Emergence and seedling growth of soybean cultivars and maturity groups under salinity

Soybean is an important agricultural crop and has, among its genotypes, a relatively wide variation in salt tolerance. As measured by vegetative growth and yield, however, the achievement or failure of a high emergence ratio and seedling establishment in saline soils can have significant economic implications in areas where soil salinity is a potential problem for soybean. This study was conducted to determine the effects of salinity, variety and maturation rate on soybean emergence and seedling growth. Included in the study were the variety ‘Manokin’; four near-isogenic sibling lines of the variety ‘Lee’ belonging to maturity groups IV, V, VI and VII; and the variety ‘Essex’ and two of its near-isogenic related lines representing maturity groups V, VI and VII, respectively. Field plots were salinized with sodium chloride and calcium chloride salts prior to planting. The soybeans were irrigated with furrow irrigation which redistributed the salts towards the tail ends of the field plots. Elevated soil salinity near the tail ends of the field significantly reduced soybean emergence rate, shoot height and root length. No significant reduction was found for emergence or seedling growth of variety ‘Manokin’ when the electrical conductivity of soil solution extract (ECe) was less than 3 dS m⁻¹. Soybean emergence and seedling growth was significantly reduced when soil ECe reached about 11 dS m⁻¹. Maturity groups V and VII of variety ‘Lee’ or V and VI of ‘Essex’ appeared to be more sensitive to salinity stress than other maturity groups. Salt tolerance of different genotypes and maturity groups should be considered, among other limiting factors, in minimizing salinity effects on soybean growth. This revised version was published online in June 2006 with corrections to the Cover Date.     

The activity of antioxidative enzymes in three strawberry cultivars related to salt-stress tolerance

Effects of salt stress on the time course of stomatal behaviors and the activity of antioxidative enzymes such as catalase (CAT) (EC 1.11.1.6), ascorbate peroxidase (APX) (EC 1.11.1.11), and glutathione reductase (GR) (EC. 1.6.4.2) were studied in three strawberry cultivars. The responses of the cultivars ‘Camarosa’, ‘Tioga,’ and ‘Chandler’ were compared when they were irrigated with nutrient solution containing 0, 8.5, 17.0, and 34.0 mM sodium chloride (NaCl) for 30 days. A significant reduction in stomatal conductance (g_s) was seen particularly on the 30th day of the salt treatments only in Camarosa, which is parallel to transpiration rate (E). CAT activities decreased in all of the salt treatments only in Tioga, while it remained almost unchanged or slightly increased depending on the period in Camarosa and Chandler. APX activity sharply increased in 17.0 and 8.5-mM NaCl treatments for 30 days in Camarosa and Tioga, respectively, whereas it linearly increased based on the NaCl treatments in Chandler. On the other hand, only Camarosa demonstrated a sharp increase in GR activity induced by salinity applied for 30 days. All the data indicated that control of the stomatal behavior, the higher salt-stress tolerance (LT₅₀) and higher constitutive activity of antioxidant enzymes made Camarosa and Tioga relatively salt-tolerant cultivars.     

Germination kinetics and seed reserve mobilization in two flax (<Emphasis Type="Italic">Linum usitatissimum</Emphasis> L.) cultivars under moderate salt stress

Because of its high contents of protein, α-linolenic-rich oil, lignans, and fiber, demand is increasing for flax(Linum usitatissi-mum L.) and flax seed oil as a food source. In this comparative survey, we examined germination and the mobilization of seed storage products (lipids and soluble proteins) of 3-d-old seedlings from two flax cultivars (N 51 and H 52) challenged with moderate salinity (up to 200 mM NaCl). At the highest salt concentration, germination appeared to be cultivar-dependent, with that of ‘N 51’ being less impaired and delayed than in ’H 52’. Sodium chloride inhibited germination via osmotic and toxic effects, so that seed viability was altered, especially in ‘H 52’. At 200 mM NaCl, lipid mobilization was delayed in the earliest germination phases. This response was associated with increased proportions of linolenic acid contents in both cultivars and more linolenic acid-rich molecular species of TAGs. Irrespective of the salt level, soluble protein contents in both cultivars decreased over time, although a salt-related precocity of protein degradation occurred at 200 mM NaCl.     

