Items from Australia.

ITEMS FROM AUSTRALIA

 

THE UNIVERSITY OF ADELAIDE

Grain Biochemistry Group, Waite Campus, Plant Science, Glen Osmond, SA 506, Australia.

 

Daryl Mares, Kolumbina Mrva, Robert Asenstorfer, Imelda Soriano, Judith Rathjen, and Michael Quinn.


Research interests. [p. 13]

  • Biochemistry and genetic control of factors that cause deterioration of wheat quality prior to harvest (preharvest sprouting and tolerance to preharvest sprouting, grain dormancy, late-maturity alpha-amylase, and black point).
  • Biochemical and genetic control of color and color stability in Asian noodles (grain and flour constituents involved in color of wheat flour and color and color stability Asian noodles, xanthophylls, flavonoids, polyphenol oxidase, peroxidase, lipoxygenase, and nutritive aspects of cereal xanthophylls, lutein and lutein esters).
  • Durum germ plasm with tolerance to hostile soils and root diseases and better adaptation to southern Australia.


Recent research. [p. 13-14]

We have focused on synthetic hexaploid wheats derived by crossing T. turgidum subsp. durum with Ae. tauschii. Over the past 4Ð5 years, around 400 synthetics have come into Australia primarily from the CIMMYT program in Mexico. This material is seen as a rich source of new genetic variation particularly for resistance to biotic and abiotic stresses. The lines have been screened for a range of biochemical traits related to color and color stability of Asian noodles (polyphenol oxidase, lipoxygenase, peroxidase, and flavonoid content) and for late-maturity alphalpha-amylase since early tests suggested that synthetics contained a high incidence of this defect.

Polyphenol oxidase (PPO). More than 30% of the primary synthetics surveyed were ranked as very low or near zero, significantly lower than the observed range for Australian bread wheat cultivars some of which are already regarded as low. Grain of these genotypes showed little or no discoloration of the seed coat even when incubated in the PPO substrate for 24 hours. By comparison, 60% of local and CIMMYT durums also were very low. A random selection of 50 Ae. tauschii from the Australian Winter Cereals Collection (AWCC) ranged between near zero and low with approximately 50% being equivalent to the near zero synthetics and durums. As with the very low PPO synthetic lines, the grains of very low PPO Ae. tauschii did not discolor even after prolonged incubation in substrate. Interestingly, parallel research and routine surveys of germ plasm from wheat-breeding programs identified two breeding lines from the wheat-breeding program at Australian Grain Technology in South Australia and an EMS-mutant that had PPO phenotypes substantially lower than the current benchmark cultivars. This material ranked midway between the lowest commercial cultivars such as Sunco, Lang, and Krichauff and zero.

Lipoxygenase (LOX). Compared with PPO, there were few primary synthetics with very low LOX. Several lines, however, were significantly lower than conventional bread wheats, in particular lines where the durum parent in the pedigree was 'Gaza / Boy'. LOX activity varied from 0.07U/g to 1.6U/g, with a mean for the collection of 0.8U/g. Very low LOX activity was more common among Australian and CIMMYT durums with 15% being less than 0.1. Interestingly, a random sample of cultivated durums from the AWCC that included many European and African cultivars gave a bimodal distribution with approximately one half similar to the Australian and CIMMYT durums and the other half in the range 0.6 to 1.1U/g. Bread wheats ranged from 0.2 to 1.5 U/g, similar to the primary synthetics with a mean of 0.8U/g. In addition to the germ plasm collections, a population derived by crossing a very low LOX durum, Kamilaroi, and the low LOX bread wheat, Sunco, was screened. A small number of lines with a bread wheat phenotype combined with the very low LOX typical of Kamilaroi were identified.

Flavonoid content. For this trait, the aim is to identify germ plasm with high flavonoid content, because these compounds turn yellow in the presence of alkali and make a significant contribution to the yellow color of alkaline noodles (Asenstorfer et al. 2006). Frequency distributions were compared with a collection of durums and wild tetraploids. The means for the primary synthetics, durums, and Ae. tauschii lines were all significantly less than the mean for current bread wheats. Despite this, there were a small number of tetraploid and Ae. tauschii lines whose grain flavonoid contents were greater than the highest bread wheat and there may be some value creating new synthetics using this material as parents.

