Rice yields and yield gaps in Southeast Asia: Past trends and future outlook

Rice production must increase to meet future food requirements amid strong competition for limited resources. Yield gap analysis is a useful method to examine how large the ranges are between potential, desirable rice yields and those actually realized in farmers’ fields. We analyzed farmers’ yields in wet and dry seasons in four intensively cropped rice areas in Southeast Asia and explored opportunities for reducing the yield gap to meet future food requirements. We found yield gaps of 2.0-5.0 t ha⁻¹ between average and climatic yield potential and 1.2-2.6 t ha⁻¹ between average and best farmers’ yields. In relative terms, average yields varied between 43% and 75% of the climatic yield potential and 61% and 83% of the best farmers’ yields. Farmers with best yields were generally more educated, and used fertilizers and labor more efficiently than average farmers. The yield gaps between average and best farmers’ yields are higher in rice-importing countries (Indonesia and Philippines) compared with rice-exporting countries (Thailand and Vietnam). Assuming no change in diet, closing the existing yield gap between average and best-yielding farmers can sufficiently cover the yield increase needed for 2050 in the three countries, except for the Philippines, where yield increase must be even higher. Trend analysis of yield increases of a population of farmers in Central Luzon (Philippines), which included a learning curve analysis, well described the process of technology adoption from 1966 to 2008, leading to higher yields. Using this analysis, for the Philippines, we predicted yields to increase (from 2007/2008 to 2050) by only 18% with current cultivars, production technologies, and prevailing conditions. Therefore, structural changes are needed to boost farmers’ yields to close the yield gap faster. Investments in technology transfer and institutional arrangements are suggested.     

Field evaluation of insect-resistant transgenic Populus nigra trees

The performance of insect-resistant transgenic poplar trees (Populusnigra) expressing a Cry1Ac gene from Bacillus thuringiensis subsp. Kurstaki HD-1 against poplar defoliators was evaluated in the field at the Manas Forest Station in Xinjiang Uygur Autonomous Region during1994–1997. The results showed that the average percentage of highly damaged leaves on the transgenic trees was 10% while that on the control trees in nearby plantations reached 80–90%. The average number of pupae per m² of soil at 20cm depth in transgenic poplar plantation was 18 which was only 20% of that found in the non-transgenic control field. The number of pupae and the leaf-damage on transgenic trees described above are all far below the threshold set for chemical protection measures. The non-transformed poplar trees grown in the same plantation with the transgenic trees were also protected indicating that cross protection occurred between these two kinds of trees. Insect-resistant transgenic poplar trees have a potential application value in afforestation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Suppressing Weeds in Direct-seeded Lowland Rice: Effects of Methods and Rates of Seeding

High weed infestation is a major constraint to widespread adoption of direct seeding of rice (Oryza sativa L.) The experiments were conducted in 1998 wet and 1999 dry seasons in the Philippines to examine the effects of seeding methods and rates on suppressing weeds in direct-seeded lowland rice. Treatments consisted of four seeding methods: conventional and modified broadcast seeding, drill seeding with east–west and north–south row orientations; three seeding rates: 40, 80 and 160 kg seed ha⁻¹ as well as two weed control levels: weed control with herbicide and no weed control. Among the seeding methods drill seeding with east–west row orientation had the lowest rice grain yield loss caused by weeds (38 % in the wet and 20 % in the dry season), whereas the highest losses because of weeds were observed with conventional broadcast seeding (59 % in the wet and 27 % in the dry season). Seeding rate was inversely correlated to weed interference. Severe rice yield reduction (71 %) caused by weeds was found at a seeding rate of 40 kg seed ha⁻¹ in the wet season. Using seeding rates of 80 and 160 kg seed ha⁻¹, respectively, lowered yield loss to 47 and 26 % in the wet season, 32 and 18 % in the dry season. Therefore suitable method and/or rate of seeding can significantly suppress weeds in direct-seeded lowland rice.     

