US Cultivars Research Articles

Novel Phr1 mutations and the evolution of phenol reaction variation in US weedy rice (Oryza sativa).

*Red rice, a major agricultural weed, is phenotypically diverse and possesses traits that are similar to both wild and cultivated rice. The genetic resources available for rice make it possible to examine the molecular basis and evolution of traits characterizing this weed. Here, we assess the phenol reaction - a classical trait for distinguishing among cultivated rice varieties - in red rice at the phenotypic and molecular levels. *We phenotyped more than 100 US weed samples for the phenol reaction and sequenced the underlying Phr1 locus in a subset of samples. Data were analyzed in combination with previously published Phr1 data for cultivated rice. *Most weed accessions (96.3%) are positive for the phenol reaction, and samples with a negative response carry loss-of-function alleles that are rare or heretofore undocumented. One such allele may have evolved through mutational convergence of a 1-bp frameshift insertion. Haplotype sharing between red rice and US cultivars suggests occasional crop-weed hybridization. *Our discovery of previously undocumented nonfunctional phr1 alleles suggests that there are likely to be other loss-of-function mutations segregating in Oryza sativa around the world. Red rice may provide a useful study system for understanding the adaptive significance of Phr1 variation in agricultural settings.

High-density Integrated Linkage Map Based on SSR Markers in Soybean

A well-saturated molecular linkage map is a prerequisite for modern plant breeding. Several genetic maps have been developed for soybean with various types of molecular markers. Simple sequence repeats (SSRs) are single-locus markers with high allelic variation and are widely applicable to different genotypes. We have now mapped 1810 SSR or sequence-tagged site markers in one or more of three recombinant inbred populations of soybean (the US cultivar ‘Jack’ × the Japanese cultivar ‘Fukuyutaka’, the Chinese cultivar ‘Peking’ × the Japanese cultivar ‘Akita’, and the Japanese cultivar ‘Misuzudaizu’ × the Chinese breeding line ‘Moshidou Gong 503’) and have aligned these markers with the 20 consensus linkage groups (LGs). The total length of the integrated linkage map was 2442.9 cM, and the average number of molecular markers was 90.5 (range of 70–114) for the 20 LGs. We examined allelic diversity for 1238 of the SSR markers among 23 soybean cultivars or lines and a wild accession. The number of alleles per locus ranged from 2 to 7, with an average of 2.8. Our high-density linkage map should facilitate ongoing and future genomic research such as analysis of quantitative trait loci and positional cloning in addition to marker-assisted selection in soybean breeding.

Inheritance of Salt Tolerance in Wild Soybean (Glycine soja Sieb. and Zucc.) Accession PI483463

Tolerant soybean (Glycine max [L.] Merr.) cultivars aid in reducing salt damage in problem fields. New genes are important to reduce losses from salt injury. Objectives of this study were to determine inheritance of salt tolerance in wild soybean (Glycine soja Sieb. and Zucc.) PI483463 and to test allelism of tolerance genes from genotypes PI483463 and S-100, a common ancestor of southern in US cultivars. Tolerant (T) PI483463 was crossed to sensitive (S) cultivar Hutcheson to study inheritance. PI483463 (T) was crossed with S-100 (T) to test for allelism. Parents, F(1) plants, F(2) populations, and F(2:3) lines were assayed in a 100 mM salt solution to determine tolerance. F(2) from T x S cross segregated 3(T):1 (S) and the F(2:3) lines responded 1 (T): 2 (segregating):1 (S). F(2) plants from PI483463 (T) x S-100 (T) segregated 15 (T):1 (S) indicating different genes from the 2 sources. Results showed that G. soja line PI483463 had a single dominant gene for salt tolerance, which was different than the gene in G. max line S-100. The symbol, Ncl2, was designated for this new salt tolerance allele.

Analysis of gene-derived SNP marker polymorphism in US wheat (Triticum aestivum L.) cultivars

In this study, we developed 359 detection primers for single nucleotide polymorphisms (SNPs) previously discovered within intron sequences of wheat genes and used them to evaluate SNP polymorphism in common wheat (Triticum aestivum L.). These SNPs showed an average polymorphism information content (PIC) of 0.18 among 20 US elite wheat cultivars, representing seven market classes. This value increased to 0.23 when SNPs were pre-selected for polymorphisms among a diverse set of 13 hexaploid wheat accessions (excluding synthetic wheats) used in the wheat SNP discovery project (http://wheat.pw.usda.gov/SNP). PIC values for SNP markers in the D genome were approximately half of those for the A and B genomes. D genome SNPs also showed a larger PIC reduction relative to the other genomes (P < 0.05) when US cultivars were compared with the more diverse set of 13 wheat accessions. Within those accessions, D genome SNPs show a higher proportion of alleles with low minor allele frequencies (<0.125) than found in the other two genomes. These data suggest that the reduction of PIC values in the D genome was caused by differential loss of low frequency alleles during the population size bottleneck that accompanied the development of modern commercial cultivars. Additional SNP discovery efforts targeted to the D genome in elite wheat germplasm will likely be required to offset the lower diversity of this genome. With increasing SNP discovery projects and the development of high-throughput SNP assay technologies, it is anticipated that SNP markers will play an increasingly important role in wheat genetics and breeding applications.