Late maturity alphalpha-amylase (LMA). More than 90% of the primary synthetics developed LMA during grain ripening and of these about half had extreme levels of alphalpha-amylase normally only seen in wheats lacking semidwarfing genes Rht1 or Rht2. Most of the primary synthetics were tall to very tall in height, despite the presence of Rht1 from the durum parent, and when a subset was compared with and without the cool temperature shock treatment normally required for good expression of LMA there was no significant difference in grain alphalpha-amylase activity at ripeness. Secondary or derived synthetics showed a similar frequency distribution to primary synthetics but in this group proportion of individuals with a low to zero LMA ranking (around 65%) was a much higher. Approximately 30% were ranked as high-LMA similar to tall LMA-prone wheat cultivars. Some Australian durum cultivars were also found to be prone to LMA.

Selection of very low PPO recombinants from a locally adapted bread wheat / primary synthetic cross that lacks LMA. Ripe grain from 1,600 BC1F2 plants were screened for PPO activity and 12 lines identified with PPO phenotype equal to the synthetic parent. The segregation ration approximated to 1 in 128. Three of these lines were further selected for plant type, plant height (semidwarf), and free-threshing habit. All of these lines appeared to be free of LMA following the standard cool temperature shock treatment.

Preharvest sprouting tolerance in white-grained wheats. A severe drought over most of the Australian wheat belt in 2006 ensured that neither preharvest sprouting nor black point were significant problems. We noted in sprouting screening trials, however, that material harvested at harvest-ripeness was more dormant (tolerant to sprouting) than expected. Ranking of cultivars was not affected and the dormancy in genotypes normally considered to be sprouting susceptible disappeared rapidly during after-ripening.

A highly significant QTL on chromosome 4A was associated with dormancy in three wheat genotypes, AUS1408, SW95-50213, and a dormant single gene red genotype, AUS1490, of diverse origin. Flanking SSR markers, gwm269 and barc170, located near the center of the QTL have been validated to two additional populations and should provide near-diagnostic tools for MAS. As previously reported, the phenotype of lines containing the 4A alleles from the dormant parent varied from dormant to intermediate dormant with both the range and absolute values dependent on temperature during grain ripening. As temperature during ripening increased, dormancy decreased, and the range for lines containing the 4A dormancy alleles increased. A DH population, dormant / intermediate dormant, that is fixed for the 4A dormancy allele but varies with respect to putative additional dormancy genes has now been phenotyped in four environments. A new QTL located on chromosome 3B appeared to explain a significant proportion of the variation.

References.

  • Asenstorfer RE, Wang Y, and Mares DJ. 2006. Chemical structure of flavonoid compounds in wheat (Triticum aestivum L.) flour that contribute to the yellow colour of Asian alkaline noodles. J Cereal Sci 43:108-119.
  • Mares DJ, Mrva K, Cheong J, Williams K, Watson B, Storlie E, Sutherland M, and ZouY. 2005. A QTL located on chromosome 4A associated with dormancy in white- and red-grained wheats of diverse origin. Theor Appl Genet 111(7):1357-1364.

 

Publications. [p. 14-15]

  • Asenstorfer RE and Mares DJ. 2006. 4,4Õ-dihydroxy-3,3Õ, 5,5Õ-tetramethoxyazodioxybenzene, and unexpected product formed during extraction of wheat flour with hydroxylamine. Tetrahedron Lett 62:9289-9293.
  • Asenstorfer RE, Kumaratilake A, and Mares DJ. 2007. An inhibitor study of the non-polyphenol oxidase darkening of yellow alkaline noodles. In: Proc 56th Aust Cereal Chem Conf.
  • Mares DJ and Mrva K. 2007. Late-maturity alpha-amylase: low falling number in wheat in the absence of preharvest sprouting. J Cereal Sci (In press).
  • Mrva K and Mares DJ. 2007. Influence of temperature on the expression of late maturity alpha-amylase. In: Proc 56th Aust Cereal Chem Conf.
  • Rathjen JR, Mares DJ, and Strouinina K. 2007. Magnetic micro-imaging of imbibing wheat grains. In: Proc 56th Aust Cereal Chem Conf.
  • Soriano IR, Mares DJ, and Graham RD. 2007. Carotenoid content of rice and stability during storage. In: Proc 56th Aust Cereal Chem Conf.