Clonal propagation of triploid <Emphasis Type="Italic">Acorus calamus</Emphasis> Linn. Using dual-phase culture system

Acorus calamus is an important medicinal plant which has been used in Indian traditional medicine since time immemorial. Various bioactive molecules, viz., acorin, α- and β-asarone, asaryldehyde, caryophylene, isoasarone, methylisoeugenol, and safrol have been isolated from this plant. However, the use of this plant for medicinal purpose has been recently banned due to the high toxic property of β-asarone. The triploid Acorus calamus is reported to be low in β-asarone content and thus found to be the ideal raw material for medicinal use. The present investigation represents our finding for successful in vitro clonal propagation of the elite triploid accessions of Acorus calamus for mass propagation. In the dual-phase culture system consisting of agar-solidified Murashige and Skoog medium overlaid by liquid fraction of the same medium, maximum multiple shoot induction was favored by supplementation of α-naphthaleneacetic acid (0.5 mg L⁻¹) and 6-benzylaminopurine (2.0 mg L⁻¹). In vitro rooting of the microshoots was maximum in the medium supplemented with indolebutyric acid at 2.0 mg L⁻¹. The well-rooted microshoots could be successfully hardened and transplanted in the field. This result can be reproduced and is a viable protocol for successful clonal propagation of the seedless triploid Acorus calamus for conservation and sustainable development.     

Inheritance and Correlation of Self-Compatibility and other Yield Components in the Apricot Hybrid F1 Populations

Summary To provide genetic basis for apricot (Prunus armeniaca Lam.) breeding, inheritance and correlation of yield components including self-compatibility, self-pollinated fruiting rate, fertile flower rate, average fruit weight and fruit number per plant were studied with 5-year-old seedlings of apricot F1 hybrids from ‘Katy’ × (‘Xinshiji’, ‘Katy’ × (‘Hongfeng’ and ‘Katy’ × (‘Taianshuixing’, respectively. Using the criteria that cultivars with self-pollinated fruiting rate ≥6% were self-compatible(SC), we found that the ratios of self-compatible (SC) to self-incompatible (SI) individuals were 27:25, 9:12 and 15:19 in the above three families, respectively, and conformed to the ratio of 1:1 segregation by χ² test, indicating that the S-locus of ‘Katy’ was heterozygous and self-compatibility was dominant to self-incompatibility. Twenty-seven seedlings from the F1 population of ‘Katy’ × ‘Xinshiji’ were chosen for S-allele-specific PCR. As a result, four S-genotypes with the ratio of 10:6:4:7 were obtained, which was linear to the 1:1:1:1 ratio by χ² test. Great differences in self-compatibility degree were observed among seedlings even with the same S-genotype. In the F1 populations, a very extensive segregation in self-pollinated fruiting rate, fertile flower rate and average fruit weight was observed, and average values of these traits were lower than that of mid-parent. Therefore, these traits were confirmed to be quantitative. However, significant differences were found in broad heritability (H _b ²) of following three characters: the H _b ² of self-pollinated fruiting rate (87.1% – 91.4%) was the greatest, with the variation mainly resulted from inheritance; fertile flower rate (36.8% – 49.1%) was the least and its variation was mainly caused by environmental factors. In addition, self-pollinated fruiting rate and fertile flower rate had very significantly positive correlations with single plant yield, so both may play important roles in the determination of single plant yield. In contrast, correlation between yield and average fruit weight was not significant.     

Trueness-To-Type and Yield Components of the Banana Hybrid Cultivar FHIA-18 Plants Regenerated Via Somatic Embryogenesis in a Bioreactor

Summary A population of 1,500 plants of the banana hybrid ‘FHIA-18’ (AAAB), regenerated from somatic embryos, which were multiplied in bioreactors, showed similar characteristics to plants propagated from shoot tip cultures both in the acclimatization stage and in field experiments carried out in Cuba. The plants originating from somatic embryos were similar to the plants obtained from shoot tips with respect to plant height, diameter of the pseudostem and number of suckers. Both groups of plants obtained from in vitro cultures were significantly different to the plants obtained from suckers during the flowering period of the mother plants, which was shortened by two months. The greater plant height and diameter of the pseudostem in the plants coming from somatic embryos and shoot tip is due to the effect of in vitro culture, and this was observed in different banana and plantain cultivars. During the second cycle of evaluation, the plants coming from the three propagation methods studied in this work had similar growth habits without significant differences in the majority of the morphological parameters evaluated. These results confirm that the difference obtained during the first cycle between the distinct populations is attributed to temporary changes. The original characteristics of the cultivar were evident from the second cycle of culture. Only 0.13% somaclonal variant was observed in the plants coming from somatic embryogenesis. These percentages are low taking into consideration that other propagated methods accept up to 5% variants in field conditions.     

