Variation for tolerance to high concentration of ferrous iron (Fe<Superscript>2+</Superscript>) in Australian hexaploid wheat

High concentration of reduced iron (Fe²⁺) in waterlogged acid soils is a constraint for growing wheat in high rainfall (waterlogged-prone) areas of Western Australia. Growing crop genotypes tolerant to high Fe²⁺ concentrations may be desirable in such situations, but there is no knowledge about the extent of variability in Fe²⁺ tolerance in the wheat germplasm. A bioassay for tolerance to high concentrations of iron in wheat was developed and optimised using Siete Cerros (Fe-tolerant) and BH1146 (Fe-intolerant) as control genotypes and a range of FeSO₄ concentrations (36, 313, 625, 1250, 1875, 2500 and 3125 μM Fe²⁺) in nutrient solution in a controlled-temperature environment. Increasing external concentration of iron decreased both shoot and root dry weight, increased shoot iron concentration and intensified the development of toxicity symptoms to a greater degree in intolerant BH1146 as compared to tolerant Siete Cerros. Increased iron supply negatively affected uptake of Ca (r = −0.41) and Mg (r = −0.40). The tolerant genotype Siete Cerros showed an improved avoidance/exclusion of high external concentration of Fe²⁺ compared with intolerant BH1146. The genotypic discrimination based on relative root dry weight and the development of toxicity symptoms was most pronounced at 625 μM Fe²⁺. This concentration was chosen for screening of 20 bread wheat and one durum genotype chosen from a preliminary screening of 94 Australian wheat genotypes. A relatively narrow but significant variation (22–38%) in terms of relative root dry weight under Fe²⁺ toxicity was observed among Australian advanced breeding lines and varieties. The presence of genotypic variation for Fe²⁺ tolerance across and within the Australian breeding programs could be exploited in a deliberate selection process to enhance Fe²⁺ tolerance in wheat. Durum wheat (Arrivato) and several Australian wheat varieties and advanced lines in this study were as tolerant to Fe²⁺ toxicity as Siete Cerros, a variety representing common parentage of iron-tolerant genotypes.     

Maize genotypes with deep root systems tolerate salt stress better than those with shallow root systems during early growth

Maize (Zea mays L.) is susceptible to salinity but shows genotypic variation for salt tolerance. How maize genotypes with contrasting root morphological traits respond to salt stress remains unclear. This study assessed genotypic variation in salinity tolerance of 20 maize genotypes with contrasting root systems exposed to NaCl for 10 days (0, 50 mM or 100 mM NaCl, added in four increments every other day from 14 days after transplanting, DAT) in a semi-hydroponic phenotyping system in a temperature-controlled greenhouse. Considerable variation was observed for each of the 12 measured shoot and root traits among the 20 genotypes under NaCl treatments. Salt stress significantly decreased biomass production by up to 54% in shoots and 37% in roots compared with the non-saline control. The 20 genotypes were classified as salt-tolerant (8 genotypes), moderately tolerant (5) and salt-sensitive (7) genotypes based on the mean shoot dry weight ratio (the ratio of shoot dry weight at 100 mM NaCl and non-saline control) ± one standard error. The more salt-tolerant genotypes (such as Jindan52) had less reductions in growth, and lower shoot Na⁺ contents and higher shoot K⁺/Na⁺ ratios under salt stress. The declared salt tolerance was positively correlated with shoot height, shoot dry weight and primary root depth, and negatively correlated with shoot Na⁺ content at 100 mM NaCl. Primary root depth is critical for identifying salt responsiveness in maize plants and could be suggested as a selection criterion for screening salt tolerance of maize during early growth. The selected salt-tolerant genotypes have potentials for cultivation in saline soils and for developing high-yielding salt-tolerant maize hybrids in future breeding programmes.     

