ABSTRACT
Rice is attacked by Steneotarsonemus spinki Smiley, a mite that has dispersed throughout many countries causing important loss on rice production. Rice plants of the variety Morelos A-92 were infested with S. spinki, and its population growth was estimated along plant development. Further, the morphological and histological injuries associated to the mite attack were characterized. The highest infestation level was obtained 13 weeks after plant infestation, with an average of 58.5 mites per plant, predominantly females. Morphological injuries were categorized from level 0 (no injuries from uninfested plants) to level 3, characterized by the highest injuries represented by blotches on the adaxial epidermis of the leaf sheath and on panicles and grains. Plants ranked within levels 0, 1, and 2 for morphological injury did not exhibit clear histological injuries, while those at level 3 exhibited histological injury characterized by destruction of cells of the adaxial epidermis, disorder, color change, and hypertrophy in the mesophyll cells, as well as color change in the abaxial epidermis. Thus, it presented a significant correlation between morphological injuries and mite density level, which can be further adopted to help the control decision-making process for this mite on rice.
Subject(s)
Mites/physiology , Oryza/parasitology , Animals , Female , Male , Mexico , Population GrowthABSTRACT
Lettuce (Lactuca sativa) is a common consumed vegetable and a major source of income and nutrition for small farmers in Mexico. This crop is infected with at least nine viruses: Mirafiori lettuce big-vein virus (MiLBVV), Lettuce big-vein associated virus (LBVaV), both transmitted by the soil-borne fungus Olpidium brassicae; Tomato spotted wilt virus (TSWV), Tomato chlorotic spot virus (TCSV), Groundnut ringspot virus (GRSV), Lettuce mottle virus (LMoV), Cucumber mosaic virus (CMV), Bidens mosaic virus (BiMV), and Lettuce mosaic virus (LMV) (1). From March to May 2012, a disease on lettuce was observed in the south region of Mexico City displaying mild to severe mosaic, leaf deformation, reduced growth, slight thickening of the main vein, and plant death. At the beginning of the epidemic there were just a few plants with visible symptoms and 7 days later the entire crop was affected, causing a loss of 93% of the plants. It was estimated by counting the number of severely affected or dead plants in three plots. No thrips, aphids, or whiteflies were observed in the crop during this time. Twenty plants with similar symptoms were collected and tested by RT-PCR using the primers LBVaVF 5'-AACACTATGGGCATCCACAT-3' and LBVaVR 5'-GCATGTCAGCAATCAGAGGA-3' specific for the coat protein gene of LBVaV, amplifying a 322-bp fragment. Primers CP829F 5'-CCWACTTCATCAGTTGAGCGCTG-3' and CP1418R 5'-TATCAGCTCCCTACACTATCCTCGC-3' were used to detect MiLBVV (2). No amplification was obtained for MiLBVaV in any plants tested. PCR products of approximately 300 bp were obtained from four out of 20 symptomatic lettuce samples tested for LBVaV, but not from healthy plant and water controls. These results suggest the presence of another virus in symptomatic lettuce plants. Amplicons were gel-purified and sequenced using LBVaVF and LBVaVR primers. A consensus sequence was generated using the Bioedit v. 5 program. Both sequences of these Mexican lettuce isolates were 100% identical (Accession Nos. KC776266.1 and KC776267.1) and had identities between 94 and 99% to all sequences of LBVaV available in GenBank. Additionally, when alignments were made using ClustalW, these sequences showed identities of 99.7% to Almeria-Spanish isolate (Accession No. AY581686.1); 99.4% to Granada-Spanish isolate (AY581689.1); 99.1% to Dutch isolate (JN710441.1), Iranian isolate (JN400921.1), Australian isolate (GU220725.1), Brazilian isolate (DQ530354.1), England isolate (AY581690.1), and American isolate (AY496053.1); 96.2% to Australian isolate (GU220722.1); 96.3% to Japanese isolate (AB190527.1); and 92.8% to Murcia-Spanish isolate (AY581691.1). Twenty lettuce plants were mechanically inoculated with leaf tissue taken from the four plants collected in the field and tested positive for LBVaV by RT-PCR; 12 days after inoculation, mosaic symptoms were observed in all inoculated plants and six of them were analyzed individually by RT-PCR obtaining a fragment of the expected size. To our knowledge, this is the first report of LBVaV infecting lettuce in Mexico. Further surveys and monitoring of LBVaV incidence and distribution in the region, vector competence of olpidium species, and impact on the crop quality are in progress. References: (1) P. M. Agenor et al. Plant Viruses 2:35, 2008. (2) R. J. Hayes et al. Plant Dis. 90:233, 2006.
