Estimates of heritability for,and relationships between,root and shoot characters of white clover. I. Replicated clonal material

Summary A total of 749 genotypes from a number of white clover (trifolium repens L.) cultivars and populations, many collected from dryland areas, were cloned and grown in field titles. Several morphological characters, including leaf size, number and diameter of large nodal roots (taproots), and proportion of root weight that was classified as taproot were measured. There was large variation between lines and genotypes for all characters measured, and differences between genotypes within lines are also reported. Broad sense heritability estimates were higher (>0.5) for leaflet width, petiole length and stolon diameter, than for all root character heritability estimates which were between 0.2 and 0.4.     

Contribution of host-pathogen interactions to the expression of the blackleg disease of spring rape (Brassica napus L.) caused by Leptosphaeria maculans (Desm.) Ces. et de not

Variation in the responses of selected genotypes of spring rape to infection by a wide range of isolates of Leptosphaeria maculans was analyzed in this study.Differences in severity of disease damage to seedlings between host and pathogen genotypes were highly significant. Interactions between host and pathogen were also highly significant. The generally resistant cultivar Wesreo was susceptible to a number of isolates whereas the normally susceptible cultivars Zollern-gold and Ceska were resistant to some isolates. Overall, however, Wesreo was resistant to a far greater number of isolates than were the susceptible genotypes.Significant differences in severity of disease damage were also observed between groups of isolates from different sites. All host genotypes were resistant to a substantially greater proportion of isolates from certain sites than from others. Interactions were again detected in that the ranking of sites on the basis of the proportion of isolates causing severe damage varied between host genotypes.The significance of host-pathogen interactions in the B. napus-L. maculans relationship is discussed with special reference to current views on the nature of horizontal resistance.     

Diversity for osmotic adjustment and root depth in TEF [Eragrostis tef (Zucc) Trotter]

Osmotic adjustment (OA) and deep roots were shown to be important drought resistance mechanism in many crop plants. In this study, geno types systematically selected from an Ethiopian endemic tef [Eragrostis tef (Zucc) Trotter] germplasm pool were evaluated for osmotic adjustment and root depth in greenhouse in several experiments. The association of these traits with other plant characters was also studied. Osmotic adjustment was investigated in two experiments. Experiment 1 was conducted using nine genotypes for two seasons (spring and fall 1996), and experiment 2 was undertaken in the spring of 1997 with 45 genotypes. In experiment 1, there were significant genotype effects on OA. Though there was also significant genotype by season interaction for OA, some of the extreme lines gave consistently high (Ada and DZ-01-99) and low (DZ-01-354 and Trotteriana) OA values across seasons. There was a significant variation among genotypes for OA in experiment 2. Osmotic adjustment was not associated with the altitude of the region of origin of the particular tef genotype. In both experiments, OA was significantly correlated across tef genotypes with delayed wilting and the maintenance of higher relative water content (RWC) under conditions of soil moisture stress. Three experiments were conducted to evaluate the phenotypic diversity for root depth. In all experiments tef genotypes differed significantly for root depth as measured at flowering time. The late maturing genotypes tended to have greater root depth as compared to early maturing genotypes. Root depth was not associated with the altitude of the region of origin of the tested genotypes. There was no association between root depth and OA across genotypes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Heterosis and heritability in crosses among Asian and Ethiopian parents of hot pepper genotypes

