Inheritance of partial resistance to Myzus persicae in lettuce

Summary The genetics of partial resistance of lettuce to Myzus persicae was studied using F₁ and F₂ generations of two crosses between a susceptible and partially resistant accession (Norden x Batacer and Liba x Norden) and three crosses in which both parents were partially resistant (Batavia la Brillante x Batacer, Batacer x Liba and CGN4741 x Batacer). Partial resistance to M. persicae inherited quantitatively, without important dominance effects. Only in the cross Batacer x Liba were significant departures of the F₁ and F₂ from the midparent found, which were probably caused by epistatic effects. Reciprocal F₁s had similar resistance levels, indicating the absence of cytoplasmic or other maternal effects. Estimates of broad-sense heritability ranged from 0.34 to 0.61. The results indicated that lines with an improved resistance level can be obtained from crosses between partially resistant accessions, preferably by line selection or the application of indirect marker aided selection.Abbreviations PR partial resistance, partially resistant - S susceptibility, susceptible     

Genetics of resistance to ascochyta blight in chickpea (Cicer arietinum L.)

Summary Six chickpea lines resistant to Ascochyta rabiei (Pass.) Lab. were crossed to four susceptible cultivars. The hybrids were resistant in all the crosses except the crosses where resistant line BRG 8 was involved. Segregation pattern for diseases reaction in F₂, BCP₁, BCP₂ and F₃ generations in field and glasshouse conditions revealed that resistance to Ascochyta blight is under the control of a single dominant gene in EC 26446, PG 82-1, P 919, P 1252-1 and NEC 2451 while a recessive gene is responsible in BRG 8. Allelic tests indicated the presence of three independently segregating genes for resistance; one dominant gene in P 1215-1 and one in EC 26446 and PG 82-1, and a recessive one in BRG 8.Research paper No. 3600     

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.     

Inheritance of tomato leaf curl virus resistance in Lycopersicon hirsutum f. glabratum

Summary Inheritance of resistance to tomato leaf curl virus (TLCV) was studied in the progenies derived from interspecific crosses between TLCV resistant Lycopersicon hirsutum f. glabratum line B 6013 and five susceptible cultivars (HS 101, HS 102, HS 110, Pusa Ruby and Punjab Chhuhara) of L. esculentum. P₁, P₂, F₁, F₂, B₁ and B₂ progenies of the five crosses were artificially inoculated with local strains of TLCV by means of the vector whitefly, Bemisia tabaci (Genn.). and the disease reaction was studied in all the crosses. Reaction of parents, F₁, F₂ and backcrosses suggests that resistance derived from L. hirsutum f. glabratum B 6013 is based on two epistatic genes, one from the wild parent and one from the cultivated one, resulting in a 13:3 segragation in the F₂.     

Inheritance of black leaf mold resistance in tomato

Summary Inheritance of black leaf mold (BLM) (caused by Pseudocercospora fuligena) resistance was studied in four crosses involving two resistant Lycopersicon accessions (PI134417, L. hirsutum and PI254655, L. esculentum) and four susceptible Asian Vegetable Research and Development Center tomato lines (CLN657BC₁F₂-267-0-3-12-7, CL143-0-10-3-0-1-10, CLN698BC₁F₂-358-4-13 and CL5915-93D₄-1-0-3). For each cross, six generations, i.e. P₁, P₂, F₁, F₂, BC₁F₁ and BC₁F₂ were evaluated following inoculations with isolate Pf-2 of P. fuligena. Chi-square analyses of the data based on the ratio of resistant to susceptible plants in the F₂ in three of four crosses gave a good fit to a segregation ratio of 1 R : 15 S, and BC₁F₂ data in three of four crosses gave an acceptable fit to the segregation ratio of 1 R : 63 S. The results indicate that resistance to BLM may be conditioned by two recessive genes acting epistatically in both PI134417 and PI254655.     