Performance of <Emphasis Type="Italic">Coffea arabica</Emphasis> F1 hybrids in agroforestry and full-sun cropping systems in comparison with American pure line cultivars

Coffea arabica F1 hybrids derived from crosses between wild Sudan-Ethiopian and American cultivars and propagated by somatic embryogenesis have been obtained in Central America. These new hybrids considerably enhanced the genetic diversity of coffee in the region. We conducted 15 trials to assess whether using hybrids represents substantial genetic progress in terms of productivity in agroforestry and full-sun cropping systems. The new germplasm was grown in the same conditions as the best American cultivar (homozygous pure lines). The results showed that yields of hybrids were earlier and superior to those of American cultivars. The hybrids were also more stable than the American cultivars in all environments. In the agroforestry system, the mean yield of hybrids was 58% higher than that of the American cultivars, while the mean yield of hybrids in the full-sun system was 34% higher. Coffee-based agroforestry systems (AS) are considered effective in protecting the environment in the volcanic cordilleras of Central America. We found that introducing hybrids in coffee-based AS can considerably increase productivity. This finding could be a convincing argument to encourage coffee growers who have adopted the full-sun cropping system to return to agroforestry cropping systems. Finally, the conditions for large-scale dissemination of those new hybrids—which represent a major innovation for C. arabica cropping—was analysed.     

An efficient <Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated transformation protocol for black pepper (<Emphasis Type="Italic">Piper nigrum</Emphasis> L.) using embryogenic mass as explant

A protocol was developed for an efficient Agrobactertium-mediated transformation of black pepper plants through somatic embryogenesis. Embryogenic mass derived from primary somatic embryos that were obtained from the micropylar region of mature germinating seeds of black pepper was found to be the ideal target tissue for transformation. Genetic fidelity test of embryogenic mass-derived plantlets by RAPD using 23 random primers revealed no genetic variation among the progenies and the parent plant. Among the antibiotics used for selection of transformants, cefotaxime at 100 μg mL⁻¹ was found to be optimum to control Agrobacterium besides its ability to promote somatic embryo proliferation. In the case of kanamycin, a step-wise increase in concentration from 25 to 50 and then to 100 μg mL⁻¹ were found to be optimum. Embryogenic mass co-cultivated with Agrobacterium carrying the β-glucuronidase (GUS) reporter gene were cultured on plant growth regulator-free Schenk and Hildebrandt (SH) medium and transformants were selected in selection medium containing cefotaxime and step-wise increase in kanamycin concentration. The transient GUS gene expression was determined histochemically. Transformants that survived in the selection medium were hardened in the greenhouse. An average of nine hardened putative plantlets was obtained per gram of embryogenic mass. The presence of transgene in these plantlets was assayed by PCR, dot blot, and Southern blot hybridization. Results presented demonstrated for the first time an efficient transformation and regeneration of black pepper without the use of growth regulators. This simple efficient procedure would allow transformation of black pepper with genes of desirable characters.     

Breeding potential of Solanum tuberosum–S. commersonii pentaploid hybrids: fertility studies and tuber evaluation

