Location: Nematology Laboratory
Title: Observations on the foliar nematode, Aphelenchoides besseyi, infecting tuberose and rice in India Authors
Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 16, 2012
Publication Date: December 12, 2012
Citation: Khan, M.R., Handoo, Z.A., Rao, U., Rao, S.B., Prasad, J.S. 2012. Observations on the foliar nematode, Aphelenchoides besseyi, infecting tuberose and rice in India. Journal of Nematology. 44(4):391-398. Interpretive Summary: Plant-parasitic nematodes are microscopic worms that feed on plants and cause an estimated ten billion dollars of crop losses each year in the United States and 100 billion dollars globally. Foliar nematodes are an important group, damaging many kinds of plants worldwide. The foliar nematodes are members of a group of nematodes that includes a few regulated and economically important plant-parasitic species, including one that causes white tip disease on rice and damages various ornamental crops. Foliar nematodes are poorly studied because most of the nematode species in this group feed on fungi instead of plants. One approach to solving the problem of identifying which of the many species in this group can damage plants is to obtain and compare anatomical features and DNA markers among many different species and populations and thereby be able to predict the disease-causing ability of new populations. In this study, an ARS scientist in collaboration with scientists from India evaluated several populations of foliar nematodes for anatomical and molecular (DNA) differences. We discovered that differences among the populations in DNA and in the head, tail, and outer surface could be a consequence of geographic or genetic variation. The results are significant because they will enable researchers to select DNA-cutting enzymes for use in molecular identification tests that will be more rapid and accurate than current tests. This research will be used by researchers, identifiers, regulators, and extension agents involved in protecting plants from damaging foliar nematodes.
Technical Abstract: The foliar nematode Aphelenchoides besseyi causes white tip disease in rice (Oryza sativa L.) and floral malady in tuberose (Polianthes tuberosa L.). This nematode is widely distributed in the rice fields of many states of India, including West Bengal (WB), Andhra Pradesh (AP), Madhya Pradesh (MP) and Gujarat. In order to generate information on intraspecific variations of A. besseyi as well as to confirm the identity of the nematode species infecting these important crops, morphological and molecular observations were taken of A. besseyi isolated from tuberose and rice from WB and rice from AP, MP and Gujarat. The observed variations among the populations in the tail, esophageal and anterior regions, including the occurrence of four as well as six lateral lines in the lateral fields, could be regarded as a consequence of host-induced or geographical variations. PCR amplification of the rDNA ITS region of rice (AP) and tuberose (WB) populations of A. besseyi generated one fragment of approximately 830 bp, and on sequencing and removal of 18S and 28S flanking sequences, the size of the ITS region was 788 bp and 791 bp for tuberose and rice population, respectively. Multiple alignments of the two sequences showed almost 100% similarity with three gaps and one mismatch. Blast analysis revealed a very high level of similarity of both the Indian strains to a Russian population with one gap and three mismatches. The Indian and Russian strains could be differentiated using restriction enzyme Bccl. Host tests revealed that rice (cv. IET 4094), oat (cv. OS-4) and teosinte (cv. TL-1) showed a typical distortion due to the infection of A. besseyi. Six germplasms of oat showed no infection of the nematode under field conditions. Local cultivars of onion, maize, chrysanthemum and Sorghum halepense were also not infected by A. besseyi.