J. N. de Vries

Isolation of an amylose-free starch mutant of the potato (Solanum tuberosum L.)

SummaryAn amylose-free potato mutant was isolated after screening 12,000 minitubers. These minitubers had been induced on stem segments of adventitious shoots, which had been regenerated on leaf explants of a monoploid potato clone after Röntgen-irradiation. The mutant character is also expressed in subterranean tubers and in microspores. Starch granules from the mutant showed a strongly reduced activity of the granule bound starch synthase and loss of the major 60 kd protein from the starch granules.

Rapid estimation of the amylose/amylopectin ratio in small amounts of tuber and leaf tissue of the potato

SummarySmall amounts of potato tuber and leaf tissues are extracted in perchloric acid. After staining with I2-KI solution absorbancies at 618 and 550 nm are measured. The amylose/amylopectin ratio can be estimated from the ratio of the absorbancies by using a formula or a graph in which the specific absorptions of the two compounds are introduced. Weighing of samples is not required. The method can be used for the estimation of the starch composition of minitubers and is especially suitable for the detection of mutants with an altered starch composition.

An interspecific cross between Allium roylei Stearn and Allium cepa L., and its backcross to A. cepa.

SummaryA cross between Allium roylei Stearn and A. cepa L. and a backcross of the probable interspecific hybrid to Allium cepa L. were realized in a simple and practical way, possibly opening up perspectives for introgression of downy mildew resistance and other characters from this wild relative into the onion germplasm.

Introgression of leaf blight resistance from Allium roylei Stearn into onion (A. cepa L.)

SummarySegregation analysis in BC1 and F2 progenies from interspecific hybrids between Allium roylei and A. cepa demonstrated that leaf blight resistance is conditioned by one single dominant gene from A. roylei. This gene, designated Bs1, was unlinked to the genes Pd1 and Pd2 determining downy mildew resistance. The prospects of exploiting A. roylei as a source for disease resistances in onion breeding are very promising.

Onion chromosome nomenclature and homoeology relationships-workshop report

SummaryParticipants in a workshop on onion chromosome nomenclature held during the Eucarpia 4th Allium Symposium, agreed to consider the nomenclature for the chromosomes of Allium cepa L. proposed by E.R. Kalkman (1984) as the standard. Recommendations were formulated for the chromosome nomenclature of species which are cross compatible with onion.

Pre- and post-fertilization barriers to backcrossing the interspecific hybrid between Allium fistulosum L. and A. cepa L. with A. cepa

SummaryTo facilitate the introgression of desirable traits of Allium fistulosum into the genome of A. cepa, several accessions of the hybrid between these species were pollinated with A. cepa as the recurrent parent, and in vitro ovary and ovule culture were performed to obtain an increase in the recovery of backcross progeny. Compared to the results obtained from seed development in planta, the increase in the number of backcross progeny was generally very limited, and in some cases even a decrease was found. Raising the sucrose concentration in the ovary culture medium resulted in a higher frequency of ovules developing back seed coats but this was not followed by an increase in the number of backcross progeny obtained. Pollen tube growth of A. cepa was disturbed in the styles of the interspecific hybrids. Per ovule, frequencies of micropylar penetration exceeded frequencies of backcross progeny only to a limited extent. Hence, it was concluded that in the tested interspecific hybrid accessions the attainable gain in viable backcross progeny by the application of in vitro culture techniques is limited by strong pre-fertilization barriers acting at the level of stylar incongruity.

Cytological studies on adventitious shoots and minitubers of a monoploid potato clone

SummaryA three step procedure for adventitious shoot regeneration on leaf explants of monoploid potato clone H7322 and a minituber induction procedure on stem segments have been described. Chromosome counts on 92 adventitious shoots showed that 85% of them had been polyploidized, i.e., 71% were diploid, 1% tetraploid, and 13% were mixoploid. Cytophotometric studies on nuclei of soil grown tubers of tetraploid cv Astarte, of 1x, 2x and 4x adventitious shoots of H7322, and of diploid H2578 showed in all cases polyploidization with prominent classes up to 8C and 16C. However, nuclei of pith cells of 5 weeks old minitubers which had developed on monoploid H7322 itself or on 1x adventitious shoots of H7322 showed predominantly 1C and 2C values. Pith cells of minitubers of monoploid H7322 were screened, after iodine staining, for the presence of variant cells containing reddish-brown staining (amylose-free) starch. In more than 75% of the investigated minitubers one or a few of such variant cells were found indicating that such a variation occurs in minitubers of monoploid potato and that this variant character is expressed in cells of vegetative storage organs like potato tubers.

Linkage of downy mildew resistance genes Pd1 and Pd2 from Allium roylei Stearn in progeny of its interspecific hybrid with onion (A. cepa L.)

SummaryMale meiosis of the interspecific hybrid between Allium roylei and A. cepa is undisturbed relative to its parents. Based on meiotic data, A. roylei is concluded to be a closer relative of A. cepa than A. fistulosum. Segregation ratios for downy mildew resistance among BC1 and F2 progenies from the F1 between A. roylei and A. cepa indicate the presence of two dominantly inherited, weakly linked nuclear resistance genes, Pd1 and Pd2, in A. roylei (recombination frequency 0.32±0.03). Presumably Pd1 and Pd2are the first genes described in Allium residing in one linkage group. The prospects of exploiting A. roylei in onion breeding seem very promising.

Independent segregation of two isozyme markers and inter-plant differences in nuclear DNA content in the interspecific backcross (Allium fistulosum L. × A. cepa L.) × A. cepa L.

SummaryFrom backcrosses of three interspecific hybrids (A. fistulosum x A. cepa) with a. cepa 14 diploid and 2 triploid plants were recovered.In this BC1 population introgression of A. fistulosum genetic material into the A. cepa nuclear genome was studied using two isozyme markers: Got-1 and Got-2. Both loci carried two alleles. A. cepa was monomorphic for both markers. A. fistulosum was polymorphic for Got-2. Based on their Got isozyme pattern seven out of the 14 diploid BC1 plants had a recombinant genotype. The loci appeared to be unlinked. Differences were observed in nuclear DNA contents between the diploid BC1 plants, indicating that gametes produced by the interspecific hybrids contained different combinations of chromosomal material from A. cepa and A. fistulosum.

High recombination between the breakpoint of a reciprocal translocation in rye (Secale cereale L.) and an interstitially located gene

SummaryThe recombination fraction between the interstitially located gene an and interchange 303 of rye was found to be 0.244±0.038 in a test cross using the translocation as the male parent. In first metaphase translocation configurations in pollen mother cells of the same plant, the chiasma frequency between an and the translocation breakpoint was found to be significantly more than twice the recombination fraction. Recombination was concluded to be masked by a difference in the alternate frequency between configurations without interstitial chiasmata and configurations with interstitial chiasmata, the effect of the first type being of major importance. Random centromere orientation of translocation multivalents with interstitial chiasmata was concluded to be a realistic assumption. The exceptionally high recombination between an and translocation 303 is discussed. Consideration is also given to the use of interchanges in the establishment of a markers chromosomal position, and to the use of translocation chromosomes in balanced systems for hybrid breeding purposes.