Feeder Roots Research Articles

Expression of defence-related genes against Phytophthora cinnamomi in five avocado rootstocks

Avocado (Persea americana) – a major fruit crop worldwide – is threatened by root rot caused by Phytophthora cinnamomi. This pathogen is known to infect the plant via the feeder roots leading to branch dieback, and eventually tree mortality. While it is known that different avocado rootstocks have varying degrees of susceptibility to Phytophthora root rot, little research has been done on the avocado–Phytophthora interaction. In this study, transcript abundance levels of defence-related genes coding for phenylalanine ammonia-lyase, lipoxygenase, pathogenesis-related protein 5, endochitinase, gluthathionine S-transferase and metallothionein were characterised and compared among five rootstocks with varying susceptibility to root rot, after exposure to P. cinnamomi. Root samples were collected at 0 h, 3 h, 6 h, 12 h, 24 h, 48 h and 72 h post-infection and transcript abundance of the defence-related genes was determined using quantitative real-time reverse transcription PCR. The results indicated the involvement of PR-5 and endochitinase in the defence response of all avocado rootstocks to P. cinnamomi but these genes could not be directly linked to the observed phenotypic resistance. PR-5 and endochitinase were highly upregulated at 72 h post-infection. Differences in transcript abundance of phenylalanine ammonia-lyase and lipoxygenase genes were seen when comparing tolerant and less tolerant rootstocks, which may suggest that transcripts of these genes contribute to resistance. These data provide important insights into plant defence and into how different avocado rootstocks may exhibit increased resistance to infection by P. cinnamomi.

Integrative diagnosis and parasitic habits of Cryphodera brinkmani a non-cyst forming heteroderid nematode intercepted on Japanese white pine bonsai trees imported into Italy

The non-cyst forming heteroderid nematode Cryphodera brinkmani was detected in Italy parasitizing roots of Japanese white pine bonsai (Pinus parviflora) trees imported from Japan. Morphology and morphometrical traits of the intercepted population on this new host for C. brinkmani were in agreement with the original description, except for some minor differences on male morphology. Integrative molecular data for this species were obtained using D2-D3 expansion regions of 28S rDNA, ITS1-rDNA, the partial 18S rDNA, and the protein-coding mitochondrial gene, cytochrome oxidase c subunit I (COI). The phylogenetic relationships of this species with other representatives of non-cyst and cyst-forming Heteroderidae using ITS1 are presented and indicated that C. brinkmani clustered together with other Cryphodera spp. and with Meloidodera alni suggesting a monophyletic origin of non-cyst forming nematodes (Heteroderinae sensu Luc et al. 1978), which have been considered close to the ancestor of most species of Heteroderidae. Histological observations of P. parviflora feeder roots infected by C. brinkmani indicated that nematode females induce similar anatomical alterations to those reported for C. kalesari, consisting of formation of a single uninucleate giant cell (nurse cell) with hypertrophied nucleus, prominenet nucleolus, thickened cell wall and expanding into the stele and in contact of xylem, vacuum cambium and phloem. These findings are in agreement with the results of the phylogenetic analysis and indicate a close relationship in the plant responses induced by Cryphodera nematode females with those caused by the genetically related Meloidodera spp., which also induce formation of a uninucletate giant cell.

New distributional record of buff coconut mealybug (Nipaecoccus nipae) in Kerala, India

The buff coconut mealybug, Nipaecoccus nipae (Maskell) (Pseudococcidae: Hemiptera), was recorded on tender feeder roots of coconut seedlings at Kayamkulam, Kerala, India. N. nipae was not located on any other arboreal parts of palm including foliage. This is a new distributional record of the pest in Kerala, South India. The concealed nature of the pest on underground feeder roots of coconut seedlings warrants thorough examination at the seedling distribution point of coconut seedlings in order to prevent the spread of this pest to other free zones of the country. Re-emergence of the pest is reported in India after a time gap of 100 years.