Twenty-one (near) pentaploid hybrids between sexually incompatible Solanum commersonii [2x(1EBN)] and cultivated S. tuberosum [4x(4EBN)] were characterized for tuber traits and fertility. A number of genotypes resembled the S. tuberosum type in terms of stolon length and eye depth and produced tubers under long day conditions. Tuber yields were not as high as expected, probably due to lack of adaptation of the S. commersonii genome to the environmental conditions in southern Italy (on average 325 g·pt⁻¹ and 285 g·pt⁻¹ in 2003 and in 2004, respectively). Compared to 2004, in the summer of 2003, characterized by extremely high temperatures, hybrids gave a higher tuber yield than the S. tuberosum control, suggesting that in our environmental conditions the wild S. commersonii genome, rather than resulting in heterosis for tuber yield, provides better adaptation to harsh environments. Although aneuploidy has often been associated with reduced fertility, several hybrids were fertile in crosses with S. tuberosum when used as female parents. In particular, the average berry set and number of seeds per berry were 38.2% and 31.8%, respectively. Based on significant relationships between ploidy levels and all yield and fertility data measured, the presence of extra chromosome affected the parameters considered: tuber yield in 2003 and 2004, percentage of fruit set, number of seeds per berry and number of seeds per pollinated flower. Regression analysis also indicated that “Residuals” were significant for all parameters measured. Therefore, additional factors (e.g. the genetic makeup of hybrids) may be key to fertility and yield.     

Molecular characterization of the recombinant inbred line population derived from a japonica-indica rice cross

Recombinant inbred line (RIL) populations of rice are useful genetic sources for map-based cloning of agronomically important genes. Zhe733 is a high-yielding indica cultivar from China conferring resistance to rice blast (RB), rice water weevil (RWW) and straighthead; whereas Kaybonnet low-phytic acid 1-1 (KBNTlpa) is a mutant of a tropical japonica cultivar from the US containing low-phytic acid with average yield, and is susceptible to some RB races, RWW, and straighthead. A 355 RIL F₁₀₋₁₁ population derived from the cross of KBNTlpa × Zhe733 was recently released. Simple sequence repeat (SSR) markers were used to evaluate 269 RILs of this population. A total of 107 polymorphic markers were mapped on all rice chromosomes representing a total of 1,016.3 cM of genetic distance. Two hundred and thirty-five KBNTlpa × Zhe733 RILs (KZRILs) were clustered into seven groups based on allele frequencies of SSR markers. Twenty-three markers (21.1%) on chromosomes 3, 6, 7, 9, and 11 were found to favor Zhe733 (χ ² = 16.8−189.7 and P < 0.01) and five markers (4.6%) on chromosome 1 and 6 were found to favor KBNTlpa (χ ² = 18.5−46.6 and P < 0.01). Marker segregations were observed to be normal for both parents except 26 (10.2%) KZRILs were found to skew toward Zhe733 (χ ² > 15.7 and P < 0.01). Furthermore, the average frequencies of heterozygosity and non-parental alleles per KZRIL were 1.3% (0.0−38.9%) and 0.4% (0.0−15.0%), respectively. Thirteen heterozygous KZRILs were found at more than five markers loci and nine KZRILs were found with more than five non-parental alleles representing 5.1 and 3.5% of 255 KZRILs. Overall, this KZRIL population is a good population with relatively low frequencies of heterozygosity and non-parental alleles, and with relatively low percentages of skewed markers and skewed KZRILs. The profiles of these SSR markers should facilitate molecular tagging critical genes controlling yield, RB, RWW, and straighthead resistance.     

QTL-based analysis of genotype-by-environment interaction for grain yield of rice in stress and non-stress environments

Use of DNA-based markers can accelerate cultivar development in variable cultivation environments since, in contrast to phenotype, DNA markers are environment-independent. In an effort to elucidate the genetic basis of genotype-by-environment interaction (G × E) for yield of rice (Oryza sativa L.), the associations between 139 AFLP markers and grain yield were determined for rice grown in fresh water (EC of 0.65 dS m⁻¹) and saline conditions (EC of 4–8 dS m⁻¹) with 0 kg ha⁻¹ or 100 kg ha⁻¹ nitrogen fertilizer in the years 2000 and 2001. A population of recombinant inbred lines of rice, developed from an IR29 × Pokkali cross, was used in the study. Both genotype × salinity and genotype × nitrogen level interactions were significant, with the genotype × salinity interaction being stronger. Through multiple regression analysis using a stepwise procedure for selecting markers, 36 markers were detected for grain yield in the four test conditions and of these 28 were detected in only one test condition implying strong environmental specificity for yield QTL expression. However, the fact that eight QTLs were detected in more than one test condition points to the existence of wide-adaptability genes in this cross. Markers with significant associations with yield explained between 37% and 48% of the yield variation in each test condition. Superior genotypes of rice were identified in all four test conditions based on their marker signatures. Furthermore, across N fertilizer regimes, yield predicted from summed additive effects of QTLs were significantly correlated with observed yield in the same year and across years. Thus marker-assisted selection can help breeders overcome the problem of low selection efficiency encountered during phenotypic selection for yield in stress environments.     

