An evaluation of the methods to estimate effective population size from measures of linkage disequilibrium.

In 1971, John Sved derived an approximate relationship between linkage disequilibrium (LD) and effective population size for an ideal finite population. This seminal work was extended by Sved and Feldman (Theor Pop Biol 4, 129, 1973) and Weir and Hill (Genetics 95, 477, 1980) who derived additional equations with the same purpose. These equations yield useful estimates of effective population size, as they require a single sample in time. As these estimates of effective population size are now commonly used on a variety of genomic data, from arrays of single nucleotide polymorphisms to whole genome data, some authors have investigated their bias through simulation studies and proposed corrections for different mating systems. However, the cause of the bias remains elusive. Here, we show the problems of using LD as a statistical measure and, analogously, the problems in estimating effective population size from such measure. For that purpose, we compare three commonly used approaches with a transition probability-based method that we develop here. It provides an exact computation of LD. We show here that the bias in the estimates of LD and effective population size are partly due to low-frequency markers, tightly linked markers or to a small total number of crossovers per generation. These biases, however, do not decrease when increasing sample size or using unlinked markers. Our results show the issues of such measures of effective population based on LD and suggest which of the method here studied should be used in empirical studies as well as the optimal distance between markers for such estimates.

Genomic inbreeding depression for climatic adaptation of tropical beef cattle.

Inbreeding has the potential to negatively impact animal performance. Strategies to monitor and mitigate inbreeding depression require that it can be accurately estimated. Here, we used genomewide SNP data to explore 3 alternative measures of genomic inbreeding: the diagonal elements of the genomic relationship matrix (FGRM), the proportion of homozygous SNP (FHOM), and the proportion of the genome covered by runs of homozygosity (FROH). We used 2,111 Brahman (BR) and 2,550 Tropical Composite (TC) cattle with phenotypes recorded for 10 traits of relevance to tropical adaptation. We further explored 3 marker densities ranging from a high-density chip (729,068 SNP), a medium-density chip (71,726 SNP) specifically designed for cattle, and a low-density chip (18,860 SNP) associated with the measures of inbreeding. Measures of FGRM were highly correlated across the 3 SNP densities and negatively correlated with FHOM and FROH in the BR population. In both populations, there was a strong positive correlation for each measure of inbreeding across the 3 SNP panels. We found significant ( < 0.01) inbreeding depression for various traits, particularly when using the highest-density SNP chip in the BR population, where inbreeding was negatively associated with coat color and coat type such that inbred animals presented shorter, slicker, and lighter coats. Based on FGRM using the medium-density chip, we found that a 1% increase in inbreeding in the BR and TC populations was associated with a decrease of 0.514 and 0.579 kg BW, respectively, in yearlings. In the TC population, a 1% increase in FHOM was associated with a decrease in BCS of -0.636% ( < 0.001). The low-density chip, comprising SNP associated with inbreeding, captured genes, and regions with pleiotropic effects ( < 0.001). However, it did not improve our ability to identify inbreeding depression, relative to the use of higher-density panels. We conclude that where heterogeneous populations are present, such as in tropical environments where composite animals abound, measures of inbreeding that do not depend on allele frequencies, such as FHOM and FROH, are preferable for estimating genomic inbreeding. Finally, the sustainable intensification of livestock systems in tropical regions will rely on genetic safeguards to ensure that productivity is improved while also adapting animals to cope with climate change. The results of this study are a step toward achieving that goal.

Multiple Independent Retroelement Insertions in the Promoter of a Stress Response Gene Have Variable Molecular and Functional Effects in Drosophila.

Promoters are structurally and functionally diverse gene regulatory regions. The presence or absence of sequence motifs and the spacing between the motifs defines the properties of promoters. Recent alternative promoter usage analyses in Drosophila melanogaster revealed that transposable elements significantly contribute to promote diversity. In this work, we analyzed in detail one of the transposable element insertions, named FBti0019985, that has been co-opted to drive expression of CG18446, a candidate stress response gene. We analyzed strains from different natural populations and we found that besides FBti0019985, there are another eight independent transposable elements inserted in the proximal promoter region of CG18446. All nine insertions are solo-LTRs that belong to the roo family. We analyzed the sequence of the nine roo insertions and we investigated whether the different insertions were functionally equivalent by performing 5'-RACE, gene expression, and cold-stress survival experiments. We found that different insertions have different molecular and functional consequences. The exact position where the transposable elements are inserted matters, as they all showed highly conserved sequences but only two of the analyzed insertions provided alternative transcription start sites, and only the FBti0019985 insertion consistently affects CG18446 expression. The phenotypic consequences of the different insertions also vary: only FBti0019985 was associated with cold-stress tolerance. Interestingly, the only previous report of transposable elements inserting repeatedly and independently in a promoter region in D. melanogaster, were also located upstream of a stress response gene. Our results suggest that functional validation of individual structural variants is needed to resolve the complexity of insertion clusters.