Identification and Characterization of Salt Tolerance of Wheat Germplasm Using a Multivariable Screening Approach

Salinity is one of the major limitations to wheat production worldwide. This study was designed to evaluate the level of genetic variation among 150 internationally derived wheat genotypes for salinity tolerance at germination, seedling and adult plant stages, with the aim of identifying new genetic resources with desirable adaptation characteristics for breeding programmes and further genetic studies. In all the growth stages, genotype and salt treatment effects were observed. Salt stress caused 33 %, 51 % and 82 % reductions in germination vigor, seedling shoot dry matter and seed grain yield, respectively. The rate of root and shoot water loss due to salt stress exhibited significant negative correlation with shoot K⁺, but not with shoot Na⁺ and shoot K⁺/Na⁺ ratio. The genotypes showed a wide spectrum of response to salt stress across the growth stages; however, four genotypes, Altay2000, 14IWWYTIR‐19 and UZ‐11CWA‐8 (tolerant) and Bobur (sensitive), exhibited consistent responses to salinity across the three growth stages. The tolerant genotypes possessed better ability to maintain stable osmotic potential, low Na⁺ accumulation, higher shoot K⁺ concentrations, higher rates of PSII activity, maximal photochemical efficiency and lower non‐photochemical quenching (NPQ), resulting in the significantly higher dry matter production observed under salt stress. The identified genotypes could be used as parents in breeding for new varieties with improved salt tolerance as well as in further genetic studies to uncover the genetic mechanisms governing salt stress response in wheat.     

Evaluation of salt tolerance in rice genotypes by physiological characters

The use of physiological characters as selection criteria in salt tolerance breeding requires the identification of the contribution each individual character makes to salt tolerance. Rice genotypes were evaluated for salt tolerance in terms of grain yield and physiological characters. Plants of twelve genotypes were grown in sand tanks in a greenhouse and irrigated with Yoshida nutrient solution. Sodium chloride and calcium chloride (5:1 molar ratio) were added at two concentrations to give moderate (4.5 dS m^-1) and high (8.3 dS m^-1) salinity treatments. One set of plants was harvested at 635 ^°Cċd (accumulative thermal time) after planting to determine LAI and mineral ion concentrations. Another set of plants was allowed to grow to maturity. High genotypic diversity for LAI and shoot ion contents was observed. LAI contributed the most to the variation of the grain yield under salt stress. Significant correlations between LAI and yield components in both salt-tolerant and-sensitive genotypes further confirmed the significant contribution of LAI to grain yield. K-Na selectivity increased with increasing salinity. Conversely, Na-Ca selectivity decreased with increasing salinity. Significant correlations were identified between grain yield and both Na-Ca and K-Na selectivity. Highly significant (p<0.001) correlations were identified between Na-Ca selectivity and the rankings among genotypes for grain yield. Thus, Na-Ca selectivity could be one salt tolerance component and an useful selection criterion in screening for salt tolerance. This revised version was published online in July 2006 with corrections to the Cover Date.     

Screening sorghum genotypes for salinity tolerant biomass production

Genetic improvement of salt tolerance is of high importance due to the extent and the constant increase in salt affected areas. Sorghum [Sorghum bicolor (L.) Moench] has been considered relatively more salt tolerant than maize and has the potential as a grain and fodder crop for salt affected areas. One hundred sorghum genotypes were screened for salinity tolerance in pots containing Alfisol and initially irrigated with a 250-mM NaCl solution in a randomized block design with three replications. Subsequently 46 selected genotypes were assessed in a second trial to confirm their responses to salinity. Substantial variation in shoot biomass ratio was identified among the genotypes. The performance of genotypes was consistent across experiments. Seven salinity tolerant and ten salinity sensitive genotypes are reported. Relative shoot lengths of seedlings were genetically correlated to the shoot biomass ratios at all stages of sampling though the relationships were not close enough to use the trait as a selection criterion. In general, the whole-plant tolerance to salinity resulted in reduced shoot Na⁺ concentration. The K⁺/Na⁺ and Ca²⁺/Na⁺ ratios were also positively related to tolerance but with a lesser r ². Therefore, it is concluded that genotypic diversity exists for salt tolerance biomass production and that Na⁺ exclusion from the shoot may be a major mechanism involved in that tolerance.     