Genetic effects on biomass yield in interspecific hybrids between Brassica napus and B. rapa

This study was conducted to estimate the genetic effects on biomass yield in the interspecific hybrids between Brassica napus and B. rapa, and to evaluate the relationship between parental genetic diversity and its effect on biomass yield of interspecific hybrids. Six cultivars and lines of oilseed B. napus and 20 cultivars of oilseed B. rapa from different regions of the world were chosen to produce interspecific hybrids using NC design II. Obvious genetic differences between B. rapa and B. napus were detected by RFLP. In addition, Chinese B. rapa and European B. rapa were shown genetically differences. Plant biomass yield from these interspecific hybrids were measured at the end of flowering period. Significant differences were detected among general combining ability (GCA) effects over two years and specific combining ability (SCA) effects differences were detected in 2000. The ratios of mean squares, (σ² _GCA(f) + σ² _GCA(m)) / (σ² _GCA(f) + σ² _GCA(m) + σ² _SCA), were 89% and 88% in 1999 and 2000, respectively. This indicates that both additive effects and non-additive effects contributed to the biomass yield of interspecific hybrids and the former played more important role. Some European B. rapa had significant negative GCA effects while many of Chinese B. rapa had significant positive GCA effects, indicating that Chinese B. rapa may be a valuable source for transferring favorable genes of biomass yield to B. napus. Significant positive correlation between parental genetic distance and biomass yield of interspecific hybrids implies that larger genetic distance results in higher biomass yield for the interspecific hybrids. A way to utilize interspecific heterosis for seed yield was discussed. This revised version was published online in July 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.     

High frequency plantlet regeneration from nodal segment culture of female <Emphasis Type="Italic">Momordica dioica</Emphasis> (Roxb.)

An in vitro propagation method for female plants of Momordica dioica (Roxb.) has been established. The nodal segments were harvested and the cut ends of the explants were sealed with wax and then surface sterilized and cultured. Bud breaking occurred on Murashige and Skoog’s (MS) agar-gelled medium + 2.0 mg L⁻¹ 6-Benzylaminopurine (BAP) + 0.1 mg L⁻¹ Indole-3 acetic acid (IAA). The cultures were amplified by passages on MS medium supplemented with 1.0 mg L⁻¹ BAP + 0.1 mg L⁻¹ IAA. Further, shoot amplification (29.2 shoots per vessel) was achieved by subculturing of in vitro regenerated shoot clump on MS medium + 0.5 mg L⁻¹ BAP + 0.1 mg L⁻¹ IAA. The micropropagated shoots were subsequently transferred for root formation on half-strength MS medium + 2.0 mg L⁻¹ Indole-3 butyric acid (IBA) with 89% success rate. The in vitro-regenerated shoots were also rooted ex vitro with 34% success. These plantlets were hardened in the greenhouse and transferred to the field. The established protocol is suitable for true to type cloning of mature female plant of M. dioica.     

Performance of various grapefruit (<Emphasis Type="Italic">Citrus paradisi</Emphasis> Macf.) and pummelo (<Emphasis Type="Italic">C. maxima</Emphasis> Merr.) cultivars under the dry tropic conditions of Mexico