Hot pepper is the most important worldwide grown and consumed spice and vegetable crop. Though hybrid breeding has been proposed for genetic improvement in the crop, but there is lack of information on heterosis in crosses among crop genotypes in Ethiopia. Twelve genotypes (nine Asian and three Ethiopian parents) of hot pepper were crossed in 2003 cropping season in a half-diallel fashion to fit Griffing’s fixed effect model analysis. An open field experiment was conducted in 2004/2005 to investigate heterosis for fourteen traits in 66 F₁ hybrids grown together with their 12 selfed parents. Highly significant genotypic differences were observed for all the traits except for leaf area. Variance component due to specific combining ability (dominance) were larger than that due to general combining ability (additive) for each of the studied traits with few exceptions. Broad sense heritability (H _b²) for fruit traits were more than 60% and with wide gap from narrow sense heritability (h _n²) for most of the important traits like number of fruit per plant (H _b² = 88.3% and h _n² = 46.0%), days to maturity (H _b² = 87.2% and h _n² = 23.1%) and dry fruit yield per plant (H _b² = 72.6% and h _n² = 14.6%). Maximum heterosis over mid-parent and better-parent, and economic superiority of hybrid over standard check were recorded, respectively for dry fruit yield per plant (163.8, 161.8 and 92.1%), number of fruits per plant (104.4, 79.6 and 136.4%) and days to maturity (−29.8, −31.5 and −23.6%). These observations suggested a possibility of utilizing dominance genetic potentiality available in diverse genotypes of the crop by heterosis breeding for improving hot pepper to the extent of better economic return compared to the current commercial cultivar under production in the country. Low narrow sense versus very high broad sense heritability for days to maturity and dry fruit yield per plant could be a sign for achievability of earliness and high fruit yield using heterosis in hot pepper. The maximum heterobeltiosis were recorded either from F₁s obtained from Ethiopian and Asian crosses or from within Asian crosses, suggesting the possibility of maximizing heterosis by considering genetically diverse parental genotypes. The manifestation of highest heterosis in hybrids from among Asian lines indicated existence of genetic diversity among Asian genotypes and the potentiality for improvement of hot pepper using genotypes from different regions of the world along with elite inbred lines from local cultivars.     

The inheritance and biochemistry of resistance to Sclerotinia sclerotiorum leaf infections in sunflower (Helianthus annuus L.)

Summary Resistance of sunflower leaves to attack by Sclerotinia sclerotiorum was studied by infecting them, in the field, with agar disks containing Sclerotinia mycelium. Resistance levels were determined by the length of lesions after a given period. There were significant differences in reaction between both sunflower hybrids and inbred lines. Different Sclerotinia isolates gave the same classification of sunflower genotypes. The results of trials repeated in one year or different years were significantly correlated. The general combining ability variance/specific combining ability variance ratio was 1.35. Strict sense heritability was 0.61±0.03. The midparent-offspring correlation coefficient was significant, but the relation between per se values of the male parents used with the values of their hybrids was much closer than that for the female parents. Mean heterosis for resistance was 28.9%, compared with the midparent. The results of the leaf resistance test are frequently correlated with levels of resistance to root attack by Sclerotinia. Possible use of this test in breeding both directly for leaf resistance and indirectly for root resistance are discussed. H.P.L. Chromatography studies of the phenols present in healthy and infected leaves distinguished 19 compounds, all of the inhibitin type. There was a large increase in phenol content in leaves infected by Sclerotinia, for all genotypes. However, more especially in uninfected leaves, the contents of 3 chromatogram peaks, numbered 4, 6 and 9, showed a close relation with levels of Sclerotinia resistance. It is proposed that these compounds could be used as markers of certain types of resistance.     

Yield of bolting winter beet (Beta vulgaris L.) as affected by plant density,genotype and environment

