Levels Of Quantitative Resistance Research Articles

Sources of resistance to Pseudomonas syringae pv. phaseolicola races in Phaseolus vulgaris

One thousand and forty‐eight Phaseolus bean accessions were evaluated for resistance to six races of Pseudomonas syringae pv. phaseolicola. The accessions originated from regions of the Americas and Africa where the disease is important and included wild type accessions and some known resistance sources. Resistance, graded on a five‐point scale, was of two types: qualitative, which was shown to be race‐specific, and quantitative. Race specific resistance genes (R‐genes) were detected in 49.4% of accessions with the following gene frequencies: R1 (10.3%), R2 (0.3%), R3 (25.0%), R4 (35.0%) and R5 (0.2%).Evidence for quantitative variation in resistance, in the absence of specific R‐genes, was shown by the distribution of infection scores, 76% of accessions showing maximum susceptibility (grades 4–5), 23% showing intermediate resistance (grades 2–4), and 1% showing high levels of quantitative resistance (grades 1–2). The last 1% of accessions showed interactions which were not race‐specific and it is suggested that they may possess race non‐specific resistance. It is possible that several of the accessions in this category carry the recessive gene derived from PI 150414. Other accessions were of unknown parentage and may represent new sources of quantitative, potentially race non‐specific, resistance. It is suggested that the combination of race specific and race non‐specific resistance could provide an effective strategy for establishing durable resistance.

Evidence of durable resistance in nine Chinese land races and one Italian cultivar ofTriticum aestivum toPuccinia striiformis

In this study carried out from 1987 to 1994, in a very conducive environment to stripe rust, nine Chinese land races and one Italian cultivar of wheat showed fair levels of quantitative resistance to rust disease. The nine old Chinese cultivars had a commercial planting history in this conducive environment ranging from 20 to 100 years, in a cultivation area of 20 to 467 thousand hectares p.a. with no apparent erosion of resistance. The Italian cultivar has been used commercially for 15 years in China without showing a decrease in the level of quantitative resistance. All these data warrant the conclusion that the ten cultivars have a form of durable resistance to stripe rust.

Rust infections of some Allium species: An assessment of germplasm for utilizable rust resistance

Isolates of three species of rust (Puccinia allii, P. mixta and Uromyces ambiguus) were each inoculated onto a range of potential host plants, selected to include the major European crop Allium species together with the commoner wild species in the section Allium. Measurements of incubation period, lesion type, latent period and pustule quantity were made in a single environment. Each isolate was able to sporulate on a range of Allium species. There was evidence of specialisation to particular sections of the genus; all the leek isolates performed well on the majority of hosts in section Allium, whilst the chive isolate grew poorly on most members of that section. Exceptions to this are exemplified by A. fistulosum being attacked by all three rust species and A. sativum being attacked by both leek and chive isolates. A continuum of reaction types was found which, for the leek isolates, ranged from the low levels of quantitative resistance in leek cultivars, through higher quantitative levels within the A. ampeloprasum complex, to qualitative resistance in several interactions in non-host sections of Allium, where the pathogen was able to infect and form colonies of some size without sporulating.

Beziehungen zwischen dem Wirkungsgrad antiphytoviraler Substanzen und dem Niveau der quantitativen Sortenresistenz sowie der Virulenz von Virusisolaten an Virus/Wirt‐Systemen der Kartoffel

Abstract Relationship between the efficiency of antiphytoviral substances, the degree of quantitative resistance of cultivars, and the virulence of virus isolates on virus/host‐systems of potato. In vitro systematically infected with potato virus S, potato virus M or potato virus X stem cuttings of different potato varieties were treated with 2,4‐dioxohexahydro‐1,3,5‐triazine and Ribavirin. The reduction of virus replication by chemotherapy differed between varieties depending on their level of quantitative resistance and the virulence of virus isolates.An increasing resistance level of cultivars and a decreasing virulence of the virus isolates resulted in a relative enhancement of the inhibitory of the antiphytoviral substances.