Identification of pearl millet [Pennisetum glaucum (L.) R. Br.] lines tolerant to soil salinity

Crop tolerance to salinity is of high importance due to the extent and the constant increase in salt-affected areas in arid and semi-arid regions. Pearl millet (Pennistum glaucum), generally considered as fairly tolerant to salinity, could be an alternative crop option for salt affected areas. To explore the genotypic variability of vegetative-stage salinity tolerance, 100 pearl millet lines from ICRISAT breeding programs were first screened in a pot culture containing Alfisol with 250 mM NaCl solution as basal application. Subsequently, 31 lines including many parents of commercial hybrids, selected from the first trial were re-tested for confirmation of the initial salinity responses. Substantial variation for salinity tolerance was found on the basis of shoot biomass ratio (shoot biomass under salinity/ non-saline control) and 22 lines with a wide range of tolerance varying from highly tolerant to sensitive entries were identified. The performance of the genotypes was largely consistent across experiments. In a separate seed germination and seedling growth study, the seed germination was found to be adversely affected (more than 70% decrease) in more than half of the genotypes with 250 mM concentration of NaCl. The root growth ratio (root growth under salinity/control) as well as shoot growth ratio was measured at 6 DAS and this did not reflect the whole plant performance at 39 DAS. In general, the whole plant salinity tolerance was associated with reduced shoot N content, increased K⁺ and Na⁺ contents. The K⁺/Na⁺ and Ca⁺⁺/Na⁺ ratios were also positively related to the tolerance but not as closely as the Na⁺ content. Therefore, it is concluded that a large scope exists for improving salt tolerance in pearl millet and that shoot Na⁺ concentration could be considered as a potential non-destructive selection criterion for vegetative-stage screening. The usefulness of this criterion for salinity response with respect to grain and stover yield remains to be investigated.     

Development of salt tolerant IR64 near isogenic lines through marker-assisted breeding

Salt stress causes considerable damage to rice with a consequent reduction in grain yield, however, conventional breeding for this stress is time-consuming and costly. Recently, marker-assisted breeding has shown enormous potential to accelerate breeding of stress tolerant varieties because of its precision, time saving, and cost effectiveness. The present study was carried out to transfer Saltol, a major QTL on chromosome 1 associated with salinity tolerance, from FL478, a tolerant genotype, into IR64, a popular lowland variety through marker-assisted backcrossing (MABC). This technique considerably enhanced the recovery rate of the recurrent parent genome within three backcross generations, which could have saved several backcrosses compared with conventional schemes to achieve the same results. By using this technique, up to 99.7% of the recurrent parent genome was recovered at BC₃F₂ generation, saving at least three backcrosses compared with conventional breeding schemes. Salinity tolerance of IR64-Saltol lines was evaluated using saline culture solution adjusted to electrical conductivity of 12 dS m^-1 using NaCl. Based on selected physiological and growth parameters, the new Saltol introgression lines showed a significantly higher tolerance of salinity than their recurrent parent IR64. The results of this study confirm the benefits of using molecular markers in plant breeding to enhance tolerance of abiotic stresses.     

Evaluation of Al-tolerance on upland and lowland types of NERICA lines under hydroponic conditions

