David M. Modise

Effects of a Selective and a Broad-Spectrum Insecticide on Parasitism Rates of Plutella xylostella (L.) (Lepidoptera: Plutellidae) and Species Richness of Its Primary Parasitoids

The direct impact of broad-spectrum insecticides on primary parasitoids is considered a major contributing factor to the high pest status of diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), in many parts of the world. As a result, selective insecticides are often put forward as a solution to the problem of integrating chemical and biological control methods. However, there is paucity of studies that have directly contrasted effects of selective and broad-spectrum insecticides on parasitism rates and parasitoid species richness in the field. We compared effects of weekly and bi-weekly application regimes of a selective insecticide (Dipel®) and a broad-spectrum insecticide (dichlorvos) on parasitism rates of P. xylostella and species richness of its primary parasitoids against unsprayed control for two cropping seasons. Parasitoids were reared from immature P. xylostella in all treatments, and parasitism rates were not significantly different among the treatments. During October–December 2011, four species of primary parasitic Hymenoptera [Cotesia vestalis (Haliday) (Braconidae), Apanteles halfordi (Ullyett) (Braconidae), Oomyzus sokolowskii (Kurdjumov) (Eulophidae), and Diadromus collaris (Gravenhorst) (Ichneumonidae)] were reared from P. xylostella larvae and pupae, whereas three parasitoid species (C. vestalis, O. sokolowskii and D. collaris) were reared during March–May 2012. Cotesia vestalis accounted for >80%of total parasitism rates in all treatments. In both seasons, parasitoid species richness was highest on the control treatment. Although two parasitoid species were recorded on all Dipel® and dichlorvos treatments during October–December 2011, only one parasitoid species was recorded on Dipel® treatments during March–May 2012 compared to two species on dichlorvos treatments. Thus, insecticide application regime had no influence on parasitoid species richness, instead insecticide type did. Since P. xylostella infestations were significantly lower in Dipel® treatments in both seasons, this study suggests that a greater impact of a selective insecticide on the pest population density can affect parasitoid species richness more than the direct impact of a broad-spectruminsecticide with a short crop residual period.

Identification and characterization of protein coding genes in monsonia (Monsonia burkeana Planch. ex harv) using a combination of approaches

The advent of next generation sequencing has made possible massive availability of sequence information for in-depth structural and functional analysis of the genes and their encoded biological state in model and non-model organisms. In this study, we demonstrate a combinatorial approach for finding protein coding genes using ab initio and extrinsic evidence-based methods in monsonia (Monsonia burkeana Planch. ex harv). This is an important herbal tea crop, yet little is known about its coding genes. To our knowledge, this is the first description of protein coding genes with detailed functional annotation in M. burkeana. This study demonstrates that (1) regions of transcript assembly potentially encode protein coding genes, (2) homologous evidence with known functions reliably assigns functions to the identified genes (3) conserved domains suggest evolutionary and functional relationship of the crop with other lineage and (4) accuracy of finding coding genes in alignment free models and in RNA-seq alignment based transcript assembly performs well. This study provides a glimpse of functional information of the protein coding region at the transcriptome level and can be used as the basis for further investigation of the underlying genetic composition and molecular functions associated with M. burkeana.

De novo transcriptome sequencing in Monsonia burkeana revealed putative genes for key metabolic pathways involved in tea quality and medicinal value

Monsonia (Monsonia burkeana Planch. ex Harv) is one of the most valuable tea and traditional medicinal plants used in Southern Africa. In spite of this, there is no sequence information regarding this plant in literature. To provide understanding of the naturally occurring tea and drug-specific products and the key pathways for the biosynthesis of these molecules, we sequenced the leaf transcriptome using Illumina MiSeq platform and generated 2,590,652 paired-end reads that were assembled de novo into 45,450 high-quality transcripts. Annotation of these transcripts revealed best hits for homology to discover more than 17,800 functional genes and conserved domains. A total of 93 KEGG pathways and associated genes encoded by more than 90% of the coding transcripts are responsible for the biosynthesis of these life-saving metabolites. We validated and enriched the genes by GO annotation and linked this to enzyme-powered pathways through interactive network map. Caffeine metabolism, flavonoid, phenylpropanoid and terpenoids biosynthesis and xenobiotics degradation were typical in tea quality and drug therapy. The relatedness of more than 80 gene families encoding key enzymes was shown using unrooted phylogenetic tree. In conclusion, the M. burkeana leaf transcriptome gives insight into tea and drug-specific products, therefore representing basis in further investigation of the plant.