Response of antioxidant activity to excess copper in two cultivars of <Emphasis Type="Italic">Brassica campestris</Emphasis> ssp. <Emphasis Type="Italic">chinensis</Emphasis> Makino

Changes in ascorbic acid content and antioxidant enzyme activities were investigated in non-heading Chinese cabbage (Brassica campestris ssp. chinensis Makino) leaves of ‘Wutacai’ and ‘Erqing’ exposed to excess copper (Cu). Cu treatment reduced the fresh weight of shoot and root by 57% and 46% in ‘Wutacai’, and 60 and 54% in ‘Erqing’, respectively. The accumulation of copper in leaves was higher in ‘Wutacai’ than that in ‘Erqing’. Compared to the control, ascorbic acid (AsA) contents were significantly decreased after copper treatment in both cultivars, while they were higher in ‘Wutacai’ than in ‘Erqing’, which may explain the higher copper-tolerance of ‘Wutacai’ with higher copper accumulation. The higher AsA contents of ‘Wutacai’ resulted from their lower activities of degrading enzymes, such as ascorbate oxydase (AAO) and ascorbate peroxidase (APX), as well as the increasing activity of dehydroascorbate reductase (DHAR) after copper treatment compared with ‘Erqing’. Copper stimulated superoxide dismutase (SOD) activity in both cultivars, but for catalase (CAT), there was little difference between both cultivars. Peroxidases (POD) activity was decreased after copper treatment in ‘Erqing’, while in ‘Wutacai’, it was significantly increased at 14 days, and POD activity was higher in ‘Wutacai’ than that in ‘Erqing’ at 21 and 28 days. Therefore, the induced increasing activity of POD in ‘Wutacai’ also played an important role in its copper tolerance.     

Different behaviour of crop species in phosphate absorption

Summary Isotopic-dilution technique was used to study the differential phosphate absorption abilities of several field crops. The response of crops was found to be inversely related to the ratio of phosphorus absorbed from the soil to that absorbed from the fertilizer. The ‘A’ values ranged from 2.03 ppm for mustard to 21.77 ppm for soybeans. A highly significant correlation (r=0.77**) was found between per cent yields and the ‘A’ values.     

Understanding osmotic stress tolerance in leaves and nodules of two <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> cultivars with contrasting drought tolerance

Drought and salinity are environmental constraints that affect crop yields worldwide. In nature, both stresses are multifaceted problems that are usually associated with other adverse circumstances which limit plant performance such as water shortage and nutrient deficits. In order to assess common features of both stresses, the effects of mannitol-induced osmotic stress were monitored using two Phaseolus vulgaris cultivars, Cv. ‘Flamingo’ (tolerant) and Cv. ‘Coco Blanc’ (sensitive) which differed in their drought and salinity tolerance. Growth, water relations, organic and inorganic compound accumulation and soluble protein contents were measured in leaves and nodules of these N₂-fixing plants. The aim of the present study was to check whether osmotic stress tolerance is associated with accumulation of some of these compounds either in leaves, nodules or both organs. At the whole-plant level, Cv. ‘Flamingo’ showed a better maintenance of plant biomass and shoot water status. At the cell level, this was related to a better osmotic adjustment ability both in leaves and nodules and also to a better adjustment of the cell wall elasticity. At the metabolic level, the contrasting accumulation of the different amino acids in nodules of each cultivar suggested that amino acids pathways can be regulated to different degrees under stress conditions. At the metabolic level, it seems that symbiosis in the sink organ (the nodule) plays a crucial role in conferring drought and salinity tolerance in the common bean.     

Nutritional role of calcium in plants

Summary Studies, using the sugar beet as a non-leguminous crop in the Imperial and San Joaquin Valleys of California, have shown by soil tests, measured crop yields, and the storage of the disaccharide sugar in the root, that calcium is a plant nutrient deficient in these desert soils. It was demonstrated by trials over three years that the drilling in seed contact of a natural gypsiferous mineral, known in commerce as „mineralag”, gave decided improvement in the crops as increasing stands and root yields on the neutral and alkaline soils under cooperative supervision of the Holly Sugar Corporation of tests by Geyser Minerals Corp., Denver, Colorado. It was established that these desert soils with organic matter contents of barely one per cent, or less, a pH of 8.0 and higher, and of excesses of other cations above standard percentages saturation of exchange capacities, the slight variations in applications of nitrogeneous, phosphatic and mixed fertilizers in conjunction with calcium, can represent imbalanced plant nutrition as shown by reduced concentrations of the disaccharide sugar in the beet root. The absence, in near total, of both the soil organic matter and the hydrogen cation, or acidity, show clearly how badly unbuffered these soils are to be ‘physiologically shocked’ by more ‘salt’ applications in fertilizers. Accordingly, when so poorly buffered, the excesses of the other cations, namely, magnesium (possibly the most disturbing), potassium and sodium beyond adsorption potentials to be active as salts, are serious disturbers to any attempt to balance plant nutrition for higher, or controlled sugar concentrations, along with higher beet yields. These studies recognize the need to consider the balance of the cationic fertility as a factor pointing to the concentration of the disaccharide sugar as well as to the tonnage yields of roots. These studies point to the need to consider the quality, first, along with the quantity of the crop as guides for wisest soil management.     