Root growth and spatio-temporal distribution of three common annual halophytes in a saline desert, northern Xinjiang

Root growth and spatial and temporal distribution in the 0-100 cm soil profiles of three common annual halophytes Salsola subcrassa, Suaeda acuminate and Petrosimonia sibirica distributed in a saline desert in north- ern Xinjiang, China were studied in 2009 and 2010. The results showed that the root systems of the three halo- phytes were of the taproot type, vertically distributed in the 90-cm soil profile, and were deepest in late July. Their taproots reached maximum depth rapidly, early in the growth period, but with rare lateral roots. They were then dug out in an orderly way, from bottom to top, exhibiting vertical development first and then horizontal development. The distribution of specific root length, which reflects the characteristics of the feeder root, was gradually increased from top to bottom, whereas root weight displayed an opposite distribution pattern. The root length distribution of the three halophytes was concentrated (62% to 76%) in the middle soil profile (20-60 cm), with less distribution in the surface (0-20 cm) and bottom (60-90 cm) soil profiles. The results indicated that the roots of the three annual halophytes grew rapidly into the deeper soil layer after germination, which ensured the plant survival and uptake of water and nutrition, and thus built up a strong tolerance to an arid, high-salt environment.

First Report of Fusarium Wilt of Strawberry Caused by Fusarium oxysporum in South Carolina.

During October 2011, wilted and dead strawberry (Fragaria × ananassa cv. Albion) plants from two commercial fields in South Carolina were sent to the Clemson University Plant Problem Clinic in Pendleton, SC. Symptoms consisted of wilting and chlorosis of foliage, scorch and dieback of older leaves, and stunting of plants. Internal vascular and cortical tissues of plant crowns showed a distinct reddish brown discoloration. To isolate the causal agent, necrotic crown tissue selected from two symptomatic plants from one location and four symptomatic plants from the other were placed on acidified potato dextrose agar (APDA) and on quarter strength acidified PDA (QPDA). Colonies with light purple mycelia and beige or orange reverse colony colors developed on APDA after 5 days of incubation at 25°C. Colonies on QPDA were light purple. Morphology, growth, and development of macroconidia and microconida were consistent with descriptions of Fusarium oxysporum Schlechtend emend. Snyder & Hansen (3). Genomic DNA from 3 isolates (11-1246A, 11-1247A, and 11-1247B) was extracted and purified according to Chi et al. (1). The internal transcribed spacer region comprising ITS1, ITS2, and 5.8S rRNA was amplified by primers ITS1 and ITS4 (4). The sequence comparison revealed a 100% match with F. oxysporum sequences in GenBank. To confirm the pathogenicity of the fungus, roots of 15 strawberry plants (cv. Albion) were cut and then five plants were soaked for 10 min in either 500 ml of conidial suspension (104 conidia/ml) of one of the two isolates or in sterile distilled water. All were then potted in 15-cm pots with artificial peat-based soil mix and maintained at 25°C in the greenhouse. After 6 weeks, all plants inoculated with isolates 1247A and B were stunted and developed wilt symptoms similar to those observed in the field, while the control plants remained healthy. Support roots on all affected plants were soft and flaccid and new feeder roots had brown lesions. Crowns of three plants inoculated with isolate 1247A and four plants inoculated with 1247B showed vascular discoloration. To reisolate, crowns were plated as above and roots were surface sterilized in 10% bleach for 1 min and rinsed in sterile distilled water prior to plating on QPDA. F. oxysporum was isolated at frequencies of 70 and 100% from crowns and 100% from roots of all inoculated plants. To our knowledge, this is the first report of the occurrence of Fusarium wilt caused by F. oxysporum on strawberry plants in South Carolina. The presence of Fusarium wilt in South Carolina should alert growers, county agents, and specialists to properly identify Fusarium wilt symptoms, which may be confused with Anthracnose or Phytophthora crown rot of strawberry. The disease has been reported previously in other countries including the United States (2).