Inheritance of groat protein percentage in Avena sativa L. × A. Fatua L. Crosses

Summary Gene action and heritability of groat protein percentage were determined in F₁, F₂, and F₃ generations of nine crosses between three Avena sativa L. cultivars and three A. fatua L. selections. Relationships among groat protein percentage, grain yield, and 100-seed weight also were evaluated. The three A. sativa parents were Dal (high grain yield and intermediate groat protein percentage), Goodland (low grain yield and high groat protein percentage), and Stout (high grain yield and low groat protein percentage). The three A. fatua parents were chosen for the study on the basis of vigorous plant growth and high groat protein percentage. The study was conducted at Madison, Wisconsin in 1979 and 1980.There was partial dominance towards low groat protein percentage. Narrow sense heritability estimates for groat protein percentage were low in Dal and Goodland crosses and intermediate in Stout crosses. In the F₂ generation, groat protein percentage was significantly higher in shattering than in nonshattering plants in 1979, but not in 1980. There were significant, positive correlations between groat protein percentage, 100-seed weight, and grain yield in F₁ and F₂ generations, but they were not large numerically. Relationships among these traits were either negative or nonsignificant in the F₃ generation. Although our results indicated that selection for higher groat protein percentage is possible when a low protein A. sativa cultivar is used, most of our simple cross progenies from A. sativa x A. fatua crosses had weak straw and were susceptible to crown rust (Puccinia coronata Cda. var. avenae Fraser and Led.).     

The inheritance of resistance to beet necrotic yellow vein virus (BNYVV) in B. vulgaris subsp. maritima, accession WB42: Statistical comparisons with Holly-1-4

In this study, the inheritance of resistance to Beet necrotic yellow vein virus (BNYVV) in accessions Holly-1-4and WB42 was investigated. Crosses between both resistant sources and susceptible parents were carried out and F₁F₂ and BC₁ populations were obtained. Virus concentrations in WB42and its F₁ populations were lower than in Holly-1-4. Observed ratios of susceptible and resistant plants in segregating populations of Holly-1-4 as well as WB42 were in agreement with hypothesis of one dominant major gene. Segregation of plants in F₂ populations obtained from crosses betweenHolly-1-4 and WB42 revealed that the resistance genes in Holly-1-4 and WB42 were nonallelic and linked loci. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance of resistance to fruit rot (Phytophthora parasiticaDast.) in tomato (Lycopersicon esculentum Mill.)

Summary Fruit rot disease caused by Phytophthora parasiticaDast. is a limiting factor in tomato production in Himachal Pradesh. 30 to 60 per cent fruits are damaged by this disease. Crosses were made between EC 54725 (Lycopersicon pimpinellifolium), a small tyuited type, resistant to fruit rot and four highly susceptible tomato commercial cultivars (Gola, Sioux, S12, and Lalmani). Studies of F₁'s, F₂'s and back crosses indicated that EC 54725 carries a dominant gene imparting resistance to fruit rot.     

Inheritance of resistance to the chlorosis component of tan spot of wheat caused by Pyrenophora tritici-repentis, races 1 and 3

The fungus Pyrenophora tritici-repentis, causal agent of tan spot of wheat, produces two phenotypically distinct symptoms, tan necrosis and extensive chlorosis. The inheritance of resistance to chlorosis induced by P. tritici-repentis races 1 and 3 was studied in crosses between common wheat resistant genotypes Erik, Hadden, Red Chief, Glenlea, and 86ISMN 2137 and susceptible genotype 6B-365. Plants were inoculated under controlled environmental conditions at the two-leaf stage and disease rating was based on presence or absence of chlorosis. In all the resistant × susceptible crosses, F₁ plants were resistant and the segregation of the F₂ generation and F₃ families indicated that a single dominant gene controlled resistance. Lack of segregation in a partial diallel series of crosses among the resistant genotypes tested with race 3␣indicated that the resistant genotypes possessed␣the same resistance gene. This resistance gene was effective against chlorosis induced by P.␣tritici-repentis races 1 and 3.     

The inheritance of resistance to Empoasca kraemeri Ross & Moore in the common bean,Phaseolus vulgaris L.

