G. M. Halloran

Evaluation of Brassica genotypes for resistance to shatter. I. Development of a laboratory test

SummaryA new test procedure for measuring shatter-resistance of siliquae of Brassica spp. is described. A siliqua with its proximal end clamped is loaded as a cantilever in a testing machine. The maximum bending moment, the corresponding stiffness and the energy to cause the siliqua to rupture were taken as measures of the resistance of the siliqua to shatter. Studies showed that ranking of accessions based on either bending moment or energy closely approximated the rankings based on observations of field shatter. A reasonably high significant negative correlation was found between percentage of shattered siliquae and both bending moment and energy (r=−0.595 and −0.531 respecitvely, P=0.001). The above results indicated that bending moment and energy could be used as criteria in evaluating rapeseed genotypes for shatter-resistance in breeding programmes.

The influence of high-molecular-weight subunits of glutenin from Triticum tauschii on flour quality of synthetic hexaploid wheat

Peak dough development times, test-bake loaf volumes and levels of non-polar and polar lipids were measured for flours from newly-synthesised hexaploid wheats obtained from crosses between Triticum turgidum conv. durum cultivars and T. tauschii accessions differing in high-molecular-weight (HMW) glutenin subunits. Synthetic hexaploids possessing subunits 5 and 10 of glutenin had longer peak dough development times and higher loaf volumes when compared with subunits 2 and 12. Using chloroform extraction, a higher ratio of non-polar to polar lipids was observed with subunits 2 and 12 compared with 5 and 10 after correcting to a constant flour protein level. The influence of the newly-identified HMW subunits combinations 2, T1, T2 and subunits 2·1, 10·1 on flour and dough properties are also reported.

Variation in high molecular weight glutenin subunits in landraces of hexaploid wheat from Afghanistan

SummaryVariation for high molecular weight (HMW) glutenin subunits is reported in Afghan hexaploid wheat landraces from different locations in the country ranging in altitude from 395 to 3170 metres. The variation appeared to be independent of the altitude and geographical location of the landraces. Studies of a number of samples from each of five sites revealed that at some sites there was allelic variation at theGlu-A1 andGlu-B1 loci coding from HMW glutenin subunits, but there was no variation at theGlu-D1 locus within and between sites.

Inheritance of supernumerary spikelets in wheat

SummaryThe inheritance of supernumerary spikelets was found to be controlled by two recessive genes with evidence for the possibility of a repressor(s) in crosses between normal and supernumerary spikelet wheats.In experimental lines with phenotypically normal heads but possessing the recessive supernumerary spikelet gene(s), increases in the number of nodes on the rachis (and hence the number of normal spikelets) fertility and grain number per head were found, as well as in the ‘normal’ Australian and American wheat cultivar Phoenix. This attribute has previously been suggested to be a way of increasing spikelet number in future wheat breeding.

The influence of certain chromosomes of the hexaploid wheat cultivar Thatcher on time to ear emergence in Chinese Spring

SummaryThe influence of vernalization on days to ear emergence in hexaploid wheat (Triticum aestivumL. em. Thell.) was examined in five Chinese Spring/Thatcher (CS/T) chromosome substitution lines. CS/T 5A and 5D were similar to normal Chinese Spring in days to ear emergence after all periods of vernalization while CS/T 3B and 5B were similar after some, but significantly earlier after other periods of vernalization When compared with Chinese Spring. In both the unvernalized condition and when vernalization did not limit development rate CS/T 7B was faster to ear emergence than Chinese Spring. These results are discussed in relation to the known chromosomal and genetical control of vernalization response.

Evaluation of Brassica genotypes for resistance to shatter. II. Variation in siliqua strengh within and between accessions

SummaryWithin-plant variation in strength of the siliquae, studied in seven Brassica accessions, appears to be mostly associated with variation in size, rather than the position of the siliquae in the infructescence. Position and strength did not show correlated variation in three accessions where the position of the siliqua in the infructescence appeared to significantly influence its strength (adjusted for the effect of size). There was significant variation in strength between plants within accessions. Considering the above results, variation between siliquae from the same accession could be reduced by sampling siliquae of average size as represented by length. When comparing accessions, a few siliquae from many plants would provide a more representative sample than many siliquae from few plants. Use of strength measures adjusted for the size of the siliquae (bending moment/length2 and energy/length) would enhance the accuracy of estimation of inherent shatter-resistance. A minimum of three to six tests per accession appeared to be necessary for satisfactory evaluation of shatter-resistance.

Genetic analysis of hexaploid wheat, Triticum aestivum using intervarietal chromosome substitution lines—protein content and grain weight

SummaryThe 21 intervarietal chromosome substitution lines of the cultivar Hope in Chinese Spring were used to analyse the genetic differences between the two cultivars Hope and Chinese Spring in grain protein content and grain weight.Only one chromosome of ‘Hope, 5D’, significantly influenced grain protein content of ‘Chinese Spring’. Its influence was of only minor effect and was to decrease protein content expression of ‘Chinese Spring’. It has been postulated that the genetic control of protein content, in this instance, is most likely due to many genes each of small effect.Five chromosomes of ‘Hope’ influenced the 1000 grain weight value of normal ‘Chinese Spring’, all increasing its expression. Chromosomes 1A, 4A and 5B were of major effect and 3A and 6A of comparatively minor effect. A minimal estimate of five genes determines the difference in grain size between these cultivars. The possible evolutionary significance of the contribution of the A genome of bread wheat to grain size determination is discussed. On the basis of certain findings of this study, proposals are made for breeding for increased grain size in hexaploid wheat.

