稻米中含二硫键蛋白对其米饭质地的影响

选用11个水稻品种,通过二硫苏糖醇（dithiothreitol,DTT）处理打破蛋白质二硫键后,观察稻米粉快速黏度仪RVA（Rapid Visco Analyzer）特征谱的形成、特征值及其米饭质地的变化,进而研究蛋白质对米饭食味品质的作用。结果表明,供试品种米粉添加DTT后,其RVA的峰值黏度和糊化温度大都显著或极显著下降,崩解值大都显著或极显著上升,RVA特征谱上升阶段的线性部分的斜率大都减少;米饭质地则大都变软变黏。稻米中由二硫键形成的蛋白质网络可能增强糊化液的刚性或蛋白质水合作用而改变淀粉的吸水性能,两者共同作用协同提高RVA的峰值黏度和糊化温度等。由二硫键结合而形成的蛋白质网络也可能是影响米饭硬度和黏性的主要作用之一。     

Characterization of segregation distortion on chromosome 3 induced in wide hybridization between indica and japonica type rice varieties

We previously surveyed chromosomal regions showing segregation distortion of RFLP markers in the F₂ population from the cross between a japonica type variety ‘Nipponbare’ and an indica type variety ‘Milyang23’, and showed that the most skewed segregation appeared on the short arm of chromosome 3. By comparison with the marker loci where distortion factors were previously identified, this region was assumed to be a gametophytic selection-2 (ga2) gene region. To evaluate this region, two near isogenic lines (NILs) were developed. One NIL had the ‘Nipponbare’ segment of this region on the genetic background of ‘Milyang23’ (NIL9-23), and the other NIL had the ‘Milyang23’ segment on the genetic background of ‘Nipponbare’ (NIL33-18). NIL9-23 and ‘Milyang23’, NIL33-18 and ‘Nipponbare’, and ‘Nipponbare’ and ‘Milyang23’ were respectively crossed to produce F₁ and F₂ populations. The F₁ plants of NIL9-23 × ‘Milyang23’ and NIL33-18 × ‘Nipponbare’ showed high seed fertility and the same pollen fertility as their parental cultivars, indicating that ga2 does not reduce seed and pollen fertility. Segregation ratio of a molecular marker on the ga2 region in the three F₂ populations was investigated to clarify whether segregation distortion occurred on the different genetic backgrounds. Segregation distortion of the ga2 region appeared in the both F₂ populations from the NIL9-23 and ‘Milyang23’ cross (background was ‘Milyang23’ homozygote) and the ‘Nipponbare’ and ‘Milyang23’ cross (background was heterozygote), but did notin the F₂ population from the NIL33-18 and ‘Nipponbare’ cross (background was ‘Nipponbare’ homozygote). This result indicates that ga2 interacts with a ‘Milyang23’ allele(s) on the different chromosomal region(s) to cause skewed segregation of the ga2 region. In addition, segregation ratio was the same between the F₂ populations from NIL9-23 × ‘Milyang23’ and ‘Nipponbare’ × ‘Milyang23’ crosses, suggesting that the both genotypes, ‘Milyang23’ homozygote and heterozygote, of gene(s) located on the different chromosomal region(s) have the same effect on the segregation distortion. This revised version was published online in July 2006 with corrections to the Cover Date.     

Detecting and estimating segregation distortion and linkage between glufosinate tolerance and blackleg resistance in Brassica napus L.

Summary The segregation and linkage between glufosinate (transgenes ‘Rf3’ and ‘T177’) and blackleg resistance genes in canola (Brassica napus L.) were assessed using F₁ microspore-derived doubled haploid (DH) populations from four crosses including reciprocals, two involving the transgene ‘Rf3’ and the other two involving the transgene ‘T177’. To relax the assumption of no segregation distortion required for the conventional analysis of segregation and linkage, we employed Bailey's analysis that allows detecting segregation distortion at linked loci. The significant departures from the 1:1 segregation were detected in the crosses involving the transgene ‘T177’ but not in the crosses involving the transgene ‘Rf3’. The apparent deficit of the herbicide tolerant DH lines in the crosses with the transgene ‘T177’ is likely due to differential selection against the gametes carrying ‘T177’ during microspore culture. The linkage was strong between blackleg resistance and the transgene ‘Rf3’ but weak or absent between blackleg resistance and the transgene ‘T177’, suggesting that the two transgenes are probably inserted into distant regions of the genome. The observed linkage offers an opportunity to develop new canola cultivars with both glufosinate tolerance conferred by transgene ‘Rf3’ and blackleg resistance.     