Root-Knot Disease Caused by Meloidogyne arenaria and M. javanica in Teak in São Paulo State, Brazil

Teak (Tectona grandis Linn. F.) is one of the most important forest crops in Brazil, occupying areas in different regions, such as Goiás, Mato Grosso, Paraná, and São Paulo states. Teak wood is used for many purposes such as shipbuilding, rolling and plywood, firewood, and charcoal. In May 2011, teak symptomatic feeder root samples, exhibiting inconspicuous, small galls, were collected in the municipality of Piracicaba, São Paulo State, Brazil (22°41'46.90″S, 47°38'36.84″W). Specimens were identified through perineal patterns and esterase phenotypes of 20 adult females (1,2). Perineal patterns and esterase phenotypes were consistent with those described for Meloidogyne arenaria (Neal, 1889) Chitwood, 1949 and M. javanica (Treub, 1885) Chitwood, 1949. Perineal patterns of M. arenaria showed a low dorsal arch, compressed dorsolaterally, with lateral field marked by some forked and broken striae; no punctate markings between anus and tail terminus were observed. Perineal patterns of M. javanica were rounded, with low dorsal arch, striae smooth, lateral field distinct, clearly demarcated from striae by parallel lines. From the esterase electrophoresis we obtained A2 (Rm:1.2;1.3) and J3 (Rm:1.0;1.25;1.4) phenotypes, typical from M. arenaria and M. javanica, respectively. To our knowledge, this is the first report of M. arenaria parasitizing teak roots in Brazil and elsewhere (new host) and the first report of M. javanica infecting teak in the State of São Paulo. Previously, M. javanica was reported to be infecting teak-growing areas in the State of Mato Grosso (3). This finding has a great importance, not only by the inclusion of these parasites in teak pathological scenario, but also for predicting possible damage in plant species used in teak-based intercropping systems.

Okra (Abelmoschus esculentus (L.) Moench) as a valuable vegetable of the world

Summary: Okra is a commercial vegetable crop with considerable area under cultivation in Africa and Asia. Okra belongs to the family Malvaceae. It probably originated in Ethiopia and is widely spread all over tropical, subtropical and warm temperate regions of the world. Okra plays an important role in the human diet by supplying fats, proteins, carbohydrates, minerals and vitamins. Moreover, its mucilage is suitable for certain medical and industrial applications. Therefore, young fruits of okra have reawakened beneficial interest in bringing this crop into commercial production. The optimum yield of okra is approximately 6.6 t ha -1 . Okra requires warm temperatures. The optimum temperatures are in the range of 20-30°C, with minimum temperatures of 18°C and maximum of 35°C. Okra needs rather high quantity of water despite having considerable drought resistance. The plant forms a deeply penetrating tap root with dense shallow feeder roots reaching out in all directions in the upper 45 cm of soil. Soil clamminess is essential during the continuation of growing period.

Host-pathogen interaction of root-knot nematode Meloidogyne incognita on pepper in the southeast of Spain

The feeder roots of pepper plants (cv. California Wonder) in Campo de Cartagena (southeast Spain) were found to be severely infected by Meloidogyne incognita. Morphometric traits, differential host test and DNA analysis based on PCR were used to characterize the nematode. Naturally and artificially infected pepper plants showed severe yellowing and stunting, with heavily deformed and damaged root systems. Root galls were spherical and commonly contained more than one female and egg masses with eggs. Typical giant cells with a granular cytoplasm and many hypertrophied nuclei were observed in histological preparations. The relationship between initial nematode population density (Pi) and pepper plant growth was tested in greenhouse experiments with inoculum levels that varied from 0 to 64 eggs and second-stage juveniles (J2) ml−1 soil. A Seinhorst model was fitted to plant height and top fresh weight data of inoculated and non-inoculated plants. The tolerance limit with respect to plant height and fresh top weight of pepper to M. incognita was estimated as 0.85 eggs and J2 ml−1 soil. The minimum relative values (m) for plant height and top fresh weight were 0.15 and 0.16, respectively, at Pi ≥ 64 eggs and J2 ml−1 soil. The maximum nematode reproduction rate (Pf/Pi) was 315.4 at an initial population density (Pi) of 4 eggs and J2 ml−1 soil. The obtained results could be used as a base to establish field experiments that allow strategies to prevent surpassing the threshold of nematodes in fields that are infested.