Effects of NaCl stress on proline and cation accumulation in salt sensitive and tolerant turfgrasses

Summary Concentrations of proline, sodium and potassium in shoot tissues of five turfgrass species were measured following exposure to 170 mM NaCl salinity stress. Salt tolerant ‘Fults’ alkaligrass and ‘Dawson’ red fescue restricted the accumulation of Na-ions to significatnly low levels compared to the salt sensitive Kentucky bluegrasses (‘Adelphi’ and ‘Ram I’) and ‘Jamestown’ red fescue. Accumulation of proline began in all species within 24 h of initiation of salt stress but at a more rapid rate and higher overall concentration for ‘Fults’ alkaligrass. Proline levels were variable and too low in relation to sodium accumulations to have any significant osmoregulatory role in salt tolerance among all cultivars tested with the possible exception of alkaligrass.     

A consensus map of rye integrating mapping data from five mapping populations

A consensus map of rye (Secale cereale L.) was constructed using JoinMap 2.0 based on mapping data from five different mapping populations, including ‘UC90’ × ‘E-line’, ‘P87’ × ‘P105’, ‘I_0.1-line’ × ‘I_0.1-line’, ‘E-line’ × ‘R-line’, and ‘Ds2’ × ‘RxL10’. The integration of the five mapping populations resulted in a 779-cM map containing 501 markers with the number of markers per chromosome ranging from 57 on 1R to 86 on 4R. The linkage sizes ranged from 71.5 cM on 2R to 148.7 cM on 4R. A comparison of the individual maps to the consensus map revealed that the linear locus order was generally in good agreement between the various populations, but the 4R orientations were not consistent among the five individual maps. The 4R short arm and long arm assignments were switched between the two population maps involving the ‘E-line’ parent and the other three individual maps. Map comparisons also indicated that marker order variations exist among the five individual maps. However, the chromosome 5R showed very little marker order variation among the five maps. The consensus map not only integrated the linkage data from different maps, but also greatly increased the map resolution, thus, facilitating molecular breeding activities involving rye and triticale.     

Molecular mapping of a resistance-specific PCR-based marker linked to a gall midge resistance gene (Gm4t) in rice

 A PCR-based marker (E20₅₇₀) linked to the gene Gm4t, which confers resistance to a dipteran pest gall midge (Orseolia oryzae), has been mapped using the restriction fragment length polymorphism (RFLP) technique in rice. Gm4t is a dominant resistance gene. We initially failed to detect useful polymorphism for this marker in a F₃ mapping population derived from a cross between two indica parents, ‘Abhaya’בShyamala’, with as many as 35 restriction enzymes. ‘Abhaya’ carries the resistance gene Gm4t and ‘Shyamala’ is susceptible to gall midge. Subsequently, E20₅₇₀ was mapped using another mapping population represented by a F₂ progeny from a cross between ‘Nipponbare’, a japonica variety, and ‘Kasalath’, an indica variety, in which the gene Gm4t was not known to be present. Gm4t mapped onto chromosome 8 between markers R1813 and S1633B. Our method, thus, presents an alternative way of mapping genes which otherwise would be difficult to map because of a lack of polymorphism between closely related parents differing in desired agronomic traits. Received: 1 April 1997 / Accepted: 13 May 1997     

Symbiotic N2 fixation in pea and field bean estimated by15N fertilizer dilution in field experiments with barley as a reference crop