Assessment of Growth, Tuber Elemental Composition, Stomatal Conductance and Chlorophyll Content of Two Potato Cultivars Under Irrigation with Fly Ash-Treated Acid Mine Drainage

The impact of fly ash (FA)-treated acid mine drainage (AMD) on growth, tuber yield and elemental composition, stomatal conductance and chlorophyll content of two potato cultivars was assessed. Two potato cultivars were irrigated with the following treatments: tap water (0% AMD/control), acid mine drainage mixed with fly ash (v/v); 25% AMD, 50% AMD & 75% AMD and untreated AMD (100% AMD). A complete randomized block design pot experiment with six replicates per treatment was conducted in two cropping seasons. Irrigation with 75% AMD in both cropping seasons significantly increased growth and tuber yield compared with control. However, unsafe levels of Ni, Zn, and Sr were found in tubers of both cultivars irrigated with FA-treated AMD treatments in both seasons. Additionally, FA-treated AMD treatments reduced leaf stomatal conductance and chlorophyll content relative to control in both cultivars. Cultivar response was found to differ with respect to all measured parameters.ResumenSe evaluó el impacto del drenaje ácido de las minas (AMD en inglés) tratado con ceniza de carbón (FA en inglés) sobre el crecimiento, rendimiento, composición elemental, conductancia estomatal y contenido de clorofila, en dos variedades de papa. Se regó a las dos variedades con los siguientes tratamientos: agua normal (0% AMD/testigo), drenaje ácido de las minas mezclado con ceniza de carbón (v/v); 25% AMD, 50% AMD & 75% AMD y AMD sin tratar (100% AMD). Durante dos ciclos de cultivo, se condujo un experimento en macetas con un diseño de bloques completos al azar con seis repeticiones por tratamiento. El riego con 75% AMD en ambos ciclos aumentó significativamente el crecimiento y el rendimiento de tubérculo en comparación con el testigo. No obstante, se encontraron niveles inseguros de Ni, Zn, y Sr en tubérculos de ambas variedades regadas con los tratamientos de AMD tratado con FA en ambos ciclos. Además, los tratamientos con AMD tratado con FA redujeron la conductancia estomatal de la hoja y el contenido de clorofila en relación con el testigo en ambas variedades. Se encontró que la respuesta varietal difería con respecto a todos los parámetros medidos.

Development, Survival, Body Weight and Oviposition Rates of Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) When Reared on Seven Cabbage Cultivars

Plant cultivars that negatively influence fitness of target phytophagous insects can be an important component of integrated pest management when they substantially restrict population growth of the target pest. In this study, the effects of seven cabbage (Brassica oleracea var. capitata L.) cultivars on survival and development of immature stages, pupal weights, moth longevity and oviposition rates of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), were evaluated in the laboratory. Under the no choice test, overall survival of P. xylostella immature stages was highest on Karabo (67.26 %) and lowest on Megaton (44.92 %). The larval and pupal developmental period, and thus generation time took longer on Empowa (18.48 d), Karabo (14.64 d) and Beverly Hills (17.48 d), while development on Hollywood F1 (13.79 d) was the fastest. Male and female P. xylostella pupal weights were lower in larvae that fed on Megaton (4.13 and 4.65 mg), Menzania (4.53 and 4.91 mg), and Hollywood F1 (4.11 and 5.08 mg), whereas pupal weights from Karabo (6.0 and 6.82 mg) were the heaviest. Unfed female moths reared on Beverly Hills lived the longest (5.05 d), whereas those reared on Leano (3.54 d) and Megaton (3.89 d) lived for a shortest period. Under the choice-test, P. xylostella laid significantly more eggs on Empowa (48.8 %) and Hollywood F1 (45.6 %) and least on Menzania (11.8 %) and Leano (10.6 %). Although these results show differential impact of the cultivars on the fitness parameters studied, low survival rate of offspring on a crop is the primary target for using plant resistance as a pest management tactic. As survival rates of immature P. xylostella were lower on Megaton together with lower pupal weights and moth longevity, which together negatively impacts fecundity, and thus overall fitness of the pest was lower when developing on it. Megaton was more resistant to P. xylostella. The results of this study show that Megaton can play a major role in restricting population growth of this pest and generational number of eggs deposited on it.

