Defence reactions in two potato cultivars following infection with two races ofPhytophthora infestans

Summary The kinetics of accumulation of chitinases, glucanases and phytoalexins were studied in two potato cultivars, differing in their degrees of vertical and horizontal resistance, when infected with two races ofPhytophthora infestans. Tuber disks of cvs Kennebec (susceptible, low horizontal resistance) and Huinkul (tolerant, high horizontal resistance) were infected with either race “0” (avirulent) or “C” (complex, race 1.3.5.7.11) ofPhytophthora infestans. Extracts of tuber tissue (0–7 days) from cv. Kennebec infected with race “0” showed a strong increase in phytoalexin production and in chitinase and glucanase activities when compared with those infected with race “C”. These results indicate that race “C” is able to block defensive reactions. No significant differences were observed in cv. Huinkul infected with both races. The contribution of these reactions to horizontal resistance is unknown, and our results would not support a conclusive role for them in the interaction.     

Allometric above-belowground biomass equations for Nothofagus pumilio (Poepp. & Endl.) natural regeneration in the Chilean Patagonia

? In the present study, allometric biomass equations were developed for Nothofagus pumilio natural regeneration relating foliage, stem and branches (aboveground), roots (belowground), and total biomass to basal diameter and total height, based on destructive measurements of 390 naturally regenerated seedlings and saplings.

? Basal diameter was the most important independent variable in all equations and accounted for more than 88% of the variability of the different biomass components. The addition of height as a second independent variable slightly improved the predictions.

? The best-fit biomass components equations that were based on combinations of basal diameter and height as independent variables had adjusted R ² values between 0.80 and 0.95 and a mean percent standard error between 21.3% and 26.6%.

? Based on the best-fit biomass equations and the natural regeneration development in a 14-years chronosequence in forests managed under shelterwood cuts, the total biomass varied from 0.9 Mg ha^?1 (0.5 Mg ha^?1 above and 0.4 Mg ha^?1 belowground) for the primary forest, before the shelterwood cuts, to 19.5 Mg ha^?1 (13.6 Mg ha^?1 above and 5.9 Mg ha^?1 belowground) 14 years after the seed cut. In the same period, carbon storage varied, from 0.5 Mg ha^?1 to 9.8 Mg ha^?1.

     

Acute toxicity of nitrite on white shrimp Litopenaeus vannamei (Boone) juveniles in low‐salinity water

The nitrite toxicity was estimated in juveniles of L. vannamei. The 24, 48, 72 and 96 h LC₅₀ of nitrite‐N on juveniles were 8.1, 7.9, 6.8 and 5.7 mg L^?1 at 0.6 g L^?1; 14.4, 9.6 8.3 and 7.0 mg L^?1 at 1.0 g L^?1; 19.4, 15.4, 13.4 and 12.4 mg L^?1 at 2.0 g L^?1 of salinity respectively. The tolerance of juveniles to nitrite decreased at 96 h of exposure by 18.6% and 54.0%, when salinity declined from 1.0 to 0.6 g L^?1 and from 2.0 to 0.6 g L^?1 respectively. The safe concentrations at salinities of 0.6, 1.0 and 2.0 g L^?1 were 0.28, 0.35 and 0.62 mg L^?1 nitrite‐N respectively. The relationship between LC₅₀ (mg L^?1), salinity (S) (g L^?1) and exposure time (T) (h) was LC₅₀ = 8.4688 + 5.6764S – 0.0762T for salinities from 0.6 to 2.0 g L^?1 and for exposure times from 24 to 96 h; the relationship between survival (%) and nitrite‐N concentration (C) for salinity of 0.6–2.0 g L^?1, nitrite‐N concentrations of 0–40 mg L^?1 and exposure times from 0 to 96 h was as follows: survival (%) = 0.8442 + 0.1909S – 0.0038T – 0.0277C + 0.0008ST + 0.0001CT–0.0029SC, and the tentative equation for predicting the 96‐h LC₅₀ to salinities from 0.6 to 35 g L^?1 in L. vannamei juveniles (3.9–4.4 g) was 96‐h LC₅₀ = 0.2127 S² + 1.558S + 5.9868. For nitrite toxicity, it is shown that a small change in salinity of waters from 2.0 to 0.6 g L^?1 is more critical for L. vannamei than when wider differences in salinity occur in brackish and marine waters (15–35 g L^?1).     

