Variation in progenies of an Arachis hypogaea x diploid wild species hybrid

Summary Derivatives of a cross between cultivated peanuts, Arachis hypogaea L. (2n=40), and the wild species collection GKP 10017 (2n=20) were compared morphologically, for leafspot resistance and for yield. The objective of the study was to determine the effects of wild species germplasm on the A. hypogaea genome. The sterile F₁ hybrid which resulted from crossing the two species was treated with colchicine to restore fertility at the 6x ploidy level. The resulting hexaploid was cytologically unstable and progeny lost chromosomes until stability was regained at the 2n=40 chromosome level. Forty-seven characters were used to analyze the variation among plants in the tetraploid interspecific hybrid population. The plants were compared to four cultivated lines plus GKP 10017. Many hybrids were intermediate to the two parents in morphology. Individual traits such as growth habit, pod and seed size, elongation of the constricted area between pods, nodulation and leaflet size were altered by the presence of GKP 10017 germplasm in many of the hybrid plants. Cercospora arachidicola Hori and Cercosporidium personatum (Berk. & Curt.) Deighton resistances were evaluated for all plants. Several hybrids had few lesions due to either leafspot pathogen. In addition, 24 largeseeded interspecific hybrid selections were compared to the cultivated variety NC 5 for yield. Five selections were superior to both parents at p=0.01. Morphology, disease resistance and yields appeared to be greatly influenced by the wild species GKP 10017 germplasm in plants of the interspecific hybrid population. The potentials of using wild species for improvement of the cultivated peanut are discussed.Paper number 5948 of the journal series of the North Carolina Agricultural Research Service, Raleigh, NC 27650. The investigation was supported in part by ICRISAT and SEA-CR grant no. 701-15-51.     

Recurrent selection progress in a population derived from an interspecific peanut cross

Summary Two cycles of recurrent selection for yield were previously conducted using a population of Arachis hypogaea L.-like tetraploid hybrid derivatives selected from among the progeny of a cross between A. hypogaea and A. cardenasii Krap. et Greg. nom. nud., a diploid species with resistance to late leafspot (Cercosporidium personatum (Burk. and Curt.) Deighton). Using the 10 highest yielding parents from each of the above cycles of recurrent selection, a study was conducted for 12 morphological traits and susceptibility to leafspot infection in a replicated test at a single location. The two parents used to initiate the interspecific hybrid population (PI 261942-3 and A. cardenasii) as well as two adapted cultivars (Florigiant and NC 7) were included as checks. The objectives of the study were to determine the amount of genetic variation remaining in the population after two cycles of recurrent selection in order to predict whether further progress from selection could be expected and determine the potential for utilizing wild species for the improvement of quantitative traits in peanut. The results indicate that significant levels of genetic variation remain in the population after two cycles of recurrent selection for all traits measured, including several components of yield and leafspot resistance. This suggests that continued progress in population improvement from further cycles of selection should be possible while enhancing the genetic diversity of cultivated peanut germplasm.Paper no. 12347 of the Journal Series of the North Carolina Agric. Res. Serv., Raleigh, NC 27695-7643. This work was partially funded by the Peanut CRSP, USAID grant number DAN-4048-G-SS-2065-00. Recommendations do not represent an official position or policy of USAID.     

Aseptic culture of gynophores to obtain peanut intersectional hybrids

Summary Cross-incompatibility between cultivated peanuts and their wild relatives outside the section Arachis has impeded the utilization of many species possessing high resistances or good qualities. Despite the great efforts made to culture immature ovules or embryos, few hybrid offspring have been obtained. In this study, gynophores from Arachis hypogaea L. pollinated with A. glabrata Benth. were cultured and F₁ hybrids seeds were harvested, and F₂ and F₃ generations produced. The characters of F₂ generation exhibited a wide range of segregation. Leaf peroxidase isozyme PAGE analysis revealed that the hybrids were quite different from their parents in relation to band number, width and isozyme activity. The zymograms of the hybrids and their parents were partially alike. This verified the authenticity of the hybrids.     

