Inheritance of partial resistance to bean rust in the common bean (Phaseolus vulgaris L.)

The inheritance of partial resistance within eight bean cultivars to a single-pustule isolate of bean rust was studied by means of a F₁ diallel test. General combining ability (GCA) and specific combining ability (SCA) were very highly significant over two seasons and in interaction with seasons. The partitioning of the sums of squares indicated the greater importance of GCA in the inheritance of the resistance. Reciprocal effects were not significant. The estimates of narrow-sense heritability in the two seasons were 0.899 ± 0.056 and 0.603 ± 0.065.     

Yield and yield components in flue-cured tobacco and their genetic analysis

Five cultivars and the half diallel set of 10 F₁ hybrids of flue-cured tobacco (Nicotiana tabacum L.) were grown in two seasons. Highly significant differences were assessed between genotypes as concerns flowering time, plant height, number of leaves, leaf length and width and yield per plot. High to moderate values for heritability in the broad sense were obtained in all cases. Hybrids, in general, flowered earlier, were taller, had fewer but shorter and wider leaves and slightly increased yield when compared with the mean value of all parents. The variance associated with general combining ability (GCA) was highly significant in all characters. The estimates of SCA were significant in most cases. High GCA/SCA ratios which largely exceeded the unity were obtained for most attributes. The negative and positive alleles were unequally distributed in the parents for all the studied traits. A small number of effective genes was obtained for all characters except plant height, where one to two groups of genes were distinguished     

A quantitative trait locus for reduced culm internode length in barley segregates as a Mendelian gene

Yield losses caused by lodging in cereals can be partially controlled by reducing plant height. A progeny of recombinant inbred lines from a cross of two Japanese barley varieties was used to study the inheritance of culm and culm internode lengths. An unexpected QTL for reduced culm length (qCUL), which affected mainly the length of the third and fourth culm internodes, was contributed by ‘Kanto Nakate Gold’. This QTL was also associated with reduced lodging in two experiments. A near-isogenic line (culm length 62.9–73.4 cm) in an ‘Azumamugi’ background, carrying a chromosome segment containing the qCUL allele from Kanto Nakate Gold, was significantly shorter than its recurrent parent (82.9–89.4 cm). The F₂ generation from the next backcross segregated for plant height in a Mendelian monogenic ratio. The qCUL locus was shown to be tightly linked (1.2 cM) with the codominant STS marker ABG608. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Combining ability analysis over environments in diallel crosses of linseed (Linum usitatissimum L.)

Summary This paper reports on combining ability studies for yield and its component traits in diallel crosses involving ten ecogeographically and genetically diverse linseed (Linum usitatissimum L.) cultivars in the F₂ generation over three locations. The general combining ability (GCA) and specific combining ability (SCA) mean squares were significant at all three locations for all traits. Combined analysis over locations showed the same trend of significance. The ratio of GCA to SCA mean squares was significant for all the traits in individual location analysis as well as in combined analysis. This indicated the predominant role of additive gene effects in the inheritance of these characters. The GCA mean squares were several times larger than SCA mean squares for all the traits, indicating the presence of considerable magnitude of additive genetic variance and the additive x additive components of the epistatic variance. Consequently, effective selection should be possible within these F₂ populations for all characters. Significant genotype-location and GCA-location interactions indicated that more than one test location is required to obtain reliable information. The inexpensive and reliable procedure used for making the choice of parents was the determination of breeding values of the parents on the relative performance of their F₂ progeny bulks.Part of the thesis submitted by the senior author in partial fulfillment of the requirements for the Ph. D. degree of the Marathwada Agricultural University, Parbhani, 431 402, India     