Evaluation of culture of the mussels Choromytilus chorus and Aulacomya ater (Molina) in northern coasts of Chile

The culture of Aulacomya ater and Choromytilus chorus in northern Chile was evaluated by collecting spat from both species from their natural environments and culturing them in an area isolated from natural populations. The spat collection at the site selected allowed the establishment of four cohorts of A. ater and six cohorts of Ch. chorus after 131 days. These cohorts were transported 250 km south for further growth, resulting in 290 ropes of Ch. chorus and 30 ropes of A. ater with an average of 900 specimens with a 13.5 mm mean size. After 29 months of cultivation, the yield was 623.7 ± 62.2 specimens of A. ater and 575.3 ± 49.3 specimens of Ch. chorus per rope of 3.5 m long. The growth attained during this period indicated values of L_∞ = 136 mm and k = 0.58 for Ch. chorus and L_∞ = 107 mm and k = 0.66 for A. ater. The Ch. chorus specimens reached greater lengths at month 15 than the A. ater specimens with the same age. For the total length–weight ratio and the soft part length–weight ratio for specimens above 60 mm in length, A. ater presented higher weights at the same lengths than Ch. chorus. We established that Ch. chorus reached its optimum soft part weight after 19 months and at a size of 82 mm, whereas this optimum was reached by A. ater after 18 months and at 68 mm. We concluded that farming both species in northern Chile was viable.     

Breeding for disease resistance of Penaeid shrimps

Diseases are a major constraint on the intensive production of shrimps. Conditions in production ponds favour disease development, and epidemics of several previously unreported diseases have occurred and caused severe losses. When elimination, eradication or cultural control is difficult, selective breeding for host resistance to the pathogen may be an attractive option for disease control. However, host resistance is not a panacea and should only be considered when (a) the disease causes severe damage (b) there are no other existing simple cost effective control measures and (c) there is demonstrable genetic variation in resistance and this is not coupled with an excessive level of negative associations with other desirable characteristics. Shrimp have only recently been domesticated and breeding for resistance only began in the mid 1990s; there is limited experience with shrimp breeding in particular and crustaceans in general. Consequently, the principles and concepts behind breeding programmes are based largely on experiences with other species in both the plant and animal kingdoms. Commercial growers now seed ponds with shrimp populations selected for resistance to Taura Syndrome Virus with excellent results, whilst up to now development of White Spot Syndrome Virus resistant populations has been an elusive goal. The original TSV resistant populations were developed using simple mass selection techniques (Colombia). In later generations family based selection has been applied on populations, which initially had survival rates of about 30%, with care taken to reduce inbreeding and loss of genetic variation. This suggests that when the original populations have a reasonable level of resistance, and straightforward, effective selection protocols exist, it is relatively simple to breed for resistance. With catastrophic diseases, such as WSSV, which cause mortalities of 98% or more the frequency of resistance is low and it is suggested that for theoretical reasons single gene, rather than polygenic, resistance is likely to develop. The low frequency of resistance genes in breeding populations may cause genetic bottlenecks which will greatly reduce the genetic variation in the populations. In order to maintain the genetic variation the genes from the small numbers of survivors should be introgressed into populations with broader genetic variability. Furthermore, in order to minimize the probability of breakdown of resistance pyramiding of resistant genes on different loci would be advantageous.Genetic variation in resistance may be encountered either in the initial base populations or may spontaneously arise due to mutations or new recombinants. With extremely prolific species such as shrimps, millions of animals can readily be screened for survival and hence resistant mutants or recombinants may be identified. Once genetic variation has been detected the most appropriate breeding methodology will depend on the nature of both the resistance and the disease or diseases that are of interest to the producers.     

