Intermediate Infection Types Research Articles

Leaf Rust Resistance in Wheat Line RL6062 is an Allele at the Lr3 Locus

ABSTRACTRL6062, a ‘Thatcher’ backcross line of wheat (Triticum aestivum L.), has resistance to leaf rust (caused by Puccinia triticina Erikss.) derived from a line of common wheat from Iran. RL6062 has an intermediate infection type (IT) of small to moderate uredinia surrounded by distinct chlorosis. RL6062 was crossed with Thatcher and the F2 seedlings and F3 families segregated for a single leaf rust resistance gene. Bulk segregant analysis of homozygous resistant and homozygous susceptible F3 families using diversity arrays technology (DArT) markers indicated that the leaf rust resistance was on chromosome 6BL. RL6062 was crossed with Thatcher lines with genes Lr9, Lr3a, Lr3b, and Lr3c that are also located on chromosome 6BL. The F2 seedlings of RL6010‐Lr9/RL6062 segregated for IT that ranged from immune response to high IT with large uredinia that lacked necrosis or chlorosis. The F3 families derived from F2 seedlings with high IT were homozygous susceptible or segregated for intermediate IT and high IT, confirming that resistance in RL6062 was not allelic to Lr9. The F2 seedlings of RL6002‐Lr3a/RL6062 segregated for IT that varied from flecks to moderately large size uredinia that lacked chlorosis or necrosis. The F3 families derived from F2 seedlings that had intermediate to high IT segregated for low IT of fleck to intermediate IT, and none of the seedlings had high IT. The lack of segregation for susceptible plants in the F3 families indicated that the leaf rust resistance in RL6062 is an allele at the Lr3 locus. Alleles at the Lr3 locus had intermediate to recessive expression.

First Report of a Wheat Leaf Rust (Puccinia triticina) Phenotype with High Virulence to Durum Wheat in the Great Plains Region of the United States.

Phenotypes of the wheat leaf rust pathogen Puccinia triticina with high virulence to tetraploid durum wheat (Triticum turgidum) are found regularly in Mexico (5), the Mediterranean region (1), the Middle East (3), and rarely in the Imperial Valley of California and the adjacent area in Arizona. Previous to 2013, these phenotypes had not been found in the Great Plains region of the United States where hexaploid, T. aestivum types of hard red winter wheat, hard red spring wheat, and durum wheat are grown. In May 2013, collections of P. triticina, the wheat leaf rust fungus identified by color, size, and shape of uredinia, were obtained from leaves of the hard red winter wheat cultivar Overley in research plots at Hutchinson, KS. A single uredinial isolate was obtained that was used in virulence testing and molecular genotyping. Urediniospores from the initial field collection were inoculated onto seedlings of the susceptible cultivar Little Club. Subsequently, single uredinia were isolated and re-increased on Little Club. The single uredinial isolate was initially inoculated to 7-day-old seedlings of 20 lines of Thatcher wheat that are near-isogenic for leaf rust resistance genes and are used in the annual virulence surveys of P. triticina in the United States (2). The phenotype of the isolate, based on virulence to the 20 differential lines, was BBBQD (2), which was identical to phenotypes of P. triticina with high virulence to durum wheat from other regions where durum wheat is commonly grown (4). This phenotype had intermediate infection type of 2+ (moderate size uredinia with chlorosis) to the line with Lr2c and high infection types of 3+ (large uredinia with no chlorosis or necrosis) to lines with genes LrB, Lr10, and Lr39/41. Overley wheat has Lr39/41. The isolate was further tested on an additional set of 27 Thatcher lines, the cultivar Gatcher with Lr27 + Lr31, and a set of 15 durum wheat cultivars that have been grown in the United States and Canada. The isolate had virulence to lines with genes Lr14b, Lr20, Lr23, Lr33, Lr44, and Lr64. Notably, the isolate had distinct low infection types to seedlings of Thatcher lines with genes Lr12, Lr13, Lr22a, Lr35, and Lr37 that are usually optimally expressed in adult plants to most P. triticina isolates. The isolate had high virulence to all of the durum wheat cultivars. The single uredinial isolate of P. triticina from Overley was also genotyped with microsatellite alleles used in previous studies with P. triticina collections from durum wheat (3). The isolate from Kansas had a highly similar genotype to other isolates of P. triticina from worldwide durum-producing regions (3). This isolate with high virulence to durum wheat most likely migrated to the southern Great Plains region from the durum-growing regions in Mexico. Cultivars such as TAM 112, Armour, Winterhawk, and Bullet with Lr39/41 and other cultivars with Overley in their pedigree are currently grown throughout the southern Great Plains. Since many of the P. triticina phenotypes with high virulence to durum wheat are virulent to Lr39/41, these cultivars may provide a pathway for the spread of these phenotypes to the major durum-producing areas of North Dakota and Saskatchewan.

