Abstract:

[Objective] A newly found rust disease widely infests leaves of Dalbergia tonkinensis (Papilionaceae) which is a high economic tree species for furniture in China, growing in Chengmai County, Hainan Province, but its pathogen is unknown. This study described the symptoms of the rust disease on D. tonkinensis and its spore morphology, then extracted the pathogen DNA, and amplified it by ITS, with which the pathogen was identified. [Method] The period of occurrence and the rate of disease incidence of D. tonkinensis were investigated on the spot, and symptoms of the disease were observed and recorded. In order to acquire the isolation of pathogen and purification, pathogenicity test was conducted by artificially inoculating healthy leaves of D. tonkinensis with urediniospore suspension. We obtained a strain of D. tonkinensis rust pure culture HNCM1 by single spore separation. The pathogen was identified with the method of the spore morphology observation combined with ITS sequence analysis.[Result] The rust of D. tonkinensis occurred on the leaves and twigs, mainly on young tender leaves, and outbroke 2 times a year, in early April to early June and mid September to early November, respectively. The disease incidence rate of D. tonkinensis was able to reach more than 75%. Uredinia hypophyllous was yellow, and powdery,at early stage, generally bore on the round or oval small projection of the abaxial leaf surface, 0.1-0.5 mm in diameter, scattered or gregarious, which might cause leaf roll or deformation, even death of whole leaf. Urediniospores were globoid or obovoid, (13-21) μm×(10-16) μm, yellow, echinulate, germ pores obscure. Telia were similar to uredini, pale white, colloid, found occasionally when it became cold. Teliospores were oblong-obovoid, oblong-ellipsoid or clavoid, (19-28) μm× (13-16)μm, single cell, wall ca. 1 μm thick, colourless, smooth, pedicels 7-10 μm long. ITS sequence of the pathogen was around 750 bp nucleotide long, and the product was then 640 bp after bidirectional sequencing and splicing, which only shared at most 90% homology with the recorded sequences in Gen Bank. [Conclusion] Based on morphological and molecular identification, the pathogen causing rust disease of D. tonkinensis is Maravalia pterocarpi in Chengmai County, Hainan Province, a fungal species which belongs to pucciniaceae maravalia of basidiomycota. The GenBank accession number of HNCM1 is KU301795. This is the first report of Maravalia pterocarpi paratisizing on D. tonkinensis and causing rust disease in China, as well as the first time to analyze Maravalia pterocarpi from the angle of the molecular biology.

Key words: rust disease, Dalbergia tonkinensis, Maravalia pterocarpi, Hainan