Lower Disease Intensity Research Articles

Screening of resistant Indonesian black rice cultivars against bacterial leaf blight

Black rice production in Indonesia constrained by the bacterial blight disease (BLB) caused by Xanthomonas oryzae pv. oryzae pathotype IV (Xoo). Breeding of BLB resistant cultivars is considered the most sustainable method for BLB disease control, both from an environmental and agricultural perspective. Indonesia has many local black rice varieties that can be used as genes resource to support breeding program producing resistant cultivars. The present research focuses on screening local Indonesian black rice cultivars for resistance against BLB and analyzing the expression of these resistance genes in black rice after inoculation with Xoo. The black rice cultivars Cempo Ireng, Pari Ireng, Melik, Pendek, and Indmira, were inoculated with Xoo while white rice cv. Conde, IRBB21, IR64, and Java14 were used as controls. We assayed the phenotypic performance of the cultivars samples after Xoo inoculation and analyzed their resistance gene expression at 24 and 96 h after Xoo inoculation semiquantitatively. The cultivar showed the best performance was selected for further analysis of the resistance genes using Real-time quantitative PCR. Cempo Ireng was indicated the most resistant cultivar against BLB disease based on the lowest disease intensity and Area Under Disease Progress Curve (AUDPC) value. Cempo Ireng expressed resistant genes xa5, Xa10, Xa21 and RPP13-like after inoculation of Xoo. The expression of xa5, Xa10, and Xa21 was up-regulated while that of RPP13-like was down-regulated in Cempo Ireng.

Effect of Pseudomonas spp on infection of Peronosporaparasitica (Pers. Fr), the pathogen of downy mildew on Chinese cabbage

This research was conducted to study the effect of the application of Pseudomonasspp on infection of Peronosporaparasitica (Pers. Fr), the pathogen of Downy mildew on Chinese cabbage. The research was conducted in the laboratory and greenhouse Department of Plant Pests and Diseases Faculty of Agriculture Sriwijaya University, Inderalaya, OganIlir South Sumatra Indonesia. The research was conducted in the laboratory and greenhouse Department of Plant Pests and Diseases Faculty of Agriculture Sriwijaya University, Inderalaya, Ogan Ilir South Sumatra Indonesia. The research was conducted using Completely Randomized Design with ten treatments including control. ie: isolate A, Isolate B, isolate C, isolate D, isolate E, isolate F, isolate G, isolate H, isolate I and control. Each treatment consists of four replications. Results of the study showed that the application of Pseudomonas spp. can suppress the infection of P. parasitica on Chinese cabbage. The lowest disease intensity was shown by treatment C (isolate Pseudomonas sp.) which was significantly different from control. The best treatment in suppressing disease severity of downy mildew on chinese cabbage was isolate H which had disease severity of 37.07 percent, which was significantly different from control and other treatment.

Integrated management of Alternaria blight of safflower under field conditions

Safflower (Carthamus tinctorius L.), is one of the oilseeds crop grown throughout the world. The crop suffers from many diseases, among that leafspot/blight caused byAlternaria carthami (Chowdhury) has become one of the major constraints in the production and productivity of safflower all over India. The disease has been reported to cause 25 to 60 per cent yield losses in safflower. Management of safflower Alternaria blight with chemicals alone needs to be discouraged due to their ill-effects. Management trials were conducted with integration of the effective fungicides, bioagents and botanicals under natural epiphytotic condition during rabi, 2013 and 2014. The disease intensity was low (14.34%) with highest reduction (74.36%) with the combination of seed treatment with T. viride @ 10 g/kg + garlic clove extract ST @ 10 ml/kg followed by foliar spray hexaconazole FS @ 0.1 %. Seed treatment with hexaconazole ST @ 1 ml/kg followed by foliar spraying of same fungicide 0.1% also showed low disease intensity of 15.46 per cent and disease control of 72.37 per cent. Seed treatment of T. viride @ 1 ml/kg + garlic clove extract @ 10 ml/kg followed by spraying of mancozeb 0.25% reduced the disease by 69.16 per cent. Significant increase in seed yield up to 54.56 per cent and highest ICBR (3.22) was recorded in treatment of T. viride ST @ 10 g/kg + garlic clove extract ST @ 10 ml/kg + hexaconazole FS @ 0.1 %.

