Susceptible Plant Genotypes Research Articles

Impact of Farm Management Practices on Downy Mildew Disease of Cucumber in High Tunnels

Downy mildew of cucumber caused by Pseudoperonospora cubensisis is a serious threat to the cucurbits production in high tunnels. In this study, the disease incidence and severity were recorded from nine high tunnel farms, located at Vehari District, Pakistan. The results revealed that downy mildew incidence was ranged from 24 to 80%. The disease development was correlated with plant genotype, sowing time, commonly used fungicides, and plant growth stages. "Kaan" was the most resistant while "Yayla" was the highly susceptible plant genotype against the disease. Cucumber sowing at mid-November showed significantly less disease over early and late sowing. Flowering was the most vulnerable stage of plants for disease development. ‘Champion’ (Copper hydroxide) followed by ‘Score’ (Difenoconazole) fungicides reduced the disease to 55% and 43%, respectively, which increased the yield 8-15 %. We conclude that the use of resistant genotype “Kaan”, protectant fungicide ‘Champion’ and appropriate sowing time Mid-November may reduce the disease incidence appreciably in high tunnels.

Morpho-genetic variability in F2 progeny cowpea genotypes tolerant to Bruchid (Callosobruchus maculatus)

Callosobruchus maculatus Fab. is a major threat to cowpea production reducing the quality, quantity and market value of cowpea grains. A cheap and easy identification method would be a valuable tool in identifying and breeding resistant genotypes in the vast cowpea germplasm. Hence, the purpose of the study was to identify and evaluate the genetics of cowpea traits between resistant and susceptible plant genotypes to C. maculatus. Contrasting qualitative and quantitative traits in C. maculatus resistant and susceptible parents were evaluated in 72 F2 progeny cowpea plants. Heritability, segregation and association of investigated traits with the C. maculatus resistant performance of the F2 cowpea genotypes were evaluated to determine closely related traits with C. maculatus resistance. Results from the study showed high heritability for all cowpea quantitative traits except leaf petiole length. Both Mendelian inheritance and non-Mendelian inheritance were observed among qualitative traits. However, association evaluation between cowpea traits and mean bruchid development period, percentage adult emergence and oviposition preference were weak (r < 0.5) and not significant (p < 0.05). This indicates that C. maculatus resistance in cowpea may be attributed to factors other than morphological variations.

Characterization of an Insecticidal Protein from Withania somnifera Against Lepidopteran and Hemipteran Pest.

Lectins are carbohydrate-binding proteins with wide array of functions including plant defense against pathogens and insect pests. In the present study, a putative mannose-binding lectin (WsMBP1) of 1124bp was isolated from leaves of Withania somnifera. The gene was expressed in E. coli, and the recombinant WsMBP1 with a predicted molecular weight of 31kDa was tested for its insecticidal properties against Hyblaea puera (Lepidoptera: Hyblaeidae) and Probergrothius sanguinolens (Hemiptera: Pyrrhocoridae). Delay in growth and metamorphosis, decreased larval body mass and increased mortality was recorded in recombinant WsMBP1-fed larvae. Histological studies on the midgut of lectin-treated insects showed disrupted and diffused secretory cells surrounding the gut lumen in larvae of H. puera and P. sanguinolens, implicating its role in disruption of the digestive process and nutrient assimilation in the studied insect pests. The present study indicates that WsMBP1 can act as a potential gene resource in future transformation programs for incorporating insect pest tolerance in susceptible plant genotypes.

Occurrence, biochemistry and biological effects of host-selective plant mycotoxins

Host-selective mycotoxins (HSTs) are various secondary metabolites or proteinaceous compounds secreted by pathogenic necrotrophic fungi that feed off on dead tissues of certain plants. Research on the HSTs has not only fundamental but also practical importance. On one hand they are implicated in the onset of devastating crop diseases. On the other hand, they have been studied as a good model for revealing the intricate mechanisms of plant-pathogen interactions. At the cellular level, HSTs target different compartments and in most instances induce programmed cell death (PCD) by a wide range of mechanisms. Often the responses provoked by HSTs resemble the effector-triggered immunity used by plant cells to combat biotrophic pathogens, which suggests that HST-producing fungi exploit the plants' own defensive systems to derive benefits. Although by definition HSTs are active only in tissues of susceptible plant genotypes, it has been demonstrated that some of them are able to influence animal cells as well. The possible effects, like cytotoxicity or cytostasis, can be harmful or beneficial and thus HSTs may either pose a health risk for humans and livestock, or be of prospective use in the fields of pharmacology, medicine and agriculture.

Plant Genotype Influences Mycorrhiza Benefits and Susceptibility to a Soil Pathogen

Abstract This study examines the role mycorrhizae may play in protecting host plants from a soil fungal pathogen. Asexual propagules of three Allium vineale genotypes were grown in the presence and absence of mycorrhizae and the pathogen, Sclerotium cepivorum (white rot), with some plants encountering the mycorrhizal fungi first and others encountering the pathogen first. A significant three-way interaction indicates plant genotypes vary in response to the combined effects of mycorrhizae and the pathogen, with the A. vineale genotype most resistant to the pathogen deriving the least growth benefit from mycorrhizae and the genotype most susceptible to the pathogen receiving the highest relative growth benefit from mycorrhizae, despite there being no difference in the level of mycorrhizal colonization among the plant genotypes. No evidence was found that the presence of mycorrhizae reduced the impact of the pathogen for the most susceptible plant genotype (B). These findings support the hypothesis the prima...

