Polymorphisms of α-amylase activity in barley landraces and cultivars from China

Summary -Amylase activity was assayed by measuring reducing power equivalent for 80 accessions of cultivated barley, Hordeum vulgare L., representing major barley growing areas of China. Replications were applied at two different levels of the experiment and enzyme activity was assayed on four consecutive days starting on the 6th day after germination. The area under the curve formed by connecting the four data points was integrated as the measurement of -amylase activity. The results established that there was extensive variation in -amylase activity in cultivated barley; about three-fold difference existed among accessions assayed. Comparisons were also made between six- and two-rowed, and between covered and naked barleys. The results showed that high -amylase activity was not necessarily associated with six-rowed type, and that covered barleys were slightly higher in -amylase activity than naked ones.     

Can Mediterranean durum wheat landraces contribute to improved grain quality attributes in modern cultivars?

The variability for quality attributes existing in a collection of 154 durum landraces from 20 Mediterranean countries and 18 modern cultivars was determined with the ultimate goal of identifying potential quality-enhancing genotypes for use in breeding programs. Field experiments were conducted during 3 years under rainfed conditions in northeastern Spain. Environmental effects were the most important in determining protein content, grain yield and yellow color index of the endosperm (grain flour), and the least important in determining EU quality index (QI), gluten strength and grain filling rate. QI is a weighed composite index determined from protein content, gluten strength, yellow color index and thousand kernel weight. Multivariate analysis detected four groups; three including landraces and one comprising modern cultivars. Landraces from the eastern Mediterranean countries had the highest mean QI and the widest variability for individual quality traits, but were characterized by relatively small grains. Landraces from the western Mediterranean countries had greater grain filling rates and heavier grains. Protein content, gluten strength and yellow color index were similar between eastern and western groups. The low QI and reduced variability characterizing the landrace group from the north Balkan Peninsula support the hypothesis of a different origin for this group. Modern cultivars, as a group, were the most productive and showed high QI, but they had the lowest grain protein content and phenotypic variability. Landraces that could be used as sources of quality-improving attributes and/or those that could be used in breeding programs without substantial quality handicaps were identified from different groups. Landraces can be particularly useful in breeding programs to improve gluten strength, grain weight and accelerate grain filling rate.     

Genome-wide indel markers shared by diverse Asian rice cultivars compared to Japanese rice cultivar ‘Koshihikari’

Insertion-deletion (indel) polymorphisms, such as simple sequence repeats, have been widely used as DNA markers to identify QTLs and genes and to facilitate rice breeding. Recently, next-generation sequencing has produced deep sequences that allow genome-wide detection of indels. These polymorphisms can potentially be used to develop high-accuracy polymerase chain reaction (PCR)-based markers. Here, re-sequencing of 5 indica, 2 aus, and 3 tropical japonica cultivars and Japanese elite cultivar ‘Koshihikari’ was performed to extract regions containing large indels (10–51 bp) shared by diverse cultivars. To design indel markers for the discrimination of genomic regions between ‘Koshihikari’ and other diverse cultivars, we subtracted the indel regions detected in ‘Koshihikari’ from those shared in other cultivars. Two sets of indel markers, KNJ8-indel (shared in eight or more cultivars, including ‘Khao Nam Jen’ as a representative tropical japonica cultivar) and C5-indel (shared in five to eight cultivars), were established, with 915 and 9,899 indel regions, respectively. Validation of the two marker sets by using 23 diverse cultivars showed a high PCR success rate (≥95%) for 83.3% of the KNJ8-indel markers and 73.9% of the C5-indel markers. The marker sets will therefore be useful for the effective breeding of Japanese rice cultivars.     

Characterization and allelism of soybean mosaic virus strain SC3 resistance in ‘Qihuang-1’ derived soybean cultivars

Soybean mosaic virus is a severe constraint of soybean production in China. A total of country-wide 22 SMV strains (SC1-SC22) were identified. Of these, SC3 is a major strain widely distributed in Huanghuai and Yangtze River Valley region of China. Soybean cultivar ‘Qihuang-1’ contains R_SC3Q locus conditioning the resistance to SC3 and is an important parental line extensively used to breed the soybean cultivars in China. The objective of this study was to elucidate the genetic pattern of SC3 resistance genes in cultivars developed from ‘Qihuang-1’ or its derivative lines. Hence, we have evaluated the SC3 resistance in 91 cultivars developed from ‘Qihuang-1’ or its derivative lines. The results showed that a total of 43 cultivars exhibited resistance to the SC3 strain. Among them, 37 cultivars were derived from ‘Qihuang-1’. Then, we have detected the R_SC3Q loci in these cultivars using four SSR markers (Satt334, Sct_033, BARCSOYSSR_13_1114 and BARCSOYSSR_13_1136). It revealed that, among the 37 resistant cultivars derived from ‘Qihuang-1’, there are 20 cultivars containing R_SC3Q loci. Moreover, the allelic relationship of resistance genes was analysed using the crosses from resistance × resistance between ‘Qihuang-1’ and its resistant derived cultivars. The results showed that the resistance genes of ‘Qihuang-1’ and its 20 cultivars were allelic. But it is not allelic with those of the other 17 cultivars, different from ‘Qihuang-1’, and also, R_SC3Q does not condition the resistance. These results will be beneficial to exploring the transmission of resistance genes of ‘Qihuang-1’ and will be useful to the disease resistance breeding of soybean.     