Improving chickpea yield by incorporating resistance to ascochyta blight

Ascochyta blight [Ascochyta rabiei (Pass.) Lab.] is the most destructive disease of chickpea (Cicer arietinum L.), but it can be managed effectively by the use of resistant cultivars. Therefore, a breeding programme was initiated during 1977–78 at ICARDA, Syria, to breed blight-resistant, high-yielding chickpeas with other desirable agronomic traits. Crosses were made in main season at Tel Hadya, Syria, and the F₁s were grown in the off season at Terbol, Lebanon. The F₂, F₄ and F₅ generations were grown in a blight nursery in the main season where blight epidemic was artificially created. The plants and progenies were scored for blight resistance and other traits. The F₃ and F₆ generations were grown in the off season under normal day length to eliminate late-maturing plants. The pedigree method of breeding was followed initially, but was later replaced by the F₄-derived family method. The yield assessment began with F₇ lines, first at ICARDA sites and later internationally. A total of 1584 ascochyta blight-resistant chickpea lines were developed with a range of maturity, plant height, and seed size not previously available to growers in the blight-endemic areas in the Mediterranean region. These included 92 lines resistant to six races of the ascochyta pathogen, and 15 large-seeded and 28 early maturity lines. New cultivars produced 33% more seed yield than the original resistant sources. The yield of chickpea declined by 340 kg ha^-1, with an increase in blight severity by one class on a 1–9 scale, reaching zero yield with the 8 and 9 classes. Development of blight-resistant lines made the introduction of winter sowing possible in the Mediterranean region with the prospect of doubling chickpea production. Twenty three cultivars have been released so far in 11 countries.Joint contribution from ICARDA and ICRISAT. ICRISAT Journal Article no. JA 1886.     

Comparison of phenotypic and molecular distances to predict heterosis and F1 performance in Ethiopian mustard (Brassica carinata A. Braun)

Predicting heterosis and F₁ performance from the parental generation could largely enhance the efficiency of breeding hybrid or synthetic cultivars. This study was undertaken to determine the relationship between parental distances estimated from phenotypic traits or molecular markers with heterosis, F₁ performance and general combining ability (GCA) in Ethiopian mustard (Brassica carinata). Nine inbred lines representing seven different geographic regions of Ethiopia were crossed in half-diallel. The nine parents along with their 36 F₁s were evaluated in a replicated field trail at three locations in Ethiopia. Distances among the parents were calculated from 14 phenotypic traits (Euclidean distance, ED) and 182 random amplified polymorphic DNA (RAPD) markers (Jaccard’s distances, JD), and correlated with heterosis, F₁ performance and GCA sum of parents (GCA_sum). The correlation between phenotypic and molecular distances was low (r=0.34, P≤0.05). Parents with low molecular distance also had low phenotypic distance, but parents with high molecular distance had either high, intermediate or low phenotypic distance. Phenotypic distance was highly significantly correlated with mid-parent heterosis (r=0.53), F₁ performance (r=0.61) and GCA (r=0.79) for seed yield. Phenotypic distance was also positively correlated with (1) heterosis, F₁ performance and GCA for plant height and seeds plant⁻¹, (2) heterosis for number of pods plant⁻¹, and (3) F₁ performance for 1,000 seed weight. Molecular distance was correlated with GCA_sum (r=0.36, P≤0.05) but not significantly with heterosis and F₁ performance for seed yield. For each parent a mean distance was calculated by averaging the distances to the eight other parents. Likewise, mean heterosis was estimated by averaging the heterosis obtained when each parent is crossed with the other eight. For seed yield, both mean ED and JD were significantly correlated with GCA (r=0.90, P≤0.01 for ED and r=0.68, P≤0.05 for JD) and mean heterosis (r=0.79, P≤0.05 for ED and r=0.77, P≤0.05 for JD). In conclusion, parental distances estimated from phenotypic traits better predicted heterosis, F₁ performance and GCA than distances estimated from RAPD markers. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Effects of fertilization on the growth,photosynthesis, and biomass accumulation in juvenile plants of three coffee (<Emphasis Type="Italic">Coffea arabica</Emphasis> L.) cultivars

We carried out a field experiment in order to study effects of fertilization in juvenile plants of three coffee (Coffea arabica) cultivars in Yunnan, SW China. Fertilization treatments included a control without fertilizer (CK), combinations of three NPK fertilization rates [high fertilization (F_H), medium fertilization (F_M), and low fertilization (F_L) with 135, 90, and 45 g per plant per year, respectively], and at two N:P₂O₅:K₂O ratios (R₁, 1:0.5:0.8; R₂, 1:0.8:0.5). The growth in juvenile plants was not altered by fertilization, with two clear growth peaks being observed in both the height and stem growth rates (RGRs) throughout a year. Both F_M and F_H resulted in significantly higher RGRs in both height and stem diameter compared to F_L and CK in all three cultivars. At the same fertilization rate, the leaf area, branch number, longest branch length, internode number, and biomass of R₂ were higher than those of R₁, and P significantly affected the root biomass and root to shoot ratio. Compared to the F_L treatment, both F_M and F_H treatments resulted in higher net photosynthetic rates and stomatal conductance across seasons, and in higher intrinsic water-use efficiency during the dry season and at the middle of the wet season. Photosynthetic nitrogen-use efficiency at R₂ was higher than that at R₁, but no significant differences were observed between the different fertilization rates. Among the three coffee cultivars, Caturra exhibited the highest height, stem diameter, longest branch length, and internode number. Our results indicated that the optimal N:P₂O₅:K₂O ratio was 1:0.8:0.5 for the juvenile growth of coffee plants. Both F_M and F_H could help optimize the growth and photosynthetic rate of coffee plants, but F_M is suitable for the ecological friendly agriculture and economic sustainability at coffee plantations.     

