Identification of sources of resistance in lettuce to the lettuce root aphid, Pemphigus bursarius

In a series of glasshouse and laboratory experiments, lettuce varieties and wild Lactuca species were screened for resistance to the lettuce root aphid, Pemphigus bursarius (Ron.). Several new sources of resistance to P. bursarius development and survival were identified. Extremely high levels of resistance were found in the wild species L. saligna, L. perennis and L. virosa. Resistance was also identified in the lettuce variety Grand Rapids. This resistance is controlled by one or two genes. At least one of these genes is not allelic to the existing Lra gene. Grand Rapids therefore represents a new source of resistance to P. bursarius. This revised version was published online in August 2006 with corrections to the Cover Date.     

Monosomic analysis of Russian wheat aphid (Diuraphis noxia) resistance in Triticum aestivum line PI137739

Summary The Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae), has become an important pest of wheat (Triticum aestivum L.) in the United States. The aphid causes a phytotoxemic reaction in wheat evidenced by local and systemic chlorosis and rolling of infested leaves. Developing resistance in wheat cultivars to D. noxia is an essential factor in controlling the damage caused by this pest. Several sources of genetic resistance to D. noxia have been identified in wheat germplasm. Monosomic analysis of the monogenic resistant T. aestivum accession PI137739 has shown that the gene (Dn1) for resistance is carried on chromosome 7D. It appears that chromosome 7B may carry a second resistance gene for D. noxia that might be a source of minor or complementary gene action for resistance.     

Interactions between plant and aphid genotypes in resistance of lettuce to Myzus persicae and Macrosiphum euphorbiae

Summary Six lettuce lines, representing two types of resistance to the green peach aphid, Myzus persicae, and a control line with high susceptibility to M. persicae were tested for resistance to six different clones of Myzus persicae and two clones of the potato aphid, Macrosiphum euphorbiae.The clones of M. persicae showed very different levels of aggressiveness on lettuce: two had a high level of reproduction, two had an intermediate level and two were poorly adapted to lettuce as a host. Differences between lettuce lines in aphid reproduction increased with increasing aggressiveness of the aphid clone, which means that aggressive clones are most effective for selection purposes. No evidence was found for clone-specific plant genotype reactions, meaning that lines resistant to one clone will also be resistant to other clones of M. persicae, allthough not neccessarily at the same level. The lettuce lines selected for partial resistance to the aggressive clone WMp1 were completely or almost completely resistant to less aggresive clones.No differences in level of reproduction were found between the two clones of M. euphorbiae and no relation was observed between resistance to M. persicae and M. euphorbiae, indicating the species-specific character of resistance to leaf aphids in lettuce.     

Resistance of lettuce (Lactuca) to the leaf aphid Nasonovia ribis nigri. 1. Transfer of resistance from L. virosa to L. sativa by interspecific crosses and selection of resistant breeding lines

Summary Interspecific crosses were carried out between the three Lactuca species L. virosa, L. serriola and L. sativa to transfer resistance to the leaf aphid Nasonovia ribis nigri from L. virosa to the cultivated lettuce. L. sativa, L. serriola was used as an intermediate parent between the other two species. Many irregularities were observed in the interspecific hybrids, ranging from premature dying of F₁ plants resulting from a kind of bastard necrosis till complete male and female sterility and deviating microsporogenesis. Using in vitro culture and after several backcrosses male and female fertile plants were obtained with a L. sativa habit and with resistance to the leaf aphid.     

Genetic control of Russian wheat aphid (Diuraphis noxia) resistance in wheat accession PI 47545

