Sebastián A. Stenglein

Angular leaf spot: a disease caused by the fungus Phaeoisariopsis griseola (Sacc.) Ferraris on Phaseolus vulgaris L.

Publisher Summary Angular leaf spot (ALS) is a disease of bean ( Phaseolus vulgaris L. ) caused by the fungus Phaeoisariopsis griseola ( Pg ). This chapter discusses the taxonomy, morphological characteristics, and host range of the pathogen. It also describes symptoms of the disease, the disease cycle, and management of the yield loss. Epidemiology, in turn, is the foundation of information-based ALS management. Knowledge of spatial and temporal disease relations and fungal-population biology should have an impact on the disease control. Studies on Pg diversity and epidemiology are integral to characterize and understand the evolution of resistance genes to Pg . Parallel investigations of the molecular determinants of Pg pathogenicity and virulence are critical to understand not only the functions but also the pathways involved in disease resistance. Genetic studies should provide the bases for the development of bean cultivar resistance to Pg . Although the Pg –bean pathosystem is complex, continued basic and applied research should provide answers to solve many of the problems encountered by bean growers.

Micromorphological variability of leaf epidermis in Mesoamerican common bean (Phaseolus vulgaris, Leguminosae)

The purpose of this work was to make a detailed description of leaf epidermal characteristics among four Mesoamerican common bean (Phaseolus vulgaris L.) types, since they may play a role in plant defence against pathogens and/or drought. Therefore, we studied variability of epidermal cell number per mm2, stomatal size and number per mm2, stomatal index, and trichome density and dimensions on both the adaxial and abaxial epidermal surfaces. In all the common bean types studied, both surfaces of the leaves were devoid of wax crystalloids. Trichome density and distribution differed among the common bean types. Furthermore, the abaxial leaf surface always presented more trichomes than the adaxial surface. The leaves were amphistomatic, with the guard cells located in line with epidermal cells. Common bean leaves presented paracytic, anomocytic and anisocytic stomatal types. All common beans presented the adaxial epidermis of the leaves with a lower density of bigger stomates than on the abaxial epidermis. Our results demonstrate that micromorphological characteristics on both leaf surfaces are variable traits among common bean types.

Taxonomy of the New World species of Lotus (Leguminosae: Loteae)

The aims of the present study were to elucidate the relationships of the New World Lotus species groups, subgenera Acmispon Raf. (sections Microlotus Benth. and Simpeteria Ottley), Hosackia Benth. and Syrmatium Vog., and to compare these results with previous classifications and recent morphological and molecular phylogenetic hypotheses. A numerical taxonomic study using unweighted pair-group arithmetic average clustering was performed. The phenogram was generated from 34 operational taxonomic units (OTUs) × 41 characters (four vegetative characters and the basic chromosome numbers, 16 epidermal traits and 20 reproductive characters). The epidermal microcharacters (epidermal cells, stomata, stomatal index and trichomes) are described and summarised for 18 species of Hosackia and Syrmatium, and the remaining characters were derived from the literature. Phenetic results resolved four groups of species which coincide with the new genera Acmispon, Hosackia Douglas ex Benth., Ottleya D.D.Sokoloff and Syrmatium proposed, having taken into consideration the most recent morphological and phylogenetic hypotheses.

Leaf epidermal microcharacters of the Old World species of Lotus (Leguminosae: Loteae) and their systematic significance

Some perennial species of Lotus L. (Leguminosae: Loteae) from the Old World constitute an important forage resource. The epidermal microcharacters of 15 species belonging to the Old World Lotus angustissimus L., L. corniculatus L., L. creticus L. and L. peregrinus L. groups were described to compute the phenetic relationships, and to compare these results with previous classifications and phylogenetic hypotheses. Data on epidermal cells, stomata, stomatal indeces and trichomes were recorded and summarised in tables and illustrations. To test the taxonomic value of epidermal features and to establish the phenetic relationships, two numerical analyses were performed. Phenograms by the unweighted pair-group method (UPGMA) of clustering were generated. Results of the numerical analysis using a basic data matrix (15 operational taxonomic units × 15 epidermal characters) suggested that epidermal characteristics make it possible to establish species and species groups relationships; however, they were not totally coincident with previous classifications. An additional analysis using epidermal characters plus other morphological characters from leaves, flowers, fruits and seeds led to establish species and species groups relationships. Results generated by the latter analysis demonstrated that epidermal traits, together with other characters, are useful and informative for testing species clustering. Phenetic results coincide with earlier classifications and chromosome-number studies and accord well with a previous phylogenetic hypothesis in showing the close relationship among species of the Old World Lotus groups included in this study.

New media for increasing sporulation and germination of Phaeoisariopsis griseola conidia

The slow growth rate of the fungus Phaeoisariopsis griseola and the availability of a homogeneous highly concentrated inoculum is an important constraint for pathogenicity or virulence studies, where plant inoculations are needed. Therefore, the purpose of this paper was to evaluate the effect of supplementing culture media with Amaranthus cruentus seed meal on fungal growth and sporulation of isolates of P. griseola belonging to the Mesoamerican and Andean groups. The amendment of PDA or V8 media with A. cruentus seed meal resulted in a considerable increase in the number of conidia and also in their capacity to germinate; this depended mostly on the stage of maturity of conidia. Mesoamerican and Andean isolates produced a different number of conidia when cultured in vitro. Furthermore, while in Mesoamerican isolates a second degree polynomial represented the relationship between number of conidia and amount of A. cruentus supplementation, in Andean isolates the relationship was linear. It seems that either one or several of the nutritional factors provided by A. cruentus contributed to the increased production of conidia and their development, resulting in faster development of the disease and an earlier appearance of symptoms. Therefore, for cultural studies, especially for inoculum production and for pathogenicity evaluations, supplementation of the media with A. cruentus seed meal proved to be a good alternative.