Showing papers on "Plant disease resistance published in 1988"

cDNA sequences for pea disease resistance response genes.

Abstract: The expression of the Group I disease resistance response genes (19149, pi176, and pi206) of Pisum sativum cv. Alaska is strongly associated with resistant interactions of the pea with the fungus Fusarium solani, the bacterium Pseudomonas syringae pv. pisi, and the fungal elicitor chitosan [19, 9, 6]. cDNAs for these genes were recloned into the Bluescript KSml3+ vector and sequenced by the Exo/Mung Bean nuclease method [3] and the method of Maxam and Gilbert [16]. Optimal alignment of the pi49 and pi176 cDNAs by the NUCALN program of Wilbur and Lipman [5] results in 696 out of 731 positions matching, plus six gaps, for an overall identity of 95o70, suggesting that these genes may be part of a multigene family. The cDNA for pi206 appears to be 5'-truncated. Although the mRNA for pi206 as measured by Northern analysis is approximately 950 nucleotides [19], the entire cDNA (excluding the poly(A) tail) is only 594 bp long. The predicted molecular weights of pi49 and pi176 are 16728 and 16901 Da, respectively, while the pi206 gene product would have to be at least 19360 Da. The 158 amino acid pi49 sequence differs by only 5 amino acid substitutions and one insertion/deletion from the 159 amino acid pi176 sequence. The FASTN and FASTP programs of Lipman and Pearson [14] were used to search for the Group I cDNA or protein sequences in the GenBank [2] Release 55.0 and PIR [10] databases, with no significant matches found. The D4HOM program [8] was used to compare the Group I sequences with other genes associated with disease resistance whose DNA or protein sequences are known, including bean chitinase [4], bean phenylalanine ammonia lyase [7], chalcone synthase from parsley [18], the pathogenesis-related protein p14 from tomato [15], pathogenesis-related protein PR-1 family from tobacco [17], and the hydroxyproline-rich glycoprotein from tomato [20]. No significant similarities were noted.

Allele-specific and Mutator-associated instability at the Rpl disease-resistance locus of maize

Abstract: The Rp1 locus of maize determines resistance to the fungal rust pathogen Puccinia sorghi In an attempt to isolate insertion mutations at Rp1 with the Mutator transposable element system, we found that Rp1 inactivation was common both in lines with Mutator activity and in controls lacking any known transposable element activity Some alleles of Rp1 are endogenously inactivated as frequently as one in five-hundred, whereas other alleles are over twenty times more stable In a standard background, no mutations of the Rp1F allele were detected in 7,339 progeny screened In a Mutator background, 27 Rp1F inactivations were isolated from 35,356 tested seedlings Although most Rp1F mutant seedlings lost resistance to all of the P sorghi isolates tested, several retained resistance to a subset of rust biotypes Some of the resistance specificity profiles obtained in these mutants are unlike any previously identified Rp1 alleles These data indicate that the Rp1 locus is composed of multiple resistance factors with variable intrinsic stabilities

Characterization of a potential source of barley yellow dwarf virus resistance for wheat

Abstract: Resistance to barley yellow dwarf virus (BYDV) has been described in lines derived from crosses between wheat and Thinopyrum intermedium. The resistance in one such line, Zhong 4, originating in China, was expressed against two different serotypes of BYDV as measured by accumulation of virus in infected seedlings. F1 hybrids between wheat (2n = 42) and Zhong 4 (2n = 56) had 49 chromosomes and intermediate levels of virus when compared to the parent lines. Cytological and molecular hybridization studies suggested that the BYDV resistance in Zhong 4 is carried on a set of seven pairs of nonwheat chromosomes that derived from a combination of the E and X genomes present in Th. intermedium.Key words: Barley yellow dwarf virus, wheat, ribosomal DNA, Agropyron intermedium, Thinopyrum intermedium, virus resistance.

Polymorphism for disease resistance in the annual legume Amphicarpaea bracteata

Abstract: Amphicarpaea bracteata plants from a single population varied greatly in disease resistance when inoculated with six different strains of the specialist pathogen Synchytrium decipiens collected from the same site. Selfed progenies of two plants exhibited heterogeneity in disease resistance. Inoculation experiments indicated that variation in disease resistance in these plant families was controlled by a single locus, with resistance exhibiting nearly complete dominance. This resistance factor was effective against only a limited number of the pathogen genotypes present in this area. Thus, its selective value will depend on the genetic structure of the pathogen population, which may result in frequency-dependent fitness variation for this trait.