Summary Genotypes of Phaseolus vulgaris differ in their level of resistance to Empoasca kraemeri, but the speed with which these differences can be accumulated into a resistant variety will depend on whether they can be detected in single F₂ plants, and on whether the genetic control of resistance is additive. Thirty-eight homozygous genotypes were therefore grown in small plots with and without insecticidal protection, and also in simulated F₂ populations containing one plant of each genotype. In addition, the F₂ and F₃ generations of crosses were studied. Both generations of a 13 parent diallel were grown with and without insecticidal protection. Six crosses, involving some of the parents in the diallel and two additional genotypes, were studied in more detail. Protected and unprotected F₂ plants from these crosses were harvested individually, and the resulting F₃ families were grown with and without protection. In all the expriments, the level of damage to the unprotected plants and the vigour of the protected plants was assessed visually by means of a numerical score, and the seed yield was measured.The performance of a single homozygous plant was a reasonable predictor of the performance of the same genotype in a small plot, but in the six crosses studies in detail, the correlations between F₂ and F₃ performance were low. In the analysis of the diallel cross, the significant differences among crosses were due to specific combining ability and not general combining ability. These results indicate that the genetic control of resistance is largely non-additive, and that F₂ selection will probably be ineffective. However, F₃ selection should be effective, and transgressive segregants for resistance should be obtainable.In some of the six crosses, the F₃ families differed both in general vigour and in narrow-sense resistance to E. kraemeri, as defined by Galwey & Evans (1982). The visual assessment of damage symptoms in each plot was related to the subsequent seed yield of the plot, but was more heritable than yield. The relationship between these two variables was investigated by the genetic correlation coefficient and by an alternative method, and was found to be partly genetically determined, but partly due to the influence of environmental factors on both variables. This indicates that screening for E. kraemeri resistance should be done by means of a visual damage score in a carefully chosen, uniform environment.     

Inheritance of seed colour in Brassica campestris L. and breeding for yellow-seeded B. napus L.

Summary Seed colour inheritance was studied in five yellow-seeded and one black-seeded B. campestris accessions. Diallel crosses between the yellow-seeded types indicated that the four var. yellow sarson accessions of Indian origin had the same genotype for seed colour but were different from the Swedish yellow-seeded breeding line. Black seed colour was dominant over yellow. The segregation patterns for seed colour in F₂ (Including reciprocals) and BC₁ (backcross of F₁ to the yellow-seeded parent) indicated that the black seed colour was conditioned by a single dominant gene. Seed colour was mainly controlled by the maternal genotype but influenced by the interplay between the maternal and endosperm and/or embryonic genotypes. For developing yellow-seeded B. napus genotypes, resynthesized B. napus lines containing genes for yellow seed (Chen et al., 1988) were crossed with B. napus of yellow/brown seeds, or with yellow-seeded B. carinata. Yellow-seeded F₂ plants were found in the crosses that involved the B. napus breeding line. However, this yellow-seeded character did not breed true up to F₄. Crosses between a yellow-seeded F₃ plant and a monogenomically controlled black-seeded B. napus line of resynthesized origin revealed that the black-seeded trait in the B. alboglabra genome was possibly governed by two independently dominant genes with duplicated effect. Crossability between the resynthesized B. napus lines as female and B. carinata as male was fairly high. The sterility of the F₁ plants prevented further breeding progress for developing yellow-seeded B. napus by this strategy.     

Identification of Resistance Genes Against Powdery Mildew in Four Accessions of Hordeum Vulgare SSP. Spontaneum

Summary Four newly detected accessions of wild barley (Hordeum vulgare ssp. spontaneum) resistant to powdery mildew caused by Blumeria graminis f. sp. hordei were studied with the aim of finding the number of genes/loci conferring the resistance of individual accessions, the type of inheritance of the genes and their relationships to the Mla locus. F₂ populations after crosses between the winter variety ‘Tiffany’ and four wild barley accessions and use of microsatellite DNA markers were focused on the identification of individual resistance genes/loci by means of their chromosomal locations. In PI466495, one locus conferring powdery mildew resistance was identified in highly significant linkage with the marker Bmac0213. This location is consistent with the known locus Mla on chromosome 1HS. In the other three accessions the resistance was determined by two independent loci. In PI466197, PI466297 and PI466461, one locus was identified on chromosome 1HS and three new loci were revealed on chromosomes 2HS (highly significant linkage with Bmac0134), 7HS (highly significant linkage with Bmag0021) and 7HL (significant linkage with EBmac0755). Our prospective aim is identification of further linked DNA markers and the exact location of the resistance genes on the barley chromosomes.     