The Russian wheat aphid, Diuraphis noxia (Mordvilko), is a major pest of cereal crops in many areas of the world, causing serious reduction in grain yield in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). Incorporating genetic resistance to D. noxia into wheat cultivars is paramount to effectively reduce damage inflicted by this pest. Genetic resistance to D. noxia has been identified in wheat, barley and rye germplasm, and several resistance genes are available for use for cultivar improvement. In the United States of America, only a few Russian wheat aphid (RWA) resistant winter wheat cultivars are currently available, and these cultivars contain only one of the six known RWA resistance genes. The objective of this study was to determine the inheritance of RWA resistance in wheat accession PI 47545, using a screening method based on differences in the leaf morphology of resistant and susceptible types following insect challenge. PI 47545 was selected for study, since it displayed high levels of resistance in a white-grained wheat background, the predominant wheat class produced in the Pacific Northwest of the USA. Segregation analysis was conducted on an F₂ population developed by cross-hybridizing the susceptible soft white winter wheat cultivar ‘Daws’ to the resistant accession PI 47545. Russian wheat aphid screening data from this population indicated that the resistance in PI 47545 is controlled by a single, dominant gene (χ² = 1.72; p ≤ 0.189). This revised version was published online in August 2006 with corrections to the Cover Date.     

The use of polyacrylamide gradient gel electrophoresis to identify variation in isozymes as markers for Lactuca species and resistance to the lettuce root aphid Pemphigus bursarius

Summary This paper describes simple, routine polyacrylamide gradient gel electrophoresis of allozyme patterns surveyed in wild populations of four Lactuca species, obtained from the Wellesbourne Vegetable Gene Bank. Using multivariate statistical techniques, four allozyme bands were identified, which distinguished the four species, and an additional two bands, which were related to the resistance of Lactuca species to the lettuce root aphid.     

Resistance to the gall mite and American gooseberry mildew in black currants in relation to season of leafing out

Summary In black currant (Ribes nigrum) backcross progenies segregating for resistance to the gall mite, Cecidophyopsis ribis Westw. (gene Ce from Ribes grossularia L.), and to American gooseberry mildew, Sphaerotheca mors-uvae (Schw.) Berk. (gene Sph ₃from R. glutinosum), significant differences in season of leafing out occurred between the resistant and susceptible classes. The data are consistent with the hypothesis that two additive genes, Lf ₁and Lf ₂, controlled season of leafing out and that Ce and Sph ₃ were linked with Lf ₁.     

An instant bioassay for resistance of lettuce to the leaf aphid Myzus persicae

Summary A reliable impression of the resistance of lettuce plants to the leaf aphid Myzus persicae can be obtained via aphid honeydew production. Under controlled temperatures, the number of honeydew droplets produced by these aphids per plant in 180 minutes with five plants per genotype offers a good criterion of this resistance.     

RFLP mapping of an aphid resistance gene in cowpea (Vigna unguiculata L. Walp)

Summary Restriction fragment length polymorphism (RFLP) analysis has several advantages over traditional methods of genetic linkage mapping, one of these being the starting point for map-based cloning. The recent development of an RFLP map of cowpea (Vigna unguiculata L. Walp) has allowed the investigation of associations between genes of interest and RFLP markers. A cross between an aphid (Aphis craccivora Koch) resistant cultivated cowpea, TT84S-2246-4, and an aphid susceptible wild cowpea, NI 963, was screened for both aphid phenotype and RFLP marker segregation. One RFLP marker, bg4D9b, was found to be tightly linked to the aphid resistance gene (Rac ₁) and several flanking markers in the same linkage group (linkage group 1) were also identified. The close association of Rac ₁ and RFLP bg4D9b presents a real potential for cloning this insect resistance gene.     

Screening for resistance against rhopalosiphum padi (L.). I. avena species and breeding lines

Summary Thirty-two accessions of Avena species and breeding lines were evaluated for resistance, primarily antibiosis, to the aphid Rhopalosiphum padi (L.) in greenhouse and growth room tests. The highest levels of resistance were found in A. barbata and in the perennial species A. macrostachya. One breeding line, Obee, was also found to have interesting resistance characters. Resistance in A. macrostachya is discussed in relation to perenniality. A different screening method for rapid testing of large collections of varieties is evaluated.     

Comparison of sources of resistance to leaf aphids in lettuce (Lactuca sativa L.)