Multiple-disease resistance in grain legumes

Abstract: The status of and problems involved in breeding cultivars with multiple disease resistance, with examples of multiple disease resistance in important grain legumes (excluding soyabeans and groundnuts) grown around the world, are reviewed.

Effects of Alternaria alternata f.sp. lycopersici toxins on pollen.

Abstract: Effects of the phytotoxic compounds (AAL-toxins) isolated from cell-free culture filtrates of Alternaria alternata f.sp. lycopersici on in vitro pollen development were studied. AAL-toxins inhibited both germination and tube growth of pollen from several Lycopersicon genotypes. Pollen from susceptible genotypes, however, was more sensitive for AAL-toxins than pollen from resistant plants, while pollen of species not belonging to the host range of the fungus was not significantly affected by the tested toxin concentrations. AAL-toxins elicit symptoms in detached leaf bioassays indistinguishable from those observed on leaves of fungal infected tomato plants, and toxins play a major role in the pathogenesis. Apparently, pathogenesis-related processes and mechanisms involved in disease resistance are expressed in both vegetative and generative tissues. This overlap in gene expression between the sporophytic and gametophytic level of a plant may be advantageously utilized in plant breeding programmes. Pollen may be used to distinguish susceptible and resistant plants and to select for resistances and tolerances against phytotoxins and other selective agents.

Somaclonal variation in celery: screening for resistance to Fusarium oxysporum f. sp. apii

Abstract: Two methods were used to screen putative Fusarium-resistant celery (Apium graveolens L.) plantlets from cell culture: placing plantlets on a mycelial mat for one month or planting them directly in Fusarium-infested soil. Resistant phenotypes were identified with both methods, but the plants grown on the mycelial mat died before they reached reproductive maturity. Four plants, K, T-2, T-3, and R-R1 from the soil screen, survived and produced viable seed. Tests of self-pollinated progeny, in field and greenhouse conditions, showed that T-2, T-3, and R-R1 were superior to the original cultivar, 5270R, with respect to disease resistance, as measured by vascular discoloration and plant height. Chi-square analysis of progeny scores for root and crown decay showed that the new variation was heritable and appeared to be conditioned by more than one locus.

Nonhost plant species as donors for resistance to pathogens with narrow host range. II. Concepts and evidence on the genetic basis of nonhost resistance

Abstract: It is commonly argued that wild plant species with a very high level of resistance to a micro-organism which is pathogenic on a crop species would be useful donors of resistance. Whether this principle is true if the wild species is a distinct nonhost, remains to be proved. It is assumed that nonhost resistance, if not based on avoidance, rests on a poor adaptation of the micro-organism to general defence mechanisms in the plant. No basic compatibility is achieved. Major-genic hypersensitive host resistance would, according to the concept, be superimposed on basic compatibility. The defence reaction is ‘switched on’ if a resistance allele recognizes a specific avirulence factor produced by the pathogen. The frequency of the resistance allele would depend on the selection pressure exerted by the pathogen population.

Genetic Uniformity and Disease Resistance in a Clonal Plant

Abstract: Contemporary theories of plant-pathogen interactions derived from agricultural systems stress that host genetic uniformity is a major cause of vulnerability to disease epidemics. Genetic uniformity also exists to various degrees in natural clonal plant populations as a result of local asexual proliferation; yet little is known about the impact of disease on such clonal plant species. Mechanisms regulating the impact of disease were examined in the clonal herb mayapple (Podophyllum peltatum). Despite the presence of a potentially damaging fungal pathogen in most mayapple colonies, the demographic impact of disease is minimal because of an effective morphological defense that prevents contact between pathogen spores and photosynthetic tissues. Invulnerability to pathogen counter-adaptation may be a common property of plant morphological defenses that function by limiting pathogen access to infection sites. Possession of such defenses may permit natural populations of clonal plants to coexist with pathogens,...

Disequilibrium between disease-resistance variants and allozyme loci in an annual legume.