Grapefruit growers in the tropics require information about existing and new citrus cultivars with high productivity potential. The objective of this study was to determine the growth, yield, and fruit quality performance of seven pigmented and four white grapefruit cultivars under the dry tropic conditions of Colima, Mexico. The trees were budded on sour orange (Citrus aurantium L.) rootstock and planted at a distance of 8 × 4 m. ‘Oroblanco’ and ‘Marsh Gardner’ white-fleshed grapefruit cultivars and ‘Chandler’, a pink-fleshed pummelo, were the largest trees with the greatest height (5.0–5.6 m), canopy diameter (6.2–6.3 m), trunk diameter (21.9–23.3 cm), and canopy volume (109–123 m³). Lower height (4.3–4.8 m) and canopy volume (73–96 m³), but with similar canopy diameter to the previously mentioned cultivars, were recorded for the remaining pigmented cultivars. ‘Chandler’ pummelo and four pigmented grapefruit cultivars (‘Shambar’, ‘Río Red’, ‘Ray Ruby’, and ‘Redblush #3’) had yearly productions of 34.8, 34.9, 34.1, 32.7, and 30.6 ton ha⁻¹, respectively. The most productive white grapefruit cultivar was ‘Marsh Gardner’ (30.5 ton ha⁻¹). Grapefruit cultivars having the largest fruit size showed a higher inverse relationship between fruit weight and yield than those with small fruit. Most genotypes had higher values of fruit weight, juice content, and maturity index than those required by the local market. The most promising grapefruit cultivars based on their acceptable growth, yield superior to 30 ton ha⁻¹, and acceptable fruit color were ‘Río Red’, ‘Shambar’, ‘Ray Ruby’, and ‘Redblush #3’.     

Response of a new IR50/Moroberekan recombinant inbred population of rice (Oryza sativa L.) from an indica × japonica cross for growth and yield traits under aerobic conditions

Genetic variability, correlation, path coefficient analysis and test of normality was conducted in an F₈ recombinant inbred aerobic rice population developed by single seed descent method to evaluate its potential as a mapping population. Estimates of genotypic variance, phenotypic variance, genotypic coefficient of variance (GCV), phenotypic coefficient of variance (PCV), heritability in the broad sense (H) and expected genetic advance at 5% selection index (GA) for grain yield and other attributing characters were computed. In all the cases, PCV was higher than GCV indicating the influence of environment on the characters. High heritability coupled with high GA was observed for several plant traits; number of tillers, plant height, total number of spikelets panicle⁻¹, biomass plant⁻¹, straw weight, harvest index and grain yield plant⁻¹ and hence offered good scope for selection. Grain yield plant⁻¹ was found to be positively correlated with plant height, number of tillers, panicle length, panicle exsertion, number of panicles plant⁻¹, single panicle weight, test weight, number of fertile spikelets panicle⁻¹, straw weight, biomass plant⁻¹, harvest index and grain breadth both at genotypic and phenotypic levels. Harvest index exerted maximum positive direct effect, followed by biomass plant⁻¹ and straw weight on grain yield plant⁻¹ at phenotypic level. Shapiro-Wilks “W test of normality” indicated that the population was skewed towards female parent IR50 for some traits and for some others towards Moroberekan, the male parent. Most of the characters that showed skewness were platykurtic with a kurtosis value of less than 3.     

Corms as a source of explants for the successful clonal propagation of <Emphasis Type="Italic">Crocus cancellatus</Emphasis>

The genus Crocus comprises plants with a potential to be developed as a new ornamental crop but to date, there are not many reports on in vitro propagation of many members of this genus. The present study involves in vitro propagation of Crocus cancellatus with ornamental and horticultural value. Two different types of corm explants (apical and basal halves of corms) were cultivated onto Murashige and Skoog’s (MS) medium supplemented with different levels of α-naphthalene acetic acid (NAA) and 6-benzylaminopurine (BAP). One to five cormlets emerged from every responding explant through direct organogenesis. Apical halves of corms were more highly responsive than basal halves and produced a maximum multiplication rate with 3.45 ± 0.06 cormlets per explant in 95.33 ± 2.33% of the explants in MS medium supplemented with 3% sucrose and 2 mg L⁻¹ NAA and 1 mg L⁻¹ BAP. The effect of cold storage temperature on in vitro cormlets sprouting was studied. Cormlets stored at 4°C for 8 weeks had more statistically significant positive effects on cormlets sprouting from the controls. In vitro rooting of cormlets was induced on MS medium without plant hormones.     