Diversity Analysis of Diazotrophic Bacteria Associated with the Roots of Tea (Camellia sinensis (L.) O. Kuntze)

The diversity elucidation by amplified ribosomal DNA restriction analysis and 16S rDNA sequencing of 96 associative diazotrophs, isolated from the feeder roots of tea on enriched nitrogen-free semisolid media, revealed the predominance of Gram-positive over Gram-negative bacteria within the Kangra valley in Himachal Pradesh, India. The Gram-positive bacteria observed belong to two taxonomic groupings; Firmicutes, including the genera Bacillus and Paenibacillus; and Actinobacteria, represented by the genus Microbacterium. The Gram-negative bacteria included alpha-Proteobacteria genera Brevundimonas, Rhizobium, and Mesorhizobium; gamma-Proteobacteria genera Pseudomonas and Stenotrophomonas; and beta-Proteobacteria genera Azospira, Burkholderia, Delftia, Herbaspirillum and Ralstonia. The low level of similarity of two isolates, with the type strains Paenibacillus xinjiangensis and Mesorhizobium albiziae, suggests the possibility of raising species novum. The bacterial strains of different phylogenetic groups exhibited distinct carbon-source utilization patterns and fatty acid methyl ester profiles. The strains differed in their nitrogenase activities with relatively high activity seen in the Gramnegative strains exhibiting the highest similarity to Azospira oryzae, Delftia lacustris and Herbaspirillum huttiense.

Involvement of Phytophthora citrophthora in Kiwifruit Decline in Turkey

AbstractVine decline of kiwifruit was found in an orchard in the Rize province in Turkey. About half of the vines showed poor growth, leaf discoloration and dieback symptoms. From the necrotic feeder roots of the diseased vines, a Phytophthora sp. was isolated. The causal agent of the disease was identified as Phytophthora citrophthora by morphological characteristics and comparing sequences of Internal Transcribed Spacer (ITS) region. Phytophthora citrophthora caused bark necroses averaging 4.2 ± 1.4 cm in length when inoculated on the rooted canes.

Phytophthora root and collar rot of mature Fraxinus excelsior in forest stands in Poland and Denmark

In recent years, Common ash (Fraxinus excelsior) throughout Europe has been severely impacted by a leaf and twig dieback caused by the hyphomycete Chalara fraxinea. The reasons for its current devastating outbreak, however, still remain unclear. Here, we report the presence of four Phytophthora taxa in declining ash stands in Poland and Denmark. Phytophthora cactorum, Phytophthora plurivora, Phytophthora taxon salixsoil and Phytophthora gonapodyides were isolated from rhizosphere soil samples and necrotic bark lesions on stems and roots of mature declining ash trees in four stands. The first three species proved to be aggressive to abscised roots, twigs and leaves of F. excelsior in inoculation experiments. Soil infestation tests also confirmed their pathogenicity towards fine and feeder roots of ash seedlings. Our results provide first evidence for an involvement of Phytophthora species as a contributing factor in current decline phenomena of F. excelsior across Europe. Specifically, they may act as a predisposing factor for trees subsequently infected by C. fraxinea. Phytophthora species from ash stands also proved to be aggressive towards a wide range of tree and shrub species commonly associated with F. excelsior in mixed stands. Although damage varied considerably depending on the Phytophthora species/isolate-host plant combination, these results show that many woody species may be a potential source for survival and inoculum build-up of soilborne Phytophthora spp. in ash stands and forest ecosystems in general.

Ascorbic acid, β-carotene, sugars, phenols, and heavy metals in sweet potatoes grown in soil fertilized with municipal sewage sludge

Municipal sewage sludge (MSS) used for land farming typically contains heavy metals that might impact crop quality and human health. A completely randomized experimental design with three treatments (six replicates each) was used to monitor the impact of mixing native soil with MSS or yard waste (YW) mixed with MSS (YW +MSS) on: i) sweet potato yield and quality; ii) concentration of seven heavy metals (Cd, Cr, Mo, Cu, Zn, Pb, and Ni) in sweet potato plant parts (edible roots, leaves, stem, and feeder roots); and iii) concentrations of ascorbic acid, total phenols, free sugars, and β-carotene in sweet potato edible roots at harvest. Soil samples were collected and analyzed for total and extractable metals using two extraction procedures, concentrated nitric acid (to extract total metals from soil) as well as CaCl2 solution (to extract soluble metals in soil that are available to plants), respectively. Elemental analyses were performed using inductively coupled plasma mass spectrometry (ICP-MS). Overall, plant available metals were greater in soils amended with MSS compared to control plots. Concentration of Pb was greater in YW than MSS amendments. Total concentrations of Pb, Ni, and Cr were greater in plants grown in MSS+YW treatments compared to control plants. MSS+YW treatments increased sweet potato yield, ascorbic acid, soluble sugars, and phenols in edible roots by 53, 28, 27, and 48%, respectively compared to plants grown in native soil. B-carotene concentration (157.5 μg g−1 fresh weight) was greater in the roots of plants grown in MSS compared to roots of plants grown in MSS+YW treatments (99.9 μg g−1 fresh weight). Concentration of heavy metals in MSS-amended soil and in sweet potato roots were below their respective permissible limits.

