First Report of the Root-Knot Nematode Meloidogyne arenaria Infecting Noni in China.

Abstract

Noni (Morinda citrifolia) is an important medicinal plant and its fruit and root are of high value. In recent years, noni has been cultivated widely on Hainan Island, China. A survey of eight commercial noni fields in four counties found that most fields had plants with symptoms consistent with damage caused by root-knot nematodes. Above-ground symptoms included reduced vigor, plant stunting, and chlorosis. Affected roots were galled, swollen, cracked, and rotten. Fruit loss associated with diseased plants was quantified as 85%. In each field, three samples were taken consisting of 15 cm wide × 20 cm deep soil (containing roots). The nematode population was extracted and quantified according to Barker (1). Nematodes were found in all soil and root samples with population densities ranging from 450 to 835 eggs and second-stage juveniles (J2s) per 200 g subsample of soil, and 685 to 985 eggs and J2s per 10 g sub-sample of fresh roots. Three single egg masses were respectively hand-picked from one sample of diseased noni roots and inoculated onto tomato plants grown with sterilized soil at 20 to 28°C in the greenhouse. After 8 weeks, nematodes were extracted from the roots of tomato plants and identified by morphology, enzyme analysis, and molecular characterization. Morphology of the female perineal patterns showed a low dorsal arch with large lateral lines separating the striae of the dorsal and ventral sectors, leading to the tail terminus; and wavy, coarse striae with forking at lateral lines and short irregular striae near the lateral lines. Enzyme analysis of the esterase phenotype was also typical of the A1 phenotype in M. arenaria. Based on the perineal pattern and esterase phenotype, the Meloidogyne species was identified as M. arenaria (Est A1) (3). Total genomic DNA was extracted from ca. 10 μl of packed second-stage juveniles (J2s) using the method of Cenis (2). The primers C2F3 (5'-GGTCAATGTTCAGAAATTTGTGG-3') and 1108 (5'-TACCTTTGACCAATCACGCT-3') (4) was used to amplify the intergenic region between COII and LrRNA genes of the mtDNA and an amplification product (1,700 bp) was obtained, similar to M. hispanica, M. incognita, and M. javanica. Root-knot nematodes (Meloidogyne spp.) have been reported to be cause disease on noni in Hawaii. However, to our knowledge, this is the first report of M. arenaria (Est A1) infecting noni in China.