Winter beet roots and shoots might be a favorable substrate for biogas production in Central Europe. However, detailed information about the attainable yield of this crop is lacking. Thus, the impact of plant density, genotype and environmental conditions on total dry matter yield of winter beet crops that bolt after winter was investigated. A significant increase of the dry matter yield (esp. shoot) was expected by harvesting the 1st shoot after flowering in June followed by a final harvest of the whole plant in July. In 2009/10, 2010/11 and 2011/12, three series of field trials with (i) 3 target plant densities (148, 246, 370 thousand plants ha⁻¹) and (ii) 3 different sugar beet genotypes were conducted at Göttingen (Lower Saxony, GER) and Kiel (Schleswig-Holstein, GER); (iii), additional field trials with 5 different sugar beet genotypes cultivated at 2 target plant densities (148, 246 thousand plants ha⁻¹) were conducted in 2011/12, to investigate the relation between maximum taproot diameter and the shoot and taproot yield of bolting winter beet. The total dry matter yield considerably varied between 4 and 23 t ha⁻¹. It was predominantly affected by the environment and to a substantially lower extent by plant density. Increasing plant densities increased the total dry matter yield, resulting in a significantly higher total dry matter yield at plant densities ≥300,000 plants ha⁻¹ compared with lower plant densities. Genotypic differences in total dry matter yield were negligibly small. Pruning in June substantially increased the total dry matter yield in July by ca. 8 t ha⁻¹ only in one out of three environments.Final yield in June (without pruning) and July (pruning in June) was positively related with cumulated temperature and global radiation, but also with taproot dry matter yield before winter. The taproot, shoot (1st, 2nd) and total plant yield were positively correlated with maximum taproot diameter.In conclusion, high dry matter yields close to yields of established energy crops grown over winter were obtained with winter beet roots and shoots only under very favorable conditions (climate, single plant size). High yields can be achieved after good pre-winter development. However, for sufficient frost tolerance the taproot size of plants must be rather small. Hence, the cultivation of bolting winter beet under Central European climate conditions has to face a severe conflict of goals concerning winter survival and yield formation.     

Genotypic variation for root pulling resistance in potato and its relationship with yield under water-deficit stress

Summary An extensively distributed root system may reduce the probability of crop failure during periods of restricted water supply. A quantitative measure of root distribution in the soil profile, i.e. pulling resistance of roots (PR), was tested at two moderately droughted tropical field sites. A total of 250 genotypes were evaluated for PR, 45 days after planting and for tuber yield at harvest at separate sites and years. The need to use genotypes adapted to a specific location for comparisons, across sites or seasons was shown by the results of a random analysis of variance model partitioning across site-season, location, and year effects for PR and tuber yield.A combined PR and growth analysis on 31 early-maturing clones, 7 of which had tubers at the time of sampling, gave significant correlations between PR and root length, dry weight of pulled and residual roots, plant height, number of stems, and in the case of the 7 genotypes with tubers, tuberlet weight and number. A regression model to predict PR based on growth analysis data is presented. Neither tuberlet weight nor number contributed significantly to the prediction once root characters and vigour-related characters were incorporated. Variation for PR among clones was significant and the means ranged from 0 kg/plant to 37 kg/plant during the 3 trials. High PR was evident in both early and late maturing clones. Drought resistance (DR), defined as high yielding ability and high PR under water deficit conditions, of the clones Huinkul and MS-35.22.R was superior to that of the high-yielding and adapted LT-7 check, while moderate levels of DR were confirmed for the clones BR-63.15, Cruza 27, Haille, and MEX-21. Tuber yield and PR under moderate drought were significantly correlated (r=0.569^***), which suggests that the PR method can be utilized to assist in the selection of high-yielding, drought resistant, potato genotypes adapted to tropics.     

大豆根内胞囊线虫的时空动态研究

于2006-2007年田间自然生长条件下,研究大豆苗期(7~37 d)胞囊线虫(4号生理小种)在根系的时空分布动态。结果表明,大豆胞囊线虫分布与根系生长状况有密切关系。出苗后7 d已有线虫侵入根内,随着根系生长发育,单位根长线虫数以及线虫总数增多,单位根长内线虫数量呈S型曲线变化。随着出苗后天数的增加,主根和侧根内线虫数量变化呈相反趋势,其中主根内线虫密度减少,侧根内线虫密度增加至相对稳定值。随着土层的加深,主根和侧根内线虫密度差异减小;5~15 cm土层根系内线虫数量及其所占比例均最大。说明苗期大豆胞囊线虫主要分布在5~15 cm土层。     

Identification of growth stage dependent expression of partial resistance of barley to powdery mildew