Multiple resistance of spinach (Spinacia oleracea L.) to cucumber mosaic and beet mild yellowing viruses

Summary The spinach cultivar “Larina” proved to be highly resistant to 4 isolates of CMV and their equal mixture (= M). Additionally a moderate level of quantitative resistance of this cultivar to BMYV was confirmed serologically by use of ELISA. Deduced from significant differences of resistance levels within the cultivars “Larina” and “Matador” associated with single isolates of CMV, 2 groups of virus isolates were classified preliminarily distinguished by their virulence. The spinach isolate SoPe 28/79, a mung bean isolate Mungo 9 and M belonged to the most virulent group differentiated by the cultivar “Matador”.

Half sib selection for resistance to powdery mildew (Erysiphe graminis DC. f.sp. secalis Marchal) in rye populations

Three rye populations originating from different cultivars were subjected to half sib progeny selection for three cycles to improve their resistance to powdery mildew (Erysiphe graminis DC. f.sp. secalis Marchal). Selection was carried out in the greenhouse (measurement of spore production at the three-leaf stage), in the field (scoring of mildew infections at ear emergence) or at both locations. All selections resulted in significant responses, the level of which varied depending on the genetic base of mildew resistance in the populations. Greenhouse selection was most effective when the frequency of dominant genes could be increased, whereas field selection was less effective. Estimates for heritability in the narrow sense ranged from 0.42-0.94 indicating that mildew resistance can be increased effectively. Inbred lines should be selected in base populations with a high level of quantitative resistance and/or a high frequency of dominant genes. For an effective resistance strategy in hybrid breeding such dominant genes are most valuable, and can be selected in young growth stages. In 'Strain CG' the increase of dominant resistance genes by early selection resulted in a significant improvement of kernel yield.

Quantitative Differences in Powdery Mildew Resistance Among Spring Barley Cultivars

AbstractQuantitative powdery mildew resistance in compatible host‐pathogen‐combinations was measured by the number of pastules/cm2 leaf area. Spring barley cultivar ‘Proctor’ was significantly less infected than ‘Golden Promise”. Using these two cultivars (having no effective major resistance gene) as controls, MO‐ and AR‐resistant cultivars were inoculated with virulent mildew isolates. ‘Mona”, ‘Grit’ and ‘Nudinka’ had a higher or, at least, the same level of quantitative resistance as ‘Proctor”. None of the remaining cultivars showed the high susceptibility expressed by ‘Golden Promise”. Ranking of host genotypes was nearly constant while that of mildew isolates varied considerably. Only a small portion of the observed variance was due to interaction between host cultivars and pathogen isolates.‘Triesdorfer Diva’ gave a resistant infection type after inoculation with different AR‐virulent isolates, indicating that this cultivar has major resistance other than that conditioned by gene Ml‐a12.

Resistance in Rice Breeding Lines to the Blast Fungus in Nepal

A total of 36 rice breeding lines including checks were evaluated for resistance to blast atRampur during 2000-2001. The experiments were conducted under both field condition andgreenhouse inoculated condition. Qualitative resistance in rice to blast was assessed based onlesion type, whereas quantitative resistance was assessed based on area under disease progresscurve (AUDPC) in the upland field condition. The number of sporulating lesions and the numberof leaves with at least one sporulating lesion per plant were considered as measures forevaluation of quantitative resistance in the greenhouse assay. The lesion type, neck blastpercentage and AUDPC data suggest that most of the rice lines possess higher level of resistanceto leaf and neck blast. The rice lines varied for the number of sporulating lesions and the numberof leaves with sporulating lesion per plant. Some lines were incompatible to virulent blastisolates, showing major resistance genes. NR 1558, NR 601-1-1-9, BW306-2 and CN 836-3-10were promising lines for quantitative resistance to both leaf and neck blast. Radha 12, Sabitri,Janaki possess higher level of quantitative resistance to blast, hence these could be promoted forcultivation in blast-prone environments. These genotypes could also be utilized as donor parentsfor breeding durable blast resistant varieties. The most virulent blast isolate could be used forevaluation of both qualitative and quantitative resistance to blast in early generation in thegreenhouse so that workload could be cut down in future works.Key words: Blast resistance; field condition; greenhouse assay; Pyricularia grisea; rice linesDOI: 10.3126/narj.v6i0.3344Nepal Agriculture Research Journal Vol.6 2005 pp.49-56