Variation in developmental patterns of wild barley (Hordeum spontaneum L.) and cultivated barley (H. vulgare L.)

SummarySix wild barley (Hordeum spontaneum) accessions, from a diverse range of habitats, and two spring-cultivated barleys, were examined for variation in durations of development phases. The durations of the leaf initiation and spikelet initiation phases were longer and spikelet growth phases shorter, in wild than in cultivated barley. Across all wild and cultivated barleys the rate and duration of spikelet initiation were negatively correlated, but neither was related to the number of spikelets per spike. The number of spikelets was positively correlated with the number of leaves and the ratio of the number of spikelets to the number of leaves declined with increasing time to anthesis, indicating that each successive leaf was associated with a diminishing increase in the number of spikelets. The duration of culm elongation and final culm length were shorter in accessions of cultivated barley compared with wild barley. This paper also discusses the feasibility for increasing the number of spikelets per spike through breeding for genetic changes in lengths of pre-anthesis phases of development.

Transfer of high kernel weight and high protein from wild tetraploid wheat (Triticum turgidum dicoccoides) to bread wheat (T. aestivum) using homologous and homoeologous recombination

SummaryWheat pentaploids were produced by hybridizing a high kernel weight (1000 grain wt=56 g), high protein (25.4%) line of wild tetraploid wheat (Triticum turgidum dicoccoides) as male parent, with the three hexaploids (T. aestivum) — normal Chinese Spring and its two homoeologous pairing mutants, ph1b and ph2. The pentaploids were crossed as female parents to the two commercial hexaploid cultivars Warigal and Barkaee and 42-chromosome stable plants selected from the F1 of the pentaploid x hexaploid crosses.Mean protein content of certain F3 lines from all six pentaploid x hexaploid crosses was significantly higher than Chinese Spring and the respective commercial hexaploid parent (p<0.005) indicating high protein had been transferred from the tetraploid to the hexaploid level.Kernel weight amongst certain F3 lines of the three pentaploids x Barkaee was significantly (p<0.0005) higher than either Chinese Spring or Barkaee, indicating the transfer also of high kernel weight from the tetraploid to the hexaploid level. However kernel weight was not significantly increased over Warigal in any F3 lines of its crosses with the three pentaploids.High levels of homoeologous chromosome pairing in the ph-mutant pentaploids, plus evidence for significant modification of the composition of high-molecular weight (HMW) glutenin subunits of grain protein in certain F3 derivatives of the ph-mutant pentaploid x hexaploid, crosses indicates that the ph-mutant-derived lines may possess novel (intergenome) genetic recombination, at least for high protein, and possibly kernel weight.

Temperature as a component of the expression of developmental responses in wheat

SummaryStudies were made of days to ear emergence under the constant temperatures of 9, 14, 19 and 25°C and 16 h photoperiod in three sets of wheat lines each possessing genotypes differing for developmental responses.Days to ear emergence in three near-isogenic lines of the wheat cultivar Triple Dirk, which differed for vernalization response, increased as the strength of the response increased. At the four temperatures Triple Dirk D (Vrn 1 vrn 2) was not significantly different from normal Triple Dirk (Vrn 1 Vrn 2) but Triple Dirk B (vrn 1 Vrn 2) was significantly (P=0.01) later than normal Triple Dirk at each temperature. This indicates that the vrn 1 allele confers stronger vernalization response than vrn 2 over the range of temperatures (9–24°C). However, Triple Dirk C (vrn 1 vrn 2) failed to head after 120 days at each temperature indicating strong interaction between vrn 1 and vrn 2 with each other (and possibly the Triple Dirk back-ground) to give a much stronger vernalization response than predictions from additivity of their individual effects.The second set comprised the four Chinese Spring/Thatcher chromosome substitution lines CS/T 3B, 6B, 7B and 5D, plus Chinese Spring and Thatcher, and were grown in the unvernalized condition. CS/T 5D was similar in days to ear emergence as Chinese Spring at all four temperatures but the other three lines were earlier to ear emergence, particularly as the temperature increased. Days to ear emergence was fastest at 14°C in all lines, except CS/T 3B, in which it decreased progressively from 9 to 24°C.The third set of Chinese Spring and Thatcher and the homoeologous group 2 chromosomes of Thatcher substituted in Chinese Spring, the group which is considered to be involved in the control of photoperiod sensitivity. The three substitution lines responded differently to temperature compared with Chinese Spring and with each other, with chromosome 2D being the least, and chromosome 2B the most, responsive to temperature.