Summary Three lines of lettuce with resistance to Nasonovia ribisnigri, based on the dominant Nr-gene, and four lines selected for partial resistance to Myzus persicae were tested against three species of leaf aphid: N. ribisnigri, M. persicae and Macrosiphum euphorbiae. The effect of the Nr-gene was also studied in a segregating F2 population.In the material tested, resistance to N. ribisnigri was exclusively based on the Nr-gene, lines selected only for resistance to M. persicae showed no resistance to N. ribisnigri. The Nr-gene also induces partial resistance to M. persicae, but the level of this resistance is influenced by other genes, because the lines with Nr-gene differed significantly from each other for reproduction of M. persicae. The Nr-gene had no effect on the resistance of lettuce to M. euphorbiae.In lines with the Nr-gene, levels of resistance to M. persicae and to M. euphorbiae were correlated, suggesting that the resistance may be determined by the same genes. The Nr-line with highest resistance to M. persicae was comparable for this characteristic to the lines selected for resistance to M. persicae.The cultivars Taiwan and Ravel possess a resistance factor to M. euphorbiae that has no effect on M. persicae or N. ribisnigri. Lines selected for resistance to M. persicae also showed partial resistance to M. euphorbiae. Based on the present results no conclusions can be drawn whether this resistance is based on the same genes that provide resistance to M. persicae, or on a resistance factor comparable to that found in Taiwan and Ravel.     

Inheritance of resistance to angular leaf spot (Isariopsis griseola Sacc.) in french bean (Phaseolus vulgaris L.)

Summary Angular leaf spot (Isariopsis griseola Sacc.) is a serious disease of French bean in the hills of India and 40 to 70 per cent of the green pods are damaged and rendered unmarketable. Crosses were made between PLB 257, (Phaseolus coccineus L.), a red flowering pole tope, resistant to angular leaf spot, and Contender (Phaseolus vulgaris L.), a highly susceptible commercial cultivar. Studies of the F₁, F₂, and F₃ progenies indicated that PLB 257, carries a recessive gene imparting resistance to angular leaf spot.     

Sources and inheritance of resistance to stemphylium leaf spot of lettuce

Summary None of the tested cultivars of lettuce was found resistant to Stemphylium leaf spot, a common disease in Israel. Within a Lactuca saligna population collected in wild lettuce in Israel, resistance was traced. Interspecific crosses of L. saligna x L. sativa were made and the mode of inheritance of resistance to this disease was studied. Resistance is apparently controlled by two genes: one dominant (Sm₁) and one recessive (sm₂).Contribution No. 1176-E 1984 series, from the ARO.     

Heritability of NaCl tolerance at the seedling stage in seven grass species

Summary Narrow sense heritabilities of tolerance to NaCl were estimated in seven grass species using seedling root length after three weeks growth in solution culture containing NaCl. Heritability estimates were obtained from i) female parent-progeny regression, and from ii) selection response and selection differential (realized heritability).Estimates from parent-progeny regression; and realized heritability respectively for each species were as follows Lolium perence L. 0.44, 0.39; Dactylis glomerata L. 0.32, 0.24; Agrostis stolonifera L. 0.28, 0.27; A. castellana L. 0.26; 0.31; Holcus lanatus L. 0.19, 0.23; Festuca rubra L. 0.44, 0.36; Pucinnellia distans (L.) Parl. 0.72, 0.77. These data suggest that in all species except perhaps H. lanatus, improvement in seedling NaCl tolerance could be obtained through further selection and breeding.     

The location and characteristics of novel sources of resistance to Bremia Lactucae Regel (downy mildew) in wild Lactuca L. Species

Summary Twenty-one accessions of 3 wild Lactuca species which could be hybridised with L. sativa, the cultivated lettuce, were inoculated at different stages of plant development with 3 multivirulent isolates of Bremia lactucae. Nineteen sources of resistance to B. lactucae, not attributable to the previously recognised resistance factors 1–11 were identified. Two lines of L. serriola showed similar resistance patterns as lines carrying R11. The resistance of some accession was incomplete particularly at the seedling stage and this phenomenon may be race specific.Tests on segregating F₂ populations of crosses between 2 different L. serriola accessions and L. sativa cultivars showed that the resistance in one line (LSE/18) appears to be inherited as a single dominant gene, which is sometimes incomplete in expression and allelic to either Dm6 or R7. The segregation patterns for resistance in PI 281876 did not give readily interpretable ratios.To assess the frequency of occurrence in B. lactucae populations of virulence factors to overcome this novel resistance, 11 of the novel sources of resistance were inoculated with numerous collections of the pathogen from the UK, Czechoslovakia and elsewhere and found to show a high level of resistance.     