Utilizing Arachis cardenasii as a source of Cercospora leafspot resistance for peanut improvement

Summary Advanced generation 40-chromosome hybrids between A. hypogaea (2n=4x=40) and a wild diploid species. A. cardenasii were evaluated for early leafspot, Cercospora arachidicola resistance and agronomic potential. The objective of this investigation was to determine if early leafspot resistance derived from a wild species could be incorporated into the A. hypogaea genome. Interspecific hybrid selections were made and then compared in the field and greenhouse to susceptible cultivars and to A. hypogaea lines which are reported to be resistant to early leafspot. Significantly higher levels of resistance were found in five hybrid selections than in cultivated lines based on numbers of lesions per leaf. In a greenhouse study, several hybrid selections also had greatly reduced sporulation from lesions as compared to A. hypogaea. Several mechanisms of resistance are believed to be present. Although hybrid selections had small seeds and low yields as compared to A. hypogaea, a new and valuable source of early leafspot resistance derived from the species A. cardenasii is present.Paper no. 8814 of the journal series of the North Carolina Agricultural Research Service, Raleigh, NC 27695. This research was partially funded by AID-Peanut CRSP grant DAN-4048-G-SS-2065-00.     

Progenies of an interspecific hybrid betweenArachis hypogaea and A.stenosperma — pest resistance and molecular homogeneity

Summary Interspecific triploid hybrids were obtained betweenArachis hypogaea L. andA. stenosperma Krapov. and W.C. Gregory by adopting hybridization coupled with rescue of the developing hybrid embryos. Two hexaploid hybrid populations were generated from triploids, somatically doubled (SD) and sexually polyploidized (SP) hexaploids. Microscopic screening for the occurrence of 2n gametes in triploid hybrids was useful to predict the production of spontaneous hexaploids. In order to facilitate maximum intergenomic recombination, the hexaploids were allowed to self for several generations (F₄) in the greenhouse. Prolific vegetative growth, pollen stainability, and seed set were observed to decline with each selfed generation. Individuals of the F₃ generation from the two hexaploid populations were evaluated for resistance to nematode (Meloidogyne arenaria Chitwood, race 1) and late leafspotCercosporidium personatum (Berk. & Curt.) Deighton under greenhouse conditions. Both SD and SP populations performed significantly better than their cultivated parent, Sunbelt Runner, and a susceptible cultivar, Florunner. At the DNA level, no significant differences were detected among hybrid individuals using cDNA clones and RAPD primers polymorphic for the two parents. Seven cDNA clones were used to probe DNA from 17 F₂ individuals and two parents and 45 RAPD primers were used to amplify DNA from 21 F₂ and F₃ individuals. No significant differences in banding patterns were observed among hybrid individuals which suggested that little or no detectable intergenomic recombination had occurred.     

Cytogenetics of interspecific hybrids in the genus Capsicum L.

Summary Crosses between a wild species C. chacoense and three cultivated species of chili pepper viz. C. annuum, C. frutescens and C. chinense yielded hybrids when C. chacoense was the seed parent but the reciprocal crosses were unsuccessful. C. chacoense × C. annuum F₁ hybrids were partly fertile and therefore an F₂ population could be raised; the other two F₁ hybrids were totally sterile. Chromosome pairing in the F₁ plants resulted largely in bivalents and a few multivalents and univalents. The genomes of the four species share large homologies and the role of chromosome structural changes in genome differentiation is suggested. Hybrid sterility is the major reproductive isolation mechanism.     

Interspecific hybrid of Helianthus annuus × H. simulans: Characterization and utilization in improvement of cultivated sunflower (H. annuus L.)

The first success at interspecific hybridization between cultivated sunflower(H. annuus) and a diploid perennial species, H. simulans is reported. The F₁s from both direct and reciprocal directions exhibited dominance of the wild species phenotype and were pollen sterile. Meiosis was irregular in the F₁ hybrids and both univalents and multivalents were observed. Multiplication of the interspecific hybrids was achieved through in vitro culture of nodal sections on Murashige & Skoog medium supplemented with 0.5 mg l^-1 benzyladenine. Fertility of the interspecific hybrids was improved by subjecting the in vitro proliferating shoots to 0.001% colchicine incorporated in the shoot multiplication medium. The amphiploids serve as fertile bridges and facilitate interspecific gene transfer through conventional breeding. This revised version was published online in July 2006 with corrections to the Cover Date.     