Effect of a Short Photoinhibition Stress on Photosynthesis,Chlorophyll a Fluorescence,and Pigment Contents of Different Maize Cultivars. Can a Rapid and Objective Stress Indicator be Found?

The effect of a short cold stress in combination with photoinhibition stress, similar to a low temperature and a high irradiance situation during early morning in the spring time, was examined on four maize cultivars common for Belgium, that differ in early vigour. After 1 h of 2 °C and 500 mol(photon) m^–2 s^–1, quantum efficiency and maximum photosynthesis rate at saturating irradiance decreased on average by 11 and 8 %, respectively. For one cultivar, Magister, the decrease was the largest: by 23 and 10 %, respectively. For this cultivar it was combined with a decrease of the water vapour conductance after the stress. The decrease of F_v/F₀ due to the cold/light stress was dependent on the cold tolerance (early vigour) of the cultivars. F_v/F₀ changed with –45.5 and –40.2 % for the cultivars Ardiles and Banguy, respectively (cultivars with a less good early vigour) in comparison to –36.3 and –35.9 % for Fjord and Magister, which have a good early vigour. Also the ratio of total chlorophylls/total carotenoids changed in dependence on cold tolerance of the cultivars. For more cold tolerant cultivars, the relative amount of total carotenoids (x+c) was higher, indicating a higher protective state. Both the parameter F_v/F₀ and the ratio of total chlorophylls to total carotenoids can be used to differentiate the cold tolerant cultivars from the cold non-tolerant ones. F_v/F₀ has the advantage because its resolving power is larger and the measurement is less expensive than determination of the pigment ratio.     

Mapping quantitative trait loci for yield components and morphological traits in an advanced backcross population between Oryza grandiglumis and the O. sativa japonica cultivar Hwaseongbyeo

Introgression has been achieved from wild species Oryza grandiglumis (2n=48, CCDD, Acc. No. 101154) into O. sativa subsp. japonica cv. Hwaseongbyeo as a recurrent parent. An advanced introgression (backcross) line, HG101, produced from a single plant from BC₅F₃ families resembled Hwaseongbyeo, but it showed differences from Hwaseongbyeo in several traits, including days to heading and culm length. To detect the introgressions, 450 microsatellite markers of known chromosomal position were used for the parental survey. Of the 450 markers, 51 (11.3%) detected O. grandiglumis segments in HG101. To characterize the effects of alien genes introgressed into HG101, an F_2:3 population (150 families) from the cross Hwaseongbyeo/HG101 was developed and evaluated for 13 agronomic traits. Several lines outperformed Hwaseongbyeo in several traits, including days to heading. Genotypes were determined for 150 F₂ plants using simple sequence repeat markers. Qualitative trait locus (QTL) analysis was carried out to determine the relationship between marker genotype and the traits evaluated. A total of 39 QTL and 1 gene conferring resistance to blast isolate were identified using single-point analysis. Phenotypic variation associated with each QTL ranged from 4.2 to 30.5%. For 18 (46.2%) of the QTL identified in this study, the O. grandiglumis-derived alleles contributed a desirable agronomic effect despite the overall undesirable characteristics of the wild phenotype. Favorable wild alleles were detected for days to heading, spikelets per panicle, and grain shape traits. Grain shape QTL for grain weight, thickness, and width identified in the F_2:3 lines were further confirmed based on the F₄ progeny test. The confirmed locus, tgw2 for grain weight is of particular interest because of its independence from undesirable height and maturity. Several QTL controlling amylose content and grain traits have not been detected in the previous QTL studies between Oryza cultivars, indicating potentially novel alleles from O. grandiglumis. The QTL detected in this study could be a rich source of natural genetic variation underlying the evolution and breeding of rice.     