Summary The total amount of nitrogen derived from symbiotic nitrogen fixation in two pea and one field bean cultivar, supplied with 50 kg N ha⁻¹ at sowing (‘starter’-N), was estimated to 165, 136, and 186 kg N ha⁻¹, respectively (three-year means). However, estimates varied considerably between the three years. At the full bloom/flat pod growth stage from 30 to 59 per cent of total N₂ fixation had taken place. The proportion of total N derived from N₂ fixation at maturity was higher in seeds than in vegetative plant parts and amounted to 59.5, 51.3 and 66.3 per cent of total above-ground plant N in the two pea cultivars and field bean, respectively (three-year means). The recovery of fertilizer N was 62.2, 70.2, 52.1, and 69.5 per cent in the two pea cultivars, field bean and barley, respectively. Growth analysis indicated that barley did not meet the claims for an ideal reference crop in the¹⁵N fertilizer dilution technique for estimating N₂ fixation in pea and field bean. ‘Starter’-N neither increased the seed yield nor the N content of the grain legumes.     

Fine-mapping of qRL6.1, a major QTL for root length of rice seedlings grown under a wide range of NH4 + concentrations in hydroponic conditions

Root system development is an important target for improving yield in cereal crops. Active root systems that can take up nutrients more efficiently are essential for enhancing grain yield. In this study, we attempted to identify quantitative trait loci (QTL) involved in root system development by measuring root length of rice seedlings grown in hydroponic culture. Reliable growth conditions for estimating the root length were first established to renew nutrient solutions daily and supply NH₄ ⁺ as a single nitrogen source. Thirty-eight chromosome segment substitution lines derived from a cross between ‘Koshihikari’, a japonica variety, and ‘Kasalath’, an indica variety, were used to detect QTL for seminal root length of seedlings grown in 5 or 500 μM NH₄ ⁺. Eight chromosomal regions were found to be involved in root elongation. Among them, the most effective QTL was detected on a ‘Kasalath’ segment of SL-218, which was localized to the long-arm of chromosome 6. The ‘Kasalath’ allele at this QTL, qRL6.1, greatly promoted root elongation under all NH₄ ⁺ concentrations tested. The genetic effect of this QTL was confirmed by analysis of the near-isogenic line (NIL) qRL6.1. The seminal root length of the NIL was 13.5–21.1% longer than that of ‘Koshihikari’ under different NH₄ ⁺ concentrations. Toward our goal of applying qRL6.1 in a molecular breeding program to enhance rice yield, a candidate genomic region of qRL6.1 was delimited within a 337 kb region in the ‘Nipponbare’ genome by means of progeny testing of F₂ plants/F₃ lines derived from a cross between SL-218 and ‘Koshihikari’.     

Response of growth and fatty acid compositions of Nannochloropsis sp. to environmental factors under elevated CO2 concentration

Nannochloropsis sp. was grown with different levels of nitrate, phosphate, salinity and temperature with CO₂ at 2,800 μl l⁻¹. Increased levels of NaNO₃ and KH₂PO₄ raised protein and polyunsaturated fatty acids (PUFAs) contents but decreased carbohydrate, total lipid and total fatty acids (TFA) contents. Nannochloropsis sp. grew well at salinities from 22 to 49 g l⁻¹, and lowering salinity enhanced TFA and PUFAs contents. TFA contents increased with the increasing temperature but PUFAs contents decreased. The highest eicosapentaenoic acid (EPA, 20:5ω3) content based on the dry mass was above 3% under low N (150 μM NaNO₃) or high N (3000 μM NaNO₃) condition. Excessive nitrate, low salinity and temperature are thus favorable factors for improving EPA yields in Nannochloropsis sp.     

Mapping quantitative trait loci associated with regeneration ability of seed callus in rice, Oryza sativa L.

 Quantitative trait loci (QTL) controlling the regeneration ability of rice seed callus were detected using 245 RFLP markers and 98 BC₁F₅ lines derived from two varieties, ‘Nipponbare’ and ‘Kasalath’. Regeneration ability was evaluated by two indices: average number of regenerated shoots per callus (NRS) and regeneration rate (RR). The BC₁F₅ lines showed continuous segregation for both indices. Five putative QTL for NRS (tentatively named qRg1, qRg2, qRg4a, qRg4b and qRg4c) located on chromosomes 1, 2 and 4 were detected. Digenic interaction among these detected QTL was not significant (P<0.01). Among the five QTL detected, four ‘Kasalath’ alleles and one ‘Nipponbare’ allele increased NRS. According to an estimate based on the nearest marker loci, the five QTL accounted for 38.5% of the total phenotypic variation of the BC₁F₅ lines. For RR, four putative QTL were detected on chromosomes 2 and 4, and all of these were in the same chromosomal regions as the NRS QTL. The four RR QTL accounted for 32.6% of the total phenotypic variation. Received: 7 November 1996 / Accepted: 25 April 1997     