Aluminum-induced oxidative stress in lymphocytes of common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>)

Several studies of fish have shown that aluminum may induce hypoxia, hypercapnia, metabolic acidosis, and respiratory failure. In lymphocytes, morphologic abnormalities and reduced immune activity have been observed. Nevertheless, there is little data on oxidative stress and such data are essential in order to identify its mechanism of action. The common carp Cyprinus carpio, an omnivorous fish commonly used in commercial aquaculture, has been proposed as a test organism in toxicologic assays due to its economic importance and wide geographic distribution. The aim of this work was to evaluate Al-induced oxidative stress in lymphocytes of the common carp C. carpio. Specimens were exposed to three different concentrations of Al (0.05, 120, and 239 mg/l) in a static exposure system for 96 h. At the end of the exposure period, blood was collected and lymphocytes were separated. Lipid peroxidation, oxidized protein content and the activity of superoxide dismutase, catalase, and glutathione peroxidase were measured. Results show that the tested Al concentrations modified the activity of antioxidant enzymes and elicited higher levels of lipid peroxidation and oxidized proteins. The degree of damage induced was concentration and tissue dependent.     

Trophic mass balanced models and dynamic simulations of benthic communities from La Rinconada Marine Reserve off northern Chile: network properties and multispecies harvest scenario assessments

• 1. Mass balanced trophic models and dynamic simulations of two benthic ecological systems from La Rinconada Marine Reserve (Antofagasta Bay, SE Pacific) were constructed.
• 2. The scallop Argopecten purpuratus is the most important benthic resource in La Rinconada Marine Reserve, followed by the carnivorous snail Thais chocolata, and the filter‐feeder bivalves Tagelus dombeii and Transennella pannosa.
• 3. Information on biomass, P/B ratios, catches, food spectrum, consumption, and dynamics of commercial and non‐commercial species was obtained and examined using Ecopath with an Ecosim software package.
• 4. The bivalves A. purpuratus and T. dombeii represented the most abundant compartments in the studied subsystems. Of the carnivores, the snail T. chocolata was dominant, followed by the crabs Cancer spp. and the functional group of large epifauna.
• 5. The two subsystems presented similar values of system throughput. The mean trophic level of their fisheries also reached similar magnitudes (2.0), showing that the harvests in each system concentrated on secondary producers. Likewise, both subsystems presented similar A/C ratios (29.9 and 30.3), suggesting that they were immature.
• 6. The results obtained using mixed trophic impact (MTI) and Ecosim (increasing the fishing mortality F_i by four times) showed that only four species propagated the highest direct and indirect effects. Coincidentally, these species are the most economically important and the changes produced by the scallop A. purpuratus are noteworthy.
• 7. With regard to the system recovery time (SRT) estimates, only three species or functional groups presented the highest magnitudes, from highest to lowest: the sea star Luidia magallanica, the scallop A. purpuratus, and the crabs Cancer spp.
• 8. The topological keystone indexes of Jordán and Libralato had divergent results. According to Jordán's index, the keystone species were L. magallanica, Cancer spp., and detritus; whereas Libralato's index showed phytoplankton to be the keystone species.
• 9. Based on the results obtained, it is concluded that trophic mass balanced models and simulated management scenarios have considerable value for planning interventions and manipulations or for planning more sustainable management strategies in La Rinconada Marine Reserve. Copyright © 2009 John Wiley & Sons, Ltd.

     

Virulence and pCM1 plasmid carriage are related to BOX-PCR fingerprint type in strains of Clavibacter michiganensis subsp. michiganensis that cause bacterial wilt and canker of tomato in Argentina

