Breeding behaviour of Kunzea pomifera (Myrtaceae): self-incompatibility, intraspecific and interspecific cross-compatibility.

To examine breeding system characteristics of the endemic Australian prostrate shrub Kunzea pomifera, artificial hybridisations were undertaken using thirteen different genotypes of K. pomifera, to elucidate: (1) self-incompatibility, (2) intraspecific cross-compatibility in the species and (3) interspecific cross-compatibility with each of K. ambigua and K. ericoides. K. pomifera exhibited very low self-compatibility, with the barrier to self-fertilisation being prevention of pollen-tube growth in the style or ovary. Following intraspecific pollination amongst a number of different genotypes of K. pomifera, 38.4% of pollinated flowers developed fruit; arrest of compatible pollen-tubes in the style, preventing fertilisation, contributes to the low fruit set in this species. Interspecific compatibility was examined between K. pomifera (pistillate parent) and K. ambigua (staminate parent) where seed set per pollinated flower (4.47) was not significantly different from intraspecific crosses (4.66). In crosses between K. pomifera (pistillate parent) and K. ericoides as staminate plant, 0.037% of pollinated flowers produced fruit, with 0.0075 seeds per pollinated flower. Reproductive barriers between these two species were evident in the style of K. pomifera, where the growing tips of the K. ericoides pollen-tubes swelled and ceased to grow.

Genetics of virulence in Leptosphaeria maculans (Desm.) Ces. et De Not., the cause of blackleg in rapeseed (Brassica napus L.).

The genetic basis of virulence of 24 isolates of L. maculans collected from various sites throughout south-eastern and south-western Australia were studied using five clone-lines of B. napus. The experimental design allowed the estimation of the environmental and genetic components of variance using a standard analysis of variance. Virulence of these isolates (as measured by the percentage of stem girdling, %G) on the clonelines NCII and Tap was found to be most likely controlled by a small number of genes; the broad-sense heritabilities were 79.7% and 67.5% for virulence on NCII and Tap, respectively. The significance of these results in relation to the potential of L. maculans in adapting to new resistant B. napus cultivars is discussed.

The genetics of blackleg [Leptosphaeria maculans (Desm.) Ces, et De Not.] resistance in rapeseed (Brassica napus L.) : I. Adult-plant resistance in F2 and first-backcross populations.

The genetic control of adult-plant blackleg [Leptosphaeria maculans (Desm.) Ces. et De Not.] resistance in rapeseed (Brassica napus L.) was studied in the F2 and first-backcross populations of the cross "Maluka" (blackleg-resistant) x "Niklas" (highly susceptible). A L. maculans isolate possessing high levels of host specificity (MB2) was used in all inoculations. Resistance/susceptibility was evaluated using three separate measures of crown-canker size, i.e. the percentage of crown girdled (%G), external lesion length (E) and internal lesion area (%II). Disease severity scores for the F2 and first-backcross populations based on E and %II gave discontinuous distributions, indicating major-gene control for these measures of resistance; but those for %G were continuous, indicating quantitative genetic control for this measure. Chi-square tests performed on the (poorly-defined) resistance classes, based on E, in the F2 and first-backcross populations indicated the likelihood for resistance being governed by a single, incompletely dominant major gene. Although the distributions of the F2 and first-backcross populations, based on%II, were clearly discontinuous, the observed segregation ratios for resistance and susceptibility did not fit any of the numerous Mendelian ratios which were considered. Differences in inheritance of resistance according to the assessment method and blackleg isolate used, were discussed.

The genetics of blackleg [Leptosphaeria maculans (Desm.) Ces. et De Not.] resistance in rapeseed (Brassica napus L.) : II. Seedling and adult-plant resistance as quantitative traits.