We evaluated Al-tolerance in 44 interspecific lines (32 upland and 12 lowland) developed from the crosses of Oryza sativa and O. glaberrima called New Rice for Africa (NERICA) with 2 O. glaberrima lines and 13 O. sativa varieties under hydroponic culture containing 0.15, 0.3, 0.6, and 1.2 mM Al (+Al) and 0 mM Al (?Al as a control). Ten upland and four lowland NERICA lines showed strong Al-tolerance judging from their higher relative root and shoot dry weights (percentage ratios of dry weights in the Al treatments to the control) than those of the tolerant O. sativa check of IR 53650. Their tolerance was supported by relatively higher root Al accumulation (dark blue color) opposite performance with common knowledge (shown pale blue color) in root using hematoxylin staining compared to the Al-susceptible genotypes identified based on relative root and shoot dry weights in the study. Net Al concentration was higher in roots than in shoots in all +Al conditions for all genotypes; however, a clear difference in the Al concentration among the Al-tolerant, Al-moderately tolerant, and Al-susceptible genotypes was observed in the shoots. Al concentrations in the shoots of the Al-tolerant and Al-moderately tolerant upland and lowland NERICA lines were significantly lower than those of its Al-susceptible counterparts in the groups under 0.6 and 1.2 mM Al conditions, respectively. Differences in root and shoot growth among the Al-tolerant, Al-moderately tolerant, and Al-susceptible NERICA lines were clearer under strong Al toxic conditions (0.6 and 1.2 mM Al) than under weak Al toxic conditions (0.15 and 0.3 mM Al).     

Growth Properties and Ion Distribution in Different Tissues of Bread Wheat Genotypes (Triticum aestivum L.) Differing in Salt Tolerance

Four bread wheat genotypes differing in salt tolerance were selected to evaluate ion distribution and growth responses with increasing salinity. Salinity was applied when the leaf 4 was fully expanded. Sodium (Na⁺), potassium (K⁺) concentrations and K⁺/Na⁺ ratio in different tissues including root, leaf‐3 blade, flag leaf sheath and flag leaf blade at three salinity levels (0, 100 and 200 mm NaCl), and also the effects of salinity on growth rate, shoot biomass and grain yield were evaluated. Salt‐tolerant genotypes (Karchia‐65 and Roshan) showed higher growth rate, grain yield and shoot biomass than salt‐sensitive ones (Qods and Shiraz). Growth rate was reduced severely in the first period (1–10 days) after salt commencements. It seems after 20 days, the major effect of salinity on shoot biomass and grain yield was due to the osmotic effect of salt, not due to Na⁺‐specific effects within the plant. Grain yield loss in salt‐tolerant genotypes was due to the decline in grain size, but the grain yield loss in salt‐sensitive ones was due to decline in grain number. Salt‐tolerant genotypes sequestered higher amounts of Na⁺ concentration in root and flag leaf sheath and maintained lower Na⁺ concentration with higher K⁺/Na⁺ ratios in flag leaf blade. This ion partitioning may be contributing to the improved salt tolerance of genotypes.     

QTL mapping for biomass and physiological parameters linked to resistance mechanisms to ferrous iron toxicity in rice

Lowland rice is often subject to iron toxicity which may lead to yield reduction. In order to cope with this nutrient disorder, plants have developed resistance strategies. The aim of this research was to assess morphological and physiological parameters linked to iron toxicity resistance mechanisms and to identify quantitative trait loci (QTLs) involved in their genetic determinism. A segregating population consisting of 164 recombinant inbred lines (RILs) derived from a cross between Azucena and IR64 was tested twice in hydroponics at the vegetative stage at 0 and 250 mg Fe²⁺ l⁻¹. Morphological traits were measured on all 164 RILs. Physiological traits, which were too time-consuming to allow their measurement on all the population, were measured on the two parents and extreme individuals only, selected on the basis of their leaf bronzing index and shoot dry weight. A total of 24 putative QTLs was identified on chromosomes 1, 2, 3, 4, 7 and 11 for leaf bronzing index, shoot water content, shoot and root dry weight, relative variation of shoot and root dry weight, shoot iron concentration, stomatal resistance and chlorophyll content index. Several QTLs were detected in overlapping regions for different parameters. The pertinence of phenotyping extreme RILs only for a QTL analysis is discussed in this study. The QTL analysis allowed to better understand the physiological response of rice in the presence of an excess of ferrous iron, inclusive the relations existing between the stomata closure, the shoot water content reduction and the oxidative stress linked to these growth conditions.     

