Root and shoot traits associated with acidity and drought tolerance in Vicia faba L. plants

Background. Abiotic stresses affect the productivity and the evolutionary pathway of adaptation in crops in different agricultural regions. Soil acidity and drought are two major abiotic stresses, when severe, reduce the suitability of fertile lands for crop production, and when moderate, reduce yield and often quality. Faba bean (Vicia faba L.) is sensitive to acidity, aluminium toxicity and limitation of soil moisture, and these stresses greatly reduce the yield potential and stability of the crop. The overall objectives of this study were to investigate complementarity in shoot and root morphological and physiological phenotypic markers to acid soil and drought adaptation in pre-flowering faba bean plants, and to identify sources of tolerance for further breeding work. These objectives were tested in light of four hypotheses: acid zone germplasm would have higher acid and Al3+ tolerance index than other germplasm (publication I); dry-zone germplasm would have more prolific root systems than wet-zone germplasm (publication II); dry-zone germplasm would maintain its root system growth better in drought than wet-zone germplasm would (publication II); and drought avoidance is based on a combination of leaf gas exchange and exploitation of soil water (publication III). Materials and Methods. Multiple sets of faba bean accessions were chosen based on their expected exposure to acidity, aluminium, or drought stresses in their regions of provenance, and based on previous research data and reports. Experiments were established in aquaponic, peat and perlite media in controlled/environment growth chambers, greenhouses and a robotic phenotyping facility to evaluate the performance of a range of faba bean accessions in acid, aluminium, and watering treatments. Key root and shoot data were collected and analysed. Results and Discussion. Acidity and Al3+-toxicity treatments were sufficiently strong to initiate detectable variation in root length, stain score and Al3+ tolerance index, SPAD value, stomatal conductance, biomass and leaf area in solution culture, peat, and perlite experiments. Roots behaved differently in response to pH and Al3+ treatment differences. Al-tolerant accessions showed contrasting shoot Al content, indicating multiple Al tolerance mechanisms in faba bean. The results of acid tolerance index in aquaponic and perlite media experiments were positively correlated. Trait expression complementarity and variability were observed across the experiments owing to differences in growth media. Accessions differed in root regrowth length in solution culture and in SPAD values and taproot length in perlite medium to changing pH and Al3+ concentrations as shown by accession by treatment interactions. Root tolerance index, root regrowth length, and SPAD values were found to be largely informative traits in solution culture, and peat and perlite pot experiments. In aquaponics experiment, 41 µmol/l Al3+ was not informative, 82 µmol/l Al3+ was informative, 123 µmol/l Al3+ was severe. As a result, 82 µmol/l Al3+ was used in the next peat and perlite experiments. However, 82 µmol/l Al3+ was found to be less informative in peat experiment, hence 123 µmol/l Al3+ could be recommended for selection of outstanding accessions in solid media. Overall, accessions responded to acid and Al3+ treatments independently. Cultivars Aurora and Messay were found to be Al3+ tolerant but acid sensitive; Kassa and GLA 1103 acid tolerant, but Al3+-sensitive; NC 58 and Dosha were tolerant to both Al3+ and acidity, while Babylon was sensitive to both. Aquaponic media for mass screening and perlite media for verification experiments were found to be convenient (publication I). Screening of germplasm for drought was successfully conducted in a perlite-based pot experiment, which allowed quicker screening of a large set of materials and enabled detection of variation in constitutive traits among accessions. Use of the GROWSCREEN Rhizo phenotyping facility allowed detection of useful differences between treatments and among accessions. In both the screening and phenotyping drought experiments, accessions originating from the drier regions of the world showed drought avoidance behaviour thereby confirming FIGS as a valuable strategy (publication II and III). In germplasm screening, root and shoot dry mass and their fractions, along with SPAD value provided useful information in discriminating accessions with potential drought-avoidance characteristics. In the phenotyping experiment, root