Identification of pre‐ and posthaustorial resistance to rust (Uromyces viciae‐fabae) in lentil (Lens culinaris) germplasm

AbstractLentil (Lens culinaris Medik.) is an important cool‐season legume that can be severely damaged by rust (Uromyces viciae‐fabae (Pers.) Schröt.) in many parts of the world. In this work, a collection of L. culinaris germplasm accessions was screened under growth chamber conditions for response to U. viciae‐fabae. Several sources of incomplete resistance have been identified, both of hypersensitive and of non‐hypersensitive nature. Incomplete hypersensitive resistance was due to a late‐acting host cell necrosis that resulted in an intermediate infection type (IT). Incomplete non‐hypersensitive resistance was due to a hampered cell penetration not associated with host cell necrosis, reducing the number of haustoria per colony and therefore hindering the growth of the colony and reducing and retarding disease development in spite of a high IT.

Chromosome Location, Linkage with Simple Sequence Repeat Markers, and Leaf Rust Resistance Conditioned by Gene Lr63 in Wheat

RL6137, a ‘Thatcher’ backcross line of wheat (Triticum aestivum L.) has resistance to Puccinia triticina (causal agent of wheat leaf rust) derived from T. monococcum To determine the chromosome location of this resistance, RL6137 was crossed with Thatcher and F2 individual seedlings were tested for segregation of leaf rust resistance and segregation of polymorphic simple sequence repeat (SSR) markers. Leaf rust resistance genotypes of F2 individuals were confirmed with segregation of F3 families. The F2 seedlings and F3 families segregated for a single leaf rust resistance gene. The SSR markers barc 57 and barc 321 located on chromosome 3AS were tightly linked with the leaf rust resistance gene. The leaf rust resistance gene in RL6137 was designated as Lr63 This gene conditions low to intermediate infection types to most P. triticina isolates and can be used in wheat improvement programs to enhance leaf rust resistance.

Virulence in Puccinia recondita f. sp. tritici Isolates from Canada to Genes for Adult-Plant Resistance to Wheat Leaf Rust.

Sixty-seven isolates of Puccinia recondita f. sp. tritici collected in Canada were tested for virulence to adult plants of Thatcher near-isogenic wheat lines with leaf rust resistance genes Lr13, Lr22a, Lr34, Lr35, and Lr13 and Lr34 combined. All of the isolates had low infection type to the Thatcher lines with Lr22a and Lr35. All isolates had lower infection type and lower rust severity on the Thatcher line with Lr34 compared with Thatcher. The isolates were polymorphic for virulence to the Thatcher line with Lr13; many isolates were completely virulent to this line, and other isolates produced very low or intermediate avirulent infection type. On the Thatcher line with Lr13 and Lr34 combined, many isolates had infection type and rust severity similar to the Thatcher line with Lr34, while other isolates had lower infection type and rust severity compared with the single-gene lines with Lr13 or Lr34. Fifteen isolates with low, intermediate, and high infection type to adult plants with Lr13 were tested for infection type on seedling plants of the Thatcher lines with resistance genes Lr13, Lr22a, Lr34, Lr35, and Lr37, and on Thatcher lines with Lr13 paired with seedling resistance genes. Most isolates were completely virulent to seedling plants with Lr13 and Lr22a. Plants with Lr37 expressed seedling resistance to all isolates tested. Seedling plants with Lr34 had lower infection types to all isolates compared with Thatcher. Seedlings with Lr35 had high infection types to most isolates, with varying amounts of chlorosis. The Thatcher lines with Lr13 plus seedling resistance genes were most resistant to the isolates that had very low infection types on adult plants with Lr13 and intermediate infection types on plants with seedling resistance genes. Genes Lr22a, Lr35, and Lr37 offer additional sources of highly effective leaf rust resistance in wheat.

Resistance to Stripe Rust in Five Durum Wheat Cultivars.

