537 RESEARCHW hite clover (Trifolium repens L.) is a major contributor of productivity and ecological services in pastures and rangelands worldwide. The advantages of including and maintaining white clover in a pasture are well documented (Chapman et al., 1993). In New Zealand alone, it is estimated that white clover adds approximately NZ$3 billion attributable to the seed industry, N fixation, and honey production . In grazed swards, white clover provides up to 400 kg N ha −1 via biological N fixation (Crush, 1987). In terms of area, white clover is the predominant temperate forage legume serving as a companion to temperate grasses in grazing systems (Laidlaw and Teuber, 2001). White clover in mixed sward pastures is estimated to occupy ?15 million ha in Australasia and 5 million ha in the United States. Globally, renewal of white clover is estimated at 3 to 4 million ha yr −1 (Mather et al., 1996).White clover breeding is important worldwide and is recognized as a priority in many countries with a pastoral-based livestock productivity system ( Jahufer et al., 2012). For example, the last checklist of white clover varieties (Caradus and Woodfield, 1997) described a total of 326 cultivars in relation to their maintainer institution, origin and breeding procedures used, agronomic performance, and disease susceptibility, among other characteristics, depending on the information available. This checklist comprises information collected from cultivars from 32 ABSTRACT White clover (Trifolium repens L.) is a major contributor of productivity and ecological services in pastures and rangelands worldwide. White clover breeding is recognized as a priority in many countries with a pastoral-based livestock productivity system. The objective of this study was to provide an updated estimate of the rate of change in genotypic value attributable to population improvement in white clover, using a set of 80 cultivars released between 1920 and 2010 by public and private plant breeding programs across 17 countries, in an experiment to evaluate forage yield across three locations in New Zealand. Overall, some New Zealand cultivars released in the 2000s were highly adapted to more stable testing environments. Geographic origin resulted in differential rates of gain. A segmental regression comparing the pre-1965 and post-1965 rates of gain was performed. The pre-1965 regression line for white clover dry matter yield resulted in an absolute rate of increase of 0.031 g m −2 yr −1 decade −1 or 0.087% decade −1 , whereas the post-1965 line resulted in an absolute rate of increase of 0.058 g m −2 yr −1 decade −1 or 0.162% decade −1 . White clover content resulted in a pre-1965 absolute rate of increase of 0.011% content decade −1 or 0.032% decade −1 on average, and the post-1965 line indicated an absolute rate of increase of 0.04% content decade −1 or 0.121% decade −1 on average. The comparisons between pre-1965 and post-1965 indicated a twofold increase for white clover dry matter yield and a fourfold increase in rates of gain for white c...
Breeding higher yielding forage species is limited by current manual harvesting and visual scoring techniques used for measuring or estimation of biomass. Automation and remote sensing for high throughput phenotyping has been used in recent years as a viable solution to this bottleneck. Here, we focus on using RGB imaging and deep learning for white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.) yield estimation in a mixed sward. We present a new convolutional neural network (CNN) architecture designed for semantic segmentation of dense pasture and canopies with high occlusion to which we have named the local context network (LC-Net). On our testing data set we obtain a mean accuracy of 95.4% and a mean intersection over union of 81.3%, outperforming other methods we have found in the literature for segmenting clover from ryegrass. Comparing the clover/vegetation fraction for visual coverage and harvested dry-matter however showed little improvement from the segmentation accuracy gains. Further gains in biomass estimation accuracy may be achievable through combining RGB with complimentary information such as volumetric data from other sensors, which will form the basis of our future work.
Red clover (Trifolium pratense L.), a key perennial pastoral species used globally, can strengthen pastural mixes to withstand increasingly disruptive weather patterns from climate change. Breeding selections can be refined for this purpose by obtaining an in-depth understanding of key functional traits. A replicated randomized complete block glasshouse pot trial was used to observe trait responses critical to plant performance under control (15% VMC), water deficit (5% VMC) and waterlogged conditions (50% VMC) in seven red clover populations and compared against white clover. Twelve morphological and physiological traits were identified as key contributors to the different plant coping mechanisms displayed. Under water deficit, the levels of all aboveground morphological traits decreased, highlighted by a 41% decrease in total dry matter and 50% decreases in both leaf number and leaf thickness compared to the control treatment. An increase in root to shoot ratio indicated a shift to prioritizing root maintenance by sacrificing shoot growth, a trait attributed to plant water deficit tolerance. Under waterlogging, a reduction in photosynthetic activity among red clover populations reduced several morphological traits including a 30% decrease in root dry mass and total dry matter, and a 34% decrease in leaf number. The importance of root morphology for waterlogging was highlighted with low performance of red clover: there was an 83% decrease in root dry mass compared to white clover which was able to maintain root dry mass and therefore plant performance. This study highlights the importance of germplasm evaluation across water stress extremes to identify traits for future breeding programs.
White clover (Trifolium repens L.) is the main legume component in temperate perennial pasture swards in New Zealand. Developing broadly adapted cultivars is an important objective in white clover breeding programs. Field trials across years, seasons, locations and grazing environments, help breeders select superior material, and assess the merit of new cultivars available to farmers. This paper is based on results from analysis of data from field trials across three locations in New Zealand: Kerikeri (cattle grazed), Palmerston North (cattle grazed) and Lincoln (sheep grazed), evaluating 44 experimental varieties and 16 cultivars for seasonal growth and leaf size. We report on performance of the 16 cultivars across the three locations. Significant genotype-by-environment interactions were estimated for seasonal growth and leaf size. The importance of conducting multi-location and year evaluation trials under cattle and sheep grazing management methods (rotational/set stocking) was demonstrated. Among the 16 cultivars, Legacy showed above average performance across all 3 locations. Hilltop when compared among similar leaf size material, showed above average seasonal growth across years under rotational sheep grazing management during the first 4 years of the trial at Lincoln. Hilltop also showed above average seasonal growth under set socking with sheep in years 5 and 6 at Lincoln.
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