First Report of Root and Crown Rot of Almond Caused by Phytophthora spp. in Turkey.

Almond (Prunus dulcis) production is currently increasing in Turkey. Losses of approximately 1% associated with root and crown rot of almond seedlings were observed in two commercial nurseries in Ankara and Düzce provinces in 2009. Aboveground symptoms were leaf chlorosis and wilt. Feeder roots were decayed, necrosis occurred on taproots and basal stems, and plants collapsed within several weeks. Roots were washed in tap water and 9 to 10 pieces (3 to 5 mm long) of root tissue taken from the margins of canker lesions, without surface disinfection, were placed on selective medium P5ARPH-CMA (2). Plates were incubated for 3 to 5 days at 20°C in darkness and a number of Phytophthora spp. were recovered. Actively growing mycelium was transferred to carrot piece agar containing β-sitosterol (per liter: carrot piece, 40 g; agar, 20 g; β-sitosterol, 20 mg). Isolates were identified as Phytophthora cactorum and P. citrophthora on the basis of morphological characteristics (1). P. cactorum produced abundant sporangia, oogonia, and paragynous antheridia on carrot piece agar plus β-sitosterol. It had conspicuously papillate and caducous sporangia with short pedicel. Sporangia were usually ovoid but sometimes nearly spherical. P. citrophthora did not produce sexual structures in single culture. It produced papillate, noncaducous sporangia, which were usually ovoid and obpyriform, often asymmetrically shaped and rarely possessed more than one apex. P. citrophthora did not grow at 35°C but it grew well at 30°C. Isolate identities were confirmed by sequence analysis of the ribosomal DNA internal transcribed spacers 1 and 2 (GenBank Accession Nos. HM357622, HM357623, HM357624, HM357625) using primers ITS1 and ITS2 (3). One representative isolate of each species was used to inoculate eight 2-year-old almond plants with an agar plug with actively growing mycelium that was attached to exposed cambium of basal stems. Agar plugs without mycelium were used for eight control plants. All plants inoculated with Phytophthora spp. collapsed within 3 to 4 weeks. Control plants remained healthy. Phytophthora spp. were reisolated from necrotic basal stems. To our knowledge, this is the first report of P. cactorum and P. citrophthora of almond in Turkey.

Ecological Relationships of Verticillium Wilt Suppression of Potato by Green Manures

Studies show that once a suppressive effect has been established, a green manure treatment for a single season is sufficient to either maintain or to re-establish the control of Verticillium wilt of potato. Verticillium wilt, caused by Verticillium dahliae Kleb., was controlled on the first years of Russet Burbank potato cropping following 2–3 successive years of green manure treatments. Following this control, yields were increased with the first year of potato cropping, but were reduced during the second consecutive year of cropping with potato. In the second year of continuous cropping with Russet Burbank, total yields were reduced by 10% and U.S. #1 tubers by 40%, and these yield reductions were accompanied by increased soil populations of V. dahliae by >5- fold. Yet, with a single season of an earlier–used green manure treatment (e.g. Austrian winter pea, sudangrass, Dwarf Essex rape, Bridger rape, oats, rye, or sweet corn), Verticillium wilt was again controlled and yields of Russet Burbank were increased to higher levels or to levels that were equivalent to those initially observed following either 2 or 3 successive seasons of green manure treatment. Green manures also demonstrated significant effects on microbial activities, which were inversely related to the incidence of Verticillium wilt. More specific effects on microbial activity and soilborne ecology were shown with increased populations of Fusarium spp. Verticillium wilt was negatively correlated with infections of potato feeder roots and stem-ends of potato tubers by F. equiseti. Exemplifying the effect of a green manure on fungal ecology, sudangrass treatments were shown to have lasting effects on Fusarium avenaceum populations with quantitative changes that extended 5 years beyond the time of soil incorporation with sudangrass.

