Selection among genotypes in final stage sugarcane trials: Effects of time of year

Low levels of commercial cane sugar (CCS) reduce relative economic value (REV) in sugarcane. In the Australian sugarcane industry, CCS is lower early (June) compared with the completion (November) of the harvest period. Performance of sugarcane genotypes in 2 Central region series and 1 Burdekin region series of final stage selection trials was examined to determine if independent selection programs are required to select elite genotypes for 2 target periods: (a) early (before July), and (b) mature (from July on). Across series, CCS (16.83 v. 12.02% fresh cane weight) and REV (AUS3937/ha v. S3123/ha) were significantly higher in the mature than in the early period, while genotypic variance for CCS (0.76 v. 0.33), and broad-sense heritability for CCS (0.96 v. 0.86) and REV (0.79 v. 0.69), were higher in the early than in the mature period. Genetic correlations between sample times less than 3 months apart were usually ≥0.9 for CCS, but generally declined to ≤0.6 for times greater than 3 months apart. Consequently, genotype × period (early compared with mature) interaction effects on CCS affected selection decisions, especially in the Central region, and genetic improvements for CCS would be expected via specific targeting of early and mature periods. However, genotype × period interaction effects were not important for cane yield or REV, such that selection for specific adaptation to early or mature periods would not improve gains in REV across the entire harvest period. Some final stage selection trials should be harvested early in the harvest period, when heritability and genotypic variance are highest, to capture high early CCS genotypes with acceptable cane yield for recycling in breeding activities. This protocol should enhance genetic gain for early CCS and simultaneously increase REV early in the harvesting period of the Australian sugar industry

Developmental and growth controls of tillering and water-soluble carbohydrate accumulation in contrasting wheat (Triticum aestivum L.) genotypes: can we dissect them?

In wheat, tillering and water-soluble carbohydrates (WSCs) in the stem are potential traits for adaptation to different environments and are of interest as targets for selective breeding. This study investigated the observation that a high stem WSC concentration (WSCc) is often related to low tillering. The proposition tested was that stem WSC accumulation is plant density dependent and could be an emergent property of tillering, whether driven by genotype or by environment. A small subset of recombinant inbred lines (RILs) contrasting for tillering was grown at different plant densities or on different sowing dates in multiple field experiments. Both tillering and WSCc were highly influenced by the environment, with a smaller, distinct genotypic component; the genotype×environment range covered 350-750 stems m and 25-210mg g WSCc. Stem WSCc was inversely related to stem number m, but genotypic rankings for stem WSCc persisted when RILs were compared at similar stem density. Low tillering-high WSCc RILs had similar leaf area index, larger individual leaves, and stems with larger internode cross-section and wall area when compared with high tillering-low WSCc RILs. The maximum number of stems per plant was positively associated with growth and relative growth rate per plant, tillering rate and duration, and also, in some treatments, with leaf appearance rate and final leaf number. A common threshold of the red:far red ratio (0.39-0.44; standard error of the difference=0.055) coincided with the maximum stem number per plant across genotypes and plant densities, and could be effectively used in crop simulation modelling as a 'cut-off' rule for tillering. The relationship between tillering, WSCc, and their component traits, as well as the possible implications for crop simulation and breeding, is discussed

Can citrate efflux from roots improve phosphorus uptake by plants? Testing the hypothesis with near-isogenic lines of wheat

Phosphorus (P) deficiency in some plant species triggers the release of organic anions such as citrate and malate from roots. These anions are widely suggested to enhance the availability of phosphate for plant uptake by mobilizing sparingly-soluble forms in the soil. Carazinho is an old wheat (Triticum aestivum) cultivar from Brazil, which secretes citrate constitutively from its root apices, and here we show that it also produces relatively more biomass on soils with low P availability than two recent Australian cultivars that lack citrate efflux. To test whether citrate efflux explains this phenotype, we generated two sets of near-isogenic lines that differ in citrate efflux and compared their biomass production in different soil types and with different P treatments in glasshouse experiments and field trials. Citrate efflux improved relative biomass production in two of six glasshouse trials but only at the lowest P treatments where growth was most severely limited by P availability. Furthermore, citrate efflux provided no consistent advantage for biomass production or yield in multiple field trials. Theoretical modeling indicates that the effectiveness of citrate efflux in mobilizing soil P is greater as the volume of soil into which it diffuses increases. As efflux from these wheat plants is restricted to the root apices, the potential for citrate to mobilize sufficient P to increase shoot biomass may be limited. We conclude that Carazinho has other attributes that contribute to its comparatively good performance in low-P soils.Peter R. Ryan, Richard A. James, Chandrakumara Weligama, Emmanuel Delhaize, Allan Rattey, David C. Lewis, William D. Bovill, Glenn McDonald, Tina M.Rathjen, Enli Wang, Neil A. Fettell and Alan E. Richardso

Focus 2014

A magazine for alumnae, alumni and friends of the Boston University School of Theology community