traits were strongly and positively correlated with each other and with shoot traits, but these correlations indicated specific plasticity of traits with watering treatments (publication III). In the well watered treatment, total dry mass was correlated with root length traits, whereas in the water-limited treatment, it was correlated with root width and convex hull area. Apparent root length density was positively correlated with second order lateral root length in the well watered treatment and with apparent specific root length in water limited treatment, indicating high surface area to volume ratio to maximize water absorption is a key strategy in droughted condition. In the water-limited treatment, root traits contributing to drought avoidance such as lateral root length and root system depth, convex hull area and root system width, and apparent root length density (publication II and III) were positively associated with shoot traits such as total dry mass, leaf number, and leaf mass fraction reported in publication III. Accession DS70622 exhibited deeper and wider growing roots that filled the root system volume with long and thin laterals. The larger root system combined with moderately high total dry mass and stomatal conductance endorsed this accession as a potential drought-avoiding candidate by effective use of water suitable in transient droughts. Accessions such as DS11320 and ILB938/2 that combined a large and thick root system with low root length density, low specific root length and low stomatal conductance can be recommended as potential sources of drought-avoiding traits by improved water use efficiency suitable in terminal droughts. Future research directions on the development of multiple abiotic stress tolerant cultivars enables climate change resilience in crops. Most acid soils are subject to Al3+-toxicity, and drought can occur on this soils as it occurs in others. Hence, multiple stress tolerance traits, mechanisms and QTLs need to be investigated in faba bean to identify host accessions with multiple tolerance to Al3+ and drought stresses for breeding of high yielding materials.Kaksi suurinta abioottista rasitetta ovat maaperän happamuus ja kuivuus, jotka alentavat tuotantoa ja rajaavat maankäyttöä viljelyssä. Härkäpapu (Vicia faba L.) on herkkä maan happamuudelle, korkeille alumiini (Al) pitoisuuksille ja kuivuudelle. Tämän tutkimuksen tavoitteena oli löytää versojen ja juurten morfologisia ja fysiologisia piirteitä, jotka liittyvät härkäpavun kuivuuden ja happamuuden sietokykyyn ja tunnistaa parhaat lajikkeet jalostusta varten. Tätä varten valittiin useita lajikkeita Etiopiasta ja Euroopasta. Kokeissa kasvualustana käytettiin vesiviljelyä, turvetta ja perliittiä. Kokeet tehtiin kasvatuskammioissa ja kasvihuoneissa Helsingin yliopistolla ja Jülich Research Centre Saksassa. Juuret reagoivat eri tavalla pH- ja Al käsittelyihin. Al kestävillä lajikkeilla löytyi eri Al pitoisuuksia versoista, mikä viittaa useisiin Al sietokyvyn mekanismeihin. Juuren sietokyvyn indeksin, juurikasvun pituuden ja SPAD-arvojen havaittiin olevan suurelta osin informatiivisia piirteitä vesiviljelmässä sekä turve ja perliitti kokeissa. Vesiviljelykokeissa käytettiin 41, 82 ja 123 µmol/l Al. 42 µmol/l pitoisuus ei tuottanut tuloksia, 82 µmol/l taas tuotti eroja lajikkeissa ja 123 µmol/l vaikutus oli voimakas. Tämän takia 82 µmol/l käytettiin turve ja perliitti kokeissa. 82 µmol/l ei kuitenkaan tuottanut tuloksia turvekokeessa, joten 123 µmol/l tulee käyttää kiinteissä kasvualustoissa. Yleisesti lajikkeet reagoivat happamuuteen ja Al pitoisuuksiin erikseen. Aurora ja Messay lajikkeet kestivät Al, mutta olivat herkkiä maan happamuudelle. Kassa ja GLA 1103 kestivät happamuutta, mutta eivät Al. NC 58 ja Dosha kestivät molempia, kun taas Babylon ei kumpaakaan. Vesiviljely toimi lajikkeiden massaseulonnassa ja perliitti kasvualusta tulosten vahvistamiseksi. Lajikkeiden seulonta kuivuuden suhteen tehtiin perliitti kokeessa. GROWSCREEN Rhizo –fenotyyppi laitteistolla määritettiin hyödyllisiä eroja lajikkeissa. Lajike DS70622 kasvatti suuren juuriston. Lajike tuottaa myös kohtalaisen suuren biomassan, mikä tekee siitä hyvän kandidaatin jalostettaessa kuivuuden sietokykyä. Lajikkeet DS11320 ja ILB938/2, joissa yhdistyy suuri juuristo, vähäinen hienojen juurien määrä ja alhainen ilmarakojen johtavuus, soveltuvat myös hyvin kuivuuden sietokyvyn jalostamiseen. Happamassa maassa on usein myös korkeat Al pitoisuudet, ja kuivuus voi tapahtua kaikkialla. Täten härkäpavun jalostamisessa pitäisi luoda lajikkeita joilla on sietokykyä useille abioottisille rasitteille