The genetic diversity of UK, US and Australian cultivars of Triticum aestivum measured by DArT markers and considered by genome

The genetic diversity of UK, US and Australian wheat varieties over the period of modern plant breeding is estimated using diversity array technology markers. Diversity is assessed by both genetic distance between varieties, by AMOVA and as the volumes of multi-dimensional convex hulls estimated from principal co-ordinate analysis. At the whole genome level the three populations are genetically distinct; this is also true of the B genome. However, the US and Australian D genomes are found to occupy the same region of diversity space and the A genomes for these countries are partially overlapping. The use of high-density genotyping with a common marker set allows an unprecedented direct comparison between the diversities of the national populations, between individual genomes and the fluctuation of diversity over time. The highest genetic diversity amongst varieties is reported in the Australian population followed by the US, which in turn is more diverse than the UK. However the average diversity of loci is higher in the US set than in the Australian. Non-random fluctuations in genetic diversity over time are observed.

Effect of temperature and water availability during late maturation of the soybean seed on germ and cotyledon isoflavone content and composition

AbstractBACKGROUND:Isoflavone content in soybean seeds is strongly influenced by both environment and genotype. However, little is known about the effect of environment and genotype on isoflavones in germ versus cotyledons. To determine the effect of temperature and soil moisture status during soybean seed development on seed isoflavone concentration and composition, a set of two French and three US cultivars of similar maturity were grown in the greenhouse. At the R6 growth stage, plants were subjected to one of three night/day temperature regimes (13/23°, 18/28° or 23/33 °C) in either optimal or sub‐optimal soil water conditions.RESULTS:In cotyledons, a three‐ to six‐fold variation in total isoflavone content was observed between the high and low temperature treatments, whereas the germ contents had less than a two‐fold variation. Soil water supply had less effect than temperature on the isoflavone contents and compositions. In both seed parts, the isoflavone concentrations were highly dependent on the cultivar.CONCLUSION:These results show that isoflavone content and composition in cotyledon and germ are unrelated and it should be possible to independently manipulate these seed traits through plant breeding and crop management systems. Copyright © 2007 Society of Chemical Industry

Assessing allergen levels in peach and nectarine cultivars

The lipid transfer protein Pru p 3 has been identified as a major peach fruit allergen. However, the putative peach member of the Bet v 1 family, Pru p 1, has been neither identified nor characterized. To determine the distribution and solubility properties of the main peach allergens and to quantify Pru p 3 and Pru p 1 levels in peach and nectarine cultivars. Peach peel and pulp were extracted using different buffers, and extracts were analyzed by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunodetection using polyclonal antibodies against lipid transfer proteins, profilins, and Bet v 1 homologues. Pru p 3 was quantified in peach and nectarine cultivars using a sandwich enzyme-linked immunosorbent assay method. A similar method was developed to quantify Pru p 1. A differential distribution between peel and pulp and different solubility properties were found for Pru p 3, Pru p 1, and peach profilin. Mean Pru p 3 levels were 132.86, 0.61, and 16.92 microg/g of fresh weight of peels, pulps, and whole fruits, respectively. The corresponding mean Pru p 1 levels were 0.62, 0.26, and 0.09 microg/g of fresh weight. Most US cultivars showed higher levels of both allergens than Spanish cultivars. The different distribution and solubility properties of the main peach allergens can determine the quality of fruit extracts used as diagnostic tools. These differences, together with the natural variation of Pru p 3 and Pru p 1 levels among peach and nectarine cultivars, can be exploited to reduce peach allergenicity by means of industrial processing and plant breeding.