籼稻二元不育系9730A及三交种的初步研究

通过对所选育的籼稻二元不育系9730A的花粉育性、自交结实率、雌性育性、对"920"的敏感性、柱头外露情况、花时、雄性不育的可恢复性及三交种的抽穗整齐度、有效穗、株高、单株产量、结实率、主茎穗长、主茎叶长、穗粒等变异度的分析,对杂交水稻三交法育种的应用价值进行初步探讨.结果认为:通过引进具有不同优良品种特性的第二保持系,可以在保持所选育杂种品种主要农艺性状整齐一致的前提下,较大幅度地拓宽品种的遗传基础,改进雄性不育系的异交性能,从而为提高杂种种子生产水平、及时利用优良常规稻育种成果材料和综合实现杂交稻品种选育过程中的多抗、广适、高产、优质育种目标提供新的途径.     

Inheritance of components of partial resistance of barley to Rhynchosporium secalis with particular reference to race specificity

Six spring barley cultivars with no known genes for resistance to specific virulences but varying in partial resistance to Rhynchosporium secalis, were crossed in all combinations (6 × 6 diallel including reciprocals). In addition to seeds from naturally selfed plants, seeds of all parent cultivars were also produced by artificial selfing (emasculation followed by pollination using pollen from the same cultivar). This ensured comparability between seeds of parents and F₁. Both sets of parents, F₁ and F₂ families were grown in the field as single spaced plants and inoculated at Zadoks growth stage 49 with spore suspensions (2 × 10⁶ spores ml^-1) of three races (pathotypes) of R. secalis (Zadoks, Chang & Konzak, 1974). Components of partial resistance, incubation period (ICP), infection frequency (IF) and spore production per lesion (SP/L) were assessed on each plant. There were highly significant differences for all three components of partial resistance in both sets of parent cultivars but rank order in both sets was similar as evidenced by correlation coefficients, r= 0.96 for ICP and IF and r= 0.87 for SP/L. All three components of partial resistance were strongly correlated with NIAB (National Institute of Agricultural Botany, Cambridge, UK) resistance ratings. Means of F₁ and F₂ families were correlated with mid-parent values for ICP and IF but not SP/L. No difference in aggressiveness was found between races but for each component of partial resistance there was a significant interaction between race and parent cultivar (artificial selfs) and, for IF and ICP, a significant interaction between race and F₁ family. There was no evidence of interaction between parent (natural selfs) and race nor between race and F₂ family. Examination of genetic control of resistance showed evidence of strong additive effects (combining ability) in both F₁ and F₂ for ICP and IF but not for SP/L. There was no evidence for maternal or reciprocal differences, but there was evidence for dominance effects although their nature differed between components of partial resistance and between F₁ and F₂ generations. In the F₁, but not the F₂ generation, several elements of dominance (direction, distribution of dominant genes between parent cultivars, specific combining ability) showed for ICP or IF (but not SP/L) significant interaction with race.     

Development and Genetic Control of Plant Architecture and Biomass in the Panicoid Grass,Setaria

The architecture of a plant affects its ability to compete for light and to respond to environmental stresses, thus affecting overall fitness and productivity. Two components of architecture, branching and height, were studied in 182 F₇ recombinant inbred lines (RILs) at the vegetative, flowering and mature developmental stages in the panicoid C₄ model grass system, Setaria. The RIL population was derived from a cross between domesticated S. italica (foxtail millet) and its wild relative S. viridis (green foxtail). In both field and greenhouse trials the wild parent was taller initially, started branching earlier, and flowered earlier, while the domesticated parent was shorter initially, but flowered later, producing a robust tall plant architecture with more nodes and leaves on the main culm and few or no branches. Biomass was highly correlated with height of the plant and number of nodes on the main culm, and generally showed a negative relationship with branch number. However, several of the RILs with the highest biomass in both trials were significantly more branched than the domesticated parent of the cross. Quantitative trait loci (QTL) analyses indicate that both height and branching are controlled by multiple genetic regions, often with QTL for both traits colocalizing in the same genomic regions. Genomic positions of several QTL colocalize with QTL in syntenic regions in other species and contain genes known to control branching and height in sorghum, maize, and switchgrass. Included in these is the ortholog of the rice SD-1 semi-dwarfing gene, which underlies one of the major Setaria height QTL. Understanding the relationships between height and branching patterns in Setaria, and their genetic control, is an important step to gaining a comprehensive knowledge of the development and genetic regulation of panicoid grass architecture.     