Interaction of Phosphate and Salinity on the Growth and Yield of Rice (Oryza sativa L.)

The role of phosphorus application on growth and yield of rice under saline conditions was studied in a set of two experiments, one in nutrient and the other in soil culture. In experiment 1, the effect of inorganic phosphate (P_i) on the growth and ionic relations of four rice cultivars, varying in salt tolerance and phosphorus use efficiency, grown in nutrient solution with and without 50 mol m^?3 NaCl was measured in a 2 week trial. The growth of all rice cultivars was affected to different degrees due to external P, in the presence of salt. External P, concentration up to 100 μM in the presence of NaCl caused stimulation of all growth parameters (shoot, root, tillering capacity), above this concentration P, had an inhibitory effect. Salt-induced P toxicity was exhibited at a much lower P, concentration (10 μM) by the salt sensitive cultivar. Increasing the supply of phosphorus (from 1 to 100 μM P_i) to the saline medium tended to decrease the concentrations of Na¹ and CI in all cultivars except IR 1561. Shoot concentrations of these saline ions were much lower in the salt tolerant and moderately salt tolerant rice cultivars. Shoot P and Zn concentrations showed an increasing trend in the presence of external P, and salt in the rooting nr -idium but most strikingly P: Zn ratio was lower in salt tolerant and moderately salt tolerant cultivars. Significantly higher concentrations of Na⁺, P and CI, and lower concentrations of Zn, were determined in the shoots of salt sensitive cultivars when exposed to salt stress in the presence of P_i Results were confirmed in naturally salt-affected soils of two different types (saline-sodic and saline) where paddy yield of NIAB 6 (salt tolerant) and IR 1561 (salt sensitive) showed improvement through moderate phosphorus supply (18 kg P ha^?1).     

Genetic variability in tolerance to cadmium and accumulation of heavy metals in pea (Pisum sativum L.)

Ninety-nine wild growing and primitive varieties of garden pea (Pisum sativum L.) were screened for tolerance to cadmium (Cd) toxicity in quartz sand culture. Cadmium tolerance was determined by the time to plant death when treated with a lethal Cd concentration (13 mg kg^-1), and by a tolerance index (TI) calculated as a ratio between biomasses of Cd-treated and untreated plants in the presence of toxic Cd concentrations (7 mg kg^-1 and 5 mg kg^-1). The Cd-tolerance index varied significantly between pea genotypes from 35% to 90% and from 54% to 100% in the presence of 7 and5 mg Cd kg^-1, respectively. Shoot Cd concentration of tolerant and sensitive genotypes grown in the presence of 5 mg Cdkg^-1 varied between 35 mg Cd kg^-1and 135 mg Cd kg^-1 (dry weight) and was negatively correlated with TI. Certain tolerant pea genotypes were characterized by a high Cd concentration in shoots. All varieties were also screened for their ability to take up heavy metals (HMs) from a slightly contaminated soil. The concentration of Cd, chromium, copper, nickel, lead, strontium and zinc in plant shoots varied between pea genotypes by a factor of 2.8, 4.9, 2.7, 3.5, 9.7, 3.9 and 4.0, respectively. The coefficients of variation between pea genotypes for HM concentration were high, varying from 23%to 39% depending on the metal. The distribution patterns for varieties based on Cd tolerance (sand culture) and HM concentrations (soil culture) were characterised by positive skewness coefficients, suggesting that the majority of pea genotypes was relatively sensitive to Cd toxicity and tended to avoid excessive accumulation of HMs in shoots. These results show that a high genetic variability exists in pea with regards to Cd tolerance and HM accumulation. Concentrations of different HMs in plants grown in soil correlated positively with each other, with the exception of chromium. There was no correlation between Cd tolerance of the varieties in sand culture, shoot concentration of HMs in soil culture, biomass production, subspecies and geographical origin of the varieties. The genetic systems controlling Cd tolerance, HM accumulation and morphological traits are therefore independent to some extent, suggesting a possibility for breeding pea cultivars characterised by high tolerance to and low concentration of HMs in shoots. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mechanisms associated with tiller suppression under stagnant flooding in rice