DNA fingerprinting of strawberry (Fragaria × ananassa) cultivars using randomly amplified polymorphic DNA (RAPD) markers

Forty-one of the major strawberry (Fragaria × ananassa Duch.) cultivars grown in the United States and Canada were examined for RAPD (randomly amplified polymorphic DNA) marker polymorphisms using 10mer primers (>50% GC content). A set of 10 primers produced 15 polymorphic fragments ranging in size between 450 and 1200 bp, which were more than sufficient to distinguish among all tested cultivars. Ten of the markers derived from seven primers were absolutely required for distinguishing the cultivars. A DNA fingerprinting table was constructed based on these results. In addition, similarity coefficients were calculated based on RAPD marker data and a dendogram was constructed using the unweighted pair group method of arithmetic averages (UPGMA). These results were compared with known pedigree data for the cultivars. Our results demonstrate that RAPD markers can be used effectively for strawberry cultivar identification. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparative genetic analysis of field resistance to downy mildew in the lettuce cultivars ‘Grand Rapids’ and ‘Iceberg’

Downy mildew on lettuce is currently controlled using host resistance genes (Dm genes) that confer race-specific resistance in seedlings. Field resistance (FR) that is active in adult plants but not seedlings was identified in the cvs. Grand Rapids and Iceberg. The goal of our study was to evaluate the utility of Grand Rapids as a source of novel Bremia resistance alleles, particularly in comparison with Iceberg. To measure FR, downy mildew symptoms were evaluated following natural infection in field experiments. The responses of Grand Rapids and Iceberg were similar in many respects. Although both cultivars had a small percentage of plants exhibiting disease symptoms, the average disease ratings were as low as for cultivars with effective Dm genes. We observed no evidence for race specificity. FR was effective over 3 years of our study, despite documented variation within pathogen populations. Both cultivars lacked all known seedling resistance genes except Dm13, which was not responsible for the resistance observed in field experiments. Similar segregation of FR was observed in F₂ populations for both Grand Rapids and Iceberg. The presence of highly susceptible families within Grand Rapids × Iceberg populations suggested the presence of at least one unique resistance allele in each cultivar. Preliminary genetic analysis of FR from Grand Rapids revealed a high estimate of narrow-sense heritability that suggested simple inheritance, but single gene models did not fit the observed data. Our results suggest that Grand Rapids may represent an underutilized resource for controlling downy mildew in lettuce.     

Postharvest life and flavor quality of three strawberry cultivars kept at 5 °C in air or air+20 kPa CO2

The postharvest life and flavor quality of three strawberry (Fragaria x ananassa D.) cultivars (Aromas, Diamante and Selva) kept at 5 °C in air or air+20 kPa CO₂ for up to 15 days were investigated. ‘Diamante’ and ‘Selva’ had better flavor quality than ‘Aromas’ strawberries, as indicated by levels of titratable acidity and total soluble solids, organic acids, sugars and some aroma compounds and by a consumer preference test. Flesh firmness was maintained in ‘Aromas’ and increased in ‘Diamante’ and ‘Selva’ strawberries during storage at 5 °C in both air and air+20 kPa CO₂. Fruit color was not affected by CO₂ treatments. The postharvest life based on appearance was 7, 9 and 9 days for ‘Aromas’, ‘Diamante’ and ‘Selva’ fruits stored in air and it was extended by 2, 2 and 4 days, respectively, by the CO₂-enriched atmosphere. However, the level and proportion of flavor components (sugars, organic acids, aroma compounds) and fermentative metabolites, as well as the results of sensory evaluations, indicated that the flavor life was shorter than postharvest life based on appearance in ‘Aromas’ fruit stored in air (5 vs. 7 days) and in CO₂-stored ‘Aromas’ (7 vs. 9 days) and ‘Selva’ (11 vs. 13 days) fruit. ‘Selva’ and ‘Diamante’ strawberries retained their flavor quality during storage at 5 °C in air for 9 days and CO₂-stored ‘Diamante’ fruit for 11 days.     