English

Tomato (Solanum lycopersicum L.) is a species of the family Solanaceae. It is herbaceous, annual to perennial, prostrate and sexually propagated plant with bisexual flower. Tomatoes are attacked by many kinds of plant pathogens such as fungi, bacteria, nematodes, viruses and viroid. Among bacterial diseases, bacterial soft rot devastates many important crops of the family Solanaceae particularly potato, eggplant and tomato, causing a huge decrease in yield and a greater loss in produce than any bacterial disease known. Yield losses due to post-harvest diseases of fruits and vegetables range from 20 to 30% but losses due to soft rot bacteria may reach up to 100% under insufficient conditions of storage facility, this have huge impacts on famers and vendors. In vitro efficacy of certain botanicals against bacterial soft rot of tomato were tested in the months of February to March, 2015 in the Department of Plant Pathology and Department of Biochemistry, Sam Higginbottom Institute of Agriculture, Technology and Sciences (Deemed University)– Allahabad, UP, India. Eight botanicals were screened in vitro, out of these, four were selected based on their performances and evaluated against the bacterial soft rot of storage tomato at 2, 4, and 8 days after inoculation. Maximum zone of inhibition was obtained with treated Control (T0b=17 mm), followed by Turmeric 30% (T4=12.4 mm), Turmeric 20% (T3=11 mm), then Neem 30% (T6) while the least zone of inhibition was recorded with untreated Control/water (T0a=0.4 mm) followed by Lemon 30% (T12=1 mm). Turmeric 30% (T4) proved to be best botanical under screening followed by Turmeric 20% (T3=11mm). In case of mean disease intensity at eight days after inoculation on storage tomato, highest mean value was recorded in Ginger 30% (T2=46.2) followed by Neem 20% (T5=44.2) and lowest value in Streptomycin (T0b=27), followed by Turmeric 20% (T3=27.6) then Turmeric 30% (T4=27.8). Among the botanicals, the lowest disease intensity was with T3=27.6 followed by T4= 27.8. Key words: Tomato, Pectobacterium carotovora subsp carotovora, botanicals, efficacy.

KETAHANAN VARIETAS PADI LOKAL MENTIK WANGI TERHADAP PENYAKIT BLAS

Mentik Wangi, one of the local rice varieties, is highly favored by rice farmers in Central Java. Marketers and consumers highly accept Mentik Wangi with its elliptical seeds because it has delicious taste and aroma. Besides having delicious taste, the variety is resistant to blast disease in various locations, whether planted in lowland or upland. In endemic blast disease areas, Mentik Wangi variety showed resistance to blast disease with low disease intensity, although the other varieties in these places showed quite high disease intensity. Rice blast disease is a disease that damages the rice not only on dry land, but also on rainfed and irrigation lands. At a high level of disease intensity, blast disease can cause yield losses of up to 100%. Planting resistant rice variety to prevent damage due to blast disease is one of the methods to blast disease control which is effective, inexpensive, and safe for the environment. However, control of blast disease with one component such as planting resistant rice is estimated to be ineffective in the long term, because the pathogen causes the blast disease to be able to adapt to the rice variety to form a new race that is more virulent. A rice variety that is originally resistant will gradually become susceptible to the new pathogen race. When the rice varieties which are resistant to blast disease is controlled by a single gene (monogenic resistant), the resistance of these varieties within 2-4 planting seasons will be broken by a new pathogenic race. Mentik Wangi that shows resistance to blast disease in various rice planting regions is expected to have some of the resistance genes, so that it can be used as a durable resistant variety. Keywords: Rice, Mentik Wangi, resistance, blast