New sources of major gene resistance in Lactuca to Bremia lactucae

Summary A total of 1789 accessions of several lettuce collections was screened to find new major gene resistance to the downy mildew fungus Bremia lactucae Regel. The accessions belonged to the species Lactuca sativa (N=1288), L. serriola (N=399), L. saligna (N=52) and L. virosa (N=50). A total of 20 races of B. lactucae were used, 14 of which were NL-races, isolated from cultivated lettuce in the Netherlands. The other six races were isolated from wild L. serriola in Czechoslovakia. The accessions were initially screened with two races: NL1 and NL3. Accessions with resistance to one or both of these races were tested with the other races. Phenotypes with new resistance were found in accessions of all four Lactuca species. Of L. sativa, four accessions were found with resistance phenotypes that could not be explained by combinations of known major genes. Many accessions of L. serriola had resistance phenotypes that indicated the presence of unknown resistance genes. All interactions between accessions of L. saligna and races of B. lactucae were incompatible in leaf disc tests, except for four accessions, which showed some sporulation with race NL6. Several accessions of L. virosa were resistant to all races used. Other accessions of L. virosa gave a race-specific interaction with B. lactucae.     

Inheritance of seed resistance to bruchids in cultivated mungbean (Vigna radiata, L. Wilczek)

Bruchid beetles or seed weevils are the most devastating stored pests of grain legumes causing considerable loss to mungbean (Vigna radiata (L.) Wilczek). Breeding for bruchid resistance is a major goal in mungbean improvement. Few sources of resistance in cultivated genepool were identified and characterized, however, there has been no study on the genetic control of the resistance. In this study, we investigated the inheritance of seed resistance to Callosobruchus chinensis (L.) and C. maculatus (F.) in two landrace mungbean accessions, V2709BG and V2802BG. The F₁, F₂ and BC generations were developed from crosses between the resistant and susceptible accessions and evaluated for resistance to the insects. It was found that resistance to bruchids in seeds is controlled by maternal plant genotype. All F₁ plants derived from both direct and reciprocal crosses exhibited resistance to the bruchids. Segregation pattern of reaction to the beetles in the F₂ and backcross populations showed that the resistance is controlled by a major gene, with resistance is dominant at varying degrees of expressivity. Although the presence of modifiers was also observed. The gene is likely the same locus in both V2709BG and V2802BG. The resistant gene is considered very useful in breeding for seed resistance to bruchids in mungbean.     

The mildew resistance gene Sph 2in relation to gall mite resistance in the black currant

Summary In black currant progenies derived from parents heterozygous for resistance to American gooseberry mildew. Sphaerotheca mors-uvae (Schw.) Berk., and to gall mite, Cecidophyopsis ribis Westw. (genes Sph ₂from the Swedish cultivar Öjebyn and Ce from Ribes grossularia L., respectively), there is invariably a defieit of mildew resistant plants. Linkage in repulsion between Sph ₂and Ce would account for the significantly greater deficit of mildew resistants in the gall mite resistant class. In contrast with published data for the mildew resistance gene Sph ₃, there is no evidence of linkage of Sph ₂with the leafing out gene Lf ₁, suggesting that the gene order is Sph ₂-Ce-Lf ₁-Sph ₃.     

Relation between wheat-rye crossability and seed set of common wheat after pollination with other species in the Hordeae

Summary Cultivars of common wheat (Triticum aestivum L. em. Thell.) of high wheat-rye (Secale cereale L.) crossability set more seed with pollen of other related species than did wheats of low wheat-rye crossability. This was found to be true for pollen parents from the genera Triticum, Aegilops, Secale, Agropyron and Elymus.