Flowering in cultivars of sesame (Sesamum indicum) Differing in photoperiodic sensitivity

Studies of flowering in sesame (Sesamum indicum L.) under different photoperiods revealed that cultivars Glauca, Venezuela-52 and Oro were short day strains while a fourth cultivar, Aceitera, proved to be day length neutral. Sensitivity to varying photoperiods, then, does not seem to be a universal characteristic of all sesame cultivars. Also, no correlation was found between photoperiodic class and latitude of origin in the cultivars studied. Inheritance studies involved crosses between the day neutral cultivar and two of the short day cultivars. In all cases, the F₂ populations demonstrated continuous variation. Most of the F₂ variability was of genetic origin and heritability values ranged from 86 to 96%. Additionally, transgressive segregation was observed for both early and late flowering. It is proposed that a minimum of three loci are involved in the inheritance of photoperiodic response in the sesame cultivars studied.     

Combining-ability analysis of somatic embryogenesis from epidermal layers in the sunflower (Helianthus annuus L.)

Crosses were made between three cytoplasmic male-sterile and five restorer sunflower inbred lines. F₁ hybrids, including their parents, were studied for their embryogenetic ability. Sterilized seeds were germinated in culture tubes on agar-solidified basal medium. Seven days after germination, epidermal layers from hypocotyls were transferred into MS and B5 liquid-midia for 5 and 8 days respectively. Then they were transferred to MS-120 solid-medium with a high level of sucrose (120 g/l). The experimental design was complete randomized blocks with three replications. Each replication per genotype consisted of three Erlenmeyer flasks with 20–25 epidermal layers (explants). Analysis of variance indicated the presence of significant variation among genotypes for all traits studied. General combining ability (GCA) and specific combining ability (SCA) showed significant effects for the studied traits. The highest value of GCA for the number of embryogenic explants per 100 explants plated (EE/100EP) belongs to parental female line ’CMS-PET1 B9’. This inberd line also gave a high positive GCA effect for the number of embryos per ten embryogenic explants (E/10EE). Additionally, it had the highest values for EE/100EP and E/10EE (41.70 and 19.28 respectively) and should be a promising parent in crossing programmes for the enhancement of somatic embryogenesis in the sunflower. The highest values of specific combining ability (SCA) for EE/100EP and E/10EE belong to the F₁ hybrid ’CMS-PET1B9 ’x’ RT1B11’ which has produced 53.45 embryogenic explants/100 explants and 9.67 embryos per ten embryogenic explants. Received: 4 December 1998 / 16 June 1999     

Genetic analysis and complementation studies on a number of mutant supernodulating soybean lines

Genetic analysis was done on a number of nitrate tolerant supernodulating (nts) mutant soybean lines. These lines are altered in the autoregulation response, and each was isolated as a separate mutational event following chemical mutagenesis. Crosses were made betweennts lines on a diallel pattern, and each was also crossed usingnts lines as female parent, to wild-type nodulation cultivars. F₁ and F₂ data were analysed from each cross for nodulation type and number. No complementation was noted wherents lines were intercrossed, suggesting that in each line the same gene was affected. Wherents lines were crossed with wild-type cultivars all the F₁ progeny were wild-type, confirming that thenls gene is recessive and, with one exception,nts 1116, all of the F₂ progeny segregated into a 3:1 wild-type to supernodulating phenotype, indicating that a single gene is involved. The hypernodulating linents 1116 gave a 1:1 ratio in its F₂ progeny when crossed with othernts lines. This line behaved as a dominant in the latter crosses. No wild-type segregants were recovered, therefore again no complementation look place. This line may be a leaky mutant with partial autoregulation as its segregation ratios do not fall into any of the obvious patterns.     

Quantitative trait loci analysis of plant height and ear height in maize (Zea mays L.)

Genetic map containing 103 microsatellite loci obtained on 200 F₂ plants derived from the cross R15 × 478 was used for quantitative trait loci (QTL) mapping in maize. QTLs were characterized in a population of 200 F_2:4 lines, derived from selfing the F₂ plants, and were evaluated with two replications in two environments. QTL determinations were made from the mean of these two environments. Plant height (PH) and ear height (EH) were measured. Using composite interval mapping (CIM) method, a total of 14 distinct QTLs were identified: nine for PH and five for EH. Additive, partial dominance, dominance, and overdominance actions existed among all detected QTLs affecting plant height and ear height. The QTLs explained 78.27% of the phenotypic variance of PH and 41.50% of EH. The 14 QTLs displayed mostly dominance or partial dominance gene action and mapped to chromosomes 2, 3, 4, 8, and 9. The text was submitted by the authors in English.     