Inheritance studies of seedling and adult-plant resistance to blackleg [Leptosphaeria maculans (Desm.) Ces. et De Not.] in rapeseed (Brassica napus L.) were conducted using 49 families derived by intercrosses between 14 randomly chosen F2 plants from the cross cv "Maluka"(resistant) cv "Niklas" (susceptible), conforming to the North Carolina mating design II (NCM-II). Four concurrent experiments were performed, where plants from each family were: (I) Spray inoculated with a 10(5) pycnidiospores/ml suspension 10 days after germination and assessed 2-weeks later for cotyledon-lesion development, (II) As for (I), but assessed 12 weeks after inoculation for crown-canker development, (III) Wound-inoculated on the stems at growth stage 2.4-2.5 on the Harper and Berkenkamp scale and assessed for crown-canker development 5 weeks after inoculation, and (IV) Spray inoculated at growth stage 2.3-2.4 with a 10(5) pycnidiospores/ml suspension and assessed for crown-canker development nine weeks after inoculation. A L. maculans isolate possessing high levels of host specificity (MB2) was used in all inoculations. Seedling resistance was evaluated using a 0-5 cotyledon-lesion severity scale. Adult-plant resistance/susceptibility was evaluated using three separate measures of crown-canker size, i.e. the percentage of crown girdled (%G), external lesion length (E) and internal lesion area (%II). Quantitative genetic analysis of blackleg resistance using the NCM-II design revealed significant non-additive genetic variances for all measures of disease severity, in all four experiments, indicating the presence of strong dominance/epistasis at loci controlling blackleg resistance. The resistance to crown-canker development, after wound-inoculation of the stem, was found to possess the highest ratio of additive to non-additive genetic variance. Crown-canker development in mature plants of the NCM-II population was not related to the degree of cotyledon-lesion development at the seedling stage, indicating the limited value of the cotyledon test in screening for adult-plant blackleg resistance. The implications of these findings to breeding for resistance to blackleg in rapeseed are discussed.

The genetics of adult-plant blackleg (Leptosphaeria maculans) resistance from Brassica juncea in B. napus.

The genetic control of adult-plant blackleg (Leptosphaeria maculans) resistance in a Brassica napus line (579NO48-109-DG-1589), designated "R13" possessing Brassica juncea-like resistance (JR), was elucidated by the analysis of segregation ratios in F2 and F3 populations from a cross between "R13" and the highly blackleg-susceptible B. napus cultivar "Tower". The F2 segregration ratios were bimodal, demonstrating that blackleg resistance in "R13" was controlled by major genes. Analysis of the segregation ratios for 13 F3 families indicated that blackleg resistance in these families was controlled by three nuclear genes, which exhibited a complex interaction. Randomly sampled plants of F3 progeny all had the normal diploid somatic chromosome number for B. napus. The similarities between the action of the three genes found in this study with those controlling blackleg resistance in B. juncea is discussed.

Variation in salinity tolerance and ion uptake in accessions of brown beetle grass [Diplachne fusca (L.) Beauv.].

Significant variation in tolerance was found in natural populations of Diplachne fusca (L.) Beauv, grown under a range of NaCl concentrations, with greatest variation in accessions from different sites and a narrower range of tolerance from those within sites. Significant differences were found between accessions for Na, Cl and K uptake. Ma and Cl concentrations were found to be higher in sheaths than in leaf blades, indicating that D. fusca has the capacity to sequester high levels of Na and Cl in the sheath away from the leaf blade as well as maintaining a high selectivity for K. over Na. The salinity level of the site from which an accession was collected did not show any correlation with the salt-tolerance of that accession. While D. fusca was found generally to be highly tolerant of NaCl (with plants surviving at 400 mol m-3 NaCl) there was variation in tolerance in its natural populations, indicating the potential for selecting to increase tolerance further.

Phylogenetic relationships of Triticum tauschii, the D genome donor to hexaploid wheat : 3. Variation in, and the genetics of, seed esterases (Est-5).