Susceptible Phase of Chili Pepper Due to Yellow Leaf Curl Begomovirus Infection

One of factors that affect the severity of plant diseases caused by virus is the time of Begomovirus infection. There is a tendency that the younger the plants are infected, the greater the damage caused by the Begomovirus infection will be. This study aimed to reveal the exact time of Begomovirus infection for the purpose of resistance plant selection and to determine the onset of Begomovirus infection which resulted in the most devastating damage to the plant. The study was conducted in a factorial randomized completely block design with two factors. The first factor was 5 chili pepper genotypes and the second factor was the infection at three phases of the plant with no infection as a control treatment. The results showed that the screening for resistant and susceptible Begomovirus infection on pepper genotypes was very effective when it was done during cotyledon phase/two leaf using individual transmission method. Genotype UNIBC GTS1 was the most susceptible to infection of Begomovirus because it had the highest disease intensity, the fastest incubation period, small plant dry weight and fruit weight per plant. In contrast, genotype IPBC 12 was the most resistant genotypes. It had lower disease intensity and long incubation period. However, despite this resistant characteristic, the weight of fruit per plant of IPBC 12 genotype was not significantly different from the susceptible genotype. Genotype IPBC 14, despite having high disease intensity, could produce the highest fruit weight per plant compared to other genotypes. The infection of Begomovirus on susceptible genotype UNIB C GTS1 at various phases of the plant growth led to the pepper fruit become shorter, lower plant dry weight, smaller numbers of fruits and fruit weight per plant. While the resistant genotypes IPBC 12 had low dry weight when infected by Begomovirus in the phase of cotyledon.

KORELASI SIFAT FISIK DAN KIMIA TANAH DENGAN INTENSITAS PENYAKIT BUSUK PANGKAL BATANG TANAMAN LADA / Correlation of Physical and Chemical Soil Characteristics with Intensity of Foot Rot Disease of Black Pepper

Foot rot disease of black pepper caused by Phytophthora capsici is the most destructive disease in Southeast Sulawesi. The disease intensity is 61.2%. This disease is difficult to control because the pathogen is soil borne and influenced by various complex environmental conditions. The study aimed to determine the correlation of physical and chemical soil characteristics with disease intensity of foot rot of black pepper. Disease intensity was assessed from the subplots of black pepper plantation of 15x15 m2 consisting of 36-40 plants. Soil samples were randomly taken from the rhizosphere of the plants in each sub plot, mixed and taken as a composite. The physical and chemical analyses were conducted in the laboratory of Physics and Chemistry of the Faculty of Agriculture, Gajah Mada University. Disease intensity and soil characteristics were analyzed its correlation using a path analysis. The results showed that soil fertility in the study area was low. The path analyses indicated that physical and chemical properties that correlated with low disease intensity were high cation exchange capacity (CEC), base saturation (BS), potassium and phosphor available as well as moisture at field capacity, whereas those induced disease development were high content of clay fraction, sand fraction, porosity, total N, C-organic and salinity. The control strategy for foot rot disease in Southeast Sulawesi was possibly by increasing CEC, BS, potassium and phosphor available, as well as by improvement of soil texture that can lower high fraction of clay, sand and soil porosity

Effects of plant morphological traits on phoma black stem in sunflower

Despite the importance of Phoma black stem of sunflower in France, no specific management tools are currently deployed to control this disease. The deployment of host plant resistance could be a cost-effective and sustainable way to manage the disease. Relationships between plant morphological traits and disease intensity may provide guidance towards the identification of sunflower morphological ideotypes associated with reduced disease intensity and therefore partial resistance. Such relationships were quantified in field experiments conducted over 2 years with a set of 21 sunflower genotypes, where several morphological attributes and several disease intensity variables were measured. Plant morphology was assessed prior to epidemic onset. Disease intensity was assessed at different scales of crop and plant hierarchy, using a nested sampling design, and implementing the concept of conditional disease intensity. The various analyses performed indicated that experimental plots grouped according to morphological attributes of sunflower at the flowering stage were associated with experimental plots grouped according to disease intensity variables, therefore indicating an association between morphological traits and disease intensity. Low disease intensity was associated with a morphological ideotype with large number of green leaves and tall stature. A sunflower plant morphological ideotype with more leaves and taller stature may represent an operational target in sunflower breeding when considering resistance to Phoma black stem.

