Morpho-physiological analysis of adaptive responses of common bean (Phaseolus vulgaris L.) to drought stress /

BibliografiaEl frijol común (Phaseolus vulgaris L.) es la leguminosa alimenticia más importante en los trópicos. Es cultivada por pequeños agricultores y por lo general expuesta a condiciones desfavorables con mínimo uso de insumos. La sequía y la baja fertilidad del suelo, especialmente deficiencias de nitrógeno (N) y fósforo (P), son principales limitaciones para el rendimiento del frijol en los sistemas de pequeños productores. El frijol puede derivar parte de su requerimiento de N de la atmósfera a través de la fijación simbiótica de nitrógeno (SNF). El estrés por sequía limita severamente la capacidad SNF de las plantas. Identificación de rasgos asociados con resistencia a sequía contribuye a mejorar el proceso de generación de genotipos de frijol adaptados a estas condiciones. Se realizaron ensayos de campo en el Centro Internacional de Agricultura Tropical (CIAT), Palmira, Colombia, para determinar la relación entre rendimiento de grano y diferentes parámetros morfo fisiológicos tales como uso efectivo del agua (EUW), biomasa dosel, removilización de fotosintatos (índice de partición vaina, índice de cosecha, índice de cosecha de vaina) y capacidad de SNF en líneas élites seleccionadas por resistencia a sequía durante la última década. También se validó la metodología de abundancia natural de 15N usando tejido de grano para cuantificar diferencias fenotípicas en la capacidad SNF y su aplicación en programas de mejoramiento. Se utilizó discriminación de isótopo de carbono (CID) para la estimación de uso eficiente del agua (WUE) y uso efectivo de agua (EUW). Se evaluaron 36 genotipos de frijol pertenecientes al acervo genético mesoamericano en condiciones de campo con dos niveles de suministro de agua (riego y sequía) en dos temporadas. Adicionalmente, se realizó un estudio en condiciones de invernadero utilizando cilindros de plástico con suelo, para determinar la relación entre rendimiento de grano y diferentes características morfo fisiológicas de raíz tales como la longitud total de raíces, producción de raíces finas y tasa de crecimiento visual de raíces. La resistencia a estrés por sequía se asoció positivamente con EUW, raíces profundas y vigorosas, mejor crecimiento de las plantas, y superior movilización de fotosintatos a la formación de vaina y granos; y negativamente con días a floración y días a madurez fisiológica. Basándose en diferencias fenotípicas obtenidas en CID, conductancia estomática, biomasa del dosel y rendimiento de grano en condiciones de sequía, las líneas evaluadas se clasificaron en dos grupos, los ahorradores y los gastadores de agua. Estos dos grupos también se diferenciaron en sus características de raíces, los gastadores de agua con un vigoroso y profundo sistema de raíces y los ahorradores con un moderado a superficial sistema de raíces con mayor presencia de raíces finas. Se utilizó el método de abundancia natural de 15N para comparar capacidad de SNF estimada convencionalmente usando tejido foliar vs tejido de grano. Los resultados mostraron una correlación positiva y significativa entre el nitrógeno derivado de la atmósfera (Ndfa) calculado utilizando tejido foliar y Ndfa usando el tejido de grano. El método usando grano mostró variabilidad fenotípica en la capacidad de SNF bajo condiciones de riego y sequía, y una reducción significativa en condiciones de sequía. Se recomienda usar este método en programas de mejoramiento de frijol para mejorar la capacidad SNF. Mejor habilidad SNF bajo estrés por sequía fue relacionada con presencia de raíces gruesas. Mayor absorción de nitrógeno del suelo fue asociado con un sistema de raíces fino y profundo. El índice de cosecha vaina, discriminación de isotopo de carbono y Ndfa usando tejido de grano podría ser criterios de selección útiles en los programas de mejoramiento para seleccionar frijol común con resistencia a la sequía.Common bean (Phaseolus vulgaris L.) is the most important food legume in the diet of poor people in the tropics. This legume is cultivated by small farmers and is usually exposed to unfavorable conditions with minimum use of inputs. Drought and low soil fertility, especially phosphorus (P) and nitrogen (N) deficiencies, are major limitations to bean yield in smallholder systems. Beans can derive part of their required N from the atmosphere through symbiotic nitrogen fixation (SNF). Drought stress severely limits SNF ability of plants. Identification of traits associated with drought resistance contributes to improving the process of designing bean genotypes adapted to these conditions. Field studies were conducted at the International Center for Tropical Agriculture (CIAT), Palmira, Colombia to determine the relationship between grain yield and different parameters in elite lines selected for drought resistance over the past decade. The selected traits were effective use of water (EUW), canopy biomass, remobilization of photosynthates to grain (pod partitioning index, harvest index and pod harvest index) and SNF ability. Moreover, in field trials we also validated the use of 15N natural abundance in grain tissue to quantify phenotypic differences in SNF ability for its implementation in breeding programs aiming to improve SNF in common bean. Carbon isotope discrimination (CID) was used for estimation of water use efficiency (WUE) and effective use of water (EUW). A set of 36 bean genotypes belonging to the Middle American gene pool were evaluated under field conditions with two levels of water supply (irrigated and rainfed) over two seasons. Additionally, a greenhouse study was conducted at CIAT using plastic cylinders with soil inserted into PVC pipes, to determine the relationship between grain yield and different root parameters such as total root length, fine root production and visual root growth rate in same group of elite lines under drought stress. Resistance to terminal drought stress was positively associated with EUW combined with a deeper and vigorous root system, better plant growth, and superior mobilization of photosynthates to pod and seed production, but negatively associated with days to flowering and days to physiological maturity. Based on phenotypic differences in CID, leaf stomatal conductance, canopy biomass and grain yield under drought stress, the tested lines were classified into two groups, water savers and water spenders. These groups also differ in their root characteristics, water spenders with a vigorous and deeper root system and water savers genotypes with a moderate to shallow root system and more presence of fine roots. We used 15N natural abundance method to compare SNF ability estimated from shoot tissue sampled at mid-pod filling growth stage vs. grain tissue sampled at harvest. The results showed a significant positive correlation between nitrogen derived from the atmosphere (Ndfa), estimated using shoot tissue at mid-pod filling, and Ndfa estimated using grain tissue at harvest. The method showed phenotypic variability in SNF ability under both drought and irrigated conditions. A significant reduction in SNF ability was observed under drought stress. We suggest that the method of estimating Ndfa using grain tissue (Ndfa-G) can be applied in bean breeding programs to improve SNF ability. Using this method of Ndfa-G, we identified bean lines that combine greater SNF ability with higher grain yield under drought stress. Better SNF ability under drought stress was related with superior presence of thick roots. Superior N uptake from the soil was associated with a large root system with more presence of fine roots. Pod harvest index, grain CID and Ndfa using grain tissue could be a useful selection criterion in breeding programs to select for drought resistance in common bean