Stagnant flooding (SF) during vegetative growth triggers stem elongation usually at the cost of tiller production in rice, reducing grain yield. To explore physiological mechanisms associated with tillering suppression under SF, three contrasting genotypes (Swarna and Swarna‐Sub1, both sensitive and IRRI154, tolerant) were evaluated under standing water depths of 0, 5, 30 and 50 cm. SF significantly suppressed tiller formation but increased plant height, root biomass, shoot elongation (ratio of plant height before and after flooding), leaf emergency and non‐structural carbohydrate (NSC) concentration (in root–shoot junction) in all genotypes at the early stage of development. Chlorophyll concentration in the upper leaves (upper most fully expanded leaf at top) was higher than in lower leaves (lowest green leaf at base), but decreased under SF in both. SF increased hydrogen peroxide (H₂O₂) at the early stage of treatment, with concomitant increase in malondialdehyde (MDA) production by stems and leaves. MDA concentration in root–shoot junction increased but delayed. Tiller number correlated negatively with plant height, shoot elongation, leaf emergency, MDA concentration in leaves and root–shoot junction, root biomass, and NSC concentration in the root–shoot junction. The results suggested existence of compensatory mechanisms between tiller growth and shoot elongation in rice for resilience under SF, where energy is mainly diverted for shoot elongation to escape flooding. The SF‐tolerant genotype produced less H₂O₂ and maintained energy balance for higher survival and better growth under stagnant flooding.     

不同耐低磷水稻基因型秧苗对难溶性磷的吸收利用

选取4个典型耐低磷水稻基因型99011、508、580和99112,并以2个磷敏感基因型99012和99056为参照,采用营养液培养和砂培的方法,研究不同磷处理对秧苗生长的影响以及不同耐低磷基因型对3种难溶性磷源(有机磷、铝磷和磷矿粉)吸收利用能力的差异。结果表明,不同无机磷处理,6个基因型生物量和根干重基本上均为全磷处理（P）>对照+铝磷（CK+Al-P）>对照+磷矿粉（CK+RP）> 对照（CK）;4个耐低磷基因型根干重和根冠比均大于2个磷敏感基因型;对于根冠比,耐低磷基因型580和99011为对照+磷矿粉（CK+RP）>对照+铝磷（CK+Al-P）> 对照（CK）> 全磷处理（P）,耐低磷基因型508、99112和磷敏感基因型99012为CK> CK+RP> CK+Al-P > P,磷敏感基因型99056为CK+Al-P > CK+RP > P>CK;缺磷处理,秧苗活化吸收难溶性磷源的能力均为OP> Al-P> RP,且不同基因型的分解吸收能力对OP为99011> 508> 580> 99012> 99112> 99056（表2）,对Al-P为580> 99011> 99112> 508> 99056> 99012（表3）,对RP为580> 99112> 99011> 508> 99012> 99056（表2）。此外,缺磷即CK处理,508对低浓度的磷吸收最多(表2和表3),而580对磷的利用效率显著高于其他基因型（表3）,这些特征可能也是它们耐低磷的重要贡献因子之一。     