The effect of the Waxy locus (Granule Bound Starch Synthase) on pasting curve characteristics in specialty rices (Oryza sativa L.)

Starch structure and functionality have a significant impact on the utilization of cereal grains as food and feed. Starch viscosity characteristics are used to characterize rice cooking, processing and eating quality. In order to examine the genetics of viscosity characteristics, we developed molecular markers for five of the major enzymes involved in starch synthesis in the endosperm: granule bound starch synthase, soluble starch synthase, rice branching enzymes 1 and 3 and starch debranching enzyme. These markers were polymorphic in a cross between specialty rice varieties of diverging amylose content and viscosity characteristics. Our results indicate that the Waxy locus, encoding the gene for granule bound starch synthase, has a significant effect on peak viscosity, hot paste viscosity, cool paste viscosity, breakdown and setback viscosity. We estimate that the tightly linked (5–10 cm)locus for starch synthase may have a lesser, additive effect. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterisation of aromatic rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) germplasm and correlation between their agronomic and quality traits

Eighty-eight aromatic cultivars collected from Maharashtra state were assessed for determinants of kernel quality (kernel size-shape, test weight and aroma) and grain morphology such as awning, lemma and palea characters, pubescence, colour of sterile lemma and apiculus colour. We, report seven cultivars—‘Girga’, ‘Kothmirsal’, ‘Kala bhat’, ‘Chimansal’, ‘Jiri’, ‘Kalsal’ ‘Velchi’ and ‘Kali kumud’ as indigenous to southern India. Of the 69 cultivars characterized for agronomic traits 36 cultivars were exquisite genotypes and possessed one or more superior traits such as early flowering, dwarf stature, higher number of productive tiller per plant; long panicles; higher number of filled grains per panicle and strong aroma. Variability in aromatic cultivars was assessed on the basis of nine traits placed aromatic rice cultivars in five clusters. Number of cultivars in each cluster ranged from 1 to 33. 27 significant correlations were obtained in the physical, agronomic and grain morphology traits. Aroma was found to be negatively associated with days to 50% flowering as well as with filled grains per panicle. However, correlation between panicle length and effective tillers with aroma was not observed. Therefore, to increase the yield, improvement in length of panicle and increasing number of productive tillers in medium or mild scented cultivars would be the best strategy.     

A proposed mechanism for loss of heterozygosity in rice hybrids

A phenomenon, loss of heterozygosity (LOH), was discovered in hybrid plants involving a selected plant (named AMR) of the Chinese rice cultivar ‘ZhongxinNo. 1’ as one parent. In these hybrids and some of their progenies, somatic variations were manifested by molecular genotypes and/or morphological phenotypes in vegetative parts of the same plant. Random amplified polymorphic DNA (RAPD) markers for the parents have been followed through the F₃ generation. RAPD markers were uniformly present or absent in all plants within some or all F₂ panicle rows derived from F₁ hybrids involving AMR. In contrast, RAPD markers segregated in the Mendelian manner for dominant markers in panicle rows derived from control hybrids. Certain F₂ panicle rows from F₁hybrids involving the special rice became fixed for all assayed RAPD markers. Genotype fixation was confirmed by molecular assays and field observations of the F₃ progenies. We propose a new biological mechanism, called ‘assortment mitosis,’ as being responsible for the observed phenomenon. The use of this mechanism in plant hybrids allows the development of uniform progenies as early as the F₂ generation. Therefore, the time required to obtain fixed non-parental type progenies for subsequent performance trials can be drastically shortened. Utilizing this mechanism in plant breeding represents a new approach and requires the modification of conventional plant breeding procedures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic effects and genotype × environment interactions for cooking quality traits in Indica-japonica crosses of rice (Oryza sativa L.)