Relationships between African species of the genus Cucumis L. Estimated by the production,vigour and fertility of F1 hybrids

Summary The production, vigour, and fertility of F₁ hybrids between nine African species of the genus Cucumis L. were studied as a measure of the relationships between the species. Hybrid plants were obtained from 29 out of the 72 possible cross combinations. Two F₁ hybrids died as seedlings, and 27 hybrids were raised to maturity. Pollen production and stainability varied greatly amongst these hybrids, as did fruit and seed set following self pollination and backcrossing with either parental species. The fruit shape of the hybrids was always intermediate between that of both parental species.Two species appeared to be closely related: C. prophetarum L. and C. anguria var. longipes A. Meeuse. Most other species produced highly to moderately fertile F₁ hybrids with at least one other species. C. metuliferus Naud. produced only sterile hybrids with C. zeyheri Sond. 2x. The results sustain the recent taxonomic classification of the genus (Jeffrey, 1980).     

Meiosis and pollen grain viability in Helianthus mollis,Helianthus salicifolius,Helianthus maximiliani and their F1 hybrids with cultivated sunflower

Three diploid perennial sunflower species are useful for variety improvement: Helianthus mollis, because of sessile leaves, H. salicifolius, because of a high oil concentration, and H. maximiliani, a potential source of resistance to Sclerotinia sclerotiorum. The crossability of these species to cultivated sunflower was examined.Hybrids were obtained from eight combinations, with 3–15 F₁ plants per combination. The F₁'s exhibited the dominant phenotype of the wild species. Pollen viability varied between 32.1 and 69.9%. Meiosis was irregular in the F₁ hybrids. At diakinesis, bivalents (62.7–97.9% of meiocytes), univalents (0–31.23%), and multivalents (3.84–7.68%) were detected. At anaphase I, chromosome bridges were detected in 6.77 to 11.44% of meiocytes. Fast chromosomes in metaphase I, and lagging chromosomes in anaphase I and telophase II were evidenced in a high percentage of meiocytes.     

Possibility of genetic improvement of pigeonpea (Cajanus cajan (L.)Millsp.) utilizing wild gene sources

Summary Various wild relatives of pigeonpea,Cajanus cajan, namely some species ofAtylosia andRhynchosia, possess desirable characteristics that could be utilized for effecting genetic improvement of this crop. In total 73 cross combinations among two cultivars ofC. cajan and one accession each of eightAtylosia species and one ofRhynchosia were attempted. Twelve hybrids were obtained. Seven of these were analysed for F₁ fertility and their utility for agronomic improvement of theC. cajan. Fertility behaviour of the different F₁ hybrids varied and indicated that potential of gene transfer between the two genera,Atylosia andCajanus, was as good as within the genusAtylosia. From F₂ and F₃ families ofC. cajan × A. scarabaeoides andC. cajan × A. albicans, plants were selected with greater physiological efficiency and agronomic superiority. The prospects of transferring pod borer resistance and higher seed protein content from someAtylosia species to pigeonpea are discussed.     

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.     

The inheritance of resistance to powdery mildew in interspecific hybrids and induced amphiploids of Zinnia elegans Jacq. and Z. angustifolia HBK

Summary Sterile interspecific hybrids and colchicine-induced amphiploids of Zinnia elegans Jacq. and Z. angustifolia HBK were examined to determine the mode of inheritance of resistance to Erysiphe cichoracearum DC ex Merat. Fertility was restored through colchicine treatment of two sterile hybrids of species reciprocal parentage which differed in ray petal response to the pathogen. Derived amphiploids were subsequently intercrossed to overcome the lack of segregation for this trait due to genetic control of pairing upon chromosome doubling. Resistance to E. cichoracearum appears to be complexly inherited in both leaves and ray florets of sterile hybrids and induced amphiploids. Two major dominant genes have been implicated in conferring resistance in ray petal tissue of derived amphiploids. Data obtained from the F₁ hybrid progeny of the intercrossed amphiploids indicate that this trait is not cytoplasmically inherited. It is speculated that the genes conferring resistance in the ray florets are acting independently from those controlling leaf resistance and that most, if not all, of the resistance genes are inherited from Z. angustifolia.Scientific Article No. A-3825, Contribution No. 6804 of the Maryland Agricultural Experiment Station.     