PROPERLY TIMED FOLIAR FERTILIZATION CAN AND SHOULD RESULT IN A YIELD BENEFIT AND NET INCREASE IN GROWER INCOME

Foliar fertilization reduces nutrient accumulation in soil, run-off and groundwater, where they contribute to salinity, eutrophication or nitrate contamination, with negative consequences to humans and the environment. Soil-applied fertilizers should be replaced in part with foliar-applied fertilizers. Foliar fertilizers can meet the crop's nutrient demand when soil temperature, moisture, pH, or salinity renders soil-applied fertilizers ineffective. Applying nutrients directly to leaves ensures that the plant's photosynthetic machinery is not compromised by low availability of an essential nutrient. Foliar-applied phloem-mobile nutrients are translocated to all plant parts, even feeder roots. However, not all nutrients are taken up through leaves and, even if taken up, some nutrients are not phloem mobile. Foliar fertilizer rates are typically lower than soil fertilizer rates, but application can be more costly. The goal of our research is to properly time the application of foliar fertilizers at specific stages of tree phenology, when nutrient demand is likely high, to increase yield, fruit size or quality, such that foliar fertilization results in a net increase in grower income even when the tree is not nutrient deficient by standard leaf analysis. A single foliar application of zinc sulphate to Citrus sinensis, 'Washington' navel orange, at 10% anthesis significantly increased fruit set through harvest in January, without impact on fruit size or quality. Later applications reduced fruit set. Winter (December) prebloom foliar application of low-biuret urea to C. reticulata, 'Nules' Clementine mandarin, increased 2-year cumulative yield of commercially valuable fruit (transverse diameter 63.51-69.85 mm) as both kg and number of fruit per tree with no effect on total yield or fruit quality. Earlier or later applications were without effect. Foliar application of potassium phosphite to Persea americana, 'Hass', at the cauliflower stage of inflorescence development significantly increased 3-year cumulative yield (kg and number of fruit per tree) of commercially valuable fruit (178-325 g per fruit) compared to trees receiving foliar- or soil-applied potassium phosphate. All cases resulted in a net increase in grower income.

First Report of Monosporascus cannonballus on Watermelon in Brazil.

In 2008 and 2009, vine decline symptoms were observed in three watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) fields located in the municipalities of Mossoró (Rio Grande do Norte State) and Quixeré (Ceará State) in northeastern Brazil. Symptoms included yellowing of crown leaves just prior to harvest and collapse of many of the vines. Mean maximum daily temperatures for the first and second half of the season were 28.6 and 25.1°C, respectively. Affected plants exhibited necrotic root systems and lacked most of the secondary and tertiary feeder roots. Numerous perithecia on the roots contained asci and ascospores characteristics of Monosporascus cannonballus Pollack & Uecker (1,2). Small pieces of primary and secondary roots were surface disinfected and plated onto potato dextrose agar (PDA) medium with 0.5 g liter-1 of streptomycin sulfate and incubated for 7 days at 25°C in the dark. Hyphal tips from all colonies were transferred to PDA and further incubated for 30 to 40 days at 25°C in the dark for subsequent growth and sporulation. Isolations consistently yielded colonies of white mycelium, which became dark grayish after 10 to 15 days, and perithecia with one-spored asci. The internal transcribed spacer regions of ribosomal DNA of isolates 18-5 and 19-1 were sequenced (GenBank Accession Nos. GQ891544 and GQ891545). These sequences were identical to sequences of M. cannonballus (GenBank Accession Nos. AM167936 and AM167937). Pathogenicity of these two isolates was confirmed on watermelon cv. Crimson Sweet in a greenhouse maintained at 25 to 30°C. Inoculum was produced in a sand-oat hulls (Avena sativa) medium (0.5 liter of sand, 46 g of ground oat hulls, and 37.5 ml of distilled water) and incubated at 25°C for 1 month. CFU were quantified by serial dilution using 1% hydroxyethyl cellulose. A sterilized mixture of equal portions (vol/vol) of sand and peat moss was used to fill 17-cm-diameter plastic pots and inoculum was added to produce an inoculum concentration of 20 CFU g-1. Five watermelon seeds planted in each pot were later thinned to one seedling per pot. There were five replicated pots for each treatment with an equal number of noninfested pots. Plants were evaluated for disease 45 days after sowing. All isolates of M. cannonballus were highly aggressive and caused severe root necrosis compared with the noninoculated controls. M. cannonballus was reisolated from symptomatic plants, confirming Koch's postulates. In 2004, M. cannonballus was reported in the same Brazilian cucurbit-growing areas causing root rot and vine decline of muskmelon (Cucumis melo L.) (3), but to our knowledge, this is the first report of M. cannonballus on watermelon in Brazil.