Indica-japonica hybridization is an important approach for developing superior performing hybrids in rice (Oryza sativa L.). In view of the scanty information available on cooking quality characters in indica-japonica crosses, an investigation was undertaken to estimate genetic and genotype × environment variance and covariance components of amylose content, gel consistency and alkali digestion value, and to determine the relative importance of direct genetic effects, maternal genetic effects and cytoplasmic effects in the genetic variations of the three quality characters. Two indica photo-sensitive genic male sterile (PGMS) lines and four japonica varieties were used as parents to make crosses. Genetic model with genotype × environment interactions for triploid endosperm was used for genetic studies of the three cooking quality characters. Variance component analysis revealed that genetic variations of the three characters were mainly attributable to direct additive and maternal additive effects, and the three traits had significant direct and maternal heritabilities. Genotype × environment interactions were mainly dominance × environment (including direct dominance × environment and maternal dominance × environment) and cytoplasm × environment interactions. Environment factors could only affect the expression extent of dominant genes, without changing their directions. Predicted values of genetic effects indicated that the parental lines, ‘VI-70’ and ‘H9304-1’, appeared to be best for amylose content, ‘T 1950’ and ‘Suxuan’ appeared to be best for gel consistency and alkali digestion value. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genotypic variation of cadmium accumulation and distribution in rice

Cadmium (Cd) is absorbed by rice root and transferred into the other rice organs including grain. A solution-culture experiment was conducted to investigate the absorption and distribution of Cd supplied at different growth stages of rice. Two rice cultivars, a japonica ‘Chucheong’ and a tongil-type ‘Milyang23’ that exhibit high and low ability of Cd absorption by root and accumulation in grain were grown in culture solution and subjected to 2 ppm CdCl2 treatment for 2 weeks at four different growth stages: before panicle initiation stage (BPI), after panicle initiation stage (API), early ripening stage (ER), and mid-ripening stage (MR). Cd concentration and accumulation in rice organs were measured at harvest. The two rice cultivars accumulated two to three times greater amounts of Cd in grain in the two Cd treatments before heading (BPI and API treatments) than in the Cd treatment after heading (ER and MR treatment). The higher grain Cd accumulation in BPI and API treatments was not attributed to the higher Cd uptake but to the higher translocation from root to shoot and the higher redistribution from shoot to grain than ER and MR treatments These results imply that the remobilization of Cd through phloem during leaf senescence is the major process for Cd accumulation in rice grain rather than direct transport of absorbed Cd through the xylem-phloem transfer to grain. ‘Milyang23’ absorbed significantly smaller amount of Cd than ‘Chucheong’. However, ‘Milyang23’ accumulated more than a three times larger amount of Cd in grain compared to ‘Chucheong’ as the former exhibited the higher root-shoot translocation and shoot-grain remobilization as well. It indicates that the greater Cd translocation from root to shoot and subsequent higher Cd remobilization from shoot to grain, not the higher absorption ability, have led to the higher Cd accumulation and concentration in grain of ‘Milyang23’.     

