Persistent Calyxes in Postbloom Fruit Drop: A Microscopy and Microanalysis Perspective

Author(s)

Rodrigues Marques, Joao Paulo ^[1] ; Sposito, Marcel Bellato ^[2] ; Amorim, Lilian ^[2] ; Montanha, Gabriel Sgarbiero ^[1] ; Silva Junior, Geraldo Jose ^[3] ; Pereira de Carvalho, Hudson Wallace ^[1] ; Appezzato-da-Gloria, Beatriz ^[2]

Affiliation

^[1] Univ Sao Paulo, Ctr Nucl Energy Agr, BR-13400970 Piracicaba - Brazil

^[2] Univ Sao Paulo, Luiz de Queiroz Coll Agr, BR-13418900 Piracicaba - Brazil

^[3] Brazilian Fund Citrus Protect, BR-14807040 Araraquara, SP - Brazil

• Document type: Journal article
• Source: PATHOGENS; v. 9, n. 4 APR 2020.
• Web of Science Citations: 0

Abstract

Citrus postbloom fruit drop, caused by Colletotrichum spp., is an important disease in the Americas. The pathogen infects citrus flowers, produces orange-brown lesions on petals, and may cause the abscission of young fruit. In diseased flowers, the calyxes remain attached to the peduncle after the young fruit drop. No anatomical and microanalysis studies have been conducted to determine whether calyx tissues can be infected by Colletotrichum spp. and why calyxes remain attached to the peduncle. Based on light microscopy, we demonstrate that the ovary abscission zone exhibits a separation region composed of layers of thickened lignified walled cells, indicating that abscission involves the disruption of cell walls. The first layers of the protective zone (PZ) are composed of densely packed cells with suberized walls produced by the wound meristem. Beneath the PZ, there is a compact mass of small cells that accumulate starch grains. X-ray fluorescence microanalysis (mu-XRF) confirmed the increased accumulation of calcium in the receptacle of the persistent calyxes compared to non-inoculated citrus flowers. Moreover, the peduncle pith and the receptacle exhibit hypertrophied cells with thick walls that may be related to calyx retention. Fungal structures are not observed inside the persistent calyx tissues. (AU)

• FAPESP's process: 15/05942-0 - Shedding light on the metabolism of nanomaterials absorbed by plants with X-ray and vibrational spectroscopy
• Grantee: Hudson Wallace Pereira de Carvalho
• Support Opportunities: Research Grants - Young Investigators Grants
• FAPESP's process: 08/54176-4 - Molecular epidemiology and management of postbloom fruit drop of citrus in new planting areas in São Paulo State
• Grantee: Lilian Amorim
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 15/19121-8 - Multi-User Equipment approved in grant 2015/05942-0: micro X-Ray Fluorescence system
• Grantee: Hudson Wallace Pereira de Carvalho
• Support Opportunities: Multi-user Equipment Program