Summary Genotypic differences for growth stage dependent expression of partial resistance to barley powdery mildew have been identified on the basis of two components of resistance in the glasshouse and the pattern of epidemic development in the field.Differences for infection frequency and proportion of sporulating colonies were highly significant between the 16 genotypes investigated at four stages of plant development in the glasshouse. Both resistance components were significantly correlated mutually (r=0.73 to 0.86) and with the infection level on leaves developed at comparable growth stages in the field (r=0.52 to 0.73). The infection level of seedlings in the glasshouse was significantly correlated with the infection level of the leaves of the first until the third node in the field (r=0.70 to 0.73). Adult plant resistance was predominantly expressed at the uppermost leaf. A clear genotype × growth stage interaction was apparent for infection level; some genotypes showed partial resistance predominantly at the seedling stage and others predominantly at the adult plant stage.Abbreviations IF Infection Frequency, number of colonies per cm² leaf area, glasshouse experiment - IL Infection Level, number of colonies per cm² leaf area, field experiment - PSC Proportion Sporulating Colonies from total number of colonies, glasshouse experiment     

Effect of leaf age on components of partial resistance in rice to leaf blast

Summary Ten rice genotypes were inoculated with a virulent isolate of Magnaporthe grisea to study the effect of leaf age on components of partial resistance, and evaluate associations between these components. The number of sporulating lesions per cm² leaf declined with increase of leaf age in all genotypes. The number of lesions per cm² leaf area in one week old leaves was about 25% that of the number in very young leaves in the susceptible cultivar CO39, but less than 2% in the more resistant cultivars IR36, IR60 and IR62. Large differences between genotypes were found for the number of sporulating lesions that developed, and this factor was closely related to the period that leaves remained susceptible after appearance. The number of lesions in the most susceptible cultivar CO39 was about 7 times that in the cultivars IR60 and IR64. Differences between genotypes were also found for lesion size. The effect of aging on average lesion size was less pronounced than on lesion density. Lesion size and lesion density were positively correlated, but a rapid decline of density was not necessarily accompanied by a rapid decline of size. No apparent differences between genotypes were observed for latent period. Genotypes with leaves that became highly resistant soon after appearance expressed higher levels of partial resistance in the field.     

Evaluation and utilisation of cacao (Theobroma cacao L.) germplasm at the International Cocoa Genebank, Trinidad

The aim of this study was to identify promising genotypes in the International Cocoa Gene bank, Trinidad (ICG,T) for use in cacao breeding. Subsets of the germ plasm collection were evaluated for bean number, bean weight, pod index (581 genotypes) and resistance to Phytophthora pod rot(500 genotypes). Among three groups of cacao assessed (For astero, Refractario and Trinitario), Trinitario had the highest percentage of genotypes (36.9%) with large bean weight (> 1.2 g), while For astero possessed the highest proportion of genotypes (22.6%) with a large number of beans (> 45). The ICS population had the highest percentage (44.1%) of genotypes with heavy beans, and IMC the highest percentage of genotypes with large bean number (68.6%). A low, but significant negative correlation (r = –0.19, p≤ 0.001) between bean number and bean weight suggests that an increase in bean number may repress an increase in bean weight and vice versa. However, inten genotypes good values of bean weight and number were combined demonstrating that selection for both large bean number and bean weight is possible. The highest percentage (28.1%) of genotypes with low pod index (< 20.1) was observed in the Trinitario group (mainly ICS). The Forastero group had the highest percentage of Phytophthora resistant accessions(18.0%). The PA population had the highest proportion of resistant (24.0%) and moderately resistant (38.0%)genotypes. Sixty-five and 99 genotypes were categorised with large bean weight and high bean number, respectively, and 60 genotypes were found with a low pod index. Seventy-eight genotypes were identified with resistance to Phytophthora podrot. A significant relationship was observed between resistance to Phytophthora pod rot (measured as the frequency of localised lesions) and bean number (r = –0.45, p ≤ 0.001)showing that the two traits may complement each other. The combination of low to intermediate pod index with moderate to high resistance to Phytophthora podrot was found in 87 genotypes, 12 of which were also reported to have resistance to witches’ broom disease. These genotypes are of high potential value in cacao breeding and their inclusion in working and corecollections would be justified. This revised version was published online in July 2006 with corrections to the Cover Date.     