Molecular marker-facilitated studies in an elite maize population: I. Linkage analysis and determination of QTL for morphological traits

Restriction fragment length polymorphisms (RFLPs) and one morphological marker were used to investigate quantitative trait loci (QTL) for morphological and physiological traits evaluated on 150 F₂₃ maize (Zea mays L.) lines derived from the cross of elite U.S. Corn Belt inbreds Mo17 and H99. F₂₃ lines were grown in a replicated experiment and evaluated for plant and ear heights and flowering traits. QTL were identified for each trait, and genetic effects were determined. Estimated gene action for the flowering traits was predominantly overdominance. Both parents contributed toward increased values for anthesis and silk emergence. QTL for increased plant and ear heights were usually contributed by the taller parent, Mo17. Estimated gene action for these traits was mainly partial to overdominance. QTL for plant height were located in the vicinity of loci defined by alleles with qualitative effects on plant height.     

QTL analysis of lodging resistance and related traits in Italian ryegrass (<Emphasis Type="Italic">Lolium multiflorum</Emphasis> Lam.)

Italian ryegrass (Lolium multiflorum Lam.) is the most widely cultivated annual forage grass in Japan. Lodging damage reduces both harvested yield and forage quality. To identify the chromosomal regions controlling lodging resistance in Italian ryegrass, we analyzed seven quantitative characters—heading date, plant height, culm weight, culm diameter, culm strength, tiller number, and culm pushing resistance—and evaluated lodging scores in the field in a two-way pseudo-testcross F₁ population. Significant correlations between most combinations of the traits examined were found. Seventeen QTLs for all traits except culm weight were detected on six of seven linkage groups by simple interval mapping using cross-pollination (CP) algorithm, and 33 independent QTLs were also detected by composite interval mapping from both male and female parental linkage maps. In addition, up to 18 QTLs for lodging scores evaluated at nine different times were detected on all linkage groups. The flanking markers of those QTLs will serve as a useful tool for marker-assisted selection of lodging resistance in Italian ryegrass.     

Inheritance of partial resistance to the leaf aphids Macrosiphum euphorbiae and Uroleucon sonchi in lettuce

The genetics of partial resistance (PR) of lettuce to the leaf aphid species Macrosiphum euphorbiae and Uroleucon sonchi was studied in F₁ and F₂ generations of six crosses between four cultivars. Partial resistance inherited mainly additively. With M. euphorbiae the estimates of broad-sense F₂ heritability were low and non-significant in crosses between parents of the same resistance level (S x S and PR x PR), and high (0.69-0.76) in crosses between parents of different resistance level (PR x S). The level of resistance in lettuce cultivars ‘Charan’ and ‘Marbello’ led to a marked reduction in percentage of plants with colonies of M. euphorbiae in a field experiment. With U. sonchi the highest estimates of F₂ heritability were found in ‘Charan x ‘Avoncrisp’ (0.51) and ‘Charan’ x ‘Chou de Naples' (0.48). In the cross ‘Charan’ x ‘Marbello’ (PR x PR) no significant segregation for resistance to M. euphorbiae was found, indicating that these cultivars may have the same genetic constitution for resistance to M. euphorbiae.‘Charan’ has additional genes for resistance to U. sonchi, that are not, or only weakly linked to the gene(s) for resistance to M. euphorbiae. The heritability estimates for the partial resistance to M. euphorbiae and U. sonchi indicate that it is possible to effectively select for these traits in plant breeding programmes.     

Distribution of the genes causing F2 chlorosis in rice cultivars of the Indica and Japonica types

Summary Chlorotic plants were segregated in F₂ populations in varietal crosses of common rice. The genetic basis and distribution of the genes causing F₂ chlorosis in native cultivars were studied to examine the role of the F₂ chlorosis in varietal differentiation of rice. It was proven that this F₂ chlorosis was controlled by a set of duplicate genes, hca-1 and hca-2. The hca-2 gene was widely distributed in native cultivars of the Japonica type, while many Indica types carried its dominant allele hca-2 ⁺. Japanese cultivar J-147 carried hca-2. The hca-1 gene was frequently distributed in cultivars containing the Hwc-2 gene for F₁ weakness. We concluded that F₂ chlorosis does not cause or promote varietal differentiation in rice.