Tan-Spot Resistance Screening of Aegilops Species

Two hundred and twelve accessions of 8 diploid and 10 polyploid species of Aegilops were evaluated for resistance to tan-spot disease of wheat, caused by Pyrenophora tritici-repentis (Died.) Drechs., under greenhouse conditions. One or more accessions of Ae. bicornis, Ae. biuncialis, Ae. Crassa, Ae. columnaris, Ae. cylindrica, Ae. speltoides, Ae. squarrosa. Ae. triaristata. Ae. triuncialis, and Ae. Ovata showed resistance following a 24-hour post-inoculation wet period. With a 36-hour wet period, diploids became only slightly or moderately susceptible and resistant polyploids became susceptible. A 48-hour wet period resulted in still greater susceptibility of both diploid and polyploid species.     

Chromosome Studies in the Genus Alstroemeria

Chromosomes of 11 cultivars of Alstroemeria were studied to determine their somatic constitutions. Two cultivars, ‘Eureka’ and ‘Zebra’, were diploid (2n = 2×= 16), six cultivars, ‘Yellow King’, ‘King Cardinal’, ‘Mona Lisa’, ‘Appelbloesem’, ‘Pink Triumph’ and ‘Rosita’ were triploid with 2n = 3×= 24, one cultivar, ‘Orange Beauty’ was a hypertriploid (2n = 3×+ 1 = 25), one cultivar, ‘Luciana’ was a hypotetraploid (2n = 4×– 1 =31) and one cultivar, ‘Jubilee’, was true tetraploid (2n = 4×= 32). This result suggests that polyploid cultivars may have more market value in this cut flower, Alstroemeria.     

Cytological and genetical studies of a male sterile celery

Summary The inheritance and nature fo male sterility of a cerley (Apium graveolens L.) strain (MS1) is reported. Male sterility in MS1 is determined by a a recessive genotype for a single locus. Tests for linkage with the isozyme chromosome markers SDH-1 and PGM-1 were negative. MS1 male sterility was associated with a defective tapetum characterized by prominent vacuoles and premature degeneration. The stamens in the male sterile strain persisted in the flowers up to stigma receptivity, while in the male fertile plants they dropped before style expansion. The male sterile flowers produced normal amounts of nectar, resulting in cross pollination by various species of pollinators. It was estimated that the sterile strain produced 30% less seed than normal male fertile. Its possible use for hybrid celery seed production is discussed.Research supported by grants from the California Celery Research Board and BARD I-483-82.     

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.     

Efficient production of doubled haploid Brassica napus plants by colchicine treatment of microspores

Summary The effect of colchicine on isolated microspore cultures of Brassica napus was evaluated in order to combine a positive effect of colchicine on the induction of embryogenesis with the possibility to induce chromosome doubling at an early developmental stage, thus avoiding the production of haploid or chimeric plants. Colchicine was added to the culture medium immediately after isolation of B. napus microspores. The cultures were incubated from 6 to 72 h with various concentrations of colchicine. Samples were taken from the regenerating embryoids after 6 weeks for ploidy determination by flow-cytometry.The highest diploidization rate was obtained after a 24 h treatment of microspores with 50 mg/l colchicine, leading to 80–90% diploid embroids. A concentration of 100 mg/l colchicine applied for the same duration resulted in a lower diploidization rate (76–80%). Treatment durations of 6 h were not long enough to induce a high rate of diploidization, whereas the application of 10 mg/l for 72 h was also very effective.A sample of the plants regenerated from the colchicine treated microspores was transferred to the greenhouse. The plants looked similar to normal diploid rapeseed plants and showed reasonable pod and seed set. Thus, an additional generation for seed increase in the greenhouse is rendered unnecessary. The advantage of applying a minimum volume of colchicine under controlled in vitro conditions means a considerable saving of time and labour in DH-breeding programs.     

Oryzalin as an Efficient Agent for Chromosome Doubling of Haploid Apple Shoots in vitro

In an outbreeding species such as apple, haploid plants may be especially useful in breeding programmes for the production of homozygous material. However, methods must be available to induce chromosome doubling in the haploid plants. Two antimitotic agents, colchicine and oryzalin, were compared as regards their efficiency in inducing chromosome doubling of in vitro haploid apple shoots. Three colchicine levels (0.025, 0.25 and 1.25 mM) and three oryzalin levels (5, 15 and 30 μM) were evaluated. Three techniques were also used and compared. Survival rate and chromosome counts were determined. Differences were observed between the two antimitotic agents and between the three techniques. This study demonstrates that oryzalin could be a better choice than colchicine for chromosome doubling on haploid apple shoots in vitro.     

Effects of homoeologous group 1 and 6 chromosomes of the Cappelle-Desprez (Bezostaya 1) substitution lines on aspects of bread-making quality of wheat

Summary The group 1 and 6 inter-varietal chromosome substitution lines of Cappelle-Desprez (Bezostaya 1) were intercrossed along with the donor and recipient varieties, Cappelle-Desprez and Bezostaya 1, to give 36 genetically different families. The analysis of the means of these families showed that variation in SDS-sedimentation volume fitted a predominantly additive model. There were no significant within or between chromosome interactions among the group 1 and 6 chromosomes. Nor was there any evidence for interactions between these chromosomes and those of the background. Significant dominance/within chromosome interactions amongst the background chromosomes were however detected. Some of the positive effects on SDS-sedimentation were associated with increased grain hardness. Chromosome effects on % grain protein were not correlated with SDS-sedimentation.     

Isolation of a Spontaneous Chromosome Translocation in Common Wheat

The genes Ms2 for male sterility and Rht10 for dominant dwarfing located on the short arm of chromosome 4D in common wheat arc closely linked. Male sterile, dwarf F₁ plants from the cross of male sterile‘Chinese Spring’× dwarf‘Ai-bian’were backcrossed with the variety‘Chinese Spring, From this offspring a spontaneous chromosome translocation was isolated resulting in a recombinant male sterile and dwarf genotype.     

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.     

Karyotype and C-banding pattern of mitotic chromosomes in alfalfa, Medicago sativa L.

Numerous cytogenetic studies have been performed on alfalfa (Medicago sativa L. 2n= 4x= 32), but only a few have examined the somatic chromosomes. Because the major factor limiting the study of somatic chromosomes of M. sativa is their rather uniform morphology, characterization was attempted using the C-banding technique instead of the traditional Feulgen method. Chromosome morphology and position of the heterochromatic bands resulted in satisfactory characterization of the chromosomes and provided further evidence of the autotetraploid origin of the species. It was possible to identify the homologous chromosomes and arrange them into eight groups of four. The ideogram of the basic genome of eight chromosomes was constructed. The impact of these results on cytogenetic studies and breeding research in alfalfa is discussed.