Potensi Jamur Perakaran sebagai Agens Pengendalian Hayati Penyakit Moler (Fusarium oxysporum f.sp. Cepae) pada Bawang Merah

<p>Desease that often occurs on the shallot is moler caused by Fusarium oxysporum f. sp. cepae (FOCe). This research was conducted to studied the potential of root-colonizing fungi to suppres moler disease on shallot. The researchs were divided into two steps that were laboratory test and screen house test used Completely Randomized Design (CRD). The treatments in screen house test were the combination of four fungi that had best capability to inhibit growth of FOCe. Each treatment was repeated three times. The result showed that root-colonizing fungi could reduce the moler disease but haven’t affect significantly growth component of shallot. Lowest disease intensity was 20% on the combination of AJ01, AJ12, AJ17, AJ18. Root-colonizing fungi have potention to decrease Moler disease.</p>

Efficacy of certain bio agents and fungicides against early blight of potato (Solanum tuberosum L.)

An experiment was conducted to evaluate the effect of bio agents (Trichoderma harzianum and Pseudomonas fluorescens) and fungicides (mancozeb) against early blight of potato caused by Alternariasolani (Ell. and Mart.) at the experimental field of Department of Plant Protection, Sam Higginbottom Institute of Agriculture, Technology and Sciences, Allahabad during Rabi Season of 2013-2014. Seven treatment including control with three replications were taken up using RBD. The treatments comprised of seed treatment and foliar spray (once and twice) of bio agents Trichoderma harzianum and Pseudomonas fluorescens while fungicide taken up was mancozeb and control (spray of plain water) was applied. Observation for per cent disease intensity was recorded at 60 and 80 days after sowing. Lowest disease intensity was recorded in mancozeb (15.07% and 18.40%, respectively) as compared to control which recorded highest disease intensity (20.91% and 33.80%, respectively).Mancozeb not only reduced disease intensity but also recorded highest yield (253.00 q/ha) as compared to control which recorded 157.83 q/ha.The bio agents Trichoderma harzianum and Pseudomonas fluorescens (seed treatment +foliar spray) were also effective in reducing the disease intensity and increasing tuber yield.

Enfermedades y componentes de rendimiento en líneas de fréjol bajo tres densidades de siembra.

The aim was to evaluate diseases and yield components in four promising bean varieties (Phaseolus vulgaris L.) in three planting spacing. The work was carried out during the dry season of 2011, in the UTEQ, Quevedo, Ecuador. Intensity of rust (Uromyces appendiculatus) and web blight (Rhizoctonia solani) were evluated in R7 (pod formation) and R8 (pod filling) growth stages; likewise, root rot (Macrophomina phaseolina and R. solani) incidente was evaluated after harvest. Some yield components were also quantified (number of nodes, pods, grains, grains per pod and sterile pods) and grain weight. A randomized complete block (RCBD) experimental design with twelve treatments and three replications in a factorial arrangement of 4 (lines promising) x 3 (plant/m) was used. Tukey test at 5% probability of error was used for comparison between treatments means. The bean promising lines EVG 06-103 and SER-03 showed lower disease intensity. An increase in density plant population caused a higher rust intensity. Bean lines SER-08 and SER-03 showed the highest productivity, according to most yield components and grain weight. Finally, the increase in plant density promoted a significant reduction in the number of pods, grains and grains per pod per plant, contrary to the observed increase in the weight of grains.