杂交粳稻亲本米质性状优异配合力的标记基因型鉴定

杂交粳稻米质整体水平不如常规粳稻也是限制杂交粳稻广泛种植的原因之一。本研究选用115个SSR引物扩增6个粳稻BT型不育系和12个恢复系的标记基因型,并分析72个F₁组合谷粒长、谷粒宽、糙米率、精米率、整精米率、垩白米率、垩白度、糊化温度、胶稠度和直链淀粉含量10个米质性状的配合力,结合亲本SSR分子标记数据和性状配合力数据筛选了10个米质性状优异配合力的标记基因型。结果共鉴定出30个SSR标记基因型与亲本10个米质性状配合力显著相关,其中25个与亲本米质性状不良配合力相关,5个与优异配合力相关。标记基因型RM263-175/180和RM444-230/240可以使F₁整精米率分别提高3.2%和2.5%。RM3-120/150可以使F₁谷粒长缩短2.4%,RM444-180/240可以使F₁谷粒宽增加2.1%。RM428-273/294可以使F₁植株上的杂交稻米直链淀粉含量减少7.0%。有8个标记基因型同时也影响产量性状配合力。RM3-120/150同时可以使F₁的每穗总粒数和每穗实粒数分别增加15.9%和10.9%。RM1211-150/160可使F₁的糙米率和精米率分别减少0.9%和1.1%,同时使F₁的每穗总粒数和每穗实粒数分别增加21.8.%和20.4%。RM23-150/160可使F₁的垩白米粒率和垩白度分别增加44.1%和45.7%,同时使F₁的单株日产量和每穗总粒数分别增加11.2%和11.6%。这些结果可用于指导亲本米质性状和产量性状配合力的分子标记辅助改良以及未来杂交粳稻组合配置中的亲本选配。     

Relationship between rice grain amylose and pasting properties for breeding better quality rice varieties

One hundred and sixty‐seven rice varieties/laudraces from 23 different rice‐growing countries were used for studying the relationship between the amylose content (AC %) and paste viscosity parameters (RVU) through Pearson correlation. AC and paste viscosity parameters were measured using Auto Analyser and Rapid Visco Analysers respectively. Based on all five RVA pasting properties, i.e. peak viscosity (PV), minimum viscosity (MV), breakdown (BD), final viscosity (FV) and setback (SB), the simple paired t‐test (at P = 0.05) was carried out to identify varieties that showed non‐significant differences (similar) from the check variety, separately for each of the four AC groups, e.g. Waxy rice AC (0–8%, n = 21) –‘IR29’ (Philippines); Low AC (8.1–16%, n = 58) –‘Koshihikari’ (Japan); Intermediate AC (16.1–24%, n = 64) –‘Local Sadri’ (Iran); high AC (>24.1%, n = 24) –‘Kasalath’ (India). Significant variation among the rice varieties for AC and pasting properties were observed. Means of the AC and the viscosity parameters including PV, MV, BD, FV and SB were 15.8, 416.1, 180.3, 235.8, 380.9 and 200.6 RVU respectively. Significant correlations existed between AC and paste viscosity parameters at AC group level. The paste viscosity parameters, i.e. PV, BD and SB are important within an AC group as far as cooking quality is concerned. In the low AC group, ‘Koshihikari’ (check) was most preferred by Japanese consumers, which was used for identifying 16 varieties that showed non‐significant differences for pasting properties with it. Some of the important Japanese varieties were ‘Todorokiwase’, ‘Owarihatamochi’, ‘Sasanishiki’, ‘Reimei’ and ‘Kinuhikari’. These varieties had good cooking quality with low AC, high PV and BD with low SB. In contrast, the Iranian cultivar ‘Local Sadri’ with good cooking quality had intermediate levels of AC and SB while recording high PV and BD. The varietal diversity for pasting properties available within each AC group may allow the breeder to make effective selections for improving the cooking quality according to consumer choice.     

Novel Wx alleles induced by chemical mutagens in rice,Oryza sativa L.

From mutant pools of two Taiwanese elite japonica cultivars, Tainung 67 and Taikeng 8, we identified 13 mutant lines possessing opaque endosperm with relatively low amylose contents (AC) ranging from 1.5% to 7.1%. Because of different AC, paste viscosities of these 13 mutant lines differed, as revealed by palatability and physicochemical properties. The mutated gene conferring opaque endosperm was isolated from the F₂ population of one mutant line, WY1× indica cv. ‘Taichung Sen 17’, by positional cloning, revealing a G3018→A3018 substitution at exon 9 of Waxy leading to a non‐synonymous mutation from alanine to valine. Two additional alleles were identified from the other 12 mutant lines, for which single‐nucleotide substitutions G2708 → A2708 and G3029 → A3029 occurred in exons 8 and 9, leading to non‐synonymous mutations from arginine to histidine and glutamic acid to lysine, respectively. The three novel wx alleles had different effects on grain quality, specifically on eating and cooking quality, and could be applied in rice breeding programmes to develop new low AC varieties by marker‐assisted selection.     