The use of coancestry based on shared segments for maintaining genetic diversity.

We have evaluated the use of genomic coancestry coefficients based on shared segments for the maintenance of genetic diversity through optimal contributions methodology for populations of three different Austrian cattle breeds. This coancestry measure has been compared with the genomic coancestry coefficient calculated on a SNP-by-SNP basis and with pedigree-based coancestry. The regressions of the shared segments coancestry on the other two coefficients suggest that the former mainly reflect Identity By Descent but with the advantage over pedigree-based coancestry of providing the realized Identity By Descent rather than an expectation. The effective population size estimated from the rate of coancestry based on shared segments was very similar to those obtained with the other coefficients and of small magnitude (from 26.24 to 111.90). This result highlights the importance of implementing active management strategies to control the increase of inbreeding and the loss of genetic diversity in livestock breeds, even when the population size is reasonably large. One problem for the implementation of coancestry based on shared segments is the need of estimating the gametic phases of the SNPs which, given the techniques used to obtain the genotypes, are a priori unknown. This study shows, through computer simulations, that using estimates of gametic phases for computing coancestry based on shared segments does not lead to a significant loss in the diversity maintained. This has been shown to be true even when the size of the population is very small as it is usually the case in populations subjected to conservation programmes.

Using genome-wide measures of coancestry to maintain diversity and fitness in endangered and domestic pig populations.

Conservation and breeding programs aim at maintaining the most diversity, thereby avoiding deleterious effects of inbreeding while maintaining enough variation from which traits of interest can be selected. Theoretically, the most diversity is maintained using optimal contributions based on many markers to calculate coancestries, but this can decrease fitness by maintaining linked deleterious variants. The heterogeneous patterns of coancestry displayed in pigs make them an excellent model to test these predictions. We propose methods to measure coancestry and fitness from resequencing data and use them in population management. We analyzed the resequencing data of Sus cebifrons, a highly endangered porcine species from the Philippines, and genotype data from the Pietrain domestic breed. By analyzing the demographic history of Sus cebifrons, we inferred two past bottlenecks that resulted in some inbreeding load. In Pietrain, we analyzed signatures of selection possibly associated with commercial traits. We also simulated the management of each population to assess the performance of different optimal contribution methods to maintain diversity, fitness, and selection signatures. Maximum genetic diversity was maintained using marker-by-marker coancestry, and least using genealogical coancestry. Using a measure of coancestry based on shared segments of the genome achieved the best results in terms of diversity and fitness. However, this segment-based management eliminated signatures of selection. We demonstrate that maintaining both diversity and fitness depends on the genomic distribution of deleterious variants, which is shaped by demographic and selection histories. Our findings show the importance of genomic and next-generation sequencing information in the optimal design of breeding or conservation programs.

First Report of Fusarium oxysporum on Sweet Pepper Seedlings in Almería, Spain.