Screening of faba bean (Vicia faba L.) accessions to acidity and aluminium stresses

Background. Faba bean is an important starch-based protein crop produced worldwide. Soil acidity and aluminium toxicity are major abiotic stresses affecting its production, so in regions where soil acidity is a problem, there is a gap between the potential and actual productivity of the crop. Hence, we set out to evaluate acidity and aluminium tolerance in a range of faba bean germplasm using solution culture and pot experiments. Methods. A set of 30 accessions was collected from regions where acidity and aluminium are or are not problems. The accessions were grown in solution culture and a subset of 10 was grown first in peat and later in perlite potting media. In solution culture, morphological parameters including taproot length, root regrowth and root tolerance index were measured, and in the pot experiments the key measurements were taproot length, plant biomass, chlorophyll concentration and stomatal conductance. Result. Responses to acidity and aluminium were apparently independent. Accessions Dosha and NC 58 were tolerant to both stress. Kassa and GLA 1103 were tolerant to acidity showing less than 3% reduction in taproot length. Aurora and Messay were tolerant to aluminium. Babylon was sensitive to both, with up to 40% reduction in taproot length from acidity and no detectable recovery from Al3+ challenge. Discussion. The apparent independence of the responses to acidity and aluminium is in agreement with the previous research findings, suggesting that crop accessions separately adapt to H+ and Al3+ toxicity as a result of the difference in the nature of soil parent materials where the accession originated. Differences in rankings between experiments were minor and attributable to heterogeneity of seed materials and the specific responses of accessions to the rooting media. Use of perlite as a potting medium offers an ideal combination of throughput, inertness of support medium, access to leaves for detection of their stress responses, and harvest of clean roots for evaluation of their growth.Peer reviewe

Diversity in root growth responses to moisture deficit in young faba bean (Vicia faba L.) plants

Background Soil moisture deficiency causes yield reduction and instability in faba bean (Vicia faba L.) production. The extent of sensitivity to drought stress varies across accessions originating from diverse moisture regimes of the world. Hence, we conducted successive greenhouse experiments in pots and rhizotrons to explore diversity in root responses to soil water deficit. Methods A set of 89 accessions from wet and dry growing regions of the world was defined according to the Focused Identification of Germplasm Strategy and screened in a perlite-sand medium under well watered conditions in a greenhouse experiment. Stomatal conductance, canopy temperature, chlorophyll concentration, and root and shoot dry weights were recorded during the fifth week of growth. Eight accessions representing the range of responses were selected for further investigation. Starting five days after germination, they were subjected to a root phenotyping experiment using the automated phenotyping platform GROWSCREEN-Rhizo. The rhizotrons were filled with peat-soil under well watered and water limited conditions. Root architectural traits were recorded five, 12, and 19 days after the treatment (DAT) began. Results In the germplasm survey, accessions from dry regions showed significantly higher values of chlorophyll concentration, shoot and root dry weights than those from wet regions. Root and shoot dry weight as well as seed weight, and chlorophyll concentration were positively correlated with each other. Accession DS70622 combined higher values of root and shoot dry weight than the rest. The experiment in GROWSCREEN-Rhizo showed large differences in root response to water deficit. The accession by treatment interactions in taproot and second order lateral root lengths were significant at 12 and 19 DAT, and the taproot length was reduced up to 57% by drought. The longest and deepest root systems under both treatment conditions were recorded by DS70622 and DS11320, and total root length of DS70622 was three times longer than that of WS99501, the shortest rooted accession. The maximum horizontal distribution of a root system and root surface coverage were positively correlated with taproot and total root lengths and root system depth. DS70622 and WS99501 combined maximum and minimum values of these traits, respectively. Thus, roots of DS70622 and DS11320, from dry regions, showed drought-avoidance characteristics whereas those of WS99501 and Melodie/2, from wet regions, showed the opposite. Discussion The combination of the germplasm survey and use of GROWSCREEN-Rhizo allowed exploring of adaptive traits and detection of root phenotypic markers for potential drought avoidance. The greater root system depth and root surface coverage, exemplified by DS70622 and DS11320, can now be tested as new sources of drought tolerance.Peer reviewe