The production of alien monosomic additions in Beta vulgaris as a source for the introgression of resistance to beet root nematode (Heterodera schachtii) from Beta species of the section Patellares

Summary Experiments were carried out for adding the chromosome carrying resistance to beet root nematode (Heterodera schachtii) from the wild Beta species of the section Patellares (B. procumbens, B. webbiana and B. patellaris) to the genome of B. vulgaris. Preliminary experiments indicated that crosses between the wild species and B. vulgaris cultivars of the mangold type yielded on average more viable F₁ hybrids than crosses with sugar and fodderbeet. However, crossability varied strongly between individual parental combinations. It was concluded that most types of B. vulgaris can be hybridized with the wild species of the section Patellares if a sufficient number of pair-crosses is made. Crosses between diploid cultivars or species of the section Vulgares and diploid wild species of the section Patellares yielded many hybrids which, however, were highly sterile. From crosses between tetraploid B. vulgaris and the wild species a great number of viable allotriploid and allotetraploid hybrids was obtained. In the backcross progenies of allotriploid hybrids 26% alien monosomic additions occurred, of which 4.1% carried the resistance bearing chromosome of B. procumbens or B. patellaris. The programme will be continued by sereening progenies of the resistant monosomic addition plants for the occurrence of resistant disomic introgression products.     

The genomes of Arachis hypogaea. 1. Cytogenetic studies of putative genome donors

Summary Cytological studies of wild diploid Arachis species in the same section of the genus (sect. Arachis) as the cultivated peanut A. hypogaea L. show, with one exception, a karyotype characterized by the presence of 9 pairs of larger chromosomes and one pair of small (A) chromosomes. The exceptional species A. batozocoi Krap. et Greg. has a more uniform karyotype. Interspecific hybrids between diploid species of similar karyotype have moderate to high pollen stainability, those involving A. batizocoi have zero pollen stainability and a very irregular PMC meiosis. Such infertile hybrids are the most likely to produce fertile, stable amphidiploids on doubling the chromosome complement. It is suggested that the cultivated peanut could have originated from such a sterile interspecific hybrid and on morphological and phytogeographic grounds the most likely genome donors are A. cardenasii (nomen nudum) and A. batizocoi of the species within section Arachis, which have been collected up to the present time.Paper number 5560 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, NC 27650     

Use of the gene pools of Triticum turgidum ssp. dicoccoides and Aegilops squarrosa for the breeding of common wheat (T. aestivum), through chromosome-doubled hybrids

Summary Triticum turgidum ssp. dicoccoides (wild emmer wheat, AABB, 2n=28) and Aegilops squarrosa (goat grass, DD, 2n=14) comprise a rich reservoir of valuable genetic material, which could be useful for the breeding of common wheat (T. aestivum, AABBDD, 2n=42). Many accessions of both wild species, most of them selected for resistance to stripe rust, were used to make amphiploids. Two strategies were applied: (1) the production of autopolyploid cytotypes of the wild species, followed by hybridisation, and (2) the production of allotriploid interspecific hybrids, followed by doubling of the number of chromosomes. The first route was unsuccessful because of failure of the crosses between the autopolyploid cytotypes, possibly due to incongruity between the two species and to reduced fertility in the autopolyploid cytotypes. The second route yielded the desired synthetic hexaploids. However, the rate of success of the crosses was low and there were great differences between years, and within years between crosses. Embryo rescue was applied to obtain the primary hybrids (2n=21), which were highly sterile and had on average 0.3 bivalents and 20.4 univalents per pollen mother cell. Various abnormalities were recorded. Doubling of the number of chromosomes sometimes occurred spontaneously or was brought about by colchicine treatment. The large scale of the interspecific hybridisation programme ensured that one-third of the female and one-sixth of the male accessions were represented in the synthetic hexaploids.     

Restoration of meiotic regularity and fertility among derivatives of Lens culinaris x L. Nigricans hybrids

Summary The wild lentil, L. nigricans is cross compatible with the cultivated species. Chromosome pairing in their F₁ hybrids is highly irregular due to a difference of three translocations between the parental species. However, the hybrids are partially fertile and in the F₂ populations there is a marked improvement in fertility. About 19% of the F₂ plants were meiotically stable, fully fertile and their chromosome arrangement was similar to that of the cultivated species. All these are clear indications for the possibility of rapid introgression between the two species and hence systematic screening of L. nigricans for traits of economic value is fully justifiable.     