UJI BEBERAPA KONSENTRASI EKSTRAK BUAH MENGKUDU (Morinda citrifolia L.) TERHADAP PENYAKIT ANTRAKNOSA YANG DISEBABKAN OLEH JAMUR COLLETOTRICHUM CAPSICI PADA BUAH CABAI MERAH PASCAPANEN

A research has been conducted to study the effect of some concentrations of Noni (Morindacitrifolia L.) fruit extract in controlling anthracnose disease, caused by Colletorichum capsici on thepost-harvested red chilli fruits. The research has been conducted experimentally using a CompletelyRandomized Design consisting of 5 treatments and 4 replications. The treatments are someconcentrations of noni fruit extract : 0%=Mo, 5%=M1,10%=M2,15%=M3 and 20%=M4. Result of theresearch indicated that the concentration of noni fruit extract gave a significantly different effect incontrolling anthracnose disease on post-harvested red chilli fruits. The concentration of noni fruit extractat 20% showed a better effect in controlling anthracnose disease on post-harvested red chilli fruits whichresulted in a smaller in-vitro colony growth of the causal fungal pathogen, a longer incubation period ofthe disease and a lower disease intensity.

Virulence variation in Alternaria mali (Roberts) and evaluation of systemic<br>acquired resistance (SAR) activators for the management of Alternaria leaf<br>blotch of apple

Alternaria leaf blotch, caused by Alternaria mali, is an economically important disease of apple (Malus xdomestica Borkh.). Twenty one isolates of Alternaria mali (Am-1 to Am-21) were obtained during the isolatecollection. The virulence was tested on detached leaves of susceptible Red Delicious cultivar and Am-1 showedhighest virulence. Two greenhouse trials were conducted using two year old grafted seedlings of Red Deliciousapple cultivar to assess the efficacy of seven SAR activators, 2,6-dichloroisonicotinic acid (INA),benzothiadiazole S-methyl ester (BTH), ?-aminobutyric acid (BABA), K2HPO4, K3PO4, Ca(OH)2 and CaCO3applied 48 hrs before and after spore inoculation. The SAR activators and a conventional synthetic fungicide(penconazole) were evaluated against most virulent isolate Am-1. Distilled sterilized water was sprayed oncontrol plants. All the SAR activators significantly lowered the disease intensity as compared to control. BABAwas most effective with least disease intensity before and after pathogenic inoculation. Penconazole provedsuperior to all the SAR activators, except BABA. The application of SAR activators before pathogeninoculation showed significantly lower disease intensity (12.71%) in comparison to SAR application afterpathogen inoculation (14.77%). This induced resistance exploiting natural defense machinery of plants could beproposed as a non-conventional and eco-friendly approach for plant protection.

Integrated Disease Management of Foliar Blight Disease of Onion: A Case Study of Application of Confounded Factorials

Foliar blight is an important disease of onion, proving a major bottleneck in its production. Six pathogens were found associated with the disease, viz., Alternaria alternata, A. porri, A. tenuissima, Stemphylium vesicarium, Colletotrichum circinans and Cladosporium allii-cepae. Integrated disease management of the crop was attempted using chemicals (mancozeb at 0.25% and hexaconazole at 0.06%), bio-control agents, Trichoderma viride (Tv-1) and Trichoderma harzianum (Th-1), each at 1×109 spores-ml and phyto-extracts (Cannabis indica and Curcuma longa, each at 10%). Mancozeb at 0.25 per cent proved most effective in managing foliar blight of onion but was at par with hexaconazole at 0.06 per cent. Among bio-control agents used, application of T. harzianum (Th-1) resulted in lower disease intensity as compared to T. viride (Tv-1), though both were statistically at par with each other, but were significantly superior over the control. The phyto-extracts, C. indica and C. longa were ineffective in the disease management.

A strategy to identify sources of quantitative resistance in pathosystems involving disease escape and physiological resistance: the case study of rice sheath blight

An epidemiology‐based strategy using rice sheath blight (ShB) as a biological model was developed that enables identification of sources of resistance. A set of 163 cultivated rice genotypes, including genotypes which had been reported to express partial resistance to ShB, and a few genotypes reported as very susceptible, were assessed using two complementary methods. First, microfield experiments allowed measurement of disease intensification at, and spread from, inoculated sources, along with morphological traits of each genotype. Secondly, detached tiller tests allowed measurement of the physiological resistance to the disease under conditions where morphology does not come into play. Multivariate analysis involving hierarchical cluster analysis, followed by multiple correspondence analysis, indicated that levels of physiological resistance, groups of plant morphology and disease levels in microfields were associated. Results from logistic regressions further indicated that a decreased number of lesions measured on detached tillers increased the odds of a rice genotype belonging to the group with low disease intensity in microfields. The combined results from microfield and detached tiller tests allowed identification of 23 genotypes with low level of disease intensity, which may be used as sources of resistance to ShB in breeding programmes. The results suggest that this strategy, which combines the crop stand and the individual tiller scales, may be applied to the identification of sources of resistance to a range of diseases with similar life cycle traits.