In March of 2013, new symptoms were observed in more than seven million nursery-grown sweet pepper (Capsicum annuum) plants in El Ejido, Almería (southern Spain). Symptoms included wilting without yellowing of leaves and stunting of plants. Plant crowns exhibited necrosis that advanced through the main root along with slight root rot. Xylem was not affected above or below the crown. Symptoms were thought to be caused by the well-known pepper pathogen Phytophthora capsici. However, sporodochia of Fusarium oxysporum were observed on plant crowns. Symptomatic seedlings (n = 200) were sampled and analyzed. Tissue from roots and epidermal crowns were plated on PDA, PARP, and Komada media, as well as stem discs on PDA and Komada. No Phytophthora sp. were observed and F. oxyporum was exclusively isolated from all 200 samples, from roots and crowns, but not from xylem. Pathogenicity of 60 of these F. oxysporum isolates was studied by inoculation onto sweet pepper plants (cv. del Piquillo) at the 2-true-leaf stage. Twelve plants per isolate, grown on autoclaved vermiculite, were inoculated by drenching with 20 ml of a conidial suspension (1 × 105 CFU/ml) of each isolate per plant. Each suspension was obtained by blending one PDA petri dish fully covered with one isolate. Non-inoculated plants served as control. Plants were maintained for 30 days in a growth chamber with a 14-h photoperiod (1.6 ×·104 lux) and temperatures at 23 to 26°C. The assay was conducted twice. Symptoms described above were reproduced on crown and roots of the inoculated plants with no symptoms in stem discs. No symptoms were observed on controls after 48 days. Host specificity was tested for 13 isolates to tomato (Solanum lycopersicum) cv. San Pedro, eggplant (S. melongena) cv. Alegria, cucumber (Cucumis sativus) cv. Marketmore, watermelon (Citrullus lanatus) cv. Sugar Baby, and Chinese cabbage (Brassica campestris subsp. condensa) cv. Kasumi (4). These plants were inoculated as previously described for pathogenicity tests (12 plants per species, repeated twice). None of the plants exhibited the characteristic symptoms after 60 days. Five isolates of F. oxysporum f. sp. radicis-cucumerinum and four isolates of F. o. f. sp radicis-lycopersici were also inoculated without any symptoms in any of the inoculated sweet pepper plants. Morphological identity of all isolates corresponded to F. oxysporum. The fungi were identified following the morphological keys and methodology provided by (1) and (2). Three isolates from the 60 tested were selected for molecular identification. Molecular identification was performed by sequencing partial TEF-1α gene (3). Subsequent database searches by BLASTn indicated that the resulting sequence of 659-bp had 100% identity with the corresponding gene sequence of F. oxysporum. The sequences were identical for the three isolates and were deposited on the EMBL Sequence Database (HG916993, HG916994, and HG916995). Results suggest that the pathogenic ability of the isolates varies from a vascular Fusarium wilt. F. oxysporum f. sp. capsici is a reported pathogen to sweet pepper (5), but the symptoms we have found are closer to those manifested by the formae speciales that causes root and crown rot of other plants. Consistent with the convention stablished for similar diseases we propose the name F. oxysporum f. sp. radicis-capsici f. sp. nov. References: (1) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell, Ames, IA, 2006. (2) P. E. Nelson et al. Fusarium species. An Ilustrated Manual for Identification. The Penn St. University Press, 1983. (3) K. O'Donnell et al. Proc. Nat. Acad. Sci. 95:2044, 1998.(4) L. M. Oelke and P. W. Bosland. Capsicum Eggplant Newsl. 20:86, 2001. (5) V. C. Rivelli. M.S. Thesis. Dep. Plant Pathol. and Crop Phys. Louisiana State Univ., Baton Rouge, 1989.

Purging deleterious mutations in conservation programmes: combining optimal contributions with inbred matings.

Conservation programmes aim at minimising the loss of genetic diversity, which allows populations to adapt to potential environmental changes. This can be achieved by calculating how many offspring every individual should contribute to the next generation to minimise global coancestry. However, an undesired consequence of this strategy is that it maintains deleterious mutations, compromising the viability of the population. In order to avoid this, optimal contributions could be combined with inbred matings, to expose and eliminate recessive deleterious mutations by natural selection in a process known as purging. Although some populations that have undergone purging experienced reduced inbreeding depression, this effect is not consistent across species. Whether purging by inbred matings is efficient in conservation programmes depends on the balance between the loss of diversity, the initial decrease in fitness and the reduction in mutational load. Here we perform computer simulations to determine whether managing a population by combining optimal contributions with inbred matings improves its long-term viability while keeping reasonable levels of diversity. We compare the management based on genealogical information with management based on molecular data to calculate coancestries. In the scenarios analysed, inbred matings never led to higher fitness and usually maintained lower diversity than random or minimum coancestry matings. Replacing genealogical with molecular coancestry can maintain a larger genetic diversity but can also lead to a lower fitness. Our results are strongly dependent on the mutational model assumed for the trait under selection, the population size during management and the reproductive rate.

First Report of Fusarium verticillioides Causing Stalk and Root Rot of Sorghum in Spain.

