The Effect of Microwave Treatment on Germination and Health of Carrot (Daucus carota L.) Seeds

The aim of the study was to evaluate the effect of microwave treatment on seed germination and health of carrot seeds using two seed lots naturally infected with the pathogens Alternaria dauci and A. radicina. Seeds of cv. Amsterdam and cv. Berlikumer varied in seed germination at the final count (50% and 29%, respectively), and seed infestation with A. radicina (38% and 5%, respectively). For treatment, seeds were placed in a Petri dish (dry treatment) or in a beaker with distilled water (wet treatment) and irradiated at power output levels 500, 650 and 750 W for 15, 30, 45, 60, 75, and 90 s. Germination and health were determined in treated and untreated (control) seed samples. Wet treatment controlled seed-borne fungi more efficiently than dry treatment. However, the exposure duration longer than 60 s frequently resulted in deterioration of seed germination. The highest seed germination in cv. Amsterdam was observed after microwave wet treatment at power output levels of 500 W for 75 s (81%), 650 W for 45 s (85%), and 750 W for 60 s (77%), whereas in the case of cv. Berlikumer this occurred when wet seeds were treated at 500 and 650 W for 60 s (46% and 43% respectively). Treating seeds soaked in water with microwaves for a period longer than 30 s, regardless of the power output, significantly decreased seed infestation with Alternaria spp. in both samples.

Key factors involved in reduction of damage to sunflower by the European sunflower moth in China through late planting

The European sunflower moth, Homoesoma nebulellum (Denis et Schiffermüller), emerged as a major new pest in Bayannur, China, in 2006. Insecticidal control with a single application is problematic because timing is critical, and multiple applications increase production and environmental costs. Management of H. nebulellum by planting date adjustment can be effective, but the optimal time window for late planting is unknown. Natural levels of H. nebulellum infestation were compared among sunflowers planted on five dates from April 25 to June 5 in two years, and the relationship between timing of adult abundance and flowering assessed. Delaying planting of sunflower from the traditional planting period of April 25 –May 5 to May 15 –June 5 significantly decreased damage by H. nebulellum. Seed infestation rate was 30–40 times higher, and number of larvae/head 75–100 times higher in the earliest two plantings than in the latest two. Within two years of implementing delayed planting in Bayannur city, infestation area decreased from 72% in 2006 to 1.5% in 2008, and production losses decreased from 4.5 ton/ha in 2006 to 0.36 ton/ha in 2008, a 97% decrease compared to 2006. Moreover, the infestation area caused by H. nebulellum was continuously controlled below 5.3% of the planting area since 2008. We found the overlap between the first two days of flowering and peak adult presence was the key factor influencing level of damage caused by H. nebulellum. Because the number of eggs laid in the first two days of flowering accounted for 68% of the total, and sunflower seed infestation rate was positively correlated with the number of trapped adults weighted by proportion of daily oviposition. Oviposition of the majority of eggs in the first two days of flowering suggests an evolutionary mechanism whereby females choose host plants most conducive to larval development, consistent with the preference-performance hypothesis.

Preparation burning may not improve short-term seed survival in an Amazonian savanna

The role of fire in the management of degraded areas remains strongly debated. Here we experimentally compare removal and infestation of popcorn kernels (Zea mays L. – Poaceae) and açaí fruits (Euterpe oleracea Mart. – Arecaceae) in one burned and two unburned savanna habitats in the eastern Brazilian Amazon. In each habitat, a total of ten experimental units (five per seed type) were installed, each with three treatments: (1) open access, (2) vertebrate access, and (3) invertebrate access. Generalized linear models showed significant differences in both seed removal (P < 0.0001) and infestation (P < 0.0001) among seed type, habitats and access treatments. Burned savanna had the highest overall seed infestation rate (24.3%) and invertebrate access increased açaí seed infestation levels to 100% in the burned savanna. Increased levels of invertebrate seed infestation in burned savanna suggest that preparation burning may be of limited use for the management and restoration of such habitats in tropical regions.

Detection of Cercospora beticola and Phoma betae on Table Beet Seed using Quantitative PCR

Cercospora beticola and Phoma betae are important pathogens of table beet, sugar beet, and Swiss chard (Beta vulgaris subsp. vulgaris), causing Cercospora leaf spot (CLS) and Phoma leaf spot, root rot, and damping-off, respectively. Both pathogens may be seedborne; however, limited evidence is available for seed infestation by C. beticola. Due to the limitations of culture-based seed assessment methods, detection of these pathogens was investigated using PCR. A P. betae-specific quantitative PCR assay was developed and used in conjunction with a C. beticola-specific assay to assess the presence of pathogen DNA in 12 table beet seed lots. DNA of C. beticola and P. betae was detected in four and eight seed lots, respectively. Plate tests and BIO-PCR confirmed the viability of each pathogen; however, competitive growth of other microbes and low incidence limited the frequency and sensitivity of detection in some seed lots. The results for P. betae support previously described infestation of seed. Further investigation of C. beticola-infested seed lots indicated the ability of seedborne C. beticola to cause CLS on plants grown from infested seed. Detection of viable C. beticola on table beet seed demonstrates the potential for pathogen dispersal and disease initiation via infested seed, and provides valuable insight into the epidemiology of CLS. Surveys of commercial table beet seed are required to determine the frequency and source of C. beticola seed infestation and its role as primary inoculum for epidemics, and to evaluate the effectiveness of seed treatments.