Multiple Treatment Meta-Analysis of Products Evaluated for Control of Fire Blight in the Eastern United States

The aim of this analysis was to estimate the effect sizes and consistency of products evaluated for fire blight control in the eastern United States over the last decade. Because only 3% of the 69 studies published from 2000 to 2008 explicitly presented a measure of within-study variability, a method for estimating the least significant difference (LSD) and, hence the sampling variance, for studies with at least two significant mean separations in the presented mean multiple comparisons was developed. Lin's concordance analysis indicated that the estimated LSD was an accurate predictor of the actual LSD based on 35 studies in a calibration evaluation (ρ(c) = 0.997). Separate multi-treatment random-effects meta-analyses were performed for three control categories: antibiotics, biological control, and plant defense-activating products and mean log response ratios relative to the nontreated controls ([Formula: see text]) were computed for each treatment and then back-transformed to obtain the mean percent disease control. None of the products evaluated performed as well as streptomycin, the standard product for fire blight control, for which the mean disease control was 68.6%. As a group, experimental antibiotics provided the best fire blight control with mean effect sizes ranging from 59.7 to 61.7%. Among the biological controls, the best control was noted for treatments combining the antibiotic streptomycin with a product based on Pantoea agglomerans (55.0% mean disease reduction) or Bacillus subtilis (53.9%). Mean disease control was 31.9, 25.7, and 22.6%, respectively, for products based on B. subtilis, Pantoea agglomerans, and Pseudomonas fluorescens without an antibiotic, suggesting that the higher efficacy of the combination treatments was due to the antibiotic. Among the plant defense-activating products, prohexadione calcium had the highest and most consistent effect size (50.7% control), while other products provided modest mean disease control of between 6.1 and 25.8%. Percent control values were significantly moderated by study location and cultivar used in the study, and were smaller, but more variable, when products were tested under high disease intensity compared with low disease intensity. Results indicate that wide-scale use of biological control and plant defense-activating products in the eastern United States is likely to remain low.

Field Evaluations of Leaf Spot Resistance and Yield in Peanut Genotypes in the United States and Bolivia.

Field experiments were conducted in 2002 to 2006 to characterize yield potential and disease resistance in the Bolivian landrace peanut (Arachis hypogaea) cv. Bayo Grande, and breeding lines developed from crosses of Bayo Grande and U.S. cv. Florida MDR-98. Diseases of interest included early leaf spot, caused by the fungus Cercospora arachidicola, and late leaf spot, caused by the fungus Cercosporidium personatum. Bayo Grande, MDR-98, and three breeding lines, along with U.S. cvs. C-99R and Georgia Green, were included in split-plot field experiments in six locations across the United States and Bolivia. Whole-plot treatments consisted of two tebuconazole applications and a nontreated control. Genotypes were the subplot treatments. Area under the disease progress curve (AUDPC) for percent defoliation due to leaf spot was lower for Bayo Grande and all breeding lines than for Georgia Green at all U.S. locations across years. AUDPC for disease incidence from one U.S. location indicated similar results. Severity of leaf spot epidemics and relative effects of the genotypes were less consistent in the Bolivian experiments. In Bolivia, there were no indications of greater levels of disease resistance in any of the breeding lines than in Bayo Grande. In the United States, yields of Bayo Grande and the breeding lines were greater than those of the other genotypes in 1 of 2 years. In Bolivia, low disease intensity resulted in the highest yields in Georgia Green, while high disease intensity resulted in comparable yields among the breeding lines, MDR-98, and C-99R. Leaf spot suppression by tebuconazole was greater in Bolivia than in the United States. This result indicates a possible higher level of fungicide resistance in the U.S. population of leaf spot pathogens. Overall, data from this study suggest that Bayo Grande and the breeding lines may be desirable germplasm for U.S. and Bolivian breeding programs or production.