Abstract: Polymorphism existed at 58% of the enzyme loci examined (11/19) in one population of the highly self-pollinated annual legume Amphicarpaea bracteata. Due to extreme gametic disequilibrium among loci, genetic variation in this population was structured into a small number of multilocus genotypes. Over 97% of the plants sampled could be grouped into two classes (biotypes "A" and "B"), each consisting of a few highly similar genotypes. The two classes had mutually exclusive sets of alleles at nine loci. These classes differed sharply in their disease resistance toward one isolate of the specialist fungal pathogen Synchytrium decipiens from their native habitat. All biotype A plants were strongly susceptible, and all biotype B plants were resistant. When plants of both biotypes were exposed to this pathogen in a greenhouse, the resistant biotype (B) exhibited a significantly higher growth rate. The strong association between plant disease-resistance phenotypes and allozyme variants implies that pathogen attack could be a major selective agent influencing the evolution of neutral or near-neutral alleles at enzyme loci in this plant.

Fungal and bacterial foliar diseases of pea, lentil, faba bean and chickpea

Abstract: Fungal foliar diseases such as downy mildew, powdery mildew, and rust of pea; blights and rust of lentil; chocolate spot, Ascochyta blight, and rust of faba bean; and Ascochyta blight, Botrytis grey mould, and rust of chickpea are serious in several countries and can devastate crops over large areas in some years. With the exception of powdery mildew, these diseases are favoured by cool and wet weather. Breeding disease resistant cultivars and the use of suitable fungicides offer effective measures of control in most cases, although breeding for multiple disease resistance merits greater effort. Bacterial diseases of the four crops are only important locally. Nevertheless, new cultivars must be tested to ensure that they do not easily succumb to bacterial pathogens.

Registration of a Powdery Mildew Resistant Sunflower Germplasm Pool, PM1

Abstract: THE powdery mildew resistant sunflower (Helianthus annuus L.) gerrnplasm pool, PM1, (Reg. no. GP-94) (PI 518661) was developed cooperatively by USDA-ARS and the North Dakota Agricultural Experiment Station, Fargo, ND, and released in September, 1987. PM1 was derived from interspecific hybridization between H. debilis Nutt. and H. annuus L. Genotypes highly resistant to powdery mildew have not been reported in sunflower. PM1 was derived by bulking equal amounts of BC2F2 seeds of three rows of BC2Pi plants having the parentage P-21/3/ H. debilis/P-2l// 'Peredovik'. The multiple-headed H. debilis parent, PI 435667 was highly resistant to sunflower powdery mildew (incited by Erysiphe cichoracearum DC.), when compared with infection in single-headed cultivated H. annum. P-21 is a reselection from Peredovik, and carries a recessive gene for male sterility. In greenhouse evaluations, both P-21 and Peredovik are highly susceptible to powdery mildew. Detailed descriptions of the gene transfer and its inheritance have been reported by Jan and Chandler (1). Their greenhouse evaluations indicated the mean infection percentage, measured as the percent of leaf surface covered by mildew, of P-21, P-21/PI 435667, and PI 435667 were 100, 15 and 0, respectively. Resistance was partially dominant in the F, and backcross progenies and was suggested [Jan and Chandler, (1)] to be under the control of one or a few major gene(s). Initially, two highly resistant F, plants of H. debilis X P-21 were identified and backcrossed to Peredovik. Three highly resistant BC,F, plants were selfpollinated or sibpollinated and three BC,F2 plants having zero infection were identified. These plants were used to pollinate P-21. The resulting BC2F, families, heterozygous for powdery mildew resistance, were sibpollinated and equal amounts of seed from each family were bulked to form the gerrnplasm pool PM1. PM1 has 87.5%cultivated//, annuusand 12.5%H. debilis nuclear genes in normal P-21 cytoplasm. It contains the partially dominant powdery mildew resistance gene(s) at a frequency of approximately 50%. It also contains a recessive genetic male-sterility gene, derived from P-21, at a frequency of approximately 50%. Even though PM1 is still heterogeneous and is expected to segregate for certain traits, most plants are of the cultivated type with a plant height of 1.7 m, single-headed and selfcompatible. Seeds are either black or black with white stripes, and have a 1 000 seed weight of 57g. Limited quantities of seeds are available from the Seedstocks Project, Agronomy Department, North Dakota State University, Fargo, ND 58105.

