Characterization of fungal pathogens and germplasm screening for disease resistance in the main production area of the common bean in Argentina.

The common bean (Phaseolus vulgaris L.) is the most important grain legume in the human diet, mainly in Africa and Latin America. Argentina is one of the five major producers of the common bean in the world, and the main cultivation areas are concentrated in the northwestern provinces of this country. Crop production of the common bean is often affected by biotic factors like some endemic fungal diseases, which exert a major economic impact on the region. The most important fungal diseases affecting the common bean in Argentina are white mold caused by Sclerotinia sclerotiorum, angular leaf spot caused by Pseudocercospora griseola, web blight and root rot caused by Rhizoctonia solani, which can cause production losses of up to 100% in the region. At the present, the most effective strategy for controlling these diseases is the use of genetic resistance. In this sense, population study and characterization of fungal pathogens are essential for developing cultivars with durable resistance. In this review we report diversity studies carried out on these three fungal pathogens affecting the common bean in northwestern Argentina, analyzing more than 200 isolates by means of molecular, morphological and pathogenic approaches. Also, the screening of physiological resistance in several common bean commercial lines and wild native germplasm is reviewed. This review contributes to the development of sustainable management strategies and cultural practices in bean production aimed to minimize yield losses due to fungal diseases in the common bean.

Nectary structure is not related to pollination system in Trichocereeae cactus from Northwest Argentina.

Floral nectaries are essential for plant reproduction but little is known about the relationship between these secretory structures and pollination system in cacti. To test phenotypic patterns in nectaries associated with pollination syndromes and/or with its pollinators, we selected from evolutionarily related genera Cleistocactus, Denmoza, and Echinopsis, a set of species with bird-pollinated flowers and floral traits that may fit with ornithophily or with sphingophily, and other set of sphingophilous species with moths as effective pollinator. Observations were made under light microscope and scanning and transmission electron microscopes. Nectaries are located at the base of the filaments welded to the tube, forming a chamber. The nectary consists of the epidermis with distinctive features in each genus, a secretory parenchyma which may be vascularized and a non-secretory vascularized parenchyma. Anatomical variants observed in nectaries of different species are not consistent with the floral pollination syndromes neither with groups of pollinators. The basic structure of the nectar chamber is relatively conserved, a fact that may be explained by phylogenetic conservatism among the genera investigated. Our results revalue the role of anatomical traits for the systematics of Cactaceae.

Effects of essential oils from two Lippia species on growth of phytopathogenic fungi / Efecto de los aceites esenciales de dos especies de Lippia sobre el crecimiento de hongos fitopatógenos

Chemical characterization of the essential oils of two Lippia species by GC-MS and NMR spectroscopy revealed that limonene (84.3%) and ß-caryophyllene (6.1%) were the most abundant components in Lippia turbinata while (6S,7S,10S)-trans-davanone (99.1%) predominated in Lippia integrifolia. Antifungal activity of the essential oils was determined by headspace volatile exposure assay against the fungal phytopathogenic Sclerotinia sclerotiorum, Sclerotium rolfsii and Rhizoctonia solani. The essential oil of L. turbinata showed potent antifungal activity against the panel of fungi tested while that the oil of L. integrifolia significantly inhibited the mycelial growth of S. rolfsii and R. solani.

La caracterización química de los aceites esenciales de dos especies de Lippia por cromatografía gaseosa-espectrometría de masas (CG-EM) y espectroscopia de RMN reveló que limoneno (84,3%) y ß-cariofileno (6,1%) fueron los componentes más abundantes de Lippia turbinata mientras que (6S,7S,10S)-trans-davanona (99,1%) predominó en Lippia integrifolia. La actividad antifúngica de los aceites esenciales se determinó por el ensayo de exposición a los vapores frente a los hongos fitopatógenos Sclerotinia sclerotiorum, Sclerotium rolfsii y Rhizoctonia solani. El aceite esencial de L. turbinata mostró una potente actividad antifúngica frente al panel de hongos ensayados, mientras que el aceite de L. integrifolia inhibió significativamente el crecimiento micelial de S. rolfsii y R. solani.

Thermal buffering capacity of the germination phenotype across the environmental envelope of the Cactaceae.

Recruitment from seeds is among the most vulnerable stage for plants as global temperatures change. While germination is the means by which the vast majority of the world's flora regenerate naturally, a framework for accurately predicting which species are at greatest risk of germination failure during environmental perturbation is lacking. Taking a physiological approach, we assess how one family, the Cactaceae, may respond to global temperature change based on the thermal buffering capacity of the germination phenotype. We selected 55 cactus species from the Americas, all geo-referenced seed collections, reflecting the broad environmental envelope of the family across 70° of latitude and 3700 m of altitude. We then generated empirical data of the thermal germination response from which we estimated the minimum (Tb ), optimum (To ) and ceiling (Tc ) temperature for germination and the thermal time (θ50 ) for each species based on the linearity of germination rate with temperature. Species with the highest Tb and lowest Tc germinated fastest, and the interspecific sensitivity of the germination rate to temperature, as assessed through θ50 , varied tenfold. A left-skewed asymmetry in the germination rate with temperature was relatively common but the unimodal pattern typical of crop species failed for nearly half of the species due to insensitivity to temperature change at To . For 32 fully characterized species, seed thermal parameters correlated strongly with the mean temperature of the wettest quarter of the seed collection sites. By projecting the mean temperature of the wettest quarter under two climate change scenarios, we predict under the least conservative scenario (+3.7°C) that 25% of cactus species will have reduced germination performance, whilst the remainder will have an efficiency gain, by the end of the 21st century.