Heat shock-induced susceptibility of green coffee leaves and berries to Colletotrichum gloeosporioides and its association to PR and hsp70 gene expression

Abstract

Colletotrichum kahawae Bridge & Waller and C. gloeosporioides Penz are both coffee ( Coffea arabica L.) pathogens but only the former induces damages on green coffee berries causing 70–80% losses, being known as coffee berry disease or CBD. The latter infects only very ripe coffee berries without destroying the seed but is also responsible for ‘dieback’ of branches in overbearing seasons. Detached green coffee berries and leaves inoculated with C. kahawae show usually symptoms 4–5 days after inoculation. With C. gloeosporioides penetration does not even occur. However, when green berries and leaves were subject to a previous heat shock of 55 °C for 30 s and then inoculated, there was a total breakdown of resistance regarding C. gloeosporioides and an acceleration of the infection process regarding C. kahawae. Heat shock-induced susceptibility decreased with time for both fungi and became null about 40–48 h after the treatment for C. gloeosporioides. The temporary loss of resistance was associated with a transient downregulation of some PR genes, namely cachi3-1, cachi4-1 and capox-1, and by a transient upregulation of cahsp70. All genes analysed under this study were expressed constitutively, two of them, cachi3-1 and cachi4-1, being up-regulated in inoculated controls. It is suggested that the synergistic presence of these constitutive defenses may be one of the mechanisms used by the plant to control resistance to C. gloeosporioides. Moreover we hypothesise that the protein coded by cahsp70 could facilitate the penetration of the pathogen. To our knowledge, this is the first time that the expression of PRs and Hsp70 coding genes is associated to heat shock-induced susceptibility.