Vijaya Singh

Morphological and architectural development of root systems in sorghum and maize

Root systems determine the capacity of a plant to access soil water and their architecture can influence adaptation to water-limited conditions. It may be possible to associate that architecture with root attributes of young plants as a basis for rapid phenotypic screening. This requires improved understanding of root system development. This study aimed to characterise the morphological and architectural development of sorghum and maize root systems by (i) clarifying the initiation and origin of roots at germination, and (ii) monitoring and quantifying the development of root systems in young plants. Three experiments were conducted with two maize and four sorghum hybrids. Sorghum produced a sole seminal (primary) root and coleoptile nodal roots emerged at the 4th–5th leaf stage, whereas maize produced 3–7 seminal (primary and scutellum) roots and coleoptile nodal roots emerged at the 2nd leaf stage. Genotypic variation in the flush angle and mean diameter of nodal roots was observed and could be considered a suitable target for large scale screening for root architecture in breeding populations. Because of the relatively late appearance of nodal roots in sorghum, such screening would require a small chamber system to grow plants until at least 6 leaves had fully expanded.

Genetic variability in high temperature effects on seed-set in sorghum

Sorghum (Sorghum bicolor (L.) Moench) is grown as a dryland crop in semiarid subtropical and tropical environments where it is often exposed to high temperatures around flowering. Projected climate change is likely to increase the incidence of exposure to high temperature, with potential adverse effects on growth, development and grain yield. The objectives of this study were to explore genetic variability for the effects of high temperature on crop growth and development, in vitro pollen germination and seed-set. Eighteen diverse sorghum genotypes were grown at day : night temperatures of 32 : 21°C (optimum temperature, OT) and 38 : 21°C (high temperature, HT during the middle of the day) in controlled environment chambers. HT significantly accelerated development, and reduced plant height and individual leaf size. However, there was no consistent effect on leaf area per plant. HT significantly reduced pollen germination and seed-set percentage of all genotypes; under HT, genotypes differed significantly in pollen viability percentage (17-63%) and seed-set percentage (7-65%). The two traits were strongly and positively associated (R2=0.93, n=36, P<0.001), suggesting a causal association. The observed genetic variation in pollen and seed-set traits should be able to be exploited through breeding to develop heat-tolerant varieties for future climates.

Insights into sorghum starch biosynthesis from structure changes induced by different growth temperatures

ABSTRACT The effects of high growth temperature on sorghum starch structures were examined from the grains of three inbred lines (BTx623, IS8525, and Karper669), and the possible mechanism by which the growth of amylopectin molecules is terminated was discussed. Sorghum plants were grown at high temperature (38/21°C day/night) and control temperature (32/22°C day/night) from sowing to maturity. The grains sampled from plants grown at high temperature had significantly lower starch weights per grain (except BTx623) and smaller starch granule sizes than those grown at control temperature. Nevertheless, the amylose contents were similar. BTx623 and IS8525 samples grown at high temperature also had higher ratios of long to short amylopectin branches and lower degree of branching than their control counterparts. These results suggested that the activities of starch biosynthetic enzymes were evidently affected by elevated growth temperature. However, the weight-average molecular weight and the z-average radius ...

Growth temperature and genotype both play important roles in sorghum grain phenolic composition

Polyphenols in sorghum grains are a source of dietary antioxidants. Polyphenols in six diverse sorghum genotypes grown under two day/night temperature regimes of optimal temperature (OT, 32/21 °C and high temperature (HT, 38/21 °C) were investigated. A total of 23 phenolic compounds were positively or tentatively identified by HPLC-DAD-ESIMS. Compared with other pigmented types, the phenolic profile of white sorghum PI563516 was simpler, since fewer polyphenols were detected. Brown sorghum IS 8525 had the highest levels of caffeic and ferulic acid, but apigenin and luteolin were not detected. Free luteolinidin and apigeninidin levels were lower under HT than OT across all genotypes (p ≤ 0.05), suggesting HT could have inhibited 3-deoxyanthocyanidins formation. These results provide new information on the effects of HT on specific polyphenols in various Australian sorghum genotypes, which might be used as a guide to grow high antioxidant sorghum grains under projected high temperature in the future.

Effects of Genotype and Growth Temperature on the Contents of Tannin, Phytate and In Vitro Iron Availability of Sorghum Grains.