A new gene for resistance in rice to Asian rice gall midge (Orseolia oryzae Wood Mason) biotype 1 population at Raipur, India

The Asian rice gall midge, Orseolia oryzae Wood Mason (Diptera: Cecidomyiidae), is a major pest of rice in several South and South East Asian countries. The maggots feed internally on the growing tips of the tillers and transform them into tubular galls, onion leaf-like structures called ‘silver shoots’ resulting into severe yield loss to the rice crop. We studied the mode of inheritance and allelic relationships of the resistance genes involved in resistant donor Line 9, a sib of a susceptible cultivar ‘Madhuri’. The segregation behaviour of F₁, F₂ and F₃ populations of the cross between Line 9 and susceptible cultivar MW10 confirmed the presence of a single dominant gene for resistance. Tests of allelism with all the known genes giving resistance to this population indicated that Line 9 possessed a new gene which was designated Gm 9 This revised version was published online in July 2006 with corrections to the Cover Date.     

Zingiberene-mediated resistance to the South American tomato pinworm derived from Lycopersicon hirsutum var. hirsutum

The Lycopersicon hirsutum var. hirsutum accession PI 127826 is recognized as a good source of resistance to arthropod pests due to the action of the allelochemical zimgiberene, a sesquiterpene present in its glandular trichomes. Five genotypes were selected from the F₂ generation of the interspecific cross Lycopersicon esculentum ‘TOM-556’ × Lycopersicon hirsutum var. hirsutum ‘PI 127826’, based on their low levels (BPX-368-clone#56) or high levels(BPX-368-clone#92, BPX-368-clone#105,BPX-368-clone#179, BPX-368-clone#250) of zingiberene. The five F₂ genotypes were tested for resistance to the South American tomato pinworm Tuta absolutaalong with accession L. esculentum ‘TOM-556’ (pinworm susceptible), and the accessions L. hirsutum var. hirsutum ‘PI 127826’ and L. pennellii ‘LA716’ (resistant). The F₂ clones selected for high foliar zingiberene levels showed lower scores for leaflet lesion type(LLT), percent leaflets attacked (PLA) and overall plant damage (OPD) than the low zingiberene genotypes. The results indicated that zingiberene mediates resistance to the South American pinworm, based on feeding and on ovipositing deterrence, in populations derived from the interspecific cross between Lycopersicon. esculentum and Lycopersicon hirsutum var. hirsutum. Indirect selection for high foliar zingiberene content is suggested as an efficient technique for breeding tomatoes for resistance to the South American tomato pinworm. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic variance components and genetic effects among eleven diverse upland cotton lines and their F2 hybrids

Selecting high yielding upland cotton, Gossypium hirsutum L. lines with improved fiber quality is a primary breeding goal. A diverse set of ten cultivars and one breeding line were crossed in a half diallel. Parents and F₂ hybrids were grown in three environments at Mississippi State, MS. Ten agronomic and fiber traits were analyzed by a mixed linear model approach based on the additive-dominance genetic model. Variance component, genetic effects and genetic correlations were calculated. ‘Acala Ultima’ was a desirable general combiner for fiber length, uniformity, strength, micronaire, lint percentage, and boll weight. ‘FiberMax 966’ was a desirable general combiner for fiber length, uniformity, strength, and all agronomic traits. ‘Tamcot Pyramid’ and M240 were poor general combiners for both fiber and agronomic traits. ‘Coker 315’ was a good general combiner for fiber length, uniformity, micronaire, boll weight, boll number, and yield. Heterozygous dominance effects were associated with several crosses, which suggest their use as hybrids.     

Inheritance of amylose content in rice (Oryza sativa L.)

