Modelling the variability of UK sugar beet yields under climate change and husbandry adaptations

In the future, UK summers are likely to be warmer and drier. Modelling differential water redistribution and uptake, we assessed the impact of future drier climates on sugar beet yields. Weather was generated for 1961–1990 (BASE) and predictions based on low‐ and high‐emission scenarios (LO, HI) described in the most recent global climate simulations by the Hadley Centre, UK. Distributions and variability of relative soil moisture deficit (rSMD) and yield gap (drought‐related yield loss, YG_dr = 1?actual yield/potential yield), and sugar yield were calculated for different time‐lines using regional weather, soil texture and management inputs. The rSMD is estimated to exceed the senescence threshold with a probability of 75% (2050sLO) to 95% (2080sHI) compared with 65% (BASE). The potential yield loss, YG_dr, is likely to increase from 17% (BASE) to 22% (2050sLO) to 35% (2080sHI). However, increasing potential growth rates (CO₂ × temperature) cause average sugar yields to rise by between 1.4 and 2 t ha^?1 (2050sLO and 2050sHI respectively). Yield variation (CV%) may increase from 15–18% (BASE) to 18–23% (2050s) and 19–25% (2080s). Differences are small between regions but large within regions because of soil variability. In future, sugar yields on sands (8 t ha^?1) are likely to increase by little (0.5–1.5 t ha^?1), but on loams yields are likely to increase from 11 to 13 t ha^?1 (2050sHI) and 15 t ha^?1 (2080sHI). Earlier sowing and later harvest are potential tools to compensate for drought‐related losses on sandy soils.     

Assessing the genetic resources to improve drought tolerance in sugar beet: agronomic traits of diverse genotypes under droughted and irrigated conditions

Drought is the major cause of sugar beet (Beta vulgaris L.) yield losses in the UK and many other regions where the crop is not normally irrigated. However, drought tolerance has not been a breeding target partly because the extent of the problem was not understood, it is difficult to design effective selection screens, and because of the suspicion that few varietal differences existed. The aim of this study was to evaluate the genetic resources necessary to improve drought tolerance. Specific objectives were to assess the degree of genotypic diversity for drought tolerance, characterise genotypic differences in response to drought, and identify sources of germplasm with greater drought tolerance than current commercial varieties. Over 3 years, 46 beet genotypes representing diverse genetic backgrounds were tested in the field under large polythene covers to impose a drought beginning approximately 40 days after emergence until harvest. Sugar, root and total dry matter yields were measured under drought and irrigated conditions. The percentage green crop cover was measured at regular intervals and used in the calculation of radiation use efficiencies for each genotype. Drought tolerance index (DTI) was computed as the fraction of irrigated yield maintained under drought, normalised by the mean yield across all genotypes in the trial. Seven genotypes were tested in all years, and the data on these were used to calculate yield stability statistics and to estimate broad-sense heritability. There were more than two-fold differences in droughted and irrigated yields between genotypes, and nearly a two-fold difference in DTI. According to an index that combines yield potential and drought tolerance, some genotypes performed better than the three locally adapted commercial varieties included in the test. There were significant effects for genotype, treatment and G×E interactions for yield components and radiation use efficiency. There were also significant genotype differences in harvest index but few significant G×E interactions. Droughted and irrigated yields were positively associated, but there was no close relation between yield potential and DTI. The seven genotypes common to all years differed in yield stability and in sensitivity to water availability. Thus, the genetic resources exist for germplasm improvement. Both yield potential and DTI (which may ensure better yield stability) should be considered simultaneously as breeding targets for drought-prone areas.     

The effects of beet yellows virus on the growth and physiology of sugar beet (Beta vulgaris)

The effect of beet yellows virus (genus Closterovirus , BYV) on sugar beet growth was studied in a series of field and glasshouse experiments. Infection reduced total plant weight by 20%, primarily through a 25% reduction in storage root growth. Sugar extraction efficiency was depressed by an increase in root impurities. BYV had little effect on above-ground yield or total crop cover but did decrease green cover significantly. Infection did not reduce water extraction depth in field experiments despite decreasing lateral root growth in the glasshouse. The growth reduction in infected plants resulted from both a decrease in net photosynthesis and an increase in the proportion of light intercepted by yellow leaves. Damage to the photosynthetic mechanism at least partly caused the reduction in net photosynthesis.     

Spatial patterns of wilting in sugar beet as an indicator for precision irrigation

Precision irrigation requires the mapping of within-field variations of water requirement. Conventional remote sensing techniques provide estimates of water status at only shallow soil depths. The ability of a water sensitive crop, sugar beet, to act as an intermediate sensor providing an integrated measure of water status throughout its rooting depth is tested here. Archive aerial photographs and satellite imagery of Eastern England show crop patterns resulting from past periglacial processes. The patterns were found to be spatially and temporally consistent. Field sampling of soil cores to 1 m depth established that the within-field wilting zones were significantly associated with coarser or shallow soils. The stress classes, determined by classification of the digitised images, were weakly correlated with total available water (Pearson correlation r = 0.588, P < 0.05). These results suggest that wilting in sugar beet can be used as an intermediate sensor for quantifying potential soil water availability within the root zone. Within-field stress maps generated in 1 year could be applied as a strategic tool allowing precision irrigation to be applied to high-value crops in following years, helping to make more sustainable use of water resources.