Association mapping of yield and its components in rice cultivars

To make advances in rice breeding it is important to understand the relatedness and ancestry of introduced rice accessions, and identify SSR markers associated with agronomically important phenotypic traits, for example yield. Ninety-two rice germplasm accessions recently introduced from seven geographic regions of Africa, Asia, and Latin America, and eleven US cultivars, included as checks, were evaluated for yield and kernel characteristics, and genotyped with 123 SSR markers. The SSR markers were highly polymorphic across all accessions. Population structure analysis identified eight main clusters for the accessions which corresponded to the major geographic regions, indicating agreement between genetic and predefined populations. Linkage disequilibrium (LD) patterns and distributions are of fundamental importance for genome-wide mapping association. LD between linked markers decreased with distance and with a substantial drop in LD decay values between 20 and 30 cM, suggesting it should be possible to achieve resolution down to the 25 cM level. For the 103 cultivars, the complex traits yield, kernel width, kernel length, kernel width/length ratio, and 1000-kernel weight, were estimated by analysis of variety trial data. The mixed linear model method was used to disclose marker-trait associations. Many of the associated markers were located in regions where QTL had previously been identified. In conclusion, association mapping in rice is a viable alternative to QTL mapping based on crosses between different lines.

Golden rice: introgression, breeding, and field evaluation

Considerable progress has been made on the genetic engineering of rice for improved nutritional content involving micronutrients and carotenoid content. Golden Rice, developed by genetic engineering (Agrobacterium and biolistic transformation) was used in rice breeding for the transfer of high-nutritional value to the local rice cultivars. Simultaneously, commercial Asian indica rice cultivars were also developed with expression of high-carotenoid levels. The lines were developed based on POSITECH (PMI) selection system or made marker free by segregating out the marker gene from the gene of interest. Anther culture was used to develop the homozygous stable lines, which could be of much use in further introgress-breeding and in farmer’s field. Enhanced carotenoids levels (up to T3 generation) were observed in a number of lines compared to the T0-T1 seeds which could be due to transgeneration effect of growing under greenhouse versus field conditions. However, a few introgressed lines showed less carotenoid levels than the original lines used in the breeding process. Agronomic performance of introgressed lines, non-transgenic controls, and transgenic golden rice (IR64 and BR29) developed at IRRI showed acceptable and comparable data under identical limited field conditions (screenhouse data). Syngenta generated a new Golden Rice (US cultivar) containing high level of carotenoids grown in the field at Louisiana, USA is expected to be available to the public domain. Incorporation of genes for carotenogenesis in seeds by transgenesis or by introgression did not change any significant agronomic characteristics in rice plants. The ongoing and future study of bioavailability, quality, larger field testing and freedom to operate will ensure the benefit of Golden Rice to the people who need them most.

A rapid procedure for analysing rice bran tocopherol, tocotrienol and γ-oryzanol contents

Tocopherols, tocotrienols and γ-oryzanol compounds are phytochemicals with antioxidant activities and potential health benefits. Their contents and isomer ratios in rice bran vary among southern US cultivars, suggesting that breeding for higher contents or a favorable ratio of these phytochemicals is feasible. Methods that can rapidly and reliably extract and quantify their contents in rice bran or whole rice kernel are necessary for breeding programs. A simple, one-step equilibrium extraction procedure coupled with reversed-phase (RP) HPLC is presented here. The one-min equilibrium extraction at a 1:60 (w/v) ratio of rice bran to methanol recovered 92 to 102% of the target phytochemicals relative to those of repeated, non-saponified, direct solvent extraction methods. At this 1:60 ratio of bran to solvent, isopropanol and methanol are superior extraction solvents relative to hexane. A modified, mobile-phase gradient with 10% of aqueous phase for the first 3-min eliminates all the methanol-soluble interfering compounds. This extraction method has the following advantages over the currently available methods: speed, no special extraction instrumentation is needed; and the extraction solvent, methanol, is compatible with subsequent quantification via RP-HPLC.

Correlation between Yielding Ability and Dry Matter Productivity during Initial Seed Filling Stage in Various Soybean Genotypes

The critical developmental stage, during which the genotypic difference in yield is determined, was identified by analyzing the correlations between seed yield and seasonal crop dry matter productivity in optimally managed fields in four seasons. The fields (fluvial sandy loam or clay loam) were managed with irrigation, pest and weed control and canopy support to prevent lodging whenever necessary. The tested genotypes included 11 Japanese old and modern cultivars, five US cultivars and one non-nodulating line. Four to eight cultivars were studied in each year. Seed yield with 15% moisture (Y) in each experimental plot varied from 255 to 498g m-2. The US cultivars and Japanese modern cultivars tended to have a higher yield than the other cultivars grown in the same year. Y significantly and positively correlated with crop growthrate (CGR) during the 20 d period after the beginning of seed filling (R5), i.e. initial seed filling stage, in all four experiments. On the other hand, correlation of seed yield with CGR before or after this period varied with the year from negative to positive correlations. A close correlation was also observed between pod growth rate during the initial seed filling and Y. These results suggest that the critical stage during which seed yield potential of soybean cultivars is determined is the initial seed filling period and the larger dry matter production during this period is closely associated withthe satisfactory growth of reproductive organs and high seed yield.

