White tip disease of rice caused by the plant-parasitic nematode Aphelenchoides besseyi is an important domestic quarantine issue causing heavy yield losses of rice. During a survey for rice diseases in 2013, suspect white tip disease of rice was observed in the cities of Changchun and Gongzhuling, Jinlin Province, China. Leaf tips of susceptible rice varieties were white or yellow, becoming brown or black as necrosis set in. Tips of developing leaves were twisted and wrinkled. The flag leaf became twisted above the panicle until development was inhibited. General stunting of the plant accompanied leaf injury. Panicles were severely reduced and produced small deformed kernels while spikelets were reduced in number. Maturity of panicles was delayed, and secondary panicles arising from the lower nodes of the panicle were sterile. Nematodes were isolated from rice grains of diseased panicles. Key morphological features were determined for females and males. Measurements of females (n = 15) were: body length 612.50 to 735.00 μm (mean 673.75 μm), body width 17.37 to 22.21 μm (mean 19.79 μm), esophagus to gland 64.44 to 68.07 μm (mean 66.26 μm), and tail 34.41 to 41.29 μm (mean 37.85 μm). Females had a relatively short ovary with oocytes arranged in several lines; posterior uterine branch two to four times as long as body width; and tail tapering, conoid, with terminus bearing a mucro with four processes arranged in a shape somewhat that of a star. Measurements of males (n = 22) were: body length 483.39 to 580.00 μm (mean 531.70 μm), body width 14.46 to 17.12 μm (mean 15.79 μm), esophagus to gland 63.97 to 66.42 μm (mean 65.20 μm), and tail 30.38 to 36.45 μm (mean 33.41 μm). Males had a curved tail about 180° when relaxed, three pairs of ventrosubmedian papillae with the first one adanal, spicula curved with a slight basal process, and terminus bearing four mucrones arranged variably. Both males and females had lateral field occupying one fourth of the body width, marked by four incisures; delicate cephalic framework; small spear with moderate-size basal knobs; excretory pore was anterior to nerve ring; and intestine joined to esophagus immediately behind median bulb (3). All morphological data and characters were consistent with A. besseyi. Molecular diagnosis as A. besseyi was confirmed after DNA was extracted from nematodes (n = 16) and the templates were used in PCR analysis. The internal transcribed spacer region (ITS) of rDNA was amplified with primers TW81 and AB28 (2). The size of PCR product was 842 bp, and this sequence (KJ009342) was submitted to GenBank and was 98% similar with that of A. besseyi isolates from India (JF826519, JF93390, JF826517, JF826518) and Russia (EU186069). Molecular identification was further confirmed by amplifying part of the ITS region and part of the 5.8 gene of rDNA using the A. besseyi-specific primers BSF and BSR (1). The amplification yielded a 312-bp product specific to A. besseyi. Morphological and molecular data confirmed that the pathogen responsible for white tip disease in Changchun and Gongzhuling was A. besseyi. While this nematode has been reported from many rice-producing areas in China, this is the first detection of A. besseyi in Jilin Province, China. References: (1) R. Q. Cui et al. Plant Quarantine (Chinese) 24:10-12, 2010. (2) S. A. Subbotin et al. Nematology 2:153, 2000. (3) G. Thorne. Principles of Nematology. McGraw-Hill, New York, 1972.
Perception of Tactile Distance on the Back