A parentage study of closely related Ukrainian wine grape varieties using microsatellite markers

Four bred grapevine varieties released for commercial cultivation in Ukraine, namely ‘Antey Magarachskii’, ‘Rubinovyi Magaracha’, ‘Granatovyi Magaracha’ and ‘Rubin Golodrigi’, and their putative parental forms were genotyped using six microsatellite loci. Genotypes were compared with breeding records to verify genetic relationships among varieties. Results of the analysis confirmed four of six parent-offspring relationships. Results of the analysis allow to assume that genotype ‘Seyve Villard 20347’ is the direct parent of ‘Antey Magarachskii’ instead of its grandparent. The first-studied accession believed to be that of ‘Granatovyi Magaracha’ was identified as impurity. In order to verify the parentage of ‘Granatovyi Magaracha’, rest accessions of that variety and its putative parent ‘Antey Magarachskii’ were additionally genotyped at 13 nuclear loci and at three chloroplast loci. The parent-offspring relationship was confirmed, as all ‘Granatovyi Magaracha’ accessions had a common allele with the parent variety ‘Antey Magarachskii’ at each locus and the same chlorotype A. Different ‘Granatovyi Magaracha’ accessions could have been obtained via vegetative propagation of two seedlings which arose from one crossing.     

Aggressive and Docile Colony Defence Patterns in Apis mellifera. A Retreater–Releaser Concept

Colony defence in Apis mellifera involves a variety of traits ranging from ‘aggressive’ (e.g. entrance guarding, recruitment of flying guards) to ‘docile’ (e.g. retreating into the nest) expression. We tested 11 colonies of three subspecies (capensis, scutellata, carnica) regarding their defensiveness. Each colony was selected as reportedly ‘aggressive’, ‘intermediate’ or ‘docile’ and consisted of about 10,000 bees. We applied three stimulation regimes (mechanical disturbance, exposure to alarm pheromones, and the combination of both) and measured their behaviours by tracking the rates of outflying bees at the entrance sites of the test hives. We provided evidence that for mechanical disturbances the test colonies resolved into two response types, if the ‘immediate’ defence response, assessed in the first minute of stimulation, was taken as a function of foraging: ‘releaser’ colonies allocated flying guards, ‘retreater’ colonies reduced the outside-hive activities. This division was observed irrespective of the subspecies membership and maintained in even roughly changing environmental conditions. However, if pheromone and mechanical stimulation were combined, the variety of colony defensiveness restricted to two further types irrespective of the subspecies membership: six of nine colonies degraded their rate of flying defenders with increasing foraging level, three of the colonies extended their ‘aggressiveness’ by increasing the defender rate with the foraging level. Such ‘super-aggressive’ colonies obviously are able to allocate two separate recruitment pools for foragers and flying defenders.     

Association-dissociation of glycinin in urea,guanidine hydrochloride and sodium dodecyl sulphate solutions

The effect of urea, guanidine hydrochloride and sodium dodecyl sulphate on glycinin, the high molecular weight protein fraction from soybean has been investigated by analytical ultracentrifugation. Urea and guanidine hydrochloride dissociate the protein to a ‘2S’ protein through the intermediary 7S and 4S proteins. Howeαer, in sodium dodecyl sulphate the protein directly dissociates to a 2S protein. Analysis of the data by calculation of per cent fraction and S_20,w value indicates that dissociation and denaturation of glycinin occur simultaneously in the presence of the aboαe reagents but to different extents.     

