Authors:Éva Sárdi, Eszter Szarka, Gábor Csilléry, and János Szarka
Plant resistance breeding has, so far, been based on specific resistance genes which regulate hypersensitive reaction, resulting in fast tissue destruction. Hungarian researchers have, however, discovered the existence of the
general defense system
), which regulates a completely different plant defense reaction. This manifests itself in tissue thickening through cell enlargement. We have studied the biochemical background of these different plant defense processes by OPLC, a forced-flow version of planar chromatography. We also exploited some basic well-known advantages of planar chromatography which made its application suitable and favorable in our experiments. As a result of analysis of time-dependent changes in carbohydrate compounds, we confirmed pathological and symptomatological observations that plants have both general and specific defense systems. These two systems have different roles and strategies in excluding pathogens, but together constitute the complete disease resistance of plants.
The most important viral pathogens of the cultivated potato are Potato virus X (PVX) and Potato virus Y (PVY), which can reduce potato production up to 80%. Thus resistance breeding is one of the major goals of plant breeders. Wild potato species are good sources of resistance (R) genes. The resistant plants respond to viral infection with hypersensitive reaction (HR) or extreme resistance (ER). HR is accompanied by programmed cell death, while ER localizes the virus at the primary infection site and limits virus replication without visible symptoms. While HR is generally strain-specific, ER can act against a broad spectrum of viral pathogens. This review aims to describe the molecular mechanisms of resistance against PVX and PVY in potato.
Authors:X.L. Liu, B.Y. Lu, C.Y. Wang, Y.J. Wang, H. Zhang, Z.R. Tian, and W.Q. Ji
The aphid Sitobion avenae F. is one of the most harmful pests of wheat growth in the world. A primary field screening test was carried out to evaluate the S. avenae resistance of 527 wheat landraces from Shaanxi. The results indicated that 25 accessions (4.74%) were resistant to S. avenae in the three consecutive seasons, of which accession S849 was highly resistant, and seven accessions were moderately resistant. The majority of S. avenae resistant accessions come from Qinling Mountains. Then, the genetic variability of a set of 33 accessions (25 S. avenae resistant and 8 S. avenae susceptible) originating from Qinling Mountains have been assessed by 20 morphological traits and 99 simple sequence repeat markers (SSRs). Morphological traits and SSRs displayed a high level of genetic diversity within 33 accessions. The clustering of the accessions based on morphological traits and SSR markers showed significant discrepancy according to the geographical distribution, resistance to S. avenae and species of accessions. The highly and moderately resistant landrace accessions were collected from the middle and the east part of Qinling Mountains with similar morphology characters, for example slender leaves with wax, lower leaf area, and high ear density. These S. avenae resistant landraces can be used in wheat aphid resistance breeding as valuable resources.
Authors:A. Ficsor, J. Bakonyi, M. Csősz, A. Tomcsányi, J. Varga, and B. Tóth
Net blotch and leaf stripe caused by Pyrenophora teres and P. graminea, respectively, are two major foliar diseases of barley. These two species are able to infect wheat, too. The species composition of these pathogens was examined, for the first time, in four different regions of Hungary in 2006–2010. Altogether 204 isolates were obtained from 99 winter barley, 55 spring barley and 50 wheat leaf samples collected in commercial fields and experimental stations, and species assignment was carried out using species-specific PCR reactions. Most isolates belonged to P. teres f. teres (68%), 26% to P. teres f. maculata and only 6% of the isolates were assigned to P. graminea. Interestingly, all but one of the P. graminea isolates came from the western part of Hungary, while both forms of P. teres occurred in each region. The distribution of mating type genes was also examined in 144 isolates. The overall ratio of MAT1 and MAT2 genes in P. graminea, P. teres f. maculata and P. teres f. teres was 5:3, and close to 2:1 and 1:1, respectively. Both MAT1 and MAT2 isolates of each fungal species/form were distributed in almost all regions over several years, indicating a high potential for sexual outcrossing within local populations of these pathogens. Our survey may be helpful to determine priorities in disease resistance breeding programs. Further studies are in progress to examine the population structure of the most abundant pathogen P. teres f. teres.
Authors:Y. Gao, Q. Sun, R. Wang, J. Feng, F. Lin, N. Cui, X. Chen, S. Xu, Y. Bai, and X. Xu
Stripe rust, caused by Puccinia striiformis Westend. f. sp. tritici Eriks., is a major disease that causes substantial losses to wheat production worldwide. The utilization of effective resistance genes in wheat cultivars is the preferred control of the disease. To study the inheritance of all-stage resistance in spring wheat cultivars Louise, WA008016, Express, Solano, Alturas and Zak from the Pacific Northwest (PNW) of the United States, the six cultivars were crossed with the Chinese susceptible variety Taichung 29. Single-spore isolates of CYR32 and CYR33, the predominant Chinese races of P. striiformis f. sp. tritici, were used to evaluate F1, F2 and BC1 generations for stripe rust resistance under controlled greenhouse conditions. Genetic analysis determined that Louise had one dominant resistance gene to CYR32, temporarily designated as YrLou. WA008016 had two dominant and one recessive resistance genes to CYR32, temporarily designated as YrWA1, YrWA2 and YrWA3, respectively. Express had a single recessive gene that conferred resistance to CYR32, temporarily designated as YrExp3. The two independent dominant genes in Solano conferring resistance to CYR32 were temporarily designated as YrSol1 and YrSol2. Alturas had two recessive genes for resistance to CYR32, temporarily designated as YrAlt1 and YrAlt2. Zak has one dominant gene for resistance to CYR33, temporarily designated as YrZak1. These six cultivars can be important resistance sources in Chinese wheat stripe rust resistance breeding.
