D. R. Marshall

Variation in epicuticular wax content in wheat.

SummaryCultivars of common wheat (Triticum aestivum L.) and durum wheat (T. turgidum L. var. durum) were evaluated for epicuticular wax content and its relationship with spectral reflectance. Epicuticular wax is associated with drought tolerance. Highly significant differences (1.51 to 2.80 mg/dm2) were found in the amount of epicuticular wax (EW) among the cultivars. Water stress significantly enhanced the level of EW. EW content under stress and control conditions were positively correlated (r=0.85, p<0.01) suggesting that selection for this trait could be practised in either environment. Surface reflectance was reduced when the waxy layer from the leaf was removed with chloroform. The reduction for the abaxial surface was twice that for the adaxial surface indicating that the abaxial surface was more waxy than the adaxial one. The mean reduction (both surfaces) termed ‘δ’ was positively correlated with the amount of EW (r=0.59, p<0.01).

Hydroxamic acids in cereal roots inhibit the growth of take-all

Abstract 2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) was the only hydroxamic acid (Hx) found in wheat ( Triticum aestivum ) roots, whereas both DIMBOA and 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) were present in the roots of triticale ( Triticosecale ) and rye ( Secale cereale ). The Hx content of wheat, triticale and rye roots was highest in the apices. Growth of two isolates of the fungus Gaeumannomyces graminis var. tritici ( Ggt ), which causes the root disease take-all, was inhibited when extracts prepared from triticale and rye roots were incorporated into nutrient media. Similar extracts from two cultivars of wheat did not inhibit the growth of Ggt . When Hx were incorporated individually into nutrient media, DIBOA inhibited the growth of Ggt at concentrations as low as 0.5 mM, whereas 1 mM DIMBOA was required to inhibit fungal growth. The decomposition products of DIBOA and DIMBOA, 2(3)-benzoxazolinone (BOA) and 6-methoxybenzoxazolinone (MBOA), respectively, were less potent inhibitors of Ggt growth than the corresponding parent Hx. The effects of the Hx at concentrations up to 5 mM were only fungistatic, as growth of the colonies resumed when they were transferred to Hx-free media. The inhibition of Ggt growth by extracts of triticale and rye is attributed to the presence of DIBOA.

Field screening ofPisum accessions to evaluate their susceptibility to the pea weevil (Coleoptera: Bruchidae)

SummarySeventeen unreplicated field trials over nine sites and four years were used to classifyPisum germplasm (P. sativum L. &P. fulvum Sibth. & Sm) as potential sources of resistance to the pea weevil,Bruchus pisorum (L.). The emergence of adult weevils from <10% of harvested seed was used as the selection criterion to indicate possible resistance. A total of 1900Pisum accessions were assessed using the field trials and 1754 of theP. sativum accessions were eliminated. However in the 18P. fulvum accessions screened, the level of infestation by pea weevil was always below the arbitrary resistance threshold selected. This suggests thatP. fulvum accessions could be a valuable source of resistance to the pea weevil.

Starch Extraction and Amylose Analysis from Half Seeds

To allow genetic analysis of starch quality in wheat and its relatives, it was necessary to develop techniques suitable for use on endosperm halves of seeds, leaving the embryo half to be grown for the next generation. Seeds were split and the endosperm end was crushed and soaked in 0.5 M NaCl overnight. The solids were ground three times in 0.5 M NaCl, the supernatant starch slurries were pooled and washed through a series of 4 M NaCl, 6 M NaCl/50 %, sucrose, 2 % sodium dodecyl sulphate solution, and acetone before being dried over silica gel. Subsamples of 1 mg of starch were dispersed in ethanol in preweighed microfuge tubes, gelatinised in NaOH solution, diluted to constant concentration, and aliquots were neutralised with citric acid, stained with iodine, diluted with water, and evaluated in an ELISA plate reader at 620 nm. The overall method provided cleaner starch than earlier methods, as shown by higher apparent amylose values, and was highly repeatable. The method was used to demonstrate the variation in amylose content within single heads of an inbred tetraploid wheat. No consistent patterns of variation due to seed location were detected but the overall breadth of variation around the median value of 27 % was ± 5 %.

Effects of dwarfing genes on yield and yield components under irrigated and rainfed conditions in wheat (Triticum aestivum L.)

SummaryNear-isogenic tall (no dwarfing gene), semidwarf (Rht1 or Rht2) and dwarf (Rht1 + Rht2 or Rht3) spring wheat lines were evaluated for yield and yield components under irrigated and rainfed conditions. Under irrigated conditions, the dwarf and the semidwarf lines exhibited a significant yield advantage over the tall lines. Under rainfed conditions, the semidwarf lines outyielded the tall as well as the dwarf lines. Percent yield reduction in response to drought stress was highest with the dwarfs and lowest with the tall lines. Dry matter production of the tall lines and that of the semidwarf lines did not differ significantly and both produced significantly more dry matter than the dwarf lines under irrigated as well as rainfed conditions. Plant height and kernel weight decreased with increasing degree of dwarfness while number of kernels per spikelet, harvest index and days to heading increased under both moisture regimes. The dwarfing genes did not have any significant influence on number of tillers/m2 and spikelets per spike in either moisture regime.

