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Jacobo-Velazquez D.A.,Texas A&M University | Gonzalez-Aguero M.,Institute of Agricultural Research | Cisneros-Zevallos L.,Texas A&M University
Scientific Reports

Plants subjected to wounding stress produce secondary metabolites. Several of these metabolites prevent chronic diseases and can be used as colorants, flavors, and as antimicrobials. This wound-induced production of plant secondary metabolites is mediated by signaling-molecules such as reactive oxygen species (ROS), ethylene (ET) and jasmonic acid (JA). However, their specific role and interactions that modulate the wound-respond in plants is not fully understood. In the present study, a subtractive cDNA library was generated, to better understand the global response of plants to wounding stress. Carrot (Daucus carota) was used as a model system for this study. A total of 335 unique expressed sequence tags (ESTs) sequences were obtained. ESTs sequences with a putative identity showed involvement in stress-signaling pathways as well as on the primary and secondary metabolism. Inhibitors of ROS biosynthesis, ET action, and JA biosynthesis alone and in combination were applied to wounded-carrots in order to determine, based on relative gene expression data, the regulatory role of ET, JA, and ROS on the wound-response in plants. Our results demonstrate that ROS play a key role as signaling-molecules for the wound-induced activation of the primary and secondary metabolism whereas ET and JA are essential to modulate ROS levels. Source

Developmental time, parasitism, emergence, longevity, fecundity and demographic parameters of population of Encarsia bimaculata Heraty and Polaszek (Hymenoptera: Aphelinidae), a parasitoid attacking Bemisia tabaci (biotype B) (Gennadius) (Homoptera: Aleyrodidae) infesting soybean, Glyine max L. (Merr), cowpea, Vigna unguiulata L. and garden bean, Phaseolus vulgaris L. (Fabeles: Fabaceae) were quantified and compared. Encarsia bimaculata was able to complete its life cycle independent of the B. tabaci instar parasitized. However, parasitoid development was significantly slower when first (19 d), second (15 d) instars or pharate adults (14 d) were parasitized compared to the third (13 d) or fourth (13 d) instars. Consequently, percent parasitism was higher when the third (51%) or fourth (46%) instars were parasitized compared to the first (22%), second (25%) instars or pharate adults (36%) of B. tabaci. Similarly, percent parasitoid emergence was significantly higher when third (83%) or fourth (76%) instars were parasitized compared to when the first (34%), second (64%) or pharate adults (54%) were parasitized. Host plant species significantly influenced egg to adult developmental time, percent parasitism and the day on which E. bimaculata nymphs hatching from eggs was first observed. More nymphs were parasitized on cowpea (40%) followed by garden bean (36%) and soybean (32%), while percent hatching was significantly higher on soybean (76%) followed by cowpea (68%) and garden bean (42%). Adult parasitoid females lived an average of 6.7 d on soybean, 7.6 d on cowpea and 7.2 d on garden bean and laid a lifetime average of 27 eggs on soybean, 31 eggs on cowpea and 30 eggs on garden bean. The daily mean fecundity of E. bimaculata was not significantly different on the three bean species. Life table parameters showed that the net reproductive rate (R(o)) was 14.50, generation time (T(c)) was 17.16, intrinsic rate of natural increase (r(m)) was 0.16, finite rate of growth (lambda) was 1.17 and doubling time (T(d)) was 4.44 for parasitoids on soybean. On cowpea, R(o) was 15.32, T(c) was 18.59, r(m) was 0.15, lambda was 1.16 and T(d) was 4.72, while, on garden bean, R(o) was 8.95, T(c) was 19.28, r(m) was 0.11, lambda was 1.12 and T(d) was 6.08. Given these life table parameters, higher population build up of the parasitoid will be expected on cowpea and soybean, respectively, compared to garden bean. Thus, for an effective augmentative release program involving E. bimaculata for the control of B. tabaci, it is important to take into consideration both the host stage of B. tabaci and the nature of the host plant on which it is developing. Source

Antoniadis V.,Democritus University of Thrace | Tsadilas C.D.,Greek National Agricultural Research Foundation | Dalias P.,Institute of Agricultural Research

