Juan Moroni

Differential tolerance of high manganese among rapeseed genotypes

Cultivation of crop cultivars resistant to high soil manganese (Mn) may reduce the negative effects of Mn toxicity on crop yield. Three studies were carried out to select Brassica genotypes (B. napus and B. rapa) resistant to high Mn concentration and to characterise the nature of any Mn resistance found. In Experiment 1, 33 B. napus and nine B. rapa genotypes were screened in a sub-irrigated nutrient solution system. Based on visual symptoms and plant size, single plants were identified with resistance to high Mn from within cultivars of four B. napus and one B. rapa. Resistance was also identified in one B. napus doubled haploid genotype. In Experiment 2, a genotype resistant to high Mn and two genotypes (progenies from Experiment 1) sensitive to high Mn were exposed to eight Mn concentrations (9–500 μM) for 2 weeks in nutrient solution. The relative shoot weight (RSW) and the relative root weight (RRW) of the genotype resistant to Mn were significantly greater at ≥100 μM Mn than both genotypes sensitive to high Mn; the sensitive genotypes reacted similarly. The three genotypes had similar tissue Mn contents and the elevated Mn tissue contents did not induce deficiencies of Mg or Fe. In Experiment 3, 12 genotypes (progenies from Experiment 1) were screened in nutrient solution at 9 μM Mn and with an additional 125 μM Mn. The RRW and RSW of the genotypes ranged from 35 to 114 and 39 to 94%, respectively. All the selections sensitive to high Mn had a RSW <60% and thus were confirmed to be Mn sensitive, while all the selections resistant to Mn had a RSW >70% and thus were confirmed as Mn resistant. This evidence confirmed the availability of rapeseed germplasm resistant to Mn toxicity with an ability to withstand high content of Mn through internal tissue tolerance. Also, the observed Mn tolerance in this material is genetically controlled and not an artifact of our screening assays.

Development and allele diversity of microsatellite markers linked to the aluminium tolerance gene Alp in barley

Aluminium (Al) toxicity is one of the main factors restricting barley production in acidic soils. The utilisation of barley cultivars tolerant to Al is one of the most economic strategies for expanding barley production in these soils. Among barley genotypes, the cultivar Dayton has been reported to exhibit the highest level of Al tolerance. The gene conferring Al tolerance in Dayton, Alp, has been mapped to the long arm of chromosome 4H using RFLP markers. However, such markers are not useful for routine marker-assisted selection in breeding programs due to the cost and labour associated with their use. To increase the ease by which marker-assisted selection can be conducted for Alp, we sought to identify microsatellite markers linked to this gene. Several such markers that flank Alp were identified in a mapping population from a cross between Dayton and Harlan Hybrid. The most tightly linked microsatellite markers, HVM68 and Bmag353, flank Alp and are 5.3 cM and 3.1 cM from this locus, respectively. The linkage between Bmag353 and Alp was validated in a separate F3 population derived from the cross between Dayton and F6ant28B48-16, where this microsatellite marker was found to predict the Al tolerance phenotype with over 95% accuracy. Allele diversity for the 3 most tightly linked microsatellite markers was evaluated among 40 barley genotypes currently used in Australian barley breeding programs. The high levels of polymorphism detected among the genotypes with the markers indicated that the microsatellite markers, especially Bmag353 and Bmac310, will be broadly useful for marker-assisted selection of Alp in breeding programs seeking to improve Al tolerance. AR M ic a d tance H. Ra m et al

Novel barley (Hordeum vulgare L.) germplasm resistant to acidic soil

Improving the resistance of barley (Hordeum vulgare L.) to acidic soils is an important goal of several barley breeding programs around the world. The identification and utilisation of novel barley sources resistant to aluminium (Al) may provide a significant and rapid advance towards that goal. Barley standards and screening protocols for selecting barley germplasm resistant to Al in nutrient solution and acidic soil were reevaluated. The assays used were quantitative in nature and were suitable for genotypic- and seedling-based selections. Although there was a broad agreement between the solution culture assays and soil assays in the ranking of genotypes it obscured the fact that misclassification of genotypes is common. Brindabella was shown to be better suited than Dayton (the current barley standard resistant to Al) as the Australian standard for resistance to acidic soils. A seedling-based Al pulse-recovery assay and an acidic soil assay were used to characterise 41 genotypes from the South and East Asian Barley Core Collection (SEA-BCC). In addition, in the acidic soil assays several standard barley and wheat genotypes were included. Three SEA-BCC genotypes were more resistant than Dayton to acidic soil while several others were similar to Dayton. The most resistant SEA-BCC genotypes Honen, Ohichi and Zairai Tanbo were of Japanese origin. Misclassification of barley genotypes and wheat genotypes for resistance to soil acidity between solution culture and acid soil assay provided strong evidence for the unsuitability of solution culture assay. Although in solution culture several barley genotypes were sensitive relative to wheat, in acidic soil they were not different from wheat. While the quest for resistant barley to acidic soils similar or better than resistant wheat still continues, it may be an unnecessary endeavour.

Use of remote sensing to determine the relationship of early vigour to grain yield in canola (Brassica napus L.) germplasm

Abstract. Early crop vigour in canola, as in other crops, is likely to result in greater competition with weeds, more rapid canopy closure, improved nutrient acquisition, improved water-use efficiency, and, potentially, greater final grain yield. Laborious measurements of crop biomass over time can be replaced with newer remote-sensing technology to aid data acquisition. Normalised difference vegetation index (NDVI) is a surrogate for biomass accumulation that can be recorded rapidly and repeatedly with inexpensive equipment. In seven small-plot field experiments conducted over a 4-year period with diverse canola germplasm (nu2009=u2009105), we have shown that NDVI measures are well correlated with final grain yield. We found NDVI values were most correlated with yield (r >0.7) if readings were taken when the crop had received 210–320 growing degree-days (usually the mid-vegetative phase of growth). It is suggested that canola breeders may use NDVI to objectively select for vigorous genotypes that are more likely to have higher grain yields.

Generation mean analysis of spring wheat ( Triticum aestivum L.) seedlings tolerant to high levels of manganese

Effective utilisation of wheat (Triticum aestivum L.) germplasm tolerant to high manganese (Mn) in a breeding program requires an understanding of the genetics of Mn tolerance. Five wheat cultivars differing in their response to high Mn were crossed in a half diallel design with no reciprocals. Seedlings of parents and progeny generations were phenotyped in high Mn nutrient solutions. Total chlorophyll concentration, which was positively correlated with leaf elongation rate during recovery from Mn stress, was used for phenotyping Mn tolerance. Means of chlorophyll concentration of P1, P2, F1, F2, BC1, and BC2 generations, in all crosses which showed significant variation among generations, were subjected to line crosses analysis to estimate gene effects. The continuous frequency distribution of seedlings with differential Mn tolerance, the similarity of the F1 and F2 means, and the high and significant levels of additive gene action indicated quantitative inheritance for Mn tolerance at seedling stage. A preponderance of additive effects indicated that selection for Mn tolerance in early generations should be effective.