Selection of wheat genotypes for biomass allocation to improve drought tolerance and carbon sequestration into soils

The biomass allocation pattern of plants to shoots and roots is a key in the cycle of elements such as carbon, water and nutrients with, for instance, the greatest allocations to roots fostering the transfer of atmospheric carbon to soils through photosynthesis. Several studies have investigated the root to shoot ratio (R:S) biomass of existing crops but variation within a crop species constitutes an important information gap for selecting genotypes aiming for increasing soil carbon stocks for climate change mitigation and food security. The objectives of this study were to evaluate agronomic performance and quantify biomass production and allocation between roots and shoots, in response to different soil water levels to select promising genotypes for breeding. Field and greenhouse experiments were carried out using 100 genotypes including wheat and Triticale under drought‐stressed and non‐stressed conditions. The experiments were set‐up using a 10 × 10 alpha lattice design with two replications under water stress and non‐stress conditions. The following phenotypic traits were collected: number of days to heading (DTH), number of productive tillers per plant (NPT), plant height (PH), days to maturity (DTM), spike length (SL), kernels per spike (KPS), thousand kernel weight (TKW), root biomass (RB), shoot biomass (SB), root to shoot ratio (R:S) and grain yield (GY). There was significant (p < 0.05) variation for grain yield and biomass production because of genotypic variation. The highest grain yield of 247.3 g/m² was recorded in the genotype LM52 and the least was in genotype Sossognon with 30 g/m². Shoot biomass ranged from 830 g/m² (genotype Arenza) to 437 g/m² (LM57), whilst root biomass ranged between 603 g/m² for Triticale and 140 g/m² for LM15 across testing sites and water regimes. Triticale also recorded the highest R:S of 1.2, whilst the least was 0.30 for wheat genotype LM18. Overall, drought stress reduced total biomass production by 35% and R:S by 14%. Genotypic variation existed for all measured traits useful for improving drought tolerance, whilst the calculated R:S values can improve accuracy in estimating C sequestration potential of wheat. Wheat genotypes LM26, LM47, BW140, LM70, LM48, BW152, LM75, BW162, LM71 and BW141 were selected for further development based on their high total biomass production, grain yield potential and genetic diversity under drought stress.     

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.     

Employment of flanking codominant STS markers to estimate allelic substitution effects of a nematode resistance locus in carrot

In carrot, two codominant sequence-tagged site (STS) markers, flanking in tight linkage the Meloidogyne javanica resistance (Mj-1) locus, were employed to investigate the association between expression of resistance and locus dosage. Phenotypic expression of homozygous resistant (R); heterozygous; and homozygous susceptible (S) individuals in an F₂ population of 396 F₂ plants from ‘Brasília-1252’ (R) × ‘B6274’ (S) was estimated for three resistance criteria: total egg production per plant (TEP), egg production per gram of fibrous root (EPG) and root gall index (RGI). The homozygous resistant class had average values of 403.9 for TEP; 147.5 for EPG and 0.8 for RGI. The heterozygous class had 1,673; 477.3; and 0.16 whereas the homozygous susceptible class had 68,604; 11,877; and 2.54, respectively. The dominance ratio (d/a) indicated that genomic region(s) derived from the resistant parent encompass genetic factor(s) with almost complete dominance for RGI (d/a = 0.93–0.94) and incomplete dominance for transformed (TEP)^0.25 and (EPG)^0.25 (d/a = 0.63–0.65). Broad sense heritabilities were high varying from 72.9% for (EPG)^0.25 to 86.0% for RGI. Narrow sense heritability values ranged from 55.9% for RGI to 64.3%for (TEP)^0.25. Highly significant orthogonal contrasts were observed between homozygous resistant vs. heterozygous for (TEP)^0.25 and (EPG)^0.25. Marker-assisted selection could greatly facilitate the incorporation of the Mj-1 allele in both male-fertile and male-sterile counterpart lines in order to obtain F₁ hybrids with the most effective levels of resistance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genotypic variation in durum wheat root systems at different stages of development in a Mediterranean environment

