Interspecific hybridization between Coffea arabica L. and tetraploid C. canephora P. Ex Fr. II. Meiosis in F1 hybrids and back crosses to C. Arabica

Summary Melosis was studied in Coffea arabica, in induced tetraploid C. canephora, in their F₁ hybrid (arabusta hybrid) and in backcross generations of the hybrid with C. arabica as recurrent parent. Irregularities were observed, consisting of univalents (especially in the arabusta hybrid), multivalents (especially in tetraploid C. canephora) and uneven distribution of chromosomes at first anaphase. Chromosome distribution was improved by backcrossing. Meiotic irregularities wer negatively correlated with pollen fertility.     

The electrofocusing composition of the Large and Small Sub-unit polypeptides of Fraction-1-Protein in rice x wheat and rice x sorghum hybrids

Summary The polypeptide composition of Fraction-1-Protein (F1P) from rice × sorghum, rice × wheat hybrids and their respective parents have been analyzed by a microelectrofocusing method. The large sub-unit (LSU) is composed of three polypeptides and the small sub-unit (SSU) of two polypeptides in rice and sorghum parents and rice × sorghum hybrids. Similarly, LSU is composed of three polypeptides in the rice and wheat parents and rice × wheat hybrids. Two polypeptides occur in the SSU of rice parent and rice × wheat hybrids where as only one polypeptide in the wheat parent. These polypeptides also differ in their isoelectric points. Based on the previous reports of F1P inheritance in hybrids in other crops, F1P analysis of rice × sorghum and rice × wheat hybrids does not seem to be an important marker to identify such intergeneric hybrids. Since this is first such report of F1P inheritance in hybrids between distantly related plants, its implication in different modes of inheritance are discussed.Abbreviations F1P Fraction-1-Protein - IEF Isoelectric focusing - pI Isoelectric points - LSU Large sub-unit - RuBPCase Ribulose 1,5-Bisphosphate Carboxylase-oxygenase - SSU Small sub-unit     

Inheritance of yield components and yield in relation to evidence for heterosis in F1 barley hybrids

Summary Yield components and yield were studied in F₁ barley hybrids produced by hand pollination or male sterility. Grain number exhibited only partial dominance but grain weight showed dominance or overdominance and contributed to the heterotic situation particularly in 2×6-row crosses. For the commercial exploitation of heterosis it is essential that hybrids should be found which show greater dominance for high grain number.     

Intergeneric hybrid between Brassica napus and Diplotaxis harra through ovary culture and the cytogenetic analysis of their progenies

Brassica napus (2n = 38) and Diplotaxis harra (2n = 26) were used to investigate gene transfer from D. harra to B. napus. Intergeneric F₁ hybrids (dihaploid 2n = 32 chromosomes) were obtained through ovary culture. The chromosome associations in the first meiotic division was (0–2)_III + (2–10)_II + (12–28)_I. Many seeds were harvested in the F₁ hybrid after backcrossing with B. napus, and from open pollination of the F₁ hybrid. Somatic chromosome numbers of BC₁ and hybrid plants varied from 2n = 26 to 52. In the first meiotic division, high frequencies of bivalent association and relatively low pollen fertility were observed. BC₂ plants generated from the BC₁ plants with 2n = 38 chromosomes, 69.6% showed 2n = 38 chromosomes. Many aneuploids with addition and deletion of chromosomes were also obtained. A bridge plant between B. napus and D. harra with 2n = 32 chromosomes should be valuable material for the breeding of brassica crops.     

Identification of somatic hybrids of dihaploid Solanum tuberosum lines and S. brevidens by species specific RAPD patterns and assessment of disease resistance of the hybrids

Summary Symmetric somatic hybrids were produced by electrofusion of protoplasts of two dihaploid tuber-bearing potato (Solanum tuberosum L.) lines and Solanum brevidens Phil., a diploid non-tuber-bearing wild potato species. A total of 985 plants was obtained. Verification of nuclear hybridity of putative hybrids was based on additive RAPD patterns, general morphological characteristics and chromosome counts. 53 (90%) calli regenerated into plants which were identified as somatic hybrids. Most of the hybrids were aneuploids at the tetraploid (4×) or hexaploid (6×) level. The 20 hybrids tested expressed a high level of resistance to potato virus Y (PVY ^N ) characteristic of the S. brevidens parent. Resistance to late blight (Phytophthora infestans (Mont.) de Bary) varied between hybrids, but was on average better than that of the fusion parents. Resistance of hybrids to bacterial stem rot (Erwinia carotovora subsp. atroseptica (van Hall) Dye) was not superior to that of commercial potato cultivars.     

Inter-and intraracial hybridization and selection for seed yield in early generations of common bean,Phaseolus vulgaris L.