Identification of quantitative trait loci (QTL) controlling resistance to pea weevil (Bruchus pisorum) in a high-density integrated DArTseq SNP-based genetic map of pea

Pea weevil (Bruchus pisorum) is a damaging insect pest affecting pea (Pisum sativum) production worldwide. No resistant cultivars are available, although some levels of incomplete resistance have been identified in Pisum germplasm. To decipher the genetic control underlying the resistance previously identify in P. sativum ssp. syriacum, a recombinant inbred line (RIL F8:9) population was developed. The RIL was genotyped through Diversity Arrays Technology PL’s DArTseq platform and screened under field conditions for weevil seed infestation and larval development along 5 environments. A newly integrated genetic linkage map was generated with a subset of 6,540 markers, assembled into seven linkage groups, equivalent to the number of haploid pea chromosomes. An accumulated distance of 2,503 cM was covered with an average density of 2.61 markers cM−1. The linkage map allowed the identification of three QTLs associated to reduced seed infestation along LGs I, II and IV. In addition, a QTL for reduced larval development was also identified in LGIV. Expression of these QTLs varied with the environment, being particularly interesting QTL BpSI.III that was detected in most of the environments studied. This high-saturated pea genetic map has also allowed the identification of seven potential candidate genes co-located with QTLs for marker-assisted selection, providing an opportunity for breeders to generate effective and sustainable strategies for weevil control.

Spatial and temporal patterns of a pulsed resource dynamically drive the distribution of specialist herbivores

Patterns and drivers of the spatio-temporal distribution of herbivores are key elements of their ecological and evolutionary impacts on plant populations. Herbivore spatial distributions may be influenced by increased (RCH: resource concentration hypothesis) or decreased (RDH: resource dilution hypothesis) resource densities, but the effect of temporal variations in resource densities on such distributions remains poorly documented. We used a survey of a masting tree species and its seed predators in Southeastern France to address the effect of a host’s pulsed resource on the spatio-temporal distributions of highly specialized insect herbivores feeding on seeds. Variations in both resource and seed predator densities were assessed by estimating seed production and seed infestation rates in focus trees during 10 consecutive years. We found increasing seed infestation rates with decreasing host tree densities in years of low seed production, indicating a RDH pattern of seed predators. However, such pattern was not persistent in years of high seed production during which seed infestation rates did not depend on host tree densities. We showed that temporal variations in resource density can lead to transience of seed predator spatial distribution. This study highlights how predictions of plant-herbivore interactions in natural ecosystems may rely on temporal components underlying RCH and RDH hypotheses.

STUDY OF CHICKPEA VARIETIES AGAINST PULSE BEETLE (CALLOSOBRUCHUS CHINENSIS) IN STORAGE

Maximum fecundity was found on genotype RVSSG-38. The adult emergence on different genotypes ranged from 7.0 to 18.0. Genotype RVSSG-44 recorded maximum percent loss in seed weight. Genotype RVSSG-43 had minimum percentage of seed infestation. Susceptibility index of pulse beetle on different genotypes of chickpea showed that there were no significant differences among different genotypes. Infestation percentage positively and significantly associated with protein content in fresh seed and infested seed. Seed size and seed shape of the genotypes did not influence the fecundity, adult emergence, total development period and susceptibility index of pulse beetle.

EVALUATION OF MORPHOLOGICAL CHARACTERS AND PROTEIN CONTENT OF CHICKPEA (CICER ARIETINUM) IN REALTION TO RESISTANCE AGAINST PULSE BEETLE (CALLOSOBRUCHUS CHINENSIS)

Twelve genotypes with variation in seed size, seed weight, seed coat colour and seed shape were included for the study. Genotype RVSSG-44 recorded maximum percent loss in seed weight. Genotype RVSSG-43 had minimum percentage of seed infestation, which was significantly less than rest of the genotypes, except JG-130 seed infestation. Susceptibility index of pulse beetle on different genotypes of chickpea showed that there were no significant differences among different genotypes. Infestation percentage positively and significantly associated with protein content in fresh seed and infested seed. However, other parameters were not associated with infestation by beetle. It ranged from 11.7 to 13.0 adult on angular and pea shape seeded genotypes, respectively. Seed size and seed shape of the genotypes did not influence the fecundity, adult emergence, total development period and susceptibility index of pulse beetle.