Durum wheat (Triticum turgidum) cultivars developed by the International Maize and Wheat Improvement Center (CIMMYT) are currently grown on more than 8 million hectares worldwide. Because of the lack of information on the genetic basis of resistance to stripe rust (caused by Puccinia striiformis), crosses in a diallel arrangement (without reciprocals) were made among five worldwide resistant cultivars and the susceptible cultivar Local Red. Inheritance of resistance was investigated in seedling and adult plant growth stages of F2 populations, and F3lines. The low seedling infection type of each resistant cultivar, namely Kroub 76, Chonta Inia, Sna 3, Syros, and Arena, was based on the additive action of the same two genes. Each of these genes conferred intermediate infection types when present alone. The field resistance of the cultivars was based on the additive action of the two genes identified in the seedlings and one additional, partially effective adult resistance gene. Segregation for plants with stripe rust severities higher than that of the parents in intercrosses of resistant cultivars indicated that some genetic diversity exists for adult genes. The resistance of these cultivars may prove to be long-lasting, since it results from the combined action of at least three genes.

Effect of three suppressors on the expression of powdery mildew resistance genes in barley

Three recessive mutagen-induced alleles that partially suppress the phenotypic expression of the semidominant powdery mildew resistance gene Mla12 have been studied. When each suppressor is present in homozygous condition, the infection type 0, conferred by gene Mla12 when homozygous, is changed to intermediate infection types. The three suppressor lines were crossed with seven near-isogenic lines with different powdery mildew resistance genes and one, M100, was crossed with nine additional lines. Seedlings of parents and from the F1and F2 generations were tested with powdery mildew isolates that possessed the appropriate avirulence and virulence genes. The segregation of phenotypes in the F2 generation disclosed that the three suppressors affected the phenotypic expression of three resistance genes, whereas that of four resistance genes remained unaffected. The suppressor in mutant M100 affected the phenotypic expression of 9 of the 10 additional resistance genes present. It is suggested that the three suppressors are mutationally modified genes involved in host defence processes. This implies that different resistance genes employ different, but overlapping, spectra of defence processes, or signal transduction pathways. Key words : barley, Hordeum vulgare, powdery mildew, Erysiphe graminis hordei, mutation, resistance, suppressor.

Leaf Rust‐Resistance Genes Lr41, Lr42, and Lr43 Transferred from Triticum tauschii to Common Wheat

In order to diversify the genetic base of resistance in hard red winter wheat (Triticum aestivum L.) to leaf rust (caused by Puccinia recondita Rob. ex Desm.), five genes for resistance were transferred from the diploid goatgrass T. tauschii (Coss.) Schmal. to hexaploid wheat lines. One of the derived lines, KS90WGRC10, had a very low infection type when inoculated with 23 cultures of P. recondita. The others, KS91WGRC11, KS92WGRC16, U1865, and U1866, had low to intermediate infection types with three cultures. Their infection types varied similarly to those of lines carrying previously transferred alleles of Lr21. WGRC10 carries a completely dominant gene, Lr41, on chromosome 1D that segregates independently of any other T. tauschii‐derived leaf rust‐resistance genes. WGRC11 carries the partially dominant gene, Lr42, also on 1D, that is linked to Lr21 with a recombination value of 0.286 ± 0.023. WGRC16 carries a partially dominant gene, Lr43, that segregates independently of all known genes for seedling resistance from T. tauschii; its chromosome location is not known. The genes carried by U1865 and U1866 are allelic to Lr21. WGRC10, WGRC11, and WGRC16 have been released as germplasms by the Wheat Genetics Resource Center.

Gene Expression in theTriticum aestivum-Puccinia reconditaf. sp.triticiGene-for-Gene System

The progeny of a selfed, single-uredinial isolate of Puccinia recondita f. sp. tritici segregated for virulence on near-isogenic Thatcher wheat lines with leaf rust resistance genes Lr2a, Lr2c, Lr2, Lr3ka, Lr11, Lr17, and Lr30. Progeny isolates that produced the lowest avirulent infection types on the homozygous Thatcher lines were assumed to be homozygous for avirulence alleles; isolates that produced intermediate infection types were assumed to be heterozygous; and isolates that produced high infection types were assumed to be homozygous for virulence alleles. The seven homozygous Thatcher lines were crossed with Thatcher to produce F 1 plants [...]