Rice Yield Gap due to Iron Toxicity in West Africa

Iron toxicity is a widespread nutrient disorder in lowland rice, notably in West Africa. It occurs in irrigated or rain-fed rice crops when the soil contains excessive amounts of iron. Associated with leaf discoloration symptoms (bronzing), this excessive iron uptake causes poor growth and tillering and leads to severe yield reductions. Field experiments were carried out in West Africa from 1994 to 1998 at two sites with high iron toxicity and one non-toxic site to assess the effects of iron toxicity on rice cropping and evaluate the tolerance of promising rice cultivars available in West Africa. To estimate yield losses caused by iron toxicity, the yield potential was simulated using the ORYZA-S rice growth and yield model. Based on the potential yield, the yield loss in an iron-toxic site is the combination of the yield gap caused by unknown site factors and the yield gap caused by iron toxicity. Compared to the referential yield obtained in a non-iron-toxic site, iron toxicity reduced rice yields by 16–78 % (mean 43 %). The extent of the yield loss depended on rice cultivar, iron toxicity intensity and crop management strategy (water control and mineral fertilisation). A strong correlation obtained between yield and the iron toxicity score, based on visual symptoms indicated an approx. 400 kg ha⁻¹ yield loss for each visual score point increase. The high genetic variability in iron toxicity tolerance and close correlation between leaf symptom score and grain yield between rice genotypes provide a good basis for breeding varieties that can produce higher yields under iron-toxic conditions.     

Genetic variation for shoot elongation before winter and its correlation with vernalization requirement in winter oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

Changing climatic conditions in north-western Europe are accompanied by occasional extreme weather conditions. This requires breeding of winter oilseed rape cultivars which are resilient to diverse abiotic stress factors, e.g. frost, drought and heat. The degree of vernalization requirement of winter oilseed rape has been found to be related to frost tolerance and winter hardiness. Shoot elongation before winter in particular has been identified as one decisive factor for frost tolerance in winter oilseed rape. However, the relationship between vernalization requirement and shoot elongation before winter is not known. In the present study the genetic variation for shoot elongation before winter and vernalization requirement of 19 genetic diverse breeding lines and cultivars were analyzed. Autumn and spring sown field experiments in multiple environments were performed to determine shoot elongation before winter and vernalization requirement, respectively. In spring sown field experiments, genotypes with a low vernalization requirement were characterized by the occurrence of long bolting plants with flower buds. Large and significant genotypic variation was found for shoot length in the autumn sown and spring sown environment. Broad sense heritability was quite high for shoot length in the spring sown environment (h²?=?97%), whereas it was only of medium size for shoot length before winter (h²?=?62%). Although the correlation between shoot length before winter and shoot length in the spring sown environment was positive (Spearman’s rank r_S?=?0.48*), a number of genotypes with reduced shoot elongation before winter and low vernalization requirement were identified. Results indicate that genotypes with a reduced shoot elongation before winter independent of their vernalization requirement can be selected in breeding programs.     

Differential tolerance to Fe and Zn deficiencies in wheat germplasm

Tolerance to Fe deficiency of wheat genotypes exhibiting differential tolerance to Zn deficiency is not known, even though the relationship between Fe nutrition and differential tolerance of wheat genotypes to Zn deficiency has been hypothesised frequently. In the present experiment, eight Triticum aestivum and two T. turigidum L. conv. durum cultivars were grown in nutrient solution deficient in either Znor Fe. Three indices of tolerance to nutrient deficiency were compared: relative [(-nutrient/+nutrient) × 100] shoot growth, shoot dry weight under nutrient deficiency and relative shoot/root dry weight ratio. Genotypes Aroona, Excalibur, Stilleto and Trident were classified as tolerant to both Zn and Fe deficiency, while durum wheats Durati and Yallaroi were sensitive to Zn deficiency and moderate to sensitive to Fe deficiency. Genotypes Excalibur, Stilleto and Trident come from the same breeding programme and have the common parent (line MEC3 =Sonora64//TZPP/YAQUI54) that could have been the donor of the genes for tolerance to Zn deficiency. When Fe-deficient, all wheat genotypes were severely chlorotic but kept producing shoot and root dry matter at a relatively high rate, making the relationship between the relative shoot growth and the relative leaf chlorophyll content poor. This is the first report of wheat genotypes exhibiting multiple tolerance to Zn and Fe deficiencies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genotypic differences in wheat Al tolerance