Nitrate leaching may be a major problem in certain soils after intensive use of nitrogen fertilizers. Moderate use of organic amendments, i.e. sewage sludge, can supply available N and reduce the accelerating use of conventional fertilizers, which may lead to slower nitrate leaching. The aim of this study was to examine nitrate mobility in Mediterranean soils of low organic matter content using soil leaching columns amended with sewage sludge and inorganic fertilizer. Eight soil samples from the Gulf of Kalloni, Lesvos Island, which typically bear the above mentioned characteristics, were used. It was found that sludge application at 10 t ha-1 increased nitrate retention capacity of soils either by rendering a smaller amount of nitrates available to leaching or by reducing the rate of NO3-N release. Average NO3-N leaching was 0.016 in control, 0.092 in sludge treatment, and 0.130 in fertilizer treatment (units in mg N kg-1 soil mm-1 eluted water). After about 100 mm of added water, cumulative leaching of NO 3-N reached a plateau in most soils, but nitrate recovery was a fraction of the added, probably due to denitrification- and immobilization- related N losses. Source

Manriquez D.,Institute of Agricultural Research | Defilippi B.G.,Institute of Agricultural Research
Acta Horticulturae

One of the main postharvest problems in kiwifruit is flesh softening, this process being in part coordinated by ethylene. Therefore, many postharvest strategies have been developed in order to reduce fruit softening, including early harvest, controlled/modified atmosphere storage, ethylene scrubbers and 1-MCP (1-methylcyclopropene) (SmartFresh SM) applications after harvest, being SmartFresh SM extensively used in the last 3 years in Chile. Under Chilean growing conditions the harvest window is quite extend depending on the growing area, going from March to May, which could be affecting the postharvest behavior of the fruit in terms of quality attributes, including firmness among others. During the last three years, a new formulation of 1-MCP has been developed for applying this molecule in preharvest (Harvista™ Technology), being the objective of this study to evaluate the effect of this molecule during harvest and postharvest of kiwifruit. For the trials we considered two applications times before harvest and two harvest opportunities based on maturity. At harvest no differences were observed for all the attributes evaluated. But for harvest time, an effect in fruit softening was observed during cold storage showing all the fruit applied with 1-MCP a higher firmness compared to control fruit, being this effect more evident in the second harvest. This effect could be explained by the effect of 1-MCP in ethylene production and respiration rate, where lower rates in both parameters were measured in kiwifruits applied with 1- MCP. In other attributes, such as total soluble solids, titratable acidity and physiological disorders, not major differences were observed. Source

Defilippi B.G.,Institute of Agricultural Research | Robledo P.,Institute of Agricultural Research | Ferreyra R.,Institute of Agricultural Research | Soto S.,Institute of Agricultural Research | Saavedra J.,Pontifical Catholic University of Valparaiso
Acta Horticulturae

Avocado quality variability is due to the broad range of conditions in which trees are grown, especially in terms of climate and soil, and also associated with different cultural practices used among avocado growers. In the last four years, we have been performing a project in order to understand this variability by determining the effect of preharvest factors (climate, nutrition, cultural management, etc.) on the postharvest life of 'Hass' avocados, shipped under regular air (RA) and controlled atmosphere (CA) conditions. Fruit was collected from 11 commercial orchards during the 2009/10, 2010/11 and 2011/12 seasons, stored under RA and CA (4%O2and 6% CO2) for 40 and 55 days at 5°C and 90% RH, and ripened at 20°C after cold storage until reaching the ready to eat stage. The postharvest parameters evaluated included flesh firmness, color, physiological disorders and days to reach ripening. A multivariate analysis was performed to determine a possible relationship between preharvest factors and postharvest avocado quality. Under both storage conditions, a high fruit variability among experimental sites was observed in the different quality attributes evaluated after storage. Among the variables studied, the days between flowering and harvest had an inverse effect on fruit firmness level after storage. A similar behavior was found for N/Ca ratio and oil content at harvest. Other factors that directly affected fruit firmness were calcium content at harvest and orchard elevation. Source

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