Sources of Resistance to Pathotype QCC of Puccinia graminis f. sp. tritici in Barley

The occurrence of a wheat stem rust (Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn.) pathotype (Pgt‐QCC) with virulence for the Rpg1 gene in barley (Hordeum vulgare L.) necessitated the search for resistant barley germplasm. From preliminary screenings of over 18 000 barley accessions, 13 lines were identified as possessing resistance to pathotype QCC: ‘Diamond’, ‘Hietpas 5’, Q21861, PC 11, PC 84, PC 249, PC 250, CI 5541, PI 452406, PI 452421, PI 477843, PI 477854, and PI 477860. This study was conducted to further characterize the reaction of the selected lines to pathotype QCC. The reaction was assessed by evaluating infection types at the seedling stage and infection responses at the adult plant stage in the greenhouse, and by evaluating disease severity and infection responses at the adult plant stage in the field compared to susceptible cultivars. Most lines exhibited low to intermediate infection types at the seedlings stage and moderately resistant to moderately susceptible infection responses at the adult plant stage in the greenhouse experiments. Among the selected lines, Q21861 exhibited the highest level of resistance at both the seedling and adult plant stages. These lines may provide an adequate level of resistance to pathotype QCC for cultivar development.

Histological responses in Hordeum chilense to brown and yellow rust fungi

The histological reaction of 16 Hordeum chilense accessions to Puccinia recondila, P. hordei and P striiformis was investigated. It is not possible to generalize about the reaction of H. chilense to these rust fungi. Several lines showed a susceptible infection type to a brown rust harvested on H. juhatum. One of these lines had an intermediate infection type to the wheat brown rust fungus. The H. chilense reaction to the yellow rust fungi ranged from susceptible to resistant. The lines differed in their response to the rust fungi, as expressed by the level of early abortion of sporelings, and the frequency of plant‐cell necrosis associated with the infection sites. All the lines caused complete early abortion associated with infrequent necrosis of the rye brown rust fungus. The responses were to some extent rust non‐specific. The differences in response between the lines may reflect differences in general defence mechanisms.

Genetic relationships between fertility and pathogenicity and virulence to rice in Magnaporthe grisea

The genetic relationships between fertility and pathogenicity and virulence to rice in Magnaporthe grisea (Hebert) Yaegashi & Udagawa were examined in four initial-generation and two second-generation families. Two isolates of M. grisea, highly virulent to rice, were crossed with fertile isolates that are pathogenic on weeping love-grass (Eragrostis curvule) and goose-grass (Eleucine indice). Approximately 30 progenies from each of the four initial-generation families were evaluated for mating type, fertility, pathogenicity, and virulence to rice differential cultivars. Most of the progenies were either nonpathogenic to rice or produced intermediate infection types. The expected 1:1 segregation for female fertility was not observed in progenies of the initial-generation families. Two highly virulent isolates, and one fertile isolate that produced small grey flecks on one rice cultivar, were selected from one of the initial-generation families as parents for two second-generation families. Nearly one-third of the progenies from one of the second-generation families were highly virulent to rice. Female fertility segregated in the expected 1:1 ratio, independent of mating type, in both families. Mating type, female fertility, and pathogenicity to rice segregated randomly; however, progenies highly virulent to rice were exclusively mating-type A and female sterile.

Histology and physiology of compatibility and incompatibility between lettuce and the downy mildew fungus, Bremia lactucae Regel

Three races of Bremia lactucae Regel and five cultivars of lettuce were investigated to determine early events which distinguish between compatible and incompatible interactions during the infection process. The time-course of the infection process was followed histologically and by the leakage of electrolytes. Infection types were graded 1 (low = incompatible), 2 and 3 (intermediate) and 4 (high = fully compatible). Low infection types were characterized by the death of host cells during penetration or 2 to 5 h after penetration, depending upon the host gene for resistance and fungal gene for avirulence. Host cells adjacent to penetrated cells were not killed. The fungus grew out of the dead, penetrated cell, and eventually died within 12 to 24 h of penetration. Intermediate infection types were characterized by large penetration pores, a delay in onset of nuclear division in the fungus, and eventual necrosis of host cells one or more days after penetration, although the fungus continued growth and sporulated sparsely. High infection types were typical of a biotrophic relationship; the fungus grew rapidly through the living host tissue and, prior to sporulation, showed little or no tendency to kill penetrated cells of the host.The cause and significance of the rapid death of host cells observed in low infection types are discussed in relation to the cause of resistance.