Summary The inheritance of low and very low amylose contents in six rice crosses and their reciprocals was studied by single grain analysis of parents F₁, F₂, B₁ and B₂ seeds. To minimize the environmental effects, the seeds of all generations of all crosses were produced in a single season. The results indicated different dosage effects in different crosses. One major gene was found to govern a difference of 6–12% in amylose content in low and intermediate amylose parents. Very low amylose content was similarly found to be governed by one major gene in crosses between very low- and low-amylose content parents. Minor genes and modifiers also seem to play some role. In the cross between two low amylose parents differing by about 2.5% in amylose content, the differences appeared to be controlled by some minor genes and modifiers. The selection program in different crosses has been suggested.     

The Deterioration of Eating and Cooking Quality Caused by High Temperature During Grain Filling in Early-Season indica Rice Cultivars

The effect of temperature during grain filling on eating and cooking quality of early-season indica rice was investigated by using four cultivars with different amylose content. Starting from flowering stage until maturity, the plants of all cultivars were subjected to two temperature treatments, referred as optimum (mean daily air temperature, 22 °C) and high (32 °C) temperature regimes. The results showed that the effect of high temperature on apparent amylose content and gel consistency in milled rice was cultivar-dependent. Under high temperature, amylose content increased for cv. Jiayu353 and remained little changed for cv. Guangluai4, which had intrinsically higher amylose content, and decreased for cv. Zhefu49 and cv. Jiazao935, which had lower amylose content. By contrast, high temperature reduced or kept stable gel consistency values for cultivars with higher amylose content and increased gel consistency values for those with lower amylose content. Moreover, high temperature significantly increased the gelatinization temperature of all cultivars. Pasting profiles and X-ray diffraction pattern of rice were also affected by temperature. The results suggest that high temperature during grain filling change the component and crystalline structure of starch and result in deterioration of eating and cooking quality for early-season indica rice.     

Inheritance of resistance to <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">melonis</Emphasis> races 0 and 2 in melon accession Tortuga

The inheritance of the resistance to Fusarium oxysporum f. sp. melonis (F.o.m.) races 0 and 2 in ‘Tortuga’, a Spanish cantalupensis accession, was studied from crosses of ‘Tortuga’ by the susceptible line ‘Piel de Sapo’ and the resistant one ‘Charentais-Fom1’ that carries the resistance gene Fom-1. The segregation patterns observed in the F₂ (‘Tortuga’ × ‘Piel de Sapo’) and the backcross (‘Piel de Sapo’ × (‘Tortuga’ × ‘Piel de Sapo’) populations, suggest that resistance of ‘Tortuga’ to races 0 and 2 of F.o.m. is conferred by two independent genes: one dominant and the other recessive. In the F2 derived from the cross between accessions ‘Tortuga’ and ‘Charentais-Fom1’, the lack of susceptible plants indicated that the two accessions are carrying the same resistance gene (Fom-1). The analysis of 158 F₂ plants (‘Tortuga’ × ‘Piel de Sapo’) with a Cleaved Amplified Polymorphic Sequence marker 618-CAPS, tightly linked to Fom-1 (0.9 cM), confirmed that ‘Tortuga’ also carries a recessive gene, that we propose to symbolize by fom-4.     

RFLP facilitated analysis of tiller and leaf angles in rice (Oryza sativa L.)

Plant type is an important composite trait associated with the yield potential in rice and other cereal crops. Several characters associated with the plant type of modern rice cultivars including tiller angle, leaf and flag leaf angle, were investigated using a complete linkage map with 115 well distributed RFLP markers and progeny testing of 2418 F₂ derived F₄ lines from a cross between O. sativa ssp. japonica cv. ‘Lemont’ and spp. indica cv. ‘Teqing’. One major gene (Ta) and 11 QTLs were largely responsible for the tremendous variation of the three plant type characters in the Lemont/Teqing F₂ population. The major gene, Ta, located between RZ228 and RG667 on chromosome 9, accounted for 47.5% of the phenotypic variation in tiller angle and had large pleiotropic effects on both leaf and flag leaf angles. This gene plus four QTLs accounted for 69.1% of the genotypic variation in tiller angle. Eight additional QTLs for leaf and flag leaf angles were also identified, which collectively explained 52.0 and 66.4% of the genotypic variation of these traits. Ta and three QTLs ( QFla2, QFla5 and QFla7) apparently affected the related plant type characters differently, suggesting their possible differential expression in different developmental stages of rice plants or possibly clustering of different genes affecting these traits. Plant type, and consequently grain yield of rice, may be improved by deliberately manipulating these QTLs in a marker-assisted selection program. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pyramiding of two bacterial blight resistance and a semidwarfing gene in Type 3 Basmati using marker-assisted selection