First Report of Phytophthora Root Rot Caused by Phytophthora cryptogea on Spinach in California.

In 2006 and 2007, commercially grown spinach (Spinacia oleracea) in California's coastal Salinas Valley (Monterey County) was affected by an unreported root rot disease. Disease was limited to patches along the edges of fields. Affected plants were stunted with chlorotic older leaves. As disease progressed, most of the older foliage first wilted and then turned tan and dry; youngest leaves remained green but were stunted and leathery in texture. Plants most severely affected died. Symptoms on roots were mostly restricted to the distal portion of the root system, where feeder roots and the main taproot turned black. Isolations from root lesions consistently resulted in the recovery of a Phytophthora sp. The isolates were heterothallic, and on the basis of morphological and cytochrome oxidase 2 gene sequence data (GenBank Accession No. GQ984233), the pathogen was identified as Phytophthora cryptogea. To evaluate pathogenicity, individual inocula of four isolates were prepared by incubating colonized 6-mm-diameter V8 agar plugs in filtered soil extract for 2 days at 20°C to induce sporangia production. These cultures were then chilled at 4°C for 20 min and returned to room temperature for 1 h to induce zoospore release (4). Four-week-old spinach plants (cv. Bolero) were uprooted, soaked in suspensions of 1.0 × 105 zoospores/ml for 10 min, and repotted. After treatment, pots were placed in shallow trays of water for 24 h to saturate the root zone, then were removed from trays and incubated in a greenhouse. After 9 days, inoculated plants showed foliar wilting and chlorosis similar to that observed in the field; after 13 days, roots were examined and found to show the black necrosis as seen in the field. P. cryptogea was isolated from all inoculated plants. Control spinach plants, treated with soil extract only, did not develop disease. This experiment was completed two times and the results were similar. To our knowledge, this is the first report of Phytophthora root rot of spinach caused by P. cryptogea in California. This finding is significant because spinach in California is subject to root rots caused by three other pathogens (Fusarium oxysporum, Pythium spp., and Rhizoctonia solani) (1); symptoms from these root rots are very similar to those caused by P. cryptogea, thereby complicating diagnosis. This pathogen has been documented on spinach in Germany and Sweden (2,3).

Growth of young budding plants as affected by type and packing density of the potting media

The effects of potting media and the degree of compaction on shoot and root growth of Hevea brasiliensis (A. Juss.) Muell. Arg. plants raised using young budding technique were determined in this study. Soils were mixed with coir dust or saw dust to a ratio of either 1:1 or 3:1 and filled into polybags with two compaction levels. Shoot diameter and dry weight, and root dry weights were measured at 12 weeks after planting and 6 weeks after cut-back. Percentages of buddable plants, grafting success, scion death and sprouting were also measured. Plants in soil-coir dust 3:1 ratio (SC31) recorded the highest seedling growth (7.2 mm in diameter) as well as scion growth (6.2 mm in diameter) while the lowest growth was observed in soil only (seedling diameter of 6.5 mm) and in soil-saw dust 3:1 (SS31) media (scion diameter of 4.4mm). Total root weight also was significantly higher in SC31 compared to those in other potting media, both at 12 weeks after planting (3.36 g plant-1) and 6 weeks after cut-back (7.99 g plant-1). Feeder root density was significantly low in currently adopted soil only treatments at both growth stages. The plants in the soil and coir dust mixed polybags had higher probability of attaining buddable girth than plants in other treatments. The level of compaction in the potting media had no significant impact on shoot or root growth parameters measured. This study showed that growth of young budding plants could significantly be improved by using a potting media of soil and coir dust with a ratio of 3:1. Relative advantages of having a polybag plant with a dense root system are discussed in relation to stress mitigation both in the nursery and field.