Clavibacter michiganensis subsp. michiganensis (Cmm) causes bacterial wilt and canker in tomato, producing important economic losses worldwide. Its virulence has been related to several putative virulence factors present on a chromosomal pathogenicity island and on plasmids pCM1 and pCM2, in strain NCPPB382. We genotypically characterized a collection of Cmm isolates from the main greenhouse tomato-producing areas of Argentina by BOX-PCR fingerprinting and screened for the presence of genes and plasmids involved in pathogenicity by PCR. In addition, we evaluated in vitro cellulolytic activity and virulence in planta of selected strains. BOX-PCR fingerprinting clustered strains into four groups. Group II was dominant and included the most virulent strains, while Group III was the smallest and had the least virulent strains. All local strains exhibited similar cellulolytic activity. Most of the examined strains carry two plasmids of similar size to those of NCPPB382, although there were strains with one or three plasmids. By PCR amplification of repA, pCM1 was detected only in strains belonging to Group III, which includes local strains closely related to reference strain NCPPB382. All analysed pathogenicity genes were widespread among strains, and so in strains belonging to Groups I and II, celA found on pCM1 in NCPPB382 could be found in the chromosome or in plasmids other than pCM1. This study contributes to a better understanding of the diversity of Cmm genetic profiles and virulence of strains present in Argentina. Such information could be useful for the selection of strains for screening of host resistance and development of resistant tomato varieties.     

Stabilization of caseinate-covered oil droplets during acidification with high methoxyl pectin

Polysaccharides are widely used in the food industry to modify the stability of protein-based drinks. However, an in depth knowledge of the interactions occurring in the system is still lacking. In this study, the interactions between sodium caseinate and high methoxyl pectin under acidification conditions were studied nondestructively and without dilution using transmission diffusing wave spectroscopy. Oil-in-water emulsions were prepared with 10% soybean oil and 0.5% sodium caseinate. Various concentrations of pectin (ranging from 0 to 0.2%) were added, and the emulsions were acidified with glucono-delta-lactone. With acidification, a "sol-gel" transition occurred and emulsions containing pectin were more stable at lower pH than those without pectin. Furthermore, the sol-gel transition of the mixtures was more sudden for control emulsions without pectin. While in control samples the final solidlike emulsion after gelation tended to be more inhomogeneous and more dissimilar to the starting emulsion, emulsions with pectin in solution gelled later under acidification. With a sufficient amount of pectin, the emulsions showed no aggregation and the destabilization pH varied depending on the amount of pectin present in the emulsions. At intermediate pH values (pH > 5.5), the emulsions displayed a decrease in particle size, more pronounced in samples containing pectin. The results collected using light scattering in concentrated systems, 10% (v/v) in our case, suggested that pectin stabilizes the emulsion oil droplets forming a network of oil droplets loosely connected by strands of pectin.     

Effects of water depth on survival and growth of <Emphasis Type="Italic">Argopecten purpuratus</Emphasis> (Lamarck, 1819) spat in northern Chile

Collection and suspended culture of Argopecten purpuratus spat in Japanese-type collectors was undertaken in the Rinconada Marine Reserve (Antofagasta, Chile) to determine growth variations between surface and bottom waters. Scallop spat was collected at 16-m depth and grown at 1- and 16-m depths. An initial settlement of ca. 13,000 post-larvae per bottom collector (2 cohorts) was observed on 3 February 2001. Two new cohorts settled in bottom collectors on 3 March, while no spat settlement occurred in surface collectors. The four cohorts exhibited substantial and different mortality rates over the study period, depending on the cohort and on-growing depth. The first and second cohorts exhibited mortality rates of 80.3 and 53.1% in bottom collectors, respectively, versus 29 and 43.6% in surface structures. The third and fourth cohorts exhibited mortality rates of 21.4 and 59.7% in bottom collectors, respectively. Mean shell height of scallop spat after 88 days of culture was 6.46 mm for the first cohort and 4.37 mm for the second cohort in bottom collectors, versus 10.33 and 7.31 mm in surface collectors, respectively. Mean post-larval growth rate in bottom collectors (86 μm day⁻¹) was significantly lower than growth rate in surface collectors (146 μm day⁻¹). Factors explaining the depth-related mortality and growth rates are discussed to improve scallop culture in the Reserve. It was concluded from the results that culture improvement in Antofagasta Bay would require collecting spat in bottom waters and raising it near the surface during initial cultivation stages.