Summary Aluminium tolerance of 83 genotypes from Croatian and Yugoslav Triticum aestivum germplasm was evaluated in nutrient solutions having Al³⁺ activities of 0, 12.5 and 25 M. Relative root length (25 M Al³⁺/0 Al) of various genotypes ranged from 2 to 97% (from very sensitive to tolerant to Al). No genotype with Al tolerance close to that of very tolerant cultivar Atlas-66 was found. Soil, climatic, fertilization, and liming effects that wheat plants giving seeds for the nutrient solution Al-tolerance screening had been subjected to during their growth cycle did not influence the Al-tolerance ranking. Significant correlation was found between screening wheat for Al tolerance in nutrient solutions and in acid Pseudogley soil amended with five rates of limestone in a greenhouse experiment. Seed protein concentration was significantly related to the Al-tolerance ranking (r² = 0.962). Such a significant correlation was not obtained in a case of rheological and other quality characteristics of seeds. Al-tolerant wheat genotypes identified in this study will be used in breeding for improved Al tolerance.Abbreviations HSD Tukey's Honestly Significant Difference - RRL-2 relative root length, in % (12.5 M Al³⁺/0 Al) - RRL-4 relative root length, in % (25 M Al³/0 Al)     

Studies on differential response of wheat cultivars to boron toxicity

Experiments were carried out to study the differential responses of different wheat cultivars to boron toxicity in field, greenhouse and growth chamber conditions. In field trials carried out at two locations, both of which are known to contain toxic amounts of water-extractable B, significant correlations were obtained between toxicity symptoms and grain yields. The only durum cultivar included in this group of experiments (Kunduru 1149) was the most sensitive of the 21 cultivars trialed. The most tolerant cultivars were of local origin. Genotype-environment interaction was considerably large. Twenty-nine bread wheat and three durum wheat cultivars were compared in a greenhouse experiment with and without the application of 40 mg L^-1 B. Again, the durums were the most sensitive cultivars. The most tolerant cultivars were either selections from local populations or had at least one parent of local origin. The detrimental effect of B on root dry matter production was much higher than on shoot dry matter (45 and 26%, respectively), but genotypical variation was greater in shoot growth retardation. While this implies the possible role of reduced translocation, high concentrations of B in the shoots of tolerant cultivars (though lower than in the sensitive cultivars) indicated the existence of other contributing mechanisms, such as tissue tolerance. Also, greater genotypical variation in older leaves showed that reduced uptake might be more important than reduced translocation in some cases. Due to the lack of correlation between results from the field and the controlled-environment studies, it was concluded that screenings should be undertaken in both situations as a means of verification. Another conclusion drawn was that symptom scoring for B tolerance was more reliable than measuring plant B concentrations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic variability of faba bean genotypes for chocolate spot (<Emphasis Type="Italic">Botrytis fabae</Emphasis>) resistance and yield

Faba bean (Vicia faba L.) has high utility as a food and soil fertility improving crop. One of the major fungal pathogens of faba bean is Botrytis fabae, the causative agent of chocolate spot. The disease affects significantly the leaf, stem, pod and seed of faba bean compromise its productivity in the smallholder farming sector. Nonetheless, there are limited resistant/tolerant faba bean varieties available and disease control technology options. Therefore, it was prudent to evaluate faba bean landraces for chocolate spot resistance. Fifty landraces together with ten improved varieties were evaluated both in the field and in the greenhouse under natural and artificial inoculation with previously selected aggressive Botrytis fabae isolate (Iso-016) from West Gojjam, in Ethiopia. There were highly significant differences (p?<?0.001) among the landraces for reaction to the disease and agronomic traits. Significant positive correlation was recorded between reaction of genotypes in the field and greenhouse disease data. The overall mean disease epidemics varied from 92.5 to 697.5 for the area under disease progress curve (AUDPC). The highest level of resistance was found in the ICARDA lines, ILB-4726, ILB-938 and BPL-710. Of all 18 landrace collections displayed significantly lower disease reaction than the susceptible check. However the resistance was moderate. The selected eighteen landraces will be recommended for use in breeding for chocolate resistance. Overall, resistance was highly heritable, suggesting that phenotypic selection can be exploited to improve chocolate spot resistance in faba bean varieties.