A life cycle method for assessment of a colliery’s eco-indicator

Global Scope and Background  The study was aimed at presenting the methodology of the process eco-indicator, in relation to hard coal mines, and thereby making evaluation of the impact of the mine’s coal extraction process on the environment. The life cycle of a mine is made up of three phases: opening and developing the mine’s deposit, extraction of the mine’s deposit, closing the mine. Methods  The assessment of environmental influence of mining operation of a colliery was executed on a basis of the life cycle analysis, in accordance with the standard series PN-EN 14040. The environmental loads caused by individual unit processes were calculated by means of the aforementioned methodology with division into the basic influence categories: human health, ecosystem quality and natural resources. The obtained values of eco-indicators for the individual unit processes made it possible to compare the unit-process-caused environmental loads. Mean values of the eco-indicators of the individual unit processes were calculated by means of the inventory analysis covering 38 collieries. Next, these indicators were used to compare environmental load values by each similar process in a colliery. A total eco-indicator was calculated for colliery by summing up the eco-indicators of the individual unit processes. The eco-indicators, structured as above, were calculated for the phase of opening out a deposit and for the phase of extraction. Results and Discussion  The model mine in the phase of extraction of a deposit causes a total environmental load which expressed in points of the eco-indicator 99 amounts to 23.9 [MEw]. In the ‘human health’ category losses amount to 8.4 per cent, in the ‘quality of ecosystem’ 0.6 per cent and in the ‘resourses’ category 91 per cent. The greatest losses in all categories are caused by the process of getting body of coal and the next greatest ones are:

Delimitation of a QTL region controlling cold tolerance at booting stage of a cultivar, ‘Lijiangxintuanheigu’, in rice, <Emphasis Type="Italic">Oryza sativa</Emphasis> L.

Low temperature at the booting stage of rice causes male sterility resulting in severe yield loss. Cold tolerance has long been an important objective in rice breeding. We identified a quantitative trait locus (QTL) for cold tolerance on the long arm of chromosome 3 from the cold-tolerant breeding line ‘Ukei 840’ by using F₂ and BC₁F₂ populations from crosses between ‘Ukei 840’ and ‘Hitomebore’. The cold tolerance of ‘Ukei 840’ is derived from the Chinese cultivar ‘Lijiangxintuanheigu’. The effect of this QTL on cold tolerance was confirmed by developing ‘Hitomebore’ chromosome segment substitution lines having ‘Lijiangxintuanheigu’ alleles on chromosome 3. By producing recombinants in chromosome 3, the QTL region for cold tolerance was delimited to the region of about 1.2-Mb region between RM3719 and RM7000. All lines heterozygous for the QTL showed seed fertilities as low as that of ‘Hitomebore’, suggesting that the ‘Lijiangxintuanheigu’ allele for cold tolerance in the QTL region is recessive. Determination of a 1.2-Mb nucleotide sequence of ‘Ukei 840’ and comparison with the published genomic sequence of ‘Nipponbare’ showed 254 SNPs, of which 11 were in coding regions of genes, seven in five genes being non-synonymous. SNPs were detected in the 5-kb upstream regions of 89 genes, but no differences of gene expression levels were detected between alleles of these genes. Although further delimitation is required to identify the gene responsible for cold tolerance of ‘Lijiangxintuanheigu’, SNP markers developed here will be useful for marker-assisted selection in a breeding program using ‘Lijiangxintuanheigu’ as a donor of cold tolerance.     

Mapping of resistance to spot blotch disease caused by Bipolaris sorokiniana in spring wheat

Spot blotch caused by Bipolaris sorokiniana is a destructive disease of wheat in warm and humid wheat growing regions of the world. The development of disease resistant cultivars is considered as the most effective control strategy for spot blotch. An intervarietal mapping population in the form of recombinant inbred lines (RILs) was developed from a cross ‘Yangmai 6’ (a Chinese source of resistance) × ‘Sonalika’ (a spot blotch susceptible cultivar). The 139 single seed descent (SSD) derived F₆, F₇, F₈ lines of ‘Yangmai 6’ × ‘Sonalika’ were evaluated for resistance to spot blotch in three blocks in each of the 3 years. Joint and/or single year analysis by composite interval mapping (CIM) and likelihood of odd ratio (LOD) >2.2, identified four quantitative trait loci (QTL) on the chromosomes 2AL, 2BS, 5BL and 6DL. These QTLs were designated as QSb.bhu-2A, QSb.bhu-2B, QSb.bhu-5B and QSb.bhu-6D, respectively. A total of 63.10% of phenotypic variation was explained by these QTLs based on the mean over years. Two QTLs on chromosomes 2B and 5B with major effects were consistent over 3 years. All QTL alleles for resistance were derived from the resistant parent ‘Yangmai 6’.