|Aruna Kilaru, Aruna|
Submitted to: Federation of European Microbiological Societies Microbiology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2007
Publication Date: 6/8/2007
Citation: Aruna Kilaru, A., Bailey, B.A., Hasenstein, K.H. 2007. Moniliophthora perniciosa produces hormones and alters endogenous auxin and salicylic acid in infected cocoa leaves. Federation of European Microbiological Societies Microbiology Letters. 274:238-244. Interpretive Summary: The plant pathogen Crinipellis perniciosa causes the disease witches’ broom on cacao, a devastating disease that severely reduces yields where it occurs. Cocoa, produced from the cacao tree, is combined with United States agricultural commodities providing a direct benefit to the American farmer. Control measures for witches’ broom on cacao are expensive to employ and are often ineffective. Understanding the interactions between the witches’ broom pathogen and cacao may provide insight as to how to control the disease. Pathogenic fungi are able to produce hormones similar to plants and these hormones can participate in the disease process. The witches’ broom pathogen gets its name due to the distorted growth it causes during the early stages of infection, responses that may be due to altered production of hormones by either the pathogen or the plant. It was discovered that the witches’ broom pathogen produces large quantities of plant growth altering hormones and that these hormones may function in the disease process. With this knowledge, it may be possible to develop new control measures that eliminate the ability of the pathogen to alter plant growth. By providing cacao farmers with new control measures for frosty pod, cocoa supplies may be stabilized resulting in increased benefits to the cacao farmer, the cocoa industry, and the American farmer.
Technical Abstract: We investigated the endogenous levels of abscisic acid (ABA), indole-3-acetic acid (IAA), jasmonic acid (JA), and salicylic acid (SA) in leaves of Theobroma cacao and the pathogen, Crinipellis perniciosa. In cacao leaves, the levels of all hormones decreased with maturity and showed no preferential distribution within the leaf. Leaf surface sterilization reduced ABA but increased JA and SA levels by 50%. Temporal profile (0-10 d) of endogenous ABA, IAA, JA, and SA in the uninfected leaves indicated wide variability. The mycelium contained ABA and IAA (50.4±5.8 and 46.4±32.9 ng'g-1 DW, respectively) and JA and SA (185.8±114.5 and 520.9±39 ng'g-1 DW, respectively). The IAA content increased 38 fold in basidiocarps. Fungal inoculation of leaves did not affect the ABA or JA content but reduced IAA and SA levels within 3-5 d. IAA and SA increased significantly in the following five days and corresponded with the transition from biotrophic to necrotrophic/saprophytic phase in the pathogen. Reverse northern hybridization showed induction of IAA and SA related transcripts in the pathogen upon host interaction and implicate IAA and SA in the induction of disease symptoms in the host and phase transition in the pathogen. Differentially expressed pathogen-related transcripts suggest hormonal effects in host pathogen interactions.