Pollen germination,pollen tube growth and fertilization following self and interspecific pollination of Paspalum species

Summary Crossability between most Paspalum species is very low. This study was undertaken to identify the impediments to hybridization. Accessions of P. intermedium Munro. ex Morong, P. jurgensii Hackel and P. dilatatum Poir were self-pollinated and crossed with one anther. Paspalum intermedium is essentially self-sterile but P. jurgensii and P. dilatatum are highly self-fertile. Following pollination, pollen germination and tube growth were studied by observing the pollinated pistils with fluorescent microscopy. Examination of self-pollinated pistils revealed that the pollen germinated shortly after contacting the stigmas. Germination was over 80% for the P. intermedium and P. dilatatum accessions but only 57% for P. jurgensii. Pollen tubes grew to the micropyle within 45 minutes after pollination in P. dilatatum and 1 hour and 15 minutes in P. jurgensii. However, in the P. intermedium accessions most tubes did not grow beyond the stigma and very few penetrated the style and ovary. Apparently stylar-incompatibility is the reason for the low selfed seed set. In the cross-pollinations, pollen germinated shortly after pollination and germination ranged from 57 to 88% for the different crosses. In all crosses the pollen tubes grew to the micropyle within 30 minutes to 2 hours after pollination indicating that a cross-incompatibility system is not the cause for low crossability among these species. By examining embryo sacs from P. intermedium × P. dilatatum, its reciprocal and P. intermedium × P. urvillei crosses, it was determined that gametes failed to unite in some crosses and this is a major reason for low crossability.     

Response to selection in F2 generations of winter wheat for resistance to head blight caused by Fusarium culmorum

Summary In a field trial, F₃ winter wheat lines from plants selected for Fusarium head blight resistance in F₂ generations of a set of crosses, composing a 10×10 half diallel, were tested with their parental lines for resistance to Fusarium culmorum. Selection responses averaged 3.7% on the head blight percentage scale and ranged from –22.0% to 27.1%. Realized heritabilities averaged 0.23 and ranged from 0 to 0.96. Significant transgression for resistance was observed which was suggested to be genetically fixed. It was estimated that resistant parents differed in one or two resistance genes. The possibility of accumulation of resistance genes was shown. The level of head blight resistance of the parental line appeared to be a good indicator of the potential resistance level of its crosses.     

Location of genes for high grain protein percentage and other quantitative traits in wild wheat Triticum turgidum var. dicoccoides

Summary The genetic control of grain protein percentage (GPP) in the wild tetraploid wheat, Triticum turgidum var. dicoccoides, was determined by crossing four accessions of this taxonomic variety with durum cultivar Inbar, and analyzing the parents, F₁ and F₂ populations. Reciprocal crosses indicated no cytoplasmic effect on GPP. The F₂ variation was continuous in all crosses, showing no transgressive segregation. However, crosses between different accessions of var. dicoccoides showed transgressive segregation indicating the presence of different genes for high GPP in these accessions. Grain protein percentage was mostly codominant with high GPP, showing either no dominance, or a weak dominance. Heritability coefficients (broad sense) ranged from 0.30 to 0.53. Correlation coefficients between GPP and yield components were usually significantly negative, with the exception of the number of spikelets per spike, and in some crosses, grain weight.The number and chromosomal location of genes coding for high GPP were determined by the association between GPP and 27 markers (23 morphological and 4 biochemical markers). For this purpose, the genetic control of these markers, their linkage groups and chromosomal location were studied. At least four loci for high GPP that segregated in the F₂ populations are suggested: one on chromosome arm 1AS, marked by the black glume gene (Bg); one on 1BS, marked by the HMW gliadin locus Gli-B1; one on group 5, marked by the genes for beaked glume (Bkg) and toothed palea (Tp); and one on group 7, marked by the kinky neck gene (Kn). The relationship between GPP and several yield components was studied in a similar manner. In general, loci of markers that correlated positively with high GPP were not correlated with a decrease in yield components. Moreover, several loci of var. dicoccoides were associated with an increase in yield components.The utilization of markers for chromosomal location of genes coding for quantitative traits is compared to the technique of aneuploid analysis, commonly used in wheat. The significance of the above findings for breeding is discussed.     

Chromosome locations of leaf rust resistance genes in selected tetraploid wheats through substitution lines

Langdon durum D-genome disomic substitution lines were used to study the chromosome locations of adult-plant leaf rust resistance genes identified from tetraploid wheat accessions. The accessions are 104 (Triticum turgidum subsp. dicoccum var. arras) and 127 (T. turgidum subsp. durum var. aestivum). The complete sets of the substitution lines were crossed as female parents with the accessions and F₁ double monosomic individuals selected at metaphase I. Segregating F₂ individuals were inoculated during the flag leaf stage with pathotype UVPrt2 of Puccinia triticina. The substitution analysis involving accession 104 showed that the gene for leaf rust resistance is located on chromosome 6B. The analysis with accession 127 indicated that chromosome 4A carries a gene for leaf rust resistance. The two novel genes are temporarily designated as Lrac104 and Lrac127, respectively from accessions 104 and 127.     

