCs) and those identified from Valencia sweet orange (linalool, limonene, myrcene, nonanal and the mixture of them) on the development of the pathogen was also evaluated. All fractions of WWs stimulated spore germination, and the flower WW exhibited the highest effect for both isolates. For quiescent appressoria (isolate 61A), the highest stimulus was observed in treatments with WWs from flower buds and the mixture and for quiescent conidia in the treatment mixture. The highest values for germ tube length were observed on the treatments mixture, YL and flower buds. For the quiescent structures, the effect of WWs was more significant for isolate 142. There was no effect of WWs on the quiescent mycelium. There was stimulation of conidia germination and hyphal branching in vivo in response mainly to treatment with WW from flower buds. The application of the mixture of WW in flowers resulted in higher severity of the PFDC. On the other hand, the CVCs showed inhibitory effect. Exposure of the isolate 61A to the volatiles (VCs) linalool, nonanal and the mixture of them, resulted in germination only at the lowest concentration. The germination on myrcene was similar to control at all doses tested as well as on limonene at doses from 0.005 to 0.25 mL mL-1. All volatiles reduced the length of the germ tube. In the case of isolate 142, a reduction in all variables for all concentration of VCs was observed. There were changes in the composition of WWs based upon times of harvesting, which partly explains the variations observed in the ability to stimulate the structures in some experiments. In flower WWs, we identified the presence of caffeine, the flavonol glycosides hesperidin and naringin, glycosylated compounds and peptides. In the plant parts of sweet orange \'Valencia\' were identified 54 VCs. The WWs have stimulatory effect on quiescent conidia and appressoria of C. acutatum in vitro and in vivo as well as in the severity of the PFDC. The VCs linalool, limonene, myrcene, nonanal and the mixture of them are, in general, inhibitory to the development of C. acutatum. (AU)

• FAPESP's process: 09/13568-0 - Isolation and identification of substances produced by citrus plants involved in the stimulation and/or dormancy breaking of quiescent structures of Colletorichum acutatum, causal agent of citrus postbloom fruit drop.
• Grantee: Simone Cristiane Brand
• Support Opportunities: Scholarships in Brazil - Master