J. López-Robles, Edaphology and Agricultural Chemistry Section, Faculty of Sciences, University of Burgos, Plaza de Misael Bañuelos s/n 09001, Burgos, Spain;
P. García-Benavides, Centro Regional de Diagnóstico (Junta de Castilla y León) Apartado 61 Salamanca, Spain; and
G. Sacristán-Pérez-Minayo, Microbiology Section, Faculty of Sciences, University of Burgos, Plaza de Misael Bañuelos s/n 09001, Burgos. Spain
During the 2009 to 2010 corn-growing (Zea mays L. cv. Alexandria) seasons, severely stunted and yellowing corn plants in several commercial fields at Aldearrubia (Salamanca Province) were observed in western Spain. The disease incidence ranged from 80 to 100%. Early symptoms consisted of severely reduced growth of the plants coupled with extensive leaf yellowing. Occurrence of the disease was estimated to cause near complete loss of the crop yields since the corn produced in affected fields was unmarketable. Disease surveys revealed high parasitism in the main and feeder roots and a large soil population of the root-knot nematode Meloidogyne spp. The nematode population was extracted and quantified from soil and root samples according to Barker (1). It was identified as the southern root-knot nematode M. incognita race 1, by female perineal pattern, host-differential test, and multiplex PCR using forward primers H-18S, CF-ITS, I-ITS, and reverse primer HCFI-28S (3,4). ITS products cloned and assayed using the ABI PRISM 3100 Genetic Analyzer (Applied Biosystems, Salamanca, Spain) were subjected to a database search using BLAST (National Centre for Biotechnology Information) to confirm the identification. These sequences exhibited 99.0% similarity with that of an M. incognita isolate from France (GenBank Accession No. AF402309.1). M. incognita was found in 80% of soil samples collected from the areas where the disease was observed and 83.5% of root samples with nematode population densities ranging from 26 to 269 eggs and second-stage juveniles (J2s) per 100 cm3 of soil and 234 to 1,634 eggs and J2s per 5 g of fresh roots. In glasshouse proofs of pathogenicity, a mix of 1,500 eggs and J2s of these populations of M. incognita were inoculated in 20-cm-diameter pots with 10 replicates with a single pregerminated seed of corn cv. Alexandria as host plant; another 10 replicates without inoculation were established as control plants. After 6 weeks, all plants inoculated were severely stunted and yellowing; infected roots showed galls on root tips and secondary feeder roots. Galling of root tips that cause stubby root symptoms prevented further root growth into deeper soil layers and induced proliferation of secondary roots, which confirmed the nematodes' pathogenicity. The severe infections in roots of corn plants suggest that parasitism of corn roots by the root-knot nematode must contribute to stunting, yellowing, and decline of corn, reducing yield by restricting access to water and nutrients that are needed for plant growth and development, and can result in the death of younger plants as previously reported (2). To our knowledge, this is the first report of M. incognita infecting corn in Spain.
References: (1) K. R. Barker. Nematode extraction and bioassays. Page 19 in: An Advanced Treatise on Meloidogyne. Vol. II, Methodology. K. R. Barker et al., eds. North Carolina State University Graphics, Raleigh, 1985. (2) T. P. Heffes et al. Nematropica 22:139, 1992. (3) L. Robertson et al. Crop Prot. 25:440, 2006. (4) C. Zijlstra. Fund. Appl. Nematol. 20:505, 1997.