The transfer of triazine resistance from Brassica napus L. to B. oleracea L. II. Morphology,fertility and cytology of the F1 hybrid

Summary F₁ hybrids of triazine resistant Brassica napus and triazine susceptible B. oleracea were morphologically intermediate to the parent species. Of 49 hybrids examined, 44 had 28 chromosomes, two had 37, one had 38 and two had 56. The 38-chromosome plant was thought to be a matromorph, the others, A₁C₁C (28), A₁C₁CC (37) or A₁A₁C₁C₁CC (56) type hybrids. Pollen stainability averaged 9.0% in the sesquidiploid, 32.0% in the tetraploids and 89.5% in the hexaploids. All the interspecific hybrids were resistant to 1.0×10^-4 mol L^-1 atrazine. The sesquidiploid hybrids produced gametes with chromosome numbers ranging from 9 to 17 and the tetraploid hybrid gametes had chromosome numbers from 15 to 22. Most hybrids produced self-seed. The partial fertility of these hybrids may permit their backcrossing to one or both parents.     

Transfer of resistance to race 2 of Plasmodiophora Brassicae from Brassica napus to cabbage (B. oleracea var. Capitata). I. Interspecific hybridization between B. napus and B. oleracea var. Capitata

Summary Interspecific hybridization between Brassica napus L. (2n=38, a₁a₁c₁c₁) and B. oleracea var. capitata L. (2x- and 4x-cabbage; 2n=2x=18, cc and 2n=4x=36, cccc) was carried out for the purpose of transferring clubroot disease resistance from the amphidiploid species to cabbage. Nineteen hybrids with three different chromosome levels (2n=28, a₁c₁c; 2n=37, a₁c₁cc and 2n=55, a₁c₁cccc) were obtained. The F₁ plants were mostly intermediate between the two parents but as the number of c genomes in the hybrids increased, the more closely the hybrids resembled the cabbage parent. All F₁ hybrids were resistant when tested against race 2 of Plasmodiophora brassicae wor. The complete dominance of resistance over susceptibility suggested that the gene(s) controlling resistance to this particular race of the clubroot pathogen is probably located on a chromosome of the a genome in Brassica.Contribution No. J654.     

Frequencies of plasmon types in a germ plasm sample of peanuts,Arachis hypogaea

Summary The plasmon constitution of 68 different accessions of cultivated peanuts (Arachis hypogaea L.) was studied in crosses with one or another of three testers: V4, VSM and HG1, having the [V4], [O] and [G] plasmons, respectively. The plasmons interact differently with three plasmon-sensitive nuclear genes, thereby determining whether the plants will be erect or trailing. From the phenotypes of the reciprocal F₁ hybrids it was concluded that the [G] plasmon of HG1 is rare-it is present in this cultivar and possibly in a few other; the [V4] plasmon is rare, being present in the V4 cultivar and possibly in a few other accessions; the [O] plasmon is widespread, being present in lines from various geographical origins and in at least three of the four botanical types of cultivated peanuts.     

Trichome characteristics of F1Lycopersicon esculentum × L. cheesmanii f. minor and L. esculentum × L. pennellii hybrids and effects on Myzus persicae

Summary The green peach aphid (Myzus persicae) is a serious pest of the tomato (Lycopersicon esculentum). Trichome-based host plant resistance of wild Lycopersicon species may offer an alternative to pesticides for management of this pest. Two wild species, Lycopersicon cheesmanii f. minor and L. pennellii, were crossed with L. esculentum and the types and densities of trichomes possessed by the F₁ hybrids measured. The effects of these trichomes on M. persicae were assessed by placing nymphs on leaves and, 96 hr later, designating each nymph as either dead, alive, emigrating off the leaf or unaccounted for. A generalised linear model was used to detect relationships between the numbers of nymphs in each designation and the densities of trichomes and leaf area. Mortality of nymphs on L. pennellii hybrids was associated with high densities of type IV and low densities of type I trichomes. Mortality of nymphs on L. cheesmanii f. minor hybrids was associated with high densities of type III trichomes. An increase in the densities of type III trichomes on L. pennellii hybrids was associated with greater numbers of nymphs emigrating off the leaf whilst unaccounted nymphs on L. pennellii hybrids were associated with increased densities of type VII and type I trichomes. Further experimentation using excised leaflets found mortality on L. pennellii hybrids may be due to nymphs being hindered by type I trichomes and increased densities of type V trichomes were associated with greater numbers of unhindered nymphs. Implications of results are discussed in the context of introducing trichome-based host plant resistance into L. esculentum.