Genetic gains in Nordic spring barley breeding over sixty years

Accurate assessments of genetic gains ensuing from plant breeding for the most important agronomic characteristics in Nordic spring barley (Hordeum vulgareL.) are not available. Hence this research was aimed to determine the rate of genetic improvement in the Nordic barley breeding pool. This study included 90, 2-row spring barley cultivars released (1942–1988) and29, 6-row spring barley cultivars released(1930–1991) adopted by Nordic farmers that were tested in four Nordic locations for three consecutive years. Relative genetic gain owing to plant breeding was 13% in2-row barley and 34% in 6-row barley for grain yield. The absolute gain for this characteristic was 13 ± 3 kg ha^-1 year ^-1 in 2-row barley, and22 ± 3 kg ha^-1 year^-1 in6-row barley. Improved yield was achieved in Nordic barley by reducing plant height(0.20 ± 0.04 cm year^-1 for 2-rowbarley and 0.16 ± 0.06 cm year^-1for 6-row cultivars), thereby reducing significantly lodging (0.5 ± 0.1%year^-1 and 0.4 ± 0.1year^-1), and increasing significantly the harvest index (0.0008 ± 0.0002year^-1 and 0.0018 ± 0.0002year^-1). Additionally, in 2-row spring barley cultivars resistance to powdery mildew (0.19 ± 0.08% year^-1)and thousand-kernel weight (0.07 ±0.03 g year^-1) were also significantly enhanced, whereas hectoliter weight was improved (0.06 ± 0.02 kg year^-1)in 6-row barley cultivars in the period investigated. This revised version was published online in August 2006 with corrections to the Cover Date.     

A methodology for heterosis breeding of common buckwheat involving the use of the self-compatibility gene derived from <Emphasis Type="Italic">Fagopyrum homotropicum</Emphasis>

We propose an alternative breeding methodology for common buckwheat (Fagopyrum esculentum Moench), involving the use of the self-compatibility (S ^h ) gene derived from F. homotropicum Ohnishi. This methodology involves inbred development of homostyle (S ^h S ^h ) and pin (ss) lines by using the self-compatibility gene (S ^h ). Further, single-cross hybrid seeds are produced using these inbred homostyle and pin lines as pollen and seed parents, respectively. This strategy successfully produced self-compatible homostyle hybrids (S ^h s); the percentage of hybrid plants among the progeny was more than 90%. In a greenhouse trial, the heterosis (best parent) in top dry weight, including stem and leaves, was 29.1–48.1% during the early growth stage. The seed yield of the progeny obtained in single-cross experiments was superior to that of an open-pollinated standard variety “Kitawasesoba” by 10% on average. These results suggest that heterosis breeding can be used to increase seed yield in common buckwheat.     

Germplasm diversity and estimate of genetic advance of four morpho-physiological traits in a world collection of jute

Summary To improve jute productivity, locating of sources of suitable quantitative-trait genes in the recently acquired world jute collection was needed. Two hundred sixteen accessions of Corchorus capsularis and 192 accessions of C. olitorius were evaluated at a jute seed research station (87°60\s'E, 23°80\s'N) for four yield and quality linked morpho-physiological traits. The objectives were to estimate the germplasm diversity, phenotypic (PCV) and genetic (GCV) coefficients of variation, broad sense heritability (h²) and genetic advance (GA) with respect to origins and traits. Irrespective of origins all the traits showed more than 60–80% diversity in both species. Trait means of diversity were significant but not the origin means. Generally, only slightly higher PCV values than GCV were obtained for all the traits in both the species. High h² values ranging from 50% to more than 98% were also found. All the traits can be simultaneously utilized for genetic gain. Most of the C. olitorius accessions with two times higher GA estimates than those of the C. capsularis are likely to be more successful for that matter. Maximum genetic gain is expected from Mutants > China > Brazil > India > Thailand > Nepal > Burma in C. capsularis while from Thailand > Tanzania > Mutants > Kenya > Other countries in C. olitorius. C. capsularis mutants with high heterogenity for most of the traits should be useful for finding many rare alleles.