A biosystematic study of the origin of the cultivated diploid potato,Solanum x Ajanhuiri Juz. et Buk.

Summary The origin and nature of the diploid cultivated potato species S. ajanhuiri Juz. et Buk. was studied. Several lines of evidence indicate that S. ajanhuiri might be derived from natural crosses between primitive cultivars of the diploid species S. stenotomum and the wild species S. megistacrolobum. Morphological comparisons were made between S. stenotomum x S. megistacrolobum F₁ hybrids and naturally occurring S. ajanhuiri to investigate this hypothesis. Comparisons were also made between S. ajanhuiri x S. stenotomum crosses and the F₂ generation of the first-mentioned cross.Crosses between the two major groups of S. ajanhuiri cultivars, Ajawiri and Yari, showed not only genetic breakdown but also a wide range of phenotypic variation similar to those of artificial F₂ families of S. stenotomum x S. megistacrolobum. Furthermore, there was strong evidence showing that the Yari group of S. ajanhuiri could almost certainly be an F₁ S. stenotomum x S. megistacrolobum hybrid, whereas the Ajawiri group could be a backcross of an F₁ hybrid to S. stenotomum. These results added further support to the hypothesis of a hybrid origin of S. ajanhuiri, as well as indicating its putative parents. It is suggested that this hybridogenic taxon be retained at the species level under the name Solanum x ajanhuiri.     

Root pulling resistance in rice: Inheritance and association with drought tolerance

Summary Avoidance of drought stress is commonly associated with root system characteristics and root development. The inheritance of root pulling resistance in rice (Oryza sativa L.) was investigated and its relationship with visual field scores for drought tolerance was studied. Transgressive segregation for high root pulling resistance was observed in 3 crosses (high x high, low x high, and intermediate x intermediate). Both dominant and additive genes control the variation. F₁ superiority for high root pulling resistance was observed and could be exploited in an F₁ hybrid breeding program. F₂ distribution curves indicated that plants highly resistant to root pulling can be obtained not only from low x high and high x high crosses, but also from intermediate x intermediate crosses. Root pulling resistance in rice has a low heritability (39 to 47%). Thus, breeding for a high root pulling resistance may best be accomplished by selection based on line means rather than individual plant selection. Field screening showed significant differences in leaf water potential among random F₃ lines. F₃ lines with higher leaf water potential had better visual scores for drought tolerance. Visual drought tolerance scores were correlated with root pulling resistance. Plants with high root pulling resistance had the ability to maintain higher leaf water potentials under severe drought stress. The usefulness of the root pulling technique in selecting drought tolerant genotypes was confirmed.     

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.     

Resistance to Septoria nodorum blotch in several Triticum species

Summary Resistance to septoria nodorum blotch in Triticum monococcum, T. tauschii, T. timopheevii, T. dicoccum and T. durum was evaluated on plants at the three-leaf stage in greenhouse tests. A high frequency of resistant genotypes was found in T. monococcum, T. tauschii and T. timopheevii, but not in T. dicoccum and T. durum. The resistance of F₁ plants of crosses of resistant T. monococcum (PI 289599) and T. timopheevii (PI 290518) accessions with susceptible common wheat cv. Park and durum wheat cv. Wakooma, respectively, was evaluated on the basis of percentage leaf necrosis, lesion number, lesion size and incubation period. No dominance was found for long incubation period, but various dominance relationships occurred for low percentage leaf necrosis, low lesion number and small lesion size, depending on the cross. Multiple regression analysis showed that lesion number contributed more to percentage leaf necrosis than lesion size or incubation period. Resistance to septoria nodorum blotch was transferred successfully from T. timopheevii to cultivated durum wheat. Resistant BC₁F₇ lines, recovered from the T. timopheevii (PI 290518) × Wakooma cross, showed normal chromosome behaviour at meiosis (14 bivalents) and were self-fertile. However, an effective level of resistance was not recovered in lines derived from the other interspecific crosses.