Blast fungus inoculation reduces accumulation and remobilization of pre-anthesis assimilates to rice grains

The importance of stored assimilates for grain development in cereals has been widely recognized, particularly in cereals exposed to stress during the grain filling period. This study was conducted to investigate the effect of the blast fungus Magnaporthe grisea on dry matter accumulation, remobilization and utilization in rice ( Oryza sativa L.) under field conditions. Four rice varieties with various levels of susceptibility to rice blast were grown in 2003 and 2004 under high and low disease intensity, caused by early inoculation and natural infection respectively. High disease intensity reduced plant height, dry matter accumulation, the harvest index and grain yield. Plants grown under high disease intensity translocated fewer stored assimilates to the grain than plants grown under low disease intensity. Dry matter translocation from the vegetative parts to the grain was significantly correlated with dry matter at anthesis (r=0.65, P l). High stress from early leaf blast caused by inoculation with the blast fungus affected overall plant growth and lowered the production of pre-anthesis assimilates, as well as causing severe levels of neck blast that resulted in a low translocation rate during the filling period, and therefore a lower grain yield than in naturally infected plants.

Estimation of Annual Mortality Rates for Eastern Oysters (Crassostrea virginica) in Chesapeake Bay Based on Box Counts and Application of Those Rates to Project Population Growth of C. virginica and C. ariakensis

In an effort to restore the ecological role of oysters in Chesapeake Bay and the economic benefits of a commercial fishery, the states of Maryland and Virginia are considering introducing the nonnative Asian oyster (Crassostrea ariakensis) into the Bay. As part of an ecological risk assessment (ERA) to evaluate the proposed action and alternatives, demographic modeling is being used to project the change in populations of both the Asian and the native eastern oyster (C. virginica) in the Bay across space and time. Annual mortality rates are vital input to the demographic model. We present two approaches for parameterizing mortality rates for C. virginica by salinity ranges and disease-intensity categories and discuss how these rates could be applied to project population growth for the Asian oyster. We estimated mortality rates from empirical data collected during annual dredge surveys of oyster beds in Maryland. We compared counts of recent boxes (dead oysters without fouling or sedimentation on the inner valve surfaces, including “gapers” of one or two weeks old with tissue remaining in the shell), old boxes (dead oysters without tissue remnants but with fouling, sedimentation or both on the inner valve surfaces), and live oysters in market-size and small classes. Our mortality estimates based on counts of recent boxes consistently differentiated between years with high disease intensity and those with low disease intensity, between wet and dry years, and between salinity zones. In contrast, traditional estimates of yearly mortality based on total box counts often were out of phase with measured levels of disease intensity and weather (dry or wet). To model populations of C. ariakensis, we propose to adjust the mortality rates for C. virginica based on research results that provide estimates of differences between the two species' resistance to MSX and dermo and to other mortality factors, such as predation.

Queen promiscuity lowers disease within honeybee colonies

Most species of social insects have singly mated queens, but in some species each queen mates with numerous males to create a colony with a genetically diverse worker force. The adaptive significance of polyandry by social insect queens remains an evolutionary puzzle. Using the honeybee (Apis mellifera), we tested the hypothesis that polyandry improves a colony's resistance to disease. We established colonies headed by queens that had been artificially inseminated by either one or 10 drones. Later, we inoculated these colonies with spores of Paenibacillus larvae, the bacterium that causes a highly virulent disease of honeybee larvae (American foulbrood). We found that, on average, colonies headed by multiple-drone inseminated queens had markedly lower disease intensity and higher colony strength at the end of the summer relative to colonies headed by single-drone inseminated queens. These findings support the hypothesis that polyandry by social insect queens is an adaptation to counter disease within their colonies.