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Title: A new rust disease on wild coffee (Psychotria nervosa) caused by Puccinia mysuruensis sp. nov

item MAHADEVAKUMAR, MAHADEV - University Of Mysore
item Szabo, Les
item EILAM, TAMAR - Tel Aviv University
item ANIKSTER, YEHOSHUA - Tel Aviv University
item JANARDHANA, G - University Of Mysore

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2016
Publication Date: 7/1/2016
Citation: Mahadevakumar, M., Szabo, L.J., Eilam, T., Anikster, Y., Janardhana, G.R. 2016. A new rust disease on wild coffee (Psychotria nervosa) caused by Puccinia mysuruensis sp. nov. Plant Disease. 100:1371-1378.

Interpretive Summary: Wild coffee (Psychotria nervosa) is an important medicinal plant and is used in various ethno-medicinal practices in India. Wild coffee is also commonly found in Central and South America and Florida where it is used as an ornamental shrub. Recently, wild coffee was found affected by a new rust disease that caused wilting and leaf loss. Disease symptoms and progressions were characterized from natural and artificially inoculate plants. The casual agent of this disease was characterized and determined to be a species of rust fungi, Puccinia mysuruensis. Characterization of the life cycle of P. mysuruensis demonstrated that it has a shortened life cycle including only two stages (telia and basidia). A region of the nuclear ribosomal RNA was sequenced and used for phylogenetic analysis. Plant pathologist and other scientists studying rust diseases will use this work.

Technical Abstract: Psychotria nervosa, commonly called wild coffee (Rubiaceae) is an important ethno-medicinal plant in India. In 2010 a new rust disease of P. nervosa was observed in three regions of Mysore District, Karnataka (India) with disease incidence ranging from 58% to 63%. Typical symptoms of rust disease were prominently visible during the early monsoon season (May-June) with chlorotic spots on the adaxial and black pustules (telia) on the abaxial leaf surface, respectively. Telia produced abundant teliospores, which were bi-celled, pedicillate and measured 33-45 × 19-30 µm. The germination of teliospores produced a typical metabasidium bearing four haploid basidiospores. Stages of disease development were studied using artificially inoculated healthy wild coffee plants. Only telia were observed on the inoculated plants indicating that this rust fungus has an abbreviated microcyclic life cycle. The complete ITS and partial LSU region of the nuclear rDNA was sequenced, but no close matches were found in public databases. The herbarium sample of Puccinia psychotriae was examined and was shown to be different with respect to telium size and teliospore dimensions (24-32 × 13-18 µm). Therefore, the rust pathogen causing wild coffee rust is a new species, P. mysuruensis.