First Report of Phytoplasma Infection of Grasses in Singapore.

In September of 2005, patches of Cynodon dactylon showing symptoms of bleached leaves were first observed in an open field in Singapore. Samples were collected from this site, from which total DNA was extracted with a Qiagen DNeasy kit (Catalog No 69104) and analyzed for phytoplasma DNA by a PCR assay with phytoplasma universal primer pairs P1/PTint (3). Resulting PCR products were each diluted 1:30 with sterilized distilled water and used in nested PCR with primer pair R16F2n and R16R2 (1). Twenty-five C. dactylon samples were assessed by this means, of which eight of eight with bleached leaves and four of seventeen symptomless samples tested positive. Widened disease surveillance identified the grasses, Axonopus compressus and Paspalum conjugatum, with similar bleached leaf symptoms in December 2006 and May 2007, respectively. Twenty-three of fifty-three A. compressus and six of twenty P. conjugatum samples were detected as positive for phytoplasma infection with the above PCR methods. A comparative analysis of sequences derived from the three grass hosts determined that the phytoplasma infecting C. dactylon (Genbank Accession No. EU234510) was most similar (>99%) to 'Candidatus Phytoplasma cynodontis' (GenBank Accession No. AB052871.1), whereas those detected in A. compressus (Genbank Accession No. EU234511) and P. conjugatum (Genbank Accession No. EU234512) were most similar (>99%) to the Brachiaria white leaf phytoplasma (GenBank Accession No. AB052872.1) (2). To our knowledge, this is the first report of phytoplasmas in C. dactylon, A. compressus, and P. conjugatum in Singapore. References: (1) I. M. Lee et al. Int. J. Syst. Evol. Microbiol. 48:1153, 1998. (2) C. Marcone et al. Int. J. Syst. Evol. Microbiol. 54:1077, 2004. (3) C. D. Smart et al. Appl. Environ. Microbiol. 62:2988, 1996.

Resistant Germplasm in Gossypium Species and Related Plants to Rotylenchulus reniformis.

Gossypium hirsutum, G. herbaceum, G. arboreum, G. barbadense, wild Gossypium spp., Hibiscus spp, and other Malvaceae were tested in the greenhouse to identify germplasm resistant to Rotylenchulus reniformis (Rr). Host resistance was based on Rr egg production per gram of root compared with known G. hirsutum susceptible 'Deltapine 16' as check. G. longicalyx and Sida rhombifolia were nonhosts. High levels of resistance were found in G. stocksii, G. somalense, and G. barbadense 'Texas 110.' Other cotton lines with potential value in breeding for Rr resistance were G. herbaceum P.I. 408775; G. arboreum P.I. 41895, P.I, 417891, CB 3839; and G. hirsutum 893. All these supported less than 20% of the egg production on the check. Seventy-three percent of the Hibiscus spp. tested were resistant. Female development and egg production reflected host resistance; healthy females and large egg masses were observed on susceptible plants, and degenerated females and small egg masses on resistant plants. Females penetrating nonhost G. longicalyx never matured to kidney shape.

Observations on the Morphology of the Pine Wood Nematode, Bursaphelenchus xylophilus.

Scans of slash pine wood chips infested with pine wood nematodes showed coiled aggregates of 5-10 nematodes in the axial resin canals, and 1-2 nematodes folded in the radial resin canals. Observations of the pine wood nematode by SEM showed the head to be offset with six labial lobes. A smaller circle of six inner lobes surrounded the stoma. A single labial sensillum was observed on each of the two subventral and two subdorsal lobes. The two opposite lobes, without sensilla, bore a pore-like amphid. The female vulva flap was observed to be a pouch. In addition to two pairs of copulatory papillae previously described for the male, three additional papillae were observed: an additional post-anal pair, and a single papilla anterior to the cloaca. Spicules were fused ventrally. Distal spicule ends terminated in two fused half discs. Caudal alae were angular at the tail terminus, but culed inward at the corners to appear oval. Lateral fields had four lateral striations.

Scanning electron microscopy of perineal patterns of three species of Meloidogyne.

The perineal pattern of Meloidogyne graminicola is oval, characterized by the anastomosing of cuticular striae converging, and elevating at the tail terminus. A deep lateral incisure forming a low arch traverses the rounded perineal pattern of Meloidogyne hapla. Punctations at the tail region of M. hapla are not observed with the scanning electron microscope. Minute crosslines invaginate with the vulvar lips of Meloidogyne incognita. Punctate indentations around the anal opening and bordering the lateral sides of the vulvar slit of M. incognita are revealed.