Sweet sorghum (Sorghum bicolor L.) is considered one of the most promising crops for bioethanol production in many countries and is a focus of bioenergy research worldwide. In July 2011, plants of the sweet sorghum cv. Suchro 506 in Oropesa (Toledo, Spain, 40.048577°N, 5.360298°W) (European Datum 1950 UTM zone 30 N) were observed with severe wilting. Upon examination, the lower internodes were found to be straw colored. When the plant was split, the internal pith was reddish, soft, and disintegrating. Small pieces of symptomatic stems and roots were surface disinfected in sodium hypochlorite (0.5% wt/vol) for 2 min and air dried. The sections were then placed on either PDA (potato dextrose agar) medium or Komada agar and incubated for 5 days at 25°C. Isolations from diseased stem and root tissue consistently yielded Fusarium verticillioides (Sacc.) Nirenberg (3). The small, hyaline, mostly single-celled, oval to club-shaped microconidia of F. verticillioides were produced in long catenate chains arising from monophialides. PCR amplification of the ITS1-5.8S-ITS2 was performed using the primers and protocols described elsewhere (4) and the fragments obtained were subsequently sequenced in both directions. Sequences were deposited in the EMBL Sequence Database (Accession Nos. HE652878, HE652879, HE652880, and HE652881). Four of the recovered F. verticilliodes isolates were tested in pathogenicity assays. One-week-old cultures of each isolate were homogenized in 400 ml of sterile water and 200 ml were used to inoculate water-growth-chamber-grown plants in 500-ml pots. Two pots each with three plants of cv. Suchro 506 were inoculated for each isolate. Water with sterile PDA was used as a control. All plants were kept at 20 to 25°C under a photoperiod of 14 h at 12,000 lux. After 21 days, above- and belowground parts were dried for 24 h at 60°C. Total length and dry weight of both sections were obtained. Inoculated plants produced root rot symptoms characteristic of F. verticillioides with dark red discolorations of the cortex of seedling roots (1), whereas the plants watered with water containing only PDA did not produce symptoms. Inoculated plants also had a decrease in dry weight for above- and belowground sections (P = 0.05) compared with the control with 43 and 47% reductions, respectively. The length of aerial parts was approximately 5% less in inoculated plants compared with control plants. F. verticillioides was reisolated from all inoculated plants. Sorghum stalk and root rot caused by F. verticillioides has been reported in different countries including India (2) and the United States (3). To our knowledge, this is the first report of F. verticillioides causing stalk and root rot of sorghum in Spain. An increase of production of this crop is expected to meet targets of the renewable energy share in Spain and any disease compromising yield may be a threat to this endeavour. References: (1) R. A. Frederiksen and G. N. Odvody. Compendium of Sorghum Diseases. The American Phytopathological Society. St. Paul, MN, 2000. (2) N. N. Khune et al. Indian Phytopathol. 37:316, 1984. (3) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006. (4) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, New York, 1990.

Using genome-wide information to minimize the loss of diversity in conservation programmes.

We study here the effect of using genome-wide marker data versus genealogical data in population management for the maintenance of diversity in conservation schemes using optimal contributions. We re-examine the benefits of using molecular data for different population and genome sizes and compare different management strategies according to the group of individuals where we take decisions (parents or offspring). We also study the consequences of using estimated genealogical coancestries calculated from molecular information. Using genome-wide marker data performed usually better than using genealogical data or estimated genealogical coancestry to maintain expected and observed heterozygosity. Furthermore, when we could take decisions acting on the offspring, a larger heterozygosity was maintained than when we based our decisions on the potential parents.

Fungal microbiota from rain water and pathogenicity of Fusarium species isolated from atmospheric dust and rainfall dust.