A field screening method to evaluate rice breeding lines for resistance to the hoja blanca virus

Abstract: SUMMARY A method is presented for rearing large colonies of viruliferous Sogatodes oryzicola, vector of the rice hoja blanca virus (RHBV). These colonies were used for field screening up to 10 000 rice breeding lines per season for resistance to RHBV. Uniform infection of check varieties in the field indicated that the method was adequate. Field release of vectors when plants were 14 days old resulted in satisfactory disease incidence, after 21 days, to distinguish lines segregating for resistance from lines uniformly resistant or susceptible. Various sources of resistance identified earlier continued to be resistant under the screening conditions. Progeny of lines identified as non-segregating resistant continued as non-segregating resistant. Resistant plants from lines segregating for resistance produced progeny lines that were segregating and non-segregating. Ratios of resistant to susceptible plants in F1 progeny of three-way crosses were consistent with earlier observations that RHBV resistance is a dominant character. The susceptibility of the commercial checks indicates that rice production in RHBV areas of tropical Latin America continues to be at risk from the virus. Virus-resistant commercial cultivars resulting from this method should be available in 2 years.

Genetic basis of resistance to zonate leaf spot disease in forage sorghum.

Abstract: Generation mean analysis was carried out for ten crosses between two resistant and two susceptible parents to find the genetic basic of resistance to zonate leaf spot disease in forage sorghum. In all crosses except one, at least one type of non-allelic interaction was present. Both additive and dominance gene effects were significant for most crosses. Duplicate type epistasis was present for the inheritance of this disease. Resistance to this disease revealed overdominance. Appropriate breeding plans were suggested to exploit the disease resistance.

Virus Cross-Protection in Transgenic Plants

Abstract: Plant virus diseases have traditionally been controlled by sanitary agronomic practices, use of virus-free propagates, controlling the insect vectors that spread the pathogen, and incorporating genes for disease resistance. These practices can, in most instances substantially reduce crop losses normally attributed to virus infections. However, changing agronomic practices and changes in virus strains often lead to significant disease losses, and the search for genetic resistance begins anew. In the majority of cases, sources of disease resistance are unavailable to the plant breeder, or if available, require many plant generations to incorporate the resistance trait into the desired cultivar. Furthermore, most of the resistance genes are effective against only a limited number of strains of the virus.

In vitro expression of partial resistance toPhytophthora palmivora by shoot cultures of papaya

Abstract: Shoot apices ofCarica papaya were multiplied in vitro on solidified nutrient media supplemented with α-naphthyl-acetic acid and 6-benzylaminopurine. The micropropagated shoots were inoculated in vitro, through a stem wound, with a sporangial suspension (1.2×104 sporangia ml-1) ofPhytophthora palmivora. The symptoms exhibited by the shoots in vitro were similar to those described previously for infection of the whole plant in the field. The time taken for the host tissue to become brown and to wilt and the time to sporulation of the pathogen were all recorded for each shoot of four varieties of papaya challenged with each of ten isolates ofP. palmivora. Significant differences were observed between host-pathogen combinations for these variables and host-specificity was detected amongst the isolates ofP. palmivora. The time taken for the shoot to wilt was positively correlated with the time to sporulation of the isolated but both these variables were negatively correlated with the time to browning of the shoot. In vitro selection for disease resistance will be useful during breeding programmes involving papaya genotypes which are maintained through clonal propagation.

Genetics of disease resistance in urdbean (Vigna mungo (L.) Hepper) to the leaf spots caused by Colletotrichum truncatum (Schw.) Andrus & Moore)

Abstract: The resistance sources among various test cultivars of urdbean to Colletotrichum truncatum, a leaf spotting pathogen, were identified and genetics of resistance was worked out by studying F1, F2 and F3 generations of crosses between resistant cultivars and the susceptible cv Kulu 4 and of those among the resistant parents The resistance was found to be controlled by single dominant genes and the resistance genes were non-allelic

Somaclonal variation in resistance of perennial ryegrass to crown rust.

Abstract: Resistance of perennial ryegrass plants regenerated fmm tissue culture (somaclones) to crown rust (Puccinri, coronafa) was assessed in growth cabinet/glasshouse experiments. Somaclones regenerated from callus cultures initiated from the vegetative tissue of three different somaclonal parent plants were tested for resistance to crown rust collected from Palmerston North and Linwln. Most plants tested were highty resistant and their leaves developed small pale yellow flecks but showed little or no sporulation. However, a few large pustules did develop on leaves of some of the somaclones. Screening experiments with rust cultures initiated from each of three single pustules showed that somaclones varied in their reaction to crown rust. Wiiin each group of somadones derived from apartiiular parent some were more susceptible. and some more resistant, than the parental genotype. Two of the somaclones obtained from one of the parent plants had very fine leaves similar to those of turf perennial ryegrass plants. Somactoning may provide an efficient technique for plant breeders to improve the crown rust resistance of both pasture and turf perennial ryegrasses.