Evaluating faba beans for rust resistance using detached leaves

A method was developed for testing detached leavesof faba beans for their response to rust disease.Leaves 5 to 8, counting from the shoot tip, wereexcised and maintained on a water-retaining medium,with 5 ppm gibberellic acid, in an enclosed box in atemperature-controlled glasshouse. Leaves treated inthis way remained in good health for up to 30 days.Rust spores were dispersed in a slurry of talc andwater and applied to the abaxial leaf surface. Diseasedevelopment of seven rust populations, collected fromseveral locations in eastern Australia, was monitoredfor 15 days on eight faba bean accessions. Fouraccessions were BPL lines which ICARDA claimed to havesome resistance, two were ILB lines from ICARDA whichhad been found to have stronger field resistance innorthern New South Wales, Australia, and the remainingtwo were known susceptibles. The detached-leaf testshowed that the two cultivars were susceptible, thefour BPL lines were intermediate and ILB 3107 and ILB3025 were slow-rusting. One rust population, which hadbeen stored under liquid nitrogen for several years,was less effective at inducing disease symptoms thanthe other six, which were all freshly collected. Theinteractions between host accessions and rustpopulations were statistically significant but minor,as the cultivars remained in their categories ofresistance or susceptibility. The detached-leaftechnique is thus suitable for use in screeningindividual plants for reaction to several differentpathogen species or genotypes without danger ofcross-contamination or induced resistance.

OPTIMIZATION OF CULTURE CONDITIONS FOR IMPROVED PLANT REGENERATION EFFICIENCY FROM WHEAT MICROSPORE CULTURE

The production of haploid plants through microspore culture is a very important tool for plant breeding. However, progress in microspore culture for many species has been hampered by a number of factors that have resulted in low recovery of regenerated green plants. In this study, a series of experiments were conducted to increase the regeneration of haploid green plants from isolated wheat microspores. The use of different basal media and variations in media components resulted in the increased recovery (approximately double) of regenerated haploid wheat plants. Our findings demonstrate that CHB medium, in combination with 2,4-d, was a better medium for embryoids induction and plant regeneration than medium MC17 with either 2,4-d or PAA growth hormones. Wheat microspores cultured without ovary co-cultivation did not respond. Furthermore, high efficiency of microspore derived embryoids (up to 296 MDEs per 100 anthers) and green plant regeneration (up to 71 green plants per 100 anthers) were achieved by the use of gelrite instead of agarose as a gelling agent, and by the addition of media additives such as spent medium or MET.

Amylose Content in Segregating Populations of Einkorn, Emmer, and Rye

Two F2 populations of Triticum monococcum (einkorn), ten of T turgidum (emmer), and 39 of Secale cereale (rye) were produced and the amylose content of the endosperm halves determined in up to 50 single seeds per population. The apparent amylose contents extended from 1.3 to 28.5 % in T. monococcum, 7.2 to 38.0 % in T. turgidum, and 0.0 to 52.3 % in S. cereale. Small F3 families were examined from two zero-amylose and one 33 %-amylose rye seeds; the low-amylose families showed amylose values from 14.9 to 28.7% but the high-amylose family had 21.0-37.8% amylose. Genetic gain was therefore easier to demonstrate for higher amylose than for lower amylose content. Part of this difference may have been attributable to the genetics of amylose content demonstrated in the various F2 families. In general, higher amylose was dominant to lower amylose content, with a 3:1 ratio being found in many families. In other families, the amylose content was more additive, with a 1:1:1:1 ratio being found in some and its modification to 1:1 in others. In one tetraploid family, high amylose was apparently recessive to low amylose content, with a 1:3 ratio. The breadth of variation in most families suggested that minor genes and modifiers determined amylose content. Significant genetic variation for amylose content was therefore demonstrated in three agriculturally and evolutionarily important species. Further progress towards enhanced amylose contents to suit particular end-uses should be possible in wheats and ryes.

Derivation of superior F5 lines from heterotic hybrids in pea

SummaryF5 seeds from six highly heterotic F1 hybrids were produced to determine whether the superior performance of F1 hyrids could be fixed in pure-line derivatives of pea (Pisum sativum L.). For each cross, 24–31 F5 lines derived from single seed descent were compared with F1 hybrids and their parents in two environments. The F1 hybrids out-yielded the best parent by up to 11%. All crosses produced F5 lines which were as high in yield as the F1 hybrids indicating that pure-line derivatives equivalent in yield to the heterotic F1 hybrid could be developed by conventional breeding. Heterosis of the F1 hybrids over the best commercial cultivar was thus a useful indicator of the future performance of the pure-line derivatives. These results indicate that overdominance was not an important component of heterosis in peas.

Starch characterisation and variability in GBSS loci of synthetic hexaploid wheats and their durum and Aegilops tauschii parents

Greater variability in starch properties is found in lower ploidy wheats than in commercial hexaploid wheats. This paper reports on the starch properties and variability in granule bound starch synthase (GBSS) loci of 17 diploid (Aegilops tauschii) and 12 tetraploid (durums) potential progenitors of wheat, compared with 29 synthetic hexaploid wheats produced from such progenitors. Starch properties examined were granule size distribution, swelling power, amylose content, gelatinisation and amylose-lipid dissociation properties. A PCR screening method was able to detect the presence or absence of each of the three GBSS genes. It also detected polymorphisms in eight diploids and nine hexaploids, all displaying the same 25 bases deletion in the D genome allele of GBSS. Two tetraploids and five hexaploids were null 4A for GBSS. There was little difference in the amylose contents and amylose-lipid dissociation peak temperatures of the synthetic hexaploids and the lower ploidy wheats. The synthetic hexaploids showed intermediate swelling power values with the durums giving the highest swelling powers. The durums also had higher B granule contents than the A. tauschii accessions, but not as high as the synthetics. However, the A. tauschii samples gave the highest gelatinisation peak temperatures. The presence of the null 4A mutation was positively correlated with swelling power, amylose content and DSC measurements. The new smaller D genome allele of GBSS was associated with slightly higher swelling power. These results confirm the value of wheat progenitor lines as sources of new starch properties for hexaploid wheat.