Background It has been predicted that the global temperature will rise in the future, which means crops including sorghum will likely be grown under higher temperatures, and consequently may affect the nutritional properties. Methods The effects of two growth temperatures (OT, day/night 32/21°C; HT 38/21°C) on tannin, phytate, mineral, and in vitro iron availability of raw and cooked grains (as porridge) of six sorghum genotypes were investigated. Results Tannin content significantly decreased across all sorghum genotypes under high growth temperature (P ≤0.05), while the phytate and mineral contents maintained the same level, increased or decreased significantly, depending on the genotype. The in vitro iron availability in most sorghum genotypes was also significantly reduced under high temperature, except for Ai4, which showed a pronounced increase (P ≤0.05). The cooking process significantly reduced tannin content in all sorghum genotypes (P ≤0.05), while the phytate content and in vitro iron availability were not significantly affected. Conclusions This research provides some new information on sorghum grain nutritional properties when grown under predicted future higher temperatures, which could be important for humans where sorghum grains are consumed as staple food.

Molecular Breeding for Complex Adaptive Traits: How Integrating Crop Ecophysiology and Modelling Can Enhance Efficiency

Progress in crop improvement is limited by the ability to identify favourable combinations of genotypes (G) and management practices (M) in relevant target environments (E) given the resources available to search among the myriad of possible combinations. To underpin yield advance we require prediction of phenotype based on genotype. In plant breeding, traditional phenotypic selection methods have involved measuring phenotypic performance of large segregating populations in multi-environment trials and applying rigorous statistical procedures based on quantitative genetic theory to identify superior individuals. Recent developments in the ability to inexpensively and densely map/sequence genomes have facilitated a shift from the level of the individual (genotype) to the level of the genomic region. Molecular breeding strategies using genome wide prediction and genomic selection approaches have developed rapidly. However, their applicability to complex traits remains constrained by gene-gene and gene-environment interactions, which restrict the predictive power of associations of genomic regions with phenotypic responses. Here it is argued that crop ecophysiology and functional whole plant modelling can provide an effective link between molecular and organism scales and enhance molecular breeding by adding value to genetic prediction approaches. A physiological framework that facilitates dissection and modelling of complex traits can inform phenotyping methods for marker/gene detection and underpin prediction of likely phenotypic consequences of trait and genetic variation in target environments. This approach holds considerable promise for more effectively linking genotype to phenotype for complex adaptive traits. Specific examples focused on drought adaptation are presented to highlight the concepts.

Effect of genotype and growth temperature on sorghum grain physical characteristics, polyphenol content, and antioxidant activity

This paper reports how genotype and growth temperature affect the physical characteristics and polyphenol content in sorghum grains. Two day/night temperature regimes, 32/21 and 38/21°C, were used to grow six sorghum genotypes (CCH1, CCH2, AQL33/QL36, Ai4, PI563516, and IS 8525). The physical characteristics (hardness, weight, and diameter) of sorghum grain and their free, bound, and total polyphenol contents were determined. Grain antioxidant activity was evaluated by 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt and 2-2-diphenyl-1-picrylhydrazyl assays. The results indicate that the weight and diameter of the sorghum kernels were significantly increased in all genotypes except for CCH1, under higher temperature, whereas kernel hardness decreased. Genotype had a significant influence polyphenol content (IS 8525 about four times higher than PI563516 under optimum temperature) and antioxidant activity, but temperature did not, with the exception of IS 8525 in which polyphenol conten...

Genetic Manipulation of Root System Architecture to Improve Drought Adaptation in Sorghum

Drought is one of the most important abiotic stresses and severely affects global agricultural production. Root system architecture (RSA) is the key determinant of water acquisition under moisture stress, and therefore has utility in breeding for drought tolerance in sorghum. Various components of RSA are known to influence drought tolerance in sorghum without any negative impact on yield. The growth angle of nodal roots is an important target trait for improving drought tolerance. Genetic variation for nodal root angle has been reported in sorghum, and this has been associated with grain yield under drought stress. Rapid advances in sorghum genomics have led to the identification of various quantitative trait loci (QTL) governing RSA, but the accuracy and preciseness in identification of QTL is the major hindrance in development of drought-tolerant cultivars through genetic manipulation of root traits. Hence, the complex genetic control of RSA and the lack of a high-throughput phenotyping platform have hampered integration of selection for RSA in breeding programs. These limitations can be overcome by designing a robust phenotyping platform that can maximize heritability and repeatability of RSA. Inclusion of the extensive phenotyping information with the recently developed genomic resources of sorghum will lead to mining of alleles that govern RSA and tailor a cultivar harboring genes for RSA that improve sorghum production under drought stress. This chapter provides an overview of the latest developments in RSA research in sorghum and gives direction to future breeding strategies to enhance the genetic gain for root traits.