Wildflower strips enhance pest regulation services in citrus orchards

Contemporary approaches to agriculture must be reimaged to include ecological techniques that maximise ecosystem services, so that food can be produced sustainably whilst simultaneously meeting yield demands. Pest regulation services, harnessed through the conservation of natural enemies in the agri-environment are an economically important service degraded by conventional citrus production practices. For the first time, a sown wildflower strip composed of native forbs and tussock-forming grasses has been investigated for its influence on natural enemies and their pest regulation services in citrus orchards. A novel management strategy was applied, using the predicted generation times of Aonidiella aurantii Maskell (Hemiptera: Diaspididae), a key pest in citrus, to determine whether cutting the wildflower strips could force spill-over of natural enemies onto the adjacent crop, enhancing pest regulation services. Three treatments applied to orange orchard alleyways were compared: i) a control treatment, the standard orchard practice of regular cutting to 5 cm throughout the year, ii) a sown wildflower treatment managed with cutting once a year in February to a height of 10 cm (standard management wildflower treatment, SMWT), and iii) the same sown wildflower treatment but managed with two additional cuts in May and June (active management wildflower treatment, AMWT). Orange tree canopies were sampled for natural enemies, and pest regulation services were quantified using sentinel prey cards baited with Ephestia kuehniella eggs. Natural enemy richness was greatest in canopies with SMWT, supporting a greater relative abundance of primary parasitoids and lower relative abundances of antagonists (ants) compared to the control. This was associated with enhanced pest regulation services (depletion of sentinel prey from baited cards), especially during the early summer months, which coincides with a critical period to control A. aurantii and other key citrus pests. In contrast, AMWT did not enhance natural enemy richness, and pest regulation services were diminished. This study suggests that leaving wildflower strips uncut throughout the season, as in SMWT, may help to mitigate pest incidence through enhanced pest regulation services. Further studies are now required to determine how this would influence populations of target pests

Use of UV-C postharvest treatment for extending fresh whole tomato (Solanum lycopersicum, cv. Zinac) shelf-life

The effect of UV-C treatments (0.32, 0.97, 2.56, 4.16 and 4.83 kJ.m(-2) at 254 nm) on the physical-chemical properties [colour, texture, total phenolic content (TPC), weight loss (WL)], and mesophylic counts of whole tomato, was evaluated during 15 days at 10 A degrees C. During storage, the Ctr samples acquired faster red colour than all UV-C samples (higher a* and lower A degrees h values). Comparing texture of Ctr and UV-C samples at 15(th) storage day, an increase of 9 and 8 % on firmness of treated samples at low UV-C intensities (0.32 and 0.97 kJ.m(-2), respectively) was observed. At the end of the storage, Ctr samples showed ca. 4 Log(10) of mesophylic load, and the samples treated at 0.97 and 4.83 kJ.m(-2) revealed the lowest microbial load (1.9 and 3.2 Log(10), respectively). These results indicate that UV-C radiation, at an appropriate dose, combined with low storage temperature (10 A degrees C) are an effective method to preserve the postharvest life of tomato, without adversely affecting quality parameters.info:eu-repo/semantics/publishedVersio