Maria A Santana

Linamarase Expression in Cassava Cultivars with Roots of Low- and High-Cyanide Content

This paper reports the expression and localization of linamarase in roots of two cassava (Manihot esculentaCrantz) cultivars of low and high cyanide. Two different patterns of linamarase activity were observed. In the low-cyanide type, young leaves displayed very high enzyme activity during the early plant growing stage (3 months), whereas in root peel, the activity increased progressively to reach a peak in 11-month-old plants. Conversely, in the high-cyanide cultivar (HCV), root peel linamarase activity decreased during the growth cycle, whereas in expanded leaves linamarase activity peaked in 11-month-old plants. The accumulation of linamarin showed a similar pattern in both cultivars, although a higher concentration was always found in the HCV. Linamarase was found mainly in laticifer cells of petioles and roots of both cultivars with no significant differences between them. At the subcellular level, there were sharp differences because linamarase was found mainly in the cell walls of the HCV, whereas in the low-cyanide cultivar, the enzyme was present in vacuoles and cell wall of laticifer cells. Reverse transcriptase-PCR on cassava tissues showed no expression of linamarase in cassava roots, thus, the transport of linamarase from shoots to roots through laticifers is proposed.

A simple and low-cost strategy for micropropagation of cassava (Manihot esculenta Crantz)

With the aim of transferring micropropagation techniques to cassava seed producers, a simple and lowcost medium for in vitro micropropagation was developed. CM6740-7 cassava cultivar from CIAT was used as planting material. Commercially available nutrients were used in order to substitute the propagation media components. A Hydro Agri´s fertilizer (12-11-18/3 (MgO-EDTA)) was used as a substitute for Murashige and Skoog macro and micronutrients. Additionally, table sugar and molasses were used as a source of carbohydrates and vitamins. Radixone 3AS from Praquim C.A. was used as a source of auxins and activol as a source of gibberellic acid. Numbers of roots and leaves, height and dry weight of plantlets was determined for each treatment and compared with a conventional micropropagation media. For all the parameter measured, the plantlets obtained on the fully substituted media showed a good growth performance. Canonical biplot analysis showed that this media was especially good for the number of nodes (multiplication rate) in 60-day-old cultured plants. The designed medium is simple, easy to prepare and allows a low-cost strategy to obtain a high quality in vitro micropropagated cassava plants and its ready availability may have an impact on the production of planting material of cassava.

Microsatellites reveal widespread predominance of an invasive over an indigenous Bemisia tabaci in Venezuela

The whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is an important pest due to its capacity for producing strong infestations and transmitting plant viruses. The New World putative species of B. tabaci complex (NW) is the indigenous whitefly of the Americas, but only the invasive Middle East-Asia Minor 1 putative species of B. tabaci complex (MEAM1), commonly referred to as the “B biotype” was identified in a limited scope sampling in Venezuela. Similarly to MEAM1 invasions elsewhere, in this South American country there has been an increase in the geographic range and abundance of B. tabaci, and in the number of viruses that it transmits since the late 1980s. We estimated the diversity of B. tabaci to elucidate their role in the epidemiology of geminiviruses in Venezuela. Thirteen microsatellite loci were screened in samples collected from 19 localities in ten major agricultural states. A Bayesian clustering method (Structure) grouped the samples into two genetic groups. Control samples from whiteflies NW and MEAM1 and partial sequencing of the mitochondrial cytochrome oxidase I gene showed that our samples of B. tabaci populations from Venezuela fall within NW and MEAM1 groups. In this survey, MEAM1 was predominant over NW whitefly in a proportion of 35:1. No evidence was observed for gene flow between indigenous and invader whitefly. Altogether, our results stress the urgency for controlling the proliferation of the invasive whitefly.

Bacillus thuringiensis improved isolation methodology from soil samples

Bacillus thuringiensis is a sporulating bacterium, which produces parasporal inclusions toxic to insects. Widely used methodologies to isolate Bt from soil consist of a thermal shock treatment followed by selective germination of spores. The results presented here suggest that a preliminary 5 h dry-heat treatment largely enhance the selectivity of these procedures.

Serratia marcescens associated with bell pepper (Capsicum annuum L.) soft-rot disease under greenhouse conditions

Soft-rotting bacteria affecting bell peppers crops represent an economically destructive disease of growing importance worldwide. In Venezuela since 2006, soft-rot symptoms have been occasionally observed in bell pepper fruits grown under greenhouse conditions. Affected fruits presented water-soaked lesions that progressed to complete fruit maceration. Bacteria were isolated from water-soaked lesions in order to identify the causal agent of this disease. Of 13 bacterial isolates recovered from affected fruits, only isolate AGPim1A was able to produce a hypersensitive reaction in tobacco plants and to reproduce soft-rot symptoms in bell peppers fruits. Several methods, including classical bacteriological tests and carbon utilization profiling, alongside with sequence analysis of 16S rRNA and housekeeping genes gyrB and groES-groEL, allowed identification of the soft-rotting bacterium as Serratia marcescens. To our knowledge, this is the first report showing a S. marcescens strain associated with soft-rot disease in bell pepper fruits.

First Report of Bell Pepper Soft-Rot Caused by Pectobacterium carotovorum subsp. brasiliense in Venezuela

Soft rot symptoms were observed during the rainy season, particularly in July, in 2008 on bell pepper (Capsicum annuum L., Hybrid RPP 1216, Syngenta) cultivated under greenhouse conditions (25/18°C, 85% RH) in Sartenejas, Miranda State, Venezuela. Initial symptoms on plants consisted of watery lesions at the basal part of the stem. As the lesions progressed, the whole stem presented water-soaked and necrotic tissue, with detached cortical tissues. Infected plants showed general wilt with defoliation. Fruits showed watery lesions that progressed until complete maceration. Plant samples displaying soft rot symptoms were collected to isolate the causal agent of the disease. Tissue from the lesions was surface-disinfected by standard protocols and ground to prepare serial-dilutions that were plated on Luria Bertani-agar medium. After 48 h of incubation at 28°C, a predominant bacterium was isolated from all samples. Five strains from independent samples were subjected to biochemical and pathogenicity tests. Al...

Detección de genes cry1 y cry2 en cepas venezolanas de Bacillus thuringiensis y sus posibles aplicaciones en el campo de la Biotecnología Agrícola

Bacillus thuringiensis (Bt) is a valuable biopesticide that is being used for the control of agricultural plagues of economic importance. Their insecticide properties are attributed to the presence of δ-endotoxins, Cry toxins, which are synthesized during the phase of sporulation of the bacterium. These toxins, when ingested by the larvae of the target insect, generate a set of physiological reactions that cause their death. The objective of the present work was the isolation and characterization of Bt strains from soils of the Guayana Region (Venezuela). Soils of different locations of Guayana were collected, dried and processed until the isolation of colonies with Bacillus spp. morphology. These colonies were grown in agar-water until sporulation and observed under the microscope for the verification of the presence of crystals, having identified 94 strains with Bacillus morphology. These strains were characterized for the presence of genes cry by the use of the PCR technique and the use of general primers for cry1 and cry2. Of the total of analyzed strains, 75% presents the genetic profile cry1/cry2, which is toxic against Lepidoptera and Diptera and may have important applications in the agricultural and health fields.