A traditional Type 3 Basmati rice cultivar grown in India is tall and lodges even under low nitrogen fertilizer dose. In addition to lodging, it is highly susceptible to several diseases and pests including bacterial blight (BB). BB resistance genes (Xa21 and xa13) and a semidwarfing gene (sd-1) were pyramided in Type 3 Basmati from a rice cultivar PR106-P2 using marker-assisted selection (MAS). Foreground selection for BB resistance genes, Xa21 and xa13 and reduced plant height gene, sd-1 was carried on the basis of linked molecular markers pTA248, RG136 and ‘h’, respectively. The BC₂F₃ progenies with both the BB resistance genes were highly resistant with lower lesion length than either of the genes individually. Background profiling of the selected 16 BC₂F₃ progenies was done using 95 anchored SSR and 12 ISSR markers. Among the selected 16 BC₂F₃ progenies, 38-5-2 and 38-5-36 closely clustered along with the recipient parent Type 3 Basmati showing above 85% genetic similarity with the same. Further selection was continued till F₅ generation for higher recovery for Type 3 Basmati characteristics. The desirable alleles of intermediate amylose content (wx) and aroma (fgr) loci of Type 3 Basmati were also tracked using the linked SSR markers. The BC₂F₅ pyramid lines T3-4, T3-5, T3-6 and T3-7 homozygous for the three target genes Xa21, xa13 and sd-1 from the donor parent with wx and fgr alleles of Type 3 Basmati had excellent cooking quality and strong aroma.     

Linked dominant alleles or inter-locus interaction results in a major shift in pomegranate fruit acidity of ‘Ganesh’ × ‘Kabul Yellow’

Summary Inheritance of fruit acidity in pomegranate (Punica granatum L.) was studied in 3 sweet or low acid (‘Ganesh’, ‘Ruby’ and ‘Kabul Yellow’) and 3 sour or high acid (‘Nana’, ‘Daru’ and ‘Double Flower’) varieties and their progenies. The F₁ and F₂ data of ‘Ganesh’ × ‘Nana’ showed that fruit acidity is monogenically controlled and the sour nature is dominant over sweet. Further, whether a genotype produces sweet or sour fruit is determined by a major gene (SS) while a few modifiers with small effects cause fluctuations in the acidity levels within sour and sweet types. All the trees of 3 crosses involving ‘Daru’ produced acidic fruits but those of (‘Ganesh’ × ‘Nana’) × ‘Daru’ reached acidity as high as 71.2 g/l which could be because of cumulative influence of modifying genes derived from the two acidic varieties ‘Nana’ and ‘Daru’. Pollination of functionally sterile ‘Double Flower’ variety with single (normal) flower types revealed that ‘Double Flower’ is a dominant mutant from an acidic fruited genotype (Ss). The segregation pattern in F₁ indicated the possible linkage between genes governing total acidity and flower type. All the F₁ hybrids between ‘Kabul Yellow’ and ‘Ganesh’ (sweet × sweet) were sour fruited with almost 8-fold jump in fruit acidity over the mid-parental value. The steep increase in acidity cannot be convincingly attributed to overdominance which is certainly rare at major gene level. Alternatively, linked dominant alleles or epistatic effect of neighboring loci which readily simulate overdominance (pseudo-overdominance) could have caused a major shift in F₁ fruit acidity.