Profiling peanut (<Emphasis Type="Italic">Arachis hypogea</Emphasis> L.) accessions and cultivars for oleic acid and yield in Botswana

The ratio of monounsaturated oleic fatty acid to polyunsaturated linoleic fatty acid (O/L) and the associated agronomic traits were profiled for local peanut (Arachis hypogaea L.) cultivars and accessions in Botswana. The research was tested on 16 entries planted in four localities across the country. The average total oil yield of the genotypes studied was about 42.1% and there was no significant difference in total oil yield (P < 0.05) across the four research sites and among all entries (accessions). The average mean O/L ratio for all entries was about 1.47. The highest was that of the locally improved variety, Peolwane (2.58), which was significantly different (P < 0.05) from all other accessions, and the lowest is that of the local accession GO 63 (1.23). This study also profiled the agronomic yield traits to identify genotypes that have both high oil quality and high yielding potential. No correlation was detected between pod yield and O/L ratio among the tested genotypes. The station with little rainfall but adequate repartition showed a very high O/L ratio for some genotypes, and future work is recommended to test this interesting observation on the correlation between moisture stress and oil quality.     

Genome composition of triploid lily cultivars derived from sexual polyploidization of Longiflorum × Asiatic hybrids (<Emphasis Type="Italic">Lilium</Emphasis>)

About 19 cultivars, which had originated from backcrosses between F1 LA (Longiflorum × Asiatic) hybrids (2n = 2x = 24) as female parents and Asiatic cultivars as male parents (2n = 2x = 24), were analyzed with genomic in situ hybridization. 17 of them were triploid (2n = 3x = 36), and two aneuploid (2n = 3x + 1 = 37). The triploid cultivars had resulted from the functional 2n eggs produced by the female parents (F1 hybrids) because first division restitution (FDR) occurred in their meiosis during megasporogenesis. Similarly, the aneuploid cultivars had originated from viable 2n + 1 eggs. The extra chromosome in cultivar 041555 or 041572 resulted from one univalent or one half-bivalent which might have lagged behind when the sister chromatids of the other univalents and half-bivalents were segregating during the FDR process in their LA hybrid parents, respectively. That the majority of cultivars possessed recombinant chromosomes showed that intergenomic recombination might play an important role during the selection of the cultivars directly from BC1 progenies. That five cultivars of the 15 recombinant cultivars only had reciprocal recombinant chromosomes and 10 cultivars had non-reciprocal recombinant chromosomes indicates that the latter are more important. Because 9 of the 10 non-reciprocal recombinant cultivars possessed substitutions for recombinant segments, it also indicated that such substitutions could be an important source for the genetic variation in the sexual triploid BC1 progenies. In such cases there was a potential for the expression of the recessive genes of the backcross parent in a nulliplex (aaa) condition in the substituted segments. Genetic variation resulting from such nulliplex loci might have played a role in the selection of some of the cultivars.     

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’.     

Genetic diversity of feral alfalfa (<Emphasis Type="Italic">Medicago</Emphasis> <Emphasis Type="Italic">sativa</Emphasis> L.) populations occurring in Manitoba,Canada and comparison with alfalfa cultivars: an analysis using SSR markers and phenotypic traits

Feral populations of cultivated crops may act as reservoirs for novel traits and aid in trait movement across the landscape. Knowledge on the genetic diversity of feral populations may provide new insights into their origin and evolution and may help in the design of efficient novel trait confinement protocols. In this study, the genetic diversity of 12 feral alfalfa (Medicago sativa) populations originating from southern Manitoba (Canada) and 10 alfalfa cultivars and a M. falcata germplasm were investigated using eight SSR markers (i.e., microsatellites) and 14 phenotypic traits. We found that the genetic diversity observed in feral populations was similar to the diversity detected among the 10 cultivars. Analysis of molecular variance revealed that there was great genetic variation within (99.8%) rather than between different feral populations. Cluster analysis (unweighted pair-group method using arithmetic average) revealed no differentiation between feral populations and cultivars for neutral loci. High levels of population differentiation for phenotypic traits (and not for neutral markers) suggest the occurrence of heterogeneous selection for adaptive traits. The phenotypic traits we studied did not distinctly separate feral populations from cultivars but there was evidence of natural selection in feral populations for traits including winter survivability, rhizome production, and prostrate growth habit. Our results suggest that feral alfalfa populations need to be considered in the risk assessment of alfalfa containing novel genetically modified (GM) traits. Further, feral alfalfa populations may be regarded as a source of new germplasm for plant improvement.