In order to determine the presence of Fusarium spp. in atmospheric dust and rainfall dust, samples were collected during September 2007, and July, August, and October 2008. The results reveal the prevalence of airborne Fusarium species coming from the atmosphere of the South East coast of Spain. Five different Fusarium species were isolated from the settling dust: Fusarium oxysporum, F. solani, F. equiseti, F. dimerum, and F. proliferatum. Moreover, rainwater samples were obtained during significant rainfall events in January and February 2009. Using the dilution-plate method, 12 fungal genera were identified from these rainwater samples. Specific analyses of the rainwater revealed the presence of three species of Fusarium: F. oxysporum, F. proliferatum and F. equiseti. A total of 57 isolates of Fusarium spp. obtained from both rainwater and atmospheric rainfall dust sampling were inoculated onto melon (Cucumis melo L.) cv. Piñonet and tomato (Lycopersicon esculentum Mill.) cv. San Pedro. These species were chosen because they are the main herbaceous crops in Almeria province. The results presented in this work indicate strongly that spores or propagules of Fusarium are able to cross the continental barrier carried by winds from the Sahara (Africa) to crop or coastal lands in Europe. Results show differences in the pathogenicity of the isolates tested. Both hosts showed root rot when inoculated with different species of Fusarium, although fresh weight measurements did not bring any information about the pathogenicity. The findings presented above are strong indications that long-distance transmission of Fusarium propagules may occur. Diseases caused by species of Fusarium are common in these areas. They were in the past, and are still today, a problem for greenhouses crops in Almería, and many species have been listed as pathogens on agricultural crops in this region. Saharan air masses dominate the Mediterranean regions. The evidence of long distance dispersal of Fusarium spp. by atmospheric dust and rainwater together with their proved pathogenicity must be taken into account in epidemiological studies.

Comparative study of the pathogenicity of seabed isolates of Fusarium equiseti and the effect of the composition of the mineral salt medium and temperature on mycelial growth.

The pathogenicity of seven strains of Fusarium equiseti isolated from seabed soil was evaluated on different host plants showing pre and post emergence damage. Radial growth of 27 strains was measured on culture media previously adjusted to different osmotic potentials with either KCl or NaCl (-1.50 to -144.54 bars) at 15°, 25° and 35° C. Significant differences and interactive effects were observed in the response of mycelia to osmotic potential and temperature.

First Report of Fusarium proliferatum Causing Rot of Garlic Bulbs in Spain.

In October of 2008, decayed garlic bulbs (Allium sativum L. cv. Blancomor de Vallelado) were received from a producer in Segovia, Spain. In November of 2009, similar symptoms were observed on stored bulbs (cvs. Blancomor de Vallelado and Garcua) from each of 30 municipalities in northwest Segovia and Valladolid. A minimum of one sample was collected from 12 localities. Pieces of symptomatic bulbs were surface disinfested for 2 to 3 min in 0.5% NaOCl and transferred to potato dextrose agar (PDA) and Komada's media. Colonies had catenate microconidia and curved macroconidia that were usually three to five septate. Microconidia were club shaped with a flattened base, aseptate, and were produced on both mono- and polyphialides. On the basis of morphological features, the fungus was identified as Fusarium proliferatum (T. Matsushima) Nirenberg (2,3). Pathogenicity tests were conducted with 12 isolates of the fungi following the method of Dugan et al. (1). Each assay with an isolate consisted of six cloves (cv. Blancomor de Vallelado) disinfested in 0.5% NaOCl for 45 s, rinsed with sterile water, and injured to a depth of 4.5 mm with a probe 1 mm in diameter. The wound was filled with PDA colonized by the appropriate isolate. Six cloves for each tested isolate received sterile agar as a control. The cloves were incubated at 25°C for 5 weeks. The test was repeated once with cv. Garcua. All isolates produced water-soaked, tan lesions. An isolate of the fungus was deposited in the collection of the Plant Production Department of the University of Almeria. No fungi were recovered from the control cloves. F. proliferatum has been reported on garlic in the northwestern United States (1) and Serbia (4). To our knowledge, this is the first report of a Fusarium sp. in the section Liseola attacking garlic in Spain. The fungus seems to be well established on this host in Spain. References: (1) F. M. Dugan et al. Phytopathology 155:437, 2007. (2) P. E. Nelson et al. Fusarium Species: An Illustrated Manual for Identification. Pennsylvania State University Press, University Park, 1983. (3) H. Nirenberg et al. Mycologia 90:434, 1998. (4) S. Stankovic et al. Eur. J. Plant Pathol. 118:165, 2007.

Lethal synergy of solar UV-radiation and H(2)O(2) on wild Fusarium solani spores in distilled and natural well water.

