Comparing Cotyledon, Leaf and Root Resistance To Downy Mildew in Radish (Raphanus Sativus L.)

Radish downy mildew (DM) is a disease caused by the oomycete Hyaloperonospora brassicae f. sp. raphani and it is a serious problem in radish production, an edible root vegetable crop of the Brassicaceae family. The objective of this research was to assess radish germplasm for DM resistance and to evaluate the response of different radish organs to the disease. Cotyledons, true-leaves and roots of 44 radish accessions were inoculated with H. brassicae isolates under controlled conditions. The cotyledons were individually evaluated 7dpi (days post-inoculation), and the leaves and roots 12dpi. DM symptoms varied with the radish genotype and plant organ analysed. Thirty-five resistant and partially resistant accessions were identified and are promising sources to DM. A significant correlation was observed between cotyledon and leaf (1st and 2nd leaves) DM resistance, but no correlation was found between the resistance of cotyledons or true-leaves and roots. Cotyledon and leaf response cannot be used to predict radish root resistance. However, cotyledon resistance has its own value because non-infected cotyledons will act as a barrier to slow disease progression to true-leaves and roots.

Inoculation Methods and Doses and Relationship with the Vegetative and Reproductive Development of Soybeans

This study aimed to evaluate and compare the method of in-furrow inoculant application with the other existing methods, as well as, in different doses in the development of soybean culture. The experimental design was randomized blocks in a two-factorial scheme (4 x 3), with four inoculation methods, without inoculation (control), by seed, in-furrow and leaf spray, with three doses, 100, 200 and 400%. Leaf and root dry mass, number of nodules, pods per plant, number of seeds per vegetables, height, knots per plant, productivity, root resistance and average chlorophyll content were measured. The combination of factors did not affect plant height, leaf dry matter, root resistance, grains and pods per plant, plant per knot and weight of 100 seeds, affecting only other parameters, in which the largest root dry matter occurred in in-furrow inoculation in the dose of 400%, with 3.82 g plant-1, against 3.43 g plant-1 in the by seed method in the same dose. In the in-furrow application at the 100% dose, the highest number of grains pod-1 occurred, with 3.42 grains pod-1, combined with an increase in pods plants-1, and a 19% increase in productivity relative to the control, and 9.5% at the third increase, in the spray. Co-inoculation methods affect the development of soybeans, and the method that provided the greatest of soybean development was by in-furrow.

Genotypic variability in radial resistance to water flow in olive roots and its response to temperature variations

As radial root resistance (Rp) represents one of the key components of the soil–plant–atmosphere continuum resistance catena modulating water transport, understanding its control is essential for physiologists, modelers and breeders. Reports of Rp, however, are still scarce and scattered in the scientific literature. In this study, we assessed genetic variability in Rp and its dependence on temperature in five widely used olive cultivars. In a first experiment, cultivar differences in Rp at 25 °C were evaluated from flow–pressure measurements in excised roots and subsequent analysis of root traits. In a second experiment, similar determinations were performed continually over a 5-h period in which temperature was gradually increased from 12 to 32 °C, enabling the assessment of Rp response to changing temperature. Despite some variability, our results did not show statistical differences in Rp among cultivars in the first experiment. In the second, cultivar differences in Rp were not significant at 12 °C, but they became so as temperature increased. Furthermore, the changes in Rp between 12 and 32 °C were higher than those expected by the temperature-driven decrease in water viscosity, with the degree of that change differing among cultivars. Also, Rp at 25 °C reached momentarily in the second experiment was consistently higher than in the first at that same, but fixed, temperature. Overall, our results suggest that there is limited variability in Rp among the studied cultivars when plants have been exposed to a given temperature for sufficient time. Temperature-induced variation in Rp might thus be partly explained by changes in membrane permeability that occur slowly, which explains why our values at 25 °C differed between experiments. The observed cultivar differences in Rp with warming also indicate faster acclimation of Rp to temperature changes in some cultivars than others.

Transcriptional Profiles of Mdwrky33 in Apple Root in Response to Infection by Pythium Ultimum, Abiotic Stresses and Chemical Treatments

Plant resistance responses to pathogen infection involve massive transcriptional reprograming and widespread redirection of cellular pathways to adjust the plant from growth to defense. Transcription factors (TFs) function at the major regulating points of gene expression, and specific TFs are known to play crucial roles in plant defense activation. Molecular defense activation in apple root from infection by oomycete necrotrophic pathogen Pythium ultimum, a primary component in a pathogen complex inciting apple replant disease, has not been investigated in detail. Base on previous transcriptome analyses, members of apple WRKY gene family have been identified as the primary candidates in regulating defense response in apple root. Among them, MdWRKY33, an orthologue of AtWRKY33 in apple genome, demonstrated as a highly-expressed WRKY with genotype-specific induction patterns during P. ultimum infection. The sequence features of MdWRKY33 and its tissue-specific expression, as well as its responses to abiotic and pharmacological treatments, added to the evidence for its functional roles in defense activation in apple root. In response to P. ultimum infection, MdWRKY33 was consistently upregulated in all eight tested apple rootstock genotypes at all timepoints. Between genotypes, the stronger induction patterns at the earlier stage of infection in resistant genotypes suggest its essential roles of contributing to apple root resistance, although plant resistance to necrotrophic pathogens is polygenetic quantitative resistance in nature. Transgenic manipulation of this gene is underway to provide more definitive functional identity in contributing to apple root resistance to P. ultimum infection

Genetic Analyses and Mapping of Pink-Root Resistance in Onion

Pink root [PR (caused by Phoma terrestris)] is a major soil-borne disease of onion (Allium cepa) and reduces both yield and quality of bulbs. PR-resistant cultivars offer the best control option for this disease. The objectives of this study were to complete genetic analyses and mapping of PR resistances from independent sources. Segregating families were developed from different sources of PR resistance and evaluated using a seedling screen. PR severity in two segregating families from the same source of resistance mapped to one position on chromosome 4 with logarithm of odds (LOD) scores of 8.0 and 10.3, and explained 28% and 35% of the phenotypic variation, respectively. Estimates of additive and dominance effects revealed this source of PR resistance is codominantly inherited. PR resistance from a second source was assessed by percent survival in the seedling evaluation, showed codominance, and mapped to the same region on chromosome 4 at LOD 12.5 and explained 54% of the phenotypic variation. This research demonstrates that PR resistance from different sources mapped to the same chromosome region and showed similar modes of inheritance.