Susan Fletcher

High-throughput phenotyping of seminal root traits in wheat.

BackgroundWater availability is a major limiting factor for wheat (Triticum aestivum L.) production in rain-fed agricultural systems worldwide. Root system architecture has important functional implications for the timing and extent of soil water extraction, yet selection for root architectural traits in breeding programs has been limited by a lack of suitable phenotyping methods. The aim of this research was to develop low-cost high-throughput phenotyping methods to facilitate selection for desirable root architectural traits. Here, we report two methods, one using clear pots and the other using growth pouches, to assess the angle and the number of seminal roots in wheat seedlings– two proxy traits associated with the root architecture of mature wheat plants.ResultsBoth methods revealed genetic variation for seminal root angle and number in the panel of 24 wheat cultivars. The clear pot method provided higher heritability and higher genetic correlations across experiments compared to the growth pouch method. In addition, the clear pot method was more efficient – requiring less time, space, and labour compared to the growth pouch method. Therefore the clear pot method was considered the most suitable for large-scale and high-throughput screening of seedling root characteristics in crop improvement programs.ConclusionsThe clear-pot method could be easily integrated in breeding programs targeting drought tolerance to rapidly enrich breeding populations with desirable alleles. For instance, selection for narrow root angle and high number of seminal roots could lead to deeper root systems with higher branching at depth. Such root characteristics are highly desirable in wheat to cope with anticipated future climate conditions, particularly where crops rely heavily on stored soil moisture at depth, including some Australian, Indian, South American, and African cropping regions.

Phenotyping novel stay-green traits to capture genetic variation in senescence dynamics

Stay-green plants retain green leaves longer after anthesis and can have improved yield, particularly under water limitation. As senescence is a dynamic process, genotypes with different senescence patterns may exhibit similar final normalised difference vegetative index (NDVI). By monitoring NDVI from as early as awn emergence to maturity, we demonstrate that analysing senescence dynamics improves insight into genotypic stay-green variation. A senescence evaluation tool was developed to fit a logistic function to NDVI data and used to analyse data from three environments for a wheat (Triticum aestivum L.) population whose lines contrast for stay-green. Key stay-green traits were estimated including, maximum NDVI, senescence rate and a trait integrating NDVI variation after anthesis, as well as the timing from anthesis to onset, midpoint and conclusion of senescence. The integrative trait and the timing to onset and mid-senescence exhibited high positive correlations with yield and a high heritability in the three studied environments. Senescence rate was correlated with yield in some environments, whereas maximum NDVI was associated with yield in a drought-stressed environment. Where resources preclude frequent measurements, we found that NDVI measurements may be restricted to the period of rapid senescence, but caution is required when dealing with lines of different phenology. In contrast, regular monitoring during the whole period after flowering allows the estimation of senescence dynamics traits that may be reliably compared across genotypes and environments. We anticipate that selection for stay-green traits will enhance genetic progress towards high-yielding, stay-green germplasm.

Stay-green traits to improve wheat adaptation in well-watered and water-limited environments

Highlight Combining stay-green traits and environmental water-stress characterization, both standardized relative to anthesis, provides a powerful method to characterize and select for adaptation to well-watered and water-stressed environments.

Post head-emergence frost resistance of barley genotypes in the northern grain region of Australia

Post head-emergence frost causes substantial losses for Australian barley producers. Varieties with improved resistance would have a significant positive impact on Australian cropping enterprises. Five barley genotypes previously tested for reproductive frost resistance in southern Australia were tested, post head-emergence, in the northern grain region of Australia and compared with the typical northern control cultivars, Gilbert and Kaputar. All tested genotypes suffered severe damage to whole heads and stems at plant minimum temperatures less than -8degreesC. In 2003, 2004 and 2005, frost events reaching a plant minimum temperature of ~-6.5degreesC did not result in the complete loss of grain yield. Rather, partial seed set was observed. The control genotype, Gilbert, exhibited seed set that was greater than or equal to that of any genotype in each year, as did Kaputar when tested in 2005. Thus, Gilbert and Kaputar were at least as resistant as any tested genotype. This contrasts with trial results from the southern grain region where Gilbert was reported to be less resistant than Franklin, Amagi Nijo and Haruna Nijo. Hence, rankings for post head-emergence frost damage in the northern grain region differ from those previously reported. These results indicate that Franklin, Amagi Nijo and Haruna Nijo are not likely to provide useful sources of frost resistance or markers to develop improved varieties for the northern grain region of Australia.

Identifying Deployment Zones for 'Eucalyptus camaldulensis' x 'E. globulus' and x 'E. grandis' Hybrids Using Factor Analytic Modelling of Genotype by Environment Interaction

Summary In this study we apply factor analytic methods to the analysis of diameter at breast height (DBH) at 3 years for 22 trials of 892 clones from four E. camaldulensis x E. globulus and six E. camaldulensis x E. grandis families established throughout Australia (Queensland, New South Wales, Victoria, Tasmania and Western Australia). Three factors were sufficient to describe the genetic variation in the data set and, on average, described 86% of the genetic variance within a trial. Estimated broad-sense heritability ranged from 0.05 to 0.85, and genetic correlation estimates between pairs of trials ranged from 0.09 to 0.99. Two-dimensional plots of factor loadings and cluster analysis of the estimated genetic correlation matrix indicated that the trials formed three groups that represent potential zones for deployment to maximise genetic gain. However, there was no geographic pattern in the distribution of the trials within these groups; further research is required to develop predictive models of the patterns in GxE for the germplasm and identify genotypes that are superior in each deployment zone.

Pathogenic variation of Pyrenophora teres f. teres in Australia

Pyrenophora teres f. teres (Ptt) is the causal agent of net form of net blotch (NFNB) – a major foliar disease of barley (Hordeum vulgare) crops worldwide. Deployment of genetic resistance in cultivars is the preferred method of control, but requires knowledge of the pathogenic variation of Ptt to be effective as spatial and temporal variation is common. In this study, 123 Ptt isolates collected from five states across Australia were examined for pathogenic variation using a set of 31 barley genotypes, composed of 11 international genotypes and 20 Australian cultivars. Barley seedlings were inoculated with spore suspensions from monoconidial isolate cultures and scored for infection response. Phenotypes were used to perform hierarchical cluster analysis for barley genotypes and Ptt isolates. Cluster analysis identified seven line groups, each containing barley genotypes that displayed similar responses to the Ptt isolates. Isolates clustered into four distinct isolate groups shown to harbour differential virulence to four key genotypes: Maritime, Prior, Skiff and Tallon. Isolates with virulence to any one of these genotypes accounted for 96.7% of the samples. Differential virulence was observed on a range of genotypes within each isolate group. The composition of isolate groups in eastern Australia was distinct from Western Australia, whereas all isolate groups were detected in southern Australia. Results suggest that cultivation of regionally adapted barley cultivars has led to regional evolution of Ptt, where the pathogen acquires virulence specific for resistance factors deployed in local cultivars. Detection of Ptt modern isolates that were highly virulent to historic cultivars indicates the long-term survival of virulence gene combinations in the pathogen population.