Environmentally-friendly disinfection methods are needed in many industrial applications. As a natural metabolite of many organisms, hydrogen peroxide (H(2)O(2))-based disinfection may be such a method as long as H(2)O(2) is used in non-toxic concentrations. Nevertheless, when applied alone as a disinfectant, H(2)O(2) concentrations need to be high enough to achieve significant pathogen reduction, and this may lead to phytotoxicity. This paper shows how H(2)O(2) disinfection concentrations could be significantly reduced by using the synergic lethality of H(2)O(2) and sunlight the first time for fungi and disinfection. Experiments were performed on spores of Fusarium solani, the ubiquitous, pytho- and human pathogenic fungus. Laboratory (250-mL bottles) and pilot plant solar reactors (2 x 14 L compound parabolic collectors, CPCs) were employed with distilled water and real well water under natural sunlight. This opens the way to applications for agricultural water resources, seed disinfection, curing of fungal skin infections, etc.

Species of Fusarium Isolated from River and Sea Water of Southeastern Spain and Pathogenicity on Four Plant Species.

Species of Fusarium were isolated from water samples collected from the Andarax River and coastal sea water of the Mediterranean in Granada and Almería provinces of southeastern Spain. In total, 18 water samples were analyzed from the Andarax River, and 10 species of Fusarium were isolated: Fusarium anthophilum, F. acuminatum, F. chlamydosporum, F. culmorum, F. equiseti, F. verticillioides, F. oxysporum, F. proliferatum, F. solani, and F. sambucinum. In addition, five species were isolated from 33 sea water samples from the Mediterranean Sea: F. equiseti, F. verticillioides, F. oxysporum, F. proliferatum, and F. solani. When considering the samples by their origins, 77.8% of the river water samples yielded at least one species of Fusarium, with F. oxysporum comprising 72.2% of the total isolates. In the case of marine water, 45.5% of the samples yielded at least one species of Fusarium, with F. solani comprising 36.3% of the total isolates. The pathogenicity of 41 isolates representing nine of the species collected from river and sea water during the study was evaluated on barley, kohlrabi, melon, and tomato. Inoculation with F. acuminatum, F. chlamydosporum, F. culmorum, F. equiseti, F. verticillioides, F. oxysporum, F. proliferatum F. solani, and F. sambucinum resulted in pre- and post-emergence damping off. Pathogenicity of Fusarium isolates did not seem to be related to the origin of the isolates (sea water or fresh water). However, the presence of pathogenic species of Fusarium in river water flowing to the sea could indicate long-distance dispersal in natural water environments.

Possibilities of the use of vinasses in the control of fungi phytopathogens.

The purpose of this research was to study the biocide effect of three agroindustrial subproducts, concretely sugar beet, sugar cane and wine vinasse. Results from in vitro testing determined that wine vinasse is what shows a 100% capacity to suppress fungal growth with concentrations between 5% and 7% for Fusarium oxysporum f.sp. melonis race 0 and 1, Sclerotinia sclerotiorum, Pythium aphanidermatum and Phytophthora parasitica and 10-15% for F. oxysporum f.sp. radicis-cucumerinum. On the other hand, sugar cane vinasse produced an increase at high concentrations and sugar beet vinasse showed an approximate 100% suppressor effect on fungal growth for only some of the phytopathogens tested: S. sclerotiorum (15%), P. aphanidermatum (7%), P. parasitica (15%) and F. oxysporum f.sp. radicis-cucumerinum (15%). In the soil samples analyzed none of the three vinasse extracts decreased fusaric microbiota, producing an increase in the three samples tested. This would implicitly convey an improvement in soil quality by producing a potential increase in bacterial and fungal microbiota.

A model for the evolution of assortative mating.

Abstract: Many animals and plants show a correlation between the traits of the individuals in the mating pair, implying assortative mating. Given the ubiquity of assortative mating in nature, why and how it has evolved remain open questions. Here we attempt to answer these questions in those cases where the trait under assortment is the same in males and females. We consider the most favorable scenario for assortment to evolve, where the same trait is under assortment and viability selection. We find conditions for assortment to evolve using a multilocus formalism in a haploid population. Our results show how epistasis in fitness between the loci that control the focal trait is crucial for assortment to evolve. We then assume specific forms of assortment in haploids and diploids and study the limiting cases of selective and nonselective mating. We find that selection for increased assortment is weak and that where increased assortment is costly, it does not invade.

First Report of Fulvia fulva, Causal Agent of Tomato Leaf Mold, in Greenhouses in Southeastern Spain.

