Rafael Arango

Analysis of the CYP51 gene and encoded protein in propiconazole-resistant isolates of Mycosphaerella fijiensis.

BACKGROUND Mycosphaerella fijiensis Morelet causes black sigatoka, the most important disease in bananas and plantains. Disease control is mainly through the application of systemic fungicides, including sterol demethylation inhibitors (DMIs). Their intensive use has favoured the appearance of resistant strains. However, no studies have been published on the possible resistance mechanisms. RESULTS In this work, the CYP51 gene was isolated and sequenced in 11 M. fijiensis strains that had shown different degrees of in vitro sensitivity to propiconazole, one of the most widely used DMI fungicides. Six mutations that could be related to the loss in sensitivity to this fungicide were found: Y136F, A313G, Y461D, Y463D, Y463H and Y463N. The mutations were analysed using a homology model of the protein that was constructed from the crystallographic structure of Mycobacterium tuberculosis (Zoff.) Lehmann & Neumann. Additionally, gene expression was determined in 13 M. fijiensis strains through quantitative analysis of products obtained by RT-PCR. CONCLUSION Several changes in the sequence of the gene encoding sterol 14alpha-demethylase were found that have been described in other fungi as being correlated with resistance to azole fungicides. No correlation was found between gene expression and propiconazole resistance.

Resistance to Tecia solanivora (Lepidoptera: Gelechiidae) in Three Transgenic Andean Varieties of Potato Expressing Bacillus thuringiensis Cry1Ac Protein

Abstract Transgenic potato, Solanum tuberosum L., plants containing a synthetic cry1Ac gene coding for the Bacillus thuringiensis (Bt) crystalline insecticidal protein were produced and evaluated for resistance to Tecia solanivora Povolny (Lepidoptera: Gelechiidae), the larvae of which attack potato tubers. In total, 43 transgenic lines of commercial Andean potato varieties Diacol Capiro, Pardo Pastusa, and Pandeazúcar were obtained. These transgenic lines were found to have one to four copies of cry1Ac per genome and expression levels of Cry1Ac protein varying from 0.02 to 17 &mgr;g/g fresh tuber tissue. Bioassays of T. solanivora larvae on these transgenic potato tubers showed 83.7–100% mortality, whereas the mortality levels on nontransgenic lines were 0–2.67%. Our data indicate the capability of Bt transgenic technology to control the T. solanivora while reducing the use of chemical insecticides. Further studies under controlled field conditions will be helpful in exploring the potential of Cry1Ac potatoes in the insect pest management strategies.

The presence and spectrum of light influences the in vitro conidia production of Mycosphaerella fijiensis causal agent of black Sigatoka

Black Sigatoka caused by Mycosphaerella fijiensis is the most important leaf disease affecting bananas and plantains in the world today. Conidia constitute one of the forms by which the disease is spread. Although light has been described as an important factor for conidial production in M. fijiensis, no detailed studies have been conducted. In a series of in vitro experiments, the production of conidia in different culture media and with different photoperiods and light spectra was assessed. Results showed that the best media for conidia production were potato dextrose agar and V8 juice agar + 0.2 g/L CaCO3. Light (15001 × ) was required for conidial production and the light spectrum used significantly influenced the number of conidia produced, with red light having the greatest positive effect. kg]Additional keyword kw]photoconidiation.

Current situation of wild Solanum spp. L. sect. Petota (Solanum, Solanaceae) in some Colombian regions

Potatoes are grown as a staple food in a number of countries around the world. Potatoes production is fourth at the worldwide level and provides carbohydrates and other nutrients in several developing countries. In South America a large diversity of wild and cultivated potato genotypes have been identified, from which several species have been described in Colombia. The last known collections of wild potato germplasm in Colombia were performed up to 1992, and we know little of wild potato distribution since that time. Several factors may threaten these populations, and we performed field surveys of the Colombian populations, as well as a literature review, studies of herbarium specimens from eight Colombian herbaria and databases from reference collections available on the internet. Based in these data we performed field trips in several Colombian regions where wild and cultivated species were reported previously. We identified Solanum andreanum Baker, S. colombianum Dunal and S. flahaultii Bitter, populations according to the taxonomic concepts of Spooner and Fajardo; or S. andreanum, S. colombianum, S. flahaultii, S. moscopanum Hawkes and S. tuquerrense Hawkes, according to the taxonomy of Hawkes. We observed habitat loss or disturbance that may partially explain the apparent decrease or eventual disappearance of some species at specific sites.