Summary Glasshouse and field experiments were carried out to compare root growth of eight durum wheat genotypes at different stages of development with different moisture levels and in different soils. Genotypic differences were found, particularly at the stem elongation and heading stages of development, but the ranking of genotypes varied in relation to soil moisture level and fertility. Differences under optimal moisture level were mainly due to differences in tillering and disappeared by considering the root number and weight per culm. Drought caused an increase in the root-to-total-plant weight ratio (18.5 vs 14.3% at heading) but also an increase in absolute root weight. Karel, the genotype with the largest root mass under drought and the greatest proportion of roots in the upper soil layers (more than 50% in the 0–20 cm layer from heading onwards), showed the lowest yield reduction under severe stress. A large root system with a high density of roots in the upper layers of the soil profile may be beneficial in Mediterranean climates.Research supported by a grant of Ministero della Pubblica Istruzione (40%).     

Simple Sequence Repeat Markers for Detecting Sources of Tolerance to PTSL Syndrome in Prunus Persica Rootstocks

Summary Peach tree short life (PTSL) is a severe and complex disease syndrome in the Southeast of the United States that causes significant damage to peach orchards and affects more than 70% of the peach acreage in the region. The ring nematode is known to be one of the major factors strongly associated with the PTSL syndrome. A peach rootstock (Guardian^? Brand BY520-9, also referred to as Guardian^? or BY520-9), which is tolerant to ring nematode and PTSL, was released in 1994. To investigate the genetic relatedness of PTSL tolerant genotypes and identify possible parents of Guardian^? selections as sources of the PTSL tolerance trait, 98 genotypes derived from the BY520-9 pedigree, and others showing different degrees of field resistance or susceptibility to PTSL, were selected for simple sequence repeat analysis. Nineteen of 32 microsatellite loci were polymorphic. Allele number averaged 2.7 per locus with heterozygosity levels ranging from 0.07 to 0.60. Cluster analysis of these genotypes produced a dendrogram in agreement with their putative pedigrees. Thirty-eight F₄ genotypes from Guardian pedigree were used for the parental identification analyses. Of those, nine most likely parental genotypes were identified for 10 field tested F₅ genotypes produced from open-pollinated selections of BY520-9.     

播种当年苜蓿根系形态特征的研究

对播种当年18个苜蓿品种材料根系形态特征进行了研究,结果表明：不同类型苜蓿根系形态指标差异明显;利用根系形态特征的10个指标对18个实验材料进行聚类,可分为4类;建议在苜蓿选种时,选取根颈直径大,入土深度深、主根长度长、侧根直径大、侧根发达的材料。     

Biometrical analysis of phosphorus use efficiency in lettuce cultivars adapted to high temperatures

With the objective of selecting phosphorus efficient lettuce cultivars adapted to high temperatures, one hundred and thirteen lettuce genotypes from the vegetable germplasm bank at CCTA-UENF, Rio de Janeiro, Brazil, were initially selected for resistance to bolting under greenhouse temperature ranging from 20 to 32 ^°C. Nineteen greater longevity genotypes were further selected and evaluated for efficiency and responsiveness to phosphorus in soils with 10 and 60 mg dm^-3 of P. The estimated genetic parameters indicated that genetic gains from selection should be expected for all traits. Based on leaf and root dry weight, Mimosa and Regina genotypes were identified as efficient users of phosphorus in soils with low P content, while BGH 292 was inefficient. The genotype graphic dispersion based on the first three canonic variables confirmed Mimosa and Regina as efficient cultivars in soil with 10 mg dm^-3 of P. Their efficiency seemed to be linked to greater capacity for phosphorus use by the plant top as well as greater root growth. Similarly, the poor performance of BGH 292 in the low P soil seemed to be associated with its low capacity of phosphorus use in the plant top and its small root growth. The α parameter identified the Mimosa genotype as efficient user but not responsive to high P levels and the Regina and BGH4064 genotypes as efficient and responsive. Mimosa is, therefore, best suited for low P-input production systems, while Regina and BGH 4064 are indicated for production systems that use P-fertilization. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

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.