Tomato (Solanum lycopersicum L.) is produced in more than 9,000 ha of greenhouses in Almería (southeastern Spain). During 2006 and 2007, a new disease was observed on almost all plants in 37 greenhouses. Yellow spots on upper and lower leaf surfaces were accompanied by gray-to-dark brown mycelia, conidiophores, and conidia on lower leaf surfaces. Affected leaves became necrotic and withered. Six isolates grown on malt extract agar (MEA) were identified as Fulvia fulva (1). The one- to three-celled conidia ranged from 21.8 × 7.8 µm to 21.5 × 6.5 µm. On MEA, potato dextrose agar, and V8 juice agar, the pathogen grew slowly; colonies were only 1 cm in diameter after 30 days. Colony color was initially intense yellow but became dark brown with age. In a growth chamber (12,000 lux for 16 h per day, 23 to 28°C, and 60 to 95% relative humidity), six pots containing five tomato plants (cv. SanPedro) at the four-true-leaf stage were inoculated with a conidial suspension (103 CFU/ml) of F. fulva. Control plants were sprayed with water. The trial was repeated once. Immediately after inoculation, plants were sealed in plastic bags for 8 days. Symptoms of the disease and signs of the pathogen were observed on all inoculated plants 18 days after inoculation. To our knowledge, this is the first report of leaf mold of tomato in Almería and it is becoming common in the greenhouse industry in this region. Reference: (1) P. Holliday and J. L. Mulder. No. 487 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1976.

Association of Olpidium bornovanus and Melon necrotic spot virus with Vine Decline of Melon in Guatemala.

Thirty-one soil samples from 14 different fields of Guatemala melon with vine decline symptoms were analyzed for the presence of organisms associated with the disease. With a soil-dilution plating method, only Macrophomina phaseolina was detected in five samples. With a melon bait plant technique, Olpidium bornovanus, often together with Melon necrotic spot virus (MNSV), was found in nearly all the samples, corresponding with all the fields studied. Other pathogens that were detected less frequently included Pythium aphanidermatum, Monosporascus cannonballus, and Rhizoctonia solani. Consequently, O. bornovanus and MNSV were uniquely associated with disease occurrence and thus are the most probable cause of melon vine decline in the fields studied.

Association of Pythium aphanidermatum with Root and Crown Rot of Melons in Honduras.

Approximately 10,000 ha of melon (Cucumis melo L.), primarily cantaloupe and honeydew types, are grown in Honduras for export to U.S. markets. In 2004 and 2005, several soil surveys were conducted in areas with a history of vine decline. Twenty-nine soil samples from six farms were collected from the rhizosphere of wilted plants. Thirty-six melon plants were planted in a mixture of each rhizosphere sample and vermiculite (1:6 v/v). The plants were maintained in a growth chamber at 23 to 25°C with a 16-h photoperiod. The first symptoms, which appeared at the one- or two-true-leaf stage, were girdling of the lower stem, leaf chlorosis, and wilting. Affected plants exhibited necrotic crowns and roots and half of all plants died less than 3 days after wilting. Isolations from washed and dried crown and roots pieces from affected plants were placed on malt extract agar. Colonies were transferred to potato carrot agar and into dishes of sterile water and immature carnation petals to aid in the identification of recovered fungi. Nearly 500 isolates of Pythium species were cultured, and approximately 60% were identified as P. aphanidermatum (Edson) Fitzp. on the basis of their toruloid sporangia, aplerotic oospores, terminal and smooth oogonia, monoclinous sac-shaped antheridia (one to two per oogonium), and abundant appressoria. The pathogenicity of nine isolates was confirmed in a growth chamber. Ten plants of melon cv. Amarillo Canario, grown in sterilized vermiculite, were inoculated at the two- or three-true-leaf stage by drenching pots with 100 ml of a suspension of each isolate (103 CFU ml-1). Noninoculated plants served as controls. There were three replicates per isolate. Plants began to die 7 days after inoculation and the incidence of the affected plants reached an average of 70%. P. aphanidermatum causing decline of melon plants has been previously reported in hot and semi-arid areas in Israel and Spain (1,2). To our knowledge, this is the first report of P. aphanidermatum pathogenic to melon plants in Honduras. References: (1) S. Pivonia et al. Plant Dis. 81:1264, 1997. (2) J. Gómez Enfermedades del Melón en los Cultivos "Sin Suelo" de la Provincia de Almería. Junta de Andalucía, 1993.