Yield Gaps of Major Cereal and Grain Legume Crops in Ethiopia: A Review

In Ethiopia, smallholder farmers are responsible for most food production. Though yield levels in grain crops have improved greatly over the years, they are still much lower than their potential. The source of yield improvements and the causes of those yield gaps are not well understood. To explain the drivers of yield gaps and current sources of yield improvements in four major cereals (teff, maize, wheat, and sorghum) and three grain legumes (faba bean, common bean, and soybean), we accessed the databases of the Global Yield Gap Atlas, the Food and Agriculture Organization of the United Nations, and the Central Statistical Agency of Ethiopia. Refereed journal articles and grey literature were sought in online databases using keywords. The results showed large increases in production of grain crops with little or no increase in areas of production. The yield increases were primarily attributed to genetic gain rather than agronomic improvements. Farmers’ yields remain far lower than those from on-farm trials and on-station trials and the calculated water-limited yield potential. Currently, yields of wheat, maize, sorghum, and common bean in Ethiopia are about 26.8, 19.7, 29.3, and 35.5% of their water-limited yield potentials. Significant portions of the yield gaps stem from low adoption and use of improved varieties, low application of inputs, continual usage of un-optimized crop management practices, and uncontrolled biotic and abiotic stresses. Proper application of fertilizers and use of improved varieties increase yield by 2 to 3 fold and 24–160%, respectively. Cereal-legume intercropping and crop rotation practices increase yield while reducing severity of pests and the need for application of synthetic fertilizers. In contrast, abiotic stresses cause yield reductions of 20–100%. Hence, dissection of the water-limited yield gap in terms of technology, resource, and efficiency yield gaps will allow the prioritization of the most effective intervention areas

Yield Gaps of Major Cereal and Grain Legume Crops in Ethiopia: A Review

In Ethiopia, smallholder farmers are responsible for most food production. Though yield levels in grain crops have improved greatly over the years, they are still much lower than their potential. The source of yield improvements and the causes of those yield gaps are not well understood. To explain the drivers of yield gaps and current sources of yield improvements in four major cereals (teff, maize, wheat, and sorghum) and three grain legumes (faba bean, common bean, and soybean), we accessed the databases of the Global Yield Gap Atlas, the Food and Agriculture Organization of the United Nations, and the Central Statistical Agency of Ethiopia. Refereed journal articles and grey literature were sought in online databases using keywords. The results showed large increases in production of grain crops with little or no increase in areas of production. The yield increases were primarily attributed to genetic gain rather than agronomic improvements. Farmers’ yields remain far lower than those from on-farm trials and on-station trials and the calculated water-limited yield potential. Currently, yields of wheat, maize, sorghum, and common bean in Ethiopia are about 26.8, 19.7, 29.3, and 35.5% of their water-limited yield potentials. Significant portions of the yield gaps stem from low adoption and use of improved varieties, low application of inputs, continual usage of un-optimized crop management practices, and uncontrolled biotic and abiotic stresses. Proper application of fertilizers and use of improved varieties increase yield by 2 to 3 fold and 24–160%, respectively. Cereal-legume intercropping and crop rotation practices increase yield while reducing severity of pests and the need for application of synthetic fertilizers. In contrast, abiotic stresses cause yield reductions of 20–100%. Hence, dissection of the water-limited yield gap in terms of technology, resource, and efficiency yield gaps will allow the prioritization of the most effective intervention areas