Transcriptional and metabolic changes associated to the infection by Fusarium verticillioides in maize inbreds with contrasting ear rot resistance.

Fusarium verticillioides causes ear rot and grain mycotoxins in maize (Zea mays L.), which are harmful to human and animal health. Breeding and growing less susceptible plant genotypes is one alternative to reduce these detrimental effects. A better understanding of the resistance mechanisms would facilitate the implementation of strategic molecular agriculture to breeding of resistant germplasm. Our aim was to identify genes and metabolites that may be related to the Fusarium reaction in a resistant (L4637) and a susceptible (L4674) inbred. Gene expression data were obtained from microarray hybridizations in inoculated and non-inoculated kernels from both inbreds. Fungal inoculation did not produce considerable changes in gene expression and metabolites in L4637. Defense-related genes changed in L4674 kernels, responding specifically to the pathogen infection. These results indicate that L4637 resistance may be mainly due to constitutive defense mechanisms preventing fungal infection. These mechanisms seem to be poorly expressed in L4674; and despite the inoculation activate a defense response; this is not enough to prevent the disease progress in this susceptible line. Through this study, a global view of differential genes expressed and metabolites accumulated during resistance and susceptibility to F. verticillioides inoculation has been obtained, giving additional information about the mechanisms and pathways conferring resistance to this important disease in maize.

Variation in reproductive capacity and virulence on different genotypes and resistance genes of Triticeae, in the cereal cyst nematode species complex

AbstractTwo sets of experiments in 1998 and 1999 studied the (a)virulence status of 14 populations of Heterodera avenae, and two populations each of H. filipjevi and H. latipons towards the resistance genes and genotypes of Triticeae, presently known to be resistant to H. avenae, the main species of the cereal cyst nematode (CCN) species complex. Susceptible controls were Triticum aestivum cv. Arminda and Triticum turgidum cv. Cham1. Even in controlled experimental conditions, host responses differed between replicates in the same test and between consecutive tests for unexplained reasons. In spite of that, it has been confirmed that several of these CCN populations differ in their intrinsic capacity to reproduce, and this has to be taken into account in resistance screening. Consequently, the (a)virulence status of a CCN population is better established by a qualitative demarcation between resistant and susceptible plant genotypes based on an average of one cyst limit per plant. The matrix inferred from such a classification of host responses of pooled 1998 and 1999 data showed a complex distribution of avirulent and virulent phenotypes in these CCN populations which seems to arise from a mosaic-like evolution. The more or less wide virulence spectrum shown by this complex of populations and species is discussed in relation to their phylogenetic relationships. Correspondence factor analysis of the pooled data demonstrated a geographical demarcation between several populations of H. avenae and the representatives of H. filipjevi and H. latipons for their (a)virulence to either Cre1 or Cre3 genes and T. aestivum AUS4930 genotype. This could reveal local or regional selection of new pathotypes, more particularly in H. avenae. Genetic introgression to improve resistance to these nematodes in both bread and durum wheats is discussed for regional and global applications.

Rapid activation of a novel plant defense gene is strictly dependent on the Arabidopsis RPM1 disease resistance locus.

We cloned and sequenced cDNAs encoded by a novel plant defense gene, ELI3, from parsley and Arabidopsis thaliana. The predicted product shares no homology to known sequences. ELI3 mRNA accumulates in A. thaliana leaves in response to challenge with phytopathogenic Pseudomonas syringae strains. The timing and magnitude of this response are dictated by the genetics of the plant-pathogen interaction being analyzed. During incompatible interactions, where resistance in the plant genotype Col-0 is dictated by the dominant RPM1 locus, ELI3 mRNA accumulates to high levels 5-10 h post-inoculation. This kinetic behavior is also generated by the presence of a cloned bacterial avirulence gene, in otherwise virulent bacteria, which triggers resistance mediated via RPM1 action. The phenotypic outcome is a hypersensitive resistance reaction visible 8-15 h post-infiltration. Thus, the induction kinetics of ELI3 mRNA accumulation are consistent with a functional role for the ELI3 gene product in establishing the resistant phenotype. In contrast, during compatible interactions with the susceptible plant genotype Nd-0, which is homozygous recessive at the rpm1 locus, ELI3 mRNA accumulates significantly only after 15 h. We show genetically that ELI3 activation is strictly dependent on the presence of dominant alleles at RPM1 using an assay generalizable to any pathogen induced plant defense phenomena.

Effects of disease resistance genes on Rhizobium symbiosis in an annual legume.

The evolution of disease resistance in plants may be constrained if genes conferring resistance to pathogens interfere with plant responses toward other, nonpathogenic organisms. To test for such effects, we compared symbiotic nitrogen fixation in Amphicarpaea bracteata plants that differed at a major locus controlling resistance to the pathogen Synchytrium decipiens. Both resistant and susceptible plant genotypes nodulated successfully and grew significantly better in the presence of Rhizobium, although growth enhancement by Rhizobium was altered by different levels of nitrate fertilization. Plants homozygous for disease resistance achieved 2% higher growth than susceptible homozygotes across all treatments, but this difference was not significant. Resistant and susceptible plant genotypes did not differ in the mean number of nodules formed per plant or in nodule diameter. However, there was highly significant variation among replicate families within each disease resistance category for both nodulation characteristics. These results imply that genetic variation exists among A. bracteata plants both for diease resistance and for traits affecting symbiotic nitrogen fixation. However, there were no evident pleiotropic effects of disease resistance genes on the plant-Rhizobium symbiosis.