Yield of hydroponically grown tomato (Solanum lycopersicon) as affected by different particle sizes of sawdust

Abstract The particle size of a growing medium is one of the most important aspects in growing crops hydroponically. A study was conducted to determine the effect of particle size of sawdust as a substrate on tomato yield, in a non-temperature-controlled plastic tunnel. Tomato plants were grown using an open-bag hydroponic system for a duration of 110 d. The plants were subjected to six different particles sizes of sawdust viz. fine (800 µm), medium (1.4 mm) and coarse (3.4 mm) and at a ratio of 50:50 (v/v), i.e. coarse:fine (CF), coarse:medium (CM) and fine:medium (FM). Particle size of treatment CF and F improved total and marketable yield of tomato fruit compared with C, M, MF and CM. This may be due to the low air-filled porosity and improved water-holding capacity of CF and F. The study suggested that the most suitable particle size of sawdust in an open-bag hydroponic system for tomato production is CF or F. This finding contributes important knowledge to the hydroponic tomato-growing industry.

Cross-species multiple environmental stress responses: An integrated approach to identify candidate genes for multiple stress tolerance in sorghum (Sorghum bicolor (L.) Moench) and related model species

[This corrects the article DOI: 10.1371/journal.pone.0192678.].

Bottom-Up Effects of Cabbage Cultivars on Fitness of a Larval Parasitoid of Plutella xylostella (L.) (Lepidoptera: Plutellidae)

As parasitoid development is dependent on resources provided by a single host, the quality and quantity of resources its herbivore host obtains from different host plants can influence parasitoid fitness. Laboratory studies were conducted on several fitness parameters (developmental time, pupal weights, longevity, fecundity and sex ratio of progeny) of a larval parasitoid Cotesia vestalis (Haliday) (Hymenoptera: Braconidae) when its host Plutella xylostella (L.) (Lepidoptera: Plutellidae) developed on seven cabbage cultivars. In addition, population increase parameters of the parasitoid were compared on the various cultivars. The generation time of the parasitoid was shortest on Karabo (10.10 days) and Leano (10.38 days), and longest on Megaton (12.57 days) and Empowa (12.80 days). The heaviest C. vestalis pupae were recorded from Menzania (5.4 mg), Megaton (5.25 mg) and Beverly Hills (4.85 mg) and the lightest on Karabo (3.8 mg). Parasitoids reared on larvae that fed on Hollywood F1 lived the longest (2.28 days) followed by Menzania (1.94 days) and Beverly Hills (1.8 days), whereas those whose hosts fed on Leano lived the shortest period (0.83 days). Despite the parasitoids from Megaton hosts being bigger, their fecundity and number of female progeny per female (16.87 and 3.60, respectively) were lowest. Cotesia vestalis fecundity and daughters produced per female were highest on hosts fed on Menzania (38.00 and 9.13, respectively) and Beverly Hills (32.87 and 9.07, respectively). As a consequence, the net reproductive rate (R0) and intrinsic rate of increase (r) were higher on Menzania (7.87 and 0.58, respectively) and Beverly Hills (8.29 and 0.62, respectively). Not only do these results suggest that the overall fitness of C. vestalis is higher on hosts developing on Menzania and Beverly Hills, the critical density of the parasitoid required to suppress the host population at a lower average density will be reached quicker on these two cultivars than on others.