Authors:M. I. E. Arabi, M. Jawhar, and E. Al-Shehadah
Powdery mildew (Blumeria graminis) is a major fungal disease of barley causing economical yield losses worldwide. Breeding for resistance to this disease is crucial due to the rapid change in pathotype patterns of B. graminis in fields. In the present work, powdery mildew-resistant barley germplasm was developed by crossing four cultivars currently used in Europe and West Asia. Out of 265 doubled haploid lines derived from these crosses, 40 lines were evaluated at seedling and adult stages. Data showed significant differences among barley lines with a continuum of resistance levels ranging from highly susceptible to tolerant which were consistent during the two growth stages. Two promising lines were more tolerant to powdery disease than the others. Across lines, there was a high correlation between field and greenhouse reaction (r=0.80, P<0.01), indicating the utility of greenhouse evaluations for screening barley for powdery mildew. This study suggests that, the newly identified resistance lines can serve as potential donors for ongoing powdery mildew resistance breeding program, and both types of seedling and adult plant resistance identified here can offer promising genetic stocks for accumulating both resistances to acquire durable resistance and long lasting control against B. graminis in Mediterranean and similar environments.
Authors:J. Chrpová, V. Šíp, L. Štočková, and V. Dumalasová
Resistance of 28 winter wheat cultivars registered in the Czech Republic and ten potential sources of resistance to Fusarium head blight (FHB) was evaluated after artificial inoculation with Fusarium culmorum in field trials lasting for three years (2008, 2009, 2010). The data on deoxynivalenol (DON) content were supplemented by symptom scores and determination of% of Fusarium damaged grains and% reductions of grain weight per spike due to infection. The examined traits were significantly interrelated and showed high variation in all years. Significantly lower DON content, combined with relatively lower manifestation of the disease was observed in the modern, commercially grown cultivars Bakfis, Graindor, Sakura and Bodycek (catalogued in the Official Journal of EU), besides Novokrymka 102, PI 166910 (line resistant to dwarf and common bunt) and Arina, which could be effectively used in resistance breeding. However, the experiments performed under high infection pressure were also able to reveal high susceptibility to FHB in some commercially grown wheat cultivars, which may pose a serious threat to wheat production.
Authors:M. I. E. Arabi, E. Al-Shehadah, and M. Jawhar
Cochliobolus sativus, the causal agent of common root rot (CRR), is a devastating fungal pathogen of barley that can cause significant yield losses worldwide. The development of resistant cultivars has proven difficult, therefore, in this work, CRR-resistant barley germplasm was developed by crossing three resistant-by-susceptible cultivars currently used in Europe and West Asia. Following greenhouse evaluations of 150 doubled haploid lines derived from these crosses, 40 lines were evaluated under artificial infection conditions using incidence and severity parameters during two consecutive seasons. Data showed significant differences among barley lines with a continuum of resistance levels ranging from highly susceptible to resistant which were consistent in both seasons. However, five promising lines had slightly lower CRR disease than the others. Additionally, significant differences (P <0.05) in mean incidence and severity values were found among lines, with values being consistently higher in the susceptible ones. However, CRR severity increased linearly as incidence increased in both seasons. All together, the present study suggests that, the newly identified resistance lines can serve as potential donors for ongoing CRR resistance breeding program to generate high-yielding commercial barley cultivars, and that the positive correlation between CRR parameters I and S may be beneficial for many types of studies on this disease.
Some wild species of the genus Oryza such as O. rufipogon and O. longistaminata show a high level of resistance to pests and diseases including rice blast (caused by Magnaporthe grisea). To transfer blast resistance from wild species into cultivatedvarieties (O. sativa), interspecific hybrids were produced and anther culture was used toaccelerate the procedure of resistance breeding. Anther culture efficiency depended onboth the medium and the genotype of the cultivated varieties and the wild species. Afterinoculation with a mixture of six strains with wide spectrum virulence, all the F1 hybridswere resistant to blast; the F2 plants segregated, from high resistance to susceptibility, anda similar result was obtained for the H1 and H2 plants. At the H3 stage, blast resistancetended to be stable and almost 100% of inoculated H5 plants were highly resistant to riceblast. For agronomic characteristics, the F2 and H1 showed segregation, but no significantdifferences were seen between the cultivated parents and the H2 to H5 generations. Theresults demonstrate that blast resistance genes can be transferred from wild rice speciesinto cultivated varieties through crossing and anther culture, and the H5 can be used asstable lines in future breeding programmes.
Authors:Cs. Bojtor, Z. Győri, P. Sipos, L. Radócz, and B. Tóth
The aim of the study was to investigate changes of photosynthetic efficiency, amount of photosynthetic pigments, superoxide dismutase (SOD) enzyme activity, and rate of lipid peroxidation in bean-rust interaction. The clarification of the role of the above changes involved in the defence mechanism can significantly contribute to the breeding of plant varieties with natural resistance. Consequently, the amount of chemicals used in food production can be significantly reduced. In the present study some principal physiological parameters, such as the relative chlorophyll content of the host plant, the amount of photosynthetic pigments, changes in photosynthetic efficiency, and the activity of superoxide-dismutase (SOD) in addition to rate of lipid peroxidation (LP) were measured. The experiment was conducted in a humidity tent. Significant decrease in the relative chlorophyll content and in the amount of photosynthetic pigments was measured. At both sampling times, an increase was found in superoxide-dismutase enzyme activity and in rate of lipid peroxidation due to the bean rust infection. Notably, in several cases the differences were significant. The results indicate that the above parameters have important role in the bean-rust interaction, which should be taken into consideration in resistance breeding.