Isoelectric focusing of seed esterase (Est-5) isozymes in 79 T. tauschii accessions from diverse sources revealed the presence of six different seed esterase phenotypes. In one of these phenotypes, exclusive to a var. meyeri accession (AUS 18989), no detectable enzymatic activity was observed. Segregation in crosses between T. tauschii (D(t)) accessions confirmed three of the seed esterase phenotypes to be alleles of the designated Est-D (t)5 gene locus; the inheritance pattern of these isozymes was not affected by the subspecies differences between the parents. On the bases of variation in Est-5 and their Glu-1 and Gli-1 gene loci (in a previous study in this series), only three strangulata accessions showed consistent homology with their prevalent gene expression in the D genome of hexaploid wheat. The implications of these observations for further interpreting the phyletic nature of the D genome donor in natural hexaploid wheat synthesis are also reported.

Evidence for AEGILOPS SHARONENSIS Eig as the Donor of the B Genome of Wheat.

A number of lines of evidence are advanced for the candidacy of Aegilops sharonensis Eig as the donor of the B genome of wheat. The cytoplasm of Ae. sharonensis is compatible with tetraploid wheat Triticum turgidum dicoccoides, as evidenced by the high level of chromosome pairing and fertility of the amphiploid Ae. sharonensisxT. turgidum dicoccoides. Ae. sharonensis chromosomes exhibit high levels of pairing with those of the B genome of wheat in hybrids with Ph-deficient hexaploid wheat and low levels of homoeologous pairing with T. monococcum chromosomes.--The amphidiploid between Ae. sharonensis and T. monococcum is very similar to T. turgidum dicoccoides in spike, spikelet and grain morphology. The karyotype of Ae. sharonensis resembles more closely that of extrapolated B genome karyotypes of wheat than do the karyotypes of other proposed B-genome donor species of Aegilops. Because of distinctiveness in cytological affinity and karyotype morphology between Ae. sharonensis and Ae. longissima, a separate genome symbol S(sh) is proposed for the former species.

Genetic analysis of grain protein percentage in wheat.

Diallel analysis techniques were used to study the genetic basis of grain protein percentage expression in wheat using eight wheats ranging from high to low in grain protein percentage and assumedly genetically diverse for this character.The F2 set of crosses exhibited strong genetic interaction for protein percentage attributable greatly to the general behaviour of Argentine IX, of high grain protein percentage, in combination with the other seven wheats. Removal of its interaction revealed additive genetic variance and moderately strong overdominance averaged over the crosses of the remaining seven parents.In the F3 and F4 generations grain protein content exhibited additive genetic variance with evidence of some non-allelic interaction in the F3. The F3 exhibited partial dominance in the inheritance of protein percentage while in the two F4 trials in different environments one exhibited a strong degree of average dominance and the other exhibited only a small degree of average dominance over all arrays.Close correspondence in the order of ranking of protein percentage of the lines (parents and hybrids) in the two F4 trials in two different environments, indicated a significant influence of genotype on the expression of this character in wheat. However, sharp differences in the nature of inheritance of high grain protein percentage between the two environments, whether by dominant or recessive genes, indicates the magnitude of the influence of the environment on its genetic expression in populations segregating for this character.

Genetic analysis of plant height in wheat.

Genetic studies of plant height were made of 8 wheats and the 28 crosses between them using the diallel method of analysis. The inheritance of plant height in a glasshouse-grown F1 diallel set in which vernalization and photoperiodic responses had been removed, indicated close to complete dominance in its expression. A similar F1 set of crosses in the field environment indicated non-allelic interaction in its expression, attributable mainly to the cultivar Chile 1B generally in its crosses with the other 7 wheats. Its removal gave close to complete average dominance in the inheritance of plant height.In the F2 generation in the field its inheritance was again subject to non-allelic interaction, attributed mainly to Chile 1B which, on removal, gave a situation of average partial dominance in height expression.Standardized deviations of Yr and (Wr + Vr) for plant height for the diallels indicated a resonably close association of tallness with dominance and shortness with recessiveness.Frequency distributions of plant height in the F1 and F2 of two crosses from the diallel confirmed certain findings of the diallel analysis.At least two groups of dominant genes were found to influence plant height expression in the crosses of the diallel ; this number must be regarded as a minimal estimate of the number of genes influencing plant height in wheat.