Summary Five parents from each of four race groups of common bean (Phaseolus vulgaris L.) were hybridized to produce five crosses within each group. Also, five crosses were made for each of the six possible combinations among four groups. Parents, F₁ and F₂, and parents, F₂ and F₃ were evaluated for seed yield in 1990 and 1991, respecitively, at two locations in Colombia.Yield of parents belonging to Middle American races and crosses among them was higher than that of races of Andean origin. Positive correlations were found among the mid-parent value, F₁, F₂ and F₃. Also, the mid-parent value predicted the mean seed yield of all possible lines that could be derived from the F-generation in 42 out of 47 crosses. Four crosses, all between common bean races of Andean and Middle American origin, indicated a possible loss of favorable epistatic parental alleles. On average, mean yield of interracial F₁ hybrids was higher than that of intraracial ones.Positive heteroris (26.4%–123.8%) over the mid-parent in 31 crosses, and F₁s yielding higher (23.7%–91.8%) than the high parent in 20 crosses and yielding higher (22.1%–53.2%) than the highest control among all parents (MAM 13) in 12 crosses, were found. Heritability, estimated by the parent-offspring regression, ranged from 0.42± 0.07 to 0.49±0.04. Expected and realized gains from selection (at 20% selection pressure) ranged from 10.3% to 21.0% over the mean of F₁ hybrids and F₂ and F₃ population bulks.     

Meiotic studies of spontaneous hybrids of Amaranthus: genome analysis

The meiotic behaviour of 13 spontaneous interspecific F₁ hybrids of Amaranthus was studied. The hybrids between species with n= 16 chromosomes had 16 bivalents but varied considerably in pollen stainability (0–55%). These results suggest the existence of cryptic structural hybridity. The hybrids involving A. cruentus (n = 17) and species with n = 16 (A. caudatus and A. quitensis) always formed 15II+1 III with very low pollen stainability (5–7%). Further observations indicated that Amaranthus species are allotetraploids with basic numbers of x= 8 and x= 9 but exhibit x= 16 and x= 17 as secondary basic numbers, as demonstrated by (a) the frequent presence of 811 + 171 in the meiosis of the hybrid A. spinosus (n = 17) × A. hybridus (n= 16); and the occurrence of secondary associations between bivalents in MI. Genomic formulae are proposed for each species, on the basis of the meiotic behaviour of the hybrids studied.     

Reproductive Behavior of Hexaploid/Diploid Wheat Hybrids 1

The bottleneck restricting introgression of useful genes directly from diploid into hexaploid wheats is the low number of BC₁F₁ seeds obtained. In crosses between hexaploid wheat (Triticum aestivum L.; AABBDD) and Aegilops squarrosa L. (DD) or T. urartu Thum. (AA), this bottleneck may be overcome simply by pollinating a sufficient number of F₁ spikes. However, hybrids between hexaploid wheat cultivars (T. aestivum) and T. monococcum L. (AA) generally are highly female-sterile, often having no pistils. One T. monococcum accession, PI 355520, when crossed with T. aestivum, produced hybrids with female fertility in the same range as that of T. aestivum/A. squarrosa or T. aestivum/T. urartu hybrids, ca. 0.5 to 1.0 backcross seed per spike. We found that female fertility was controlled by two duplicate genes in PI 355520, and that this accession can be used as a bridging parent to introgress genes from other T. monococcum accessions into hexaploid wheat. Pairing of homologous chromosomes was less frequent and weaker in such crosses than in T. aestivum/A. squarrosa crosses, but homoeologous bivalents occurred at a rate of almost 0.5 II per cell. Restitution division was detected in crosses involving all three diploid species and was confirmed cytologically in crosses with PI 355520. Chromosome numbers of BC₁F₁ plants ranged from 35 to 67; plants with 49 or more chromosomes occurred at frequencies of 0.09 to 0.21 among progeny of A. squarrosa and T. urartu and 0.29 in progeny of T. aestivum/T. monococcum crosses involving PI 355520. These results are consistent with those of previous studies, demonstrating the potential of direct Hexaploid/diploid crosses for rapidly introgressing useful genes into Hexaploid wheat with minimum disturbance of the background genotype.     

A gene for hybrid necrosis in an inbred line of rye (Secale cereale L.)

Summary An inbred line of rye (Secale cereale L.) has been found to carry a gene for hybrid necrosis. This gene was detected in crosses with a highly crossable wheat (Triticum aestivum L.) genotype which carries the gene Ne₂. This appears to be the first report of a gene for hybrid necrosis being present in the rye genome.     

Incongruity of interspecific and intergeneric crosses involving Nicotiana and Petunia species that exhibit potential for somatic hybridization

Summary Extensive pollinations were made in attempts to produce selected intergeneric or interspecific hybrids using Nicotiana and Petunia species that exhibit potential for somatic hybridization. Pollination between pairs of species was done by standard and bud-pollination methods. Nicotiana alata or N. tabacum when pollinated reciprocally with selected Petunia species failed to produce hybrids. Likewise, no interspecific hybrids were obtained between Petunia parviflora and 4 Petunia species or P. hybrida. The type of incongruity existing between these species is discussed in relation to the production of hybrids by standard In vitro techniques as compared to somatic hybridization.On leave from the Department of Horticulture, Michigan State University, E. Lansing, Michigan, USA. supported by a European Molecular Biology Organization (EMBO) fellowship and The Fred C. Gloeckner Foundation, N. Y., USA.Supported by the Agricultural Research Council.