First Report of Root-Knot Nematode Meloidogyne hispanica Infecting Grapevines in Southern Spain.

Some commercial vineyards producing the 'Condado de Huelva' wine denomination of origin in Almonte, Bonares, and Rociana (Huelva Province), southern Spain, showed general decline in sandy soils in 2009. Disease surveys revealed severe infections of grapevine rootstock Richter 110 feeder roots and heavy soil infestations by a root-knot nematode (Meloidogyne sp.). Infected plants showed a general decline as the only visible aboveground symptom, but when roots were inspected, moderate to small galls on secondary feeder roots were detected. The Meloidogyne sp. population was extracted and quantified from soil and root samples as previously described (1) and identified by the female perineal pattern, esterase (Est) and malate dehydrogenase (Mdh) phenotypes, and sequencing and maximum parsimony (MP) analysis of the ribosomal DNA region D2-D3 of 28S (2,4). Morphology of the perineal patterns and measurements of the second-stage juveniles (J2s) matched those of the original description of Meloidogyne hispanica (3). Enzyme analysis revealed two slow and a medium Est bands, a strong band, and two additional weaker bands coincident with the S2-M1 and N3 Mdh M. hispanica phenotypes (2,4). D2-D3 sequences of all three populations sampled were 100% homologous (GenBank Accession No. GQ375158). Phylogenetic analyses with MP of those sequences placed the Meloidogyne sp. in a clade (100% support) that included all M. hispanica sequences available from the GenBank database (4). M. hispanica was first found in Seville Province, southern Spain, infecting rootstocks of Prunus spp. Its distribution has been confirmed worldwide on different agricultural crops. Thus, M. hispanica has been reported to be infecting grapevines in South Africa and Australia (4); however, to our knowledge, this is the first report of M. hispanica infecting grapevines in Europe. Our data suggest that M. hispanica may pose a threat for vineyard production in southern Spain since M. hispanica was found in 52.63 and 47.36% of soil and root samples, respectively, from 19 fields in 'Condado de Huelva', with nematode population densities ranging from 2.4 to 129.6 eggs and J2s per 100 cm3 of soil and 1 to 1,797 eggs and J2s per gram of fresh roots. Furthermore, genes that confer resistance to other common root-knot nematodes reported on grapevine in Europe may not protect against M. hispanica.

Responses to precipitation treatment for Haloxylon ammodendron growing on contrasting textured soils

AbstractThe responses to precipitation of Haloxylon ammodendron (C.A. Mey.) Bunge (Chenopodiaceae), a small xerophilous tree growing on contrasting textured soils, were evaluated under no, natural, and double precipitation treatments during the entire growing season of 2006. The contrasting textured soils are sandy and heavy textured, and both are the original habitat of H. ammodendron at the south edge of Gubantonggute Desert, Central Asia. Photosynthesis, leaf water potential, transpiration, water use efficiency and leaf biomass production were monitored throughout the growing season. Root distribution of H. ammodendron was evaluated at the end of the experiment. Overall, this small tree did not show significant response to a large summer precipitation pulse or precipitation treatments, in terms of photosynthetic carbon assimilation on either soil. The leaf water potential, transpiration, and water use efficiency appeared to be highly sensitive to a large precipitation pulse and precipitation treatments in sandy soil; and leaf biomass production was also much higher for plants in sandy than that of heavy‐textured soil. In sandy soil, defoliation occurred when pre‐dawn leaf water potential dropped below −3.0 MPa, while in heavy‐textured soil, defoliation occurred when pre‐dawn leaf water potential dropped below −3.75 MPa. For similar above‐ground parts, the small trees at the sandy site developed much deeper root systems and had nearly double the surface area of feeder roots compared to those at the heavy‐textured site. Partially owning to the deeper and larger root system, H. ammodendron growing at coarse‐textured site was in better water conditions than those at heavy‐textured site under the same climatic conditions.