Symbiotic efficiency and compatibility of native rhizobia in northern Thailand with different soybean cultivars

Symbiotic efficiency and compatibility of 81 isolates of native bradyrhizobia from irrigated areas in northern Thailand with four soybean cultivars and one cowpea cultivar were evaluated under laboratory conditions. Effectiveness and / or compatibility of the tested isolates were compared with those of a standard strain (Bradyrhizobium japonicum CB 1809) by using plants grown on plastic seed bags. Effectiveness of the isolates was also estimated using uninoculated control plants grown in a nitrogen-free solution. Nodulation of a wide range of host plants by the majority of the tested isolates was observed, which agreed well with the results of our previous field experiment (Shutsrirung et al. 2002: Soil Sci. Plant Nutr., 48, 491–499). Up to 75% of the tested isolates induced a higher growth efficiency than that of the uninoculated control in association with one of the tested cultivars, Black soybean. Comparision with uninoculated control plants, enable to estimate the proportion of the tested isolates leading to effective growth promotion (E + e) of each cultivar, namely, Black soybean (local Thai cultivar), 75%; Cowpea, 82%; SJ5 (commercial Thai cultivar), 33%; Bragg (US cultivar), 33%; and Improved Pelican (US cultivar), 9%. These results indicated that although isolates with a high infectiveness with both “Asian-type” and “US-type” soybeans could be found, a high frequency of isolates leading to inefficient nodules was observed in the US cultivar, suggesting the presence of genetic differences in the soybean cultivars that express high-preference (efficient nodules) or low-preference (inefficient nodules) for a certain group of tested isolates. Based on the results of this laboratory experiment together with our previous field experiment, native rhizobial populations in the irrigated area of northern Thailand could be separated into three groups; Group 1: rhizobium strains showing a high effectiveness with only Asian cultivars, Group 2: strains showing a high effectiveness with only US origin cultivars, and Group 3: strains showing a high effectiveness with both Asian and US origin cultivars. The majority of the native rhizobial populations belonged to Group 1. The isolates in Group 3 may display a high potential for manipulating useful rhizobial inoculant.

Symbiotic efficiency and compatibility of native rhizobia in northern Thailand with different soybean cultivars

Symbiotic efficiencies and compatibilities between native rhizobia and 17 soybean cultivars including Asian and US ones were investigated in a farmer field in a traditional soybean-growing area of northern Thailand where inoculation had never been practiced. The field is representative of the soybean cultivation area in the cool-dry season with irrigated lowland rice-based system in the upper northern region. Nodule dry weight of the tested soybean cultivars revealed good nodulation ability of the native rhizobia with both Asian and US soybean cultivars. This result indicates the presence of a wide genetic host range of the native rhizobial populations in this soybean-growing area. Relative ureide index, nitrogen-fixing efficiency and seed yield of the tested soybean cultivars indicated that on the average, “Asian-type” soybeans exhibited a higher symbiotic performance than the “US-type” soybeans with the native rhizobia. Among all the tested soybean cultivars, Dempo, a local Indonesian cultivar, produced maximum seed yield (1.8 t ha−1). Among the tested US culti vars, Bossier showed the highest symbiotic performance in terms of nodule dry weight, shoot dry weight and total nitrogen accumulation. However, the highest seed yield was found in another US soybean cultivar, Valder. This was probably due to the new development of high nodulation at later growth stages, i.e. the pod-filling stage. Two Thai breeding cultivars, CM60 and CMU001 derived from US cultivars, produced a higher seed yield (1.5 and 1.8 t ha−1, respectively) than their parent cultivars, Williams and Pakchong (0.9 and 1.1 t ha−1, respectively). Due to the high effectiveness of the native rhizobial populations, inoculation may not be necessary for many soybean cultivars grown in this area. However, it appeared that the symbiotic efficiency depended largely on the soybean cultivars. Therefore, when new breeding cultivars are released, the symbiotic performance of these new cultivars with the native rhizobia should be assessed.

Variation in traits associated with chilling tolerance during emergence in cowpea germplasm

Warm-season annuals are sensitive to chilling temperatures. For cowpea, chilling tolerance during emergence has been associated with two independent seed traits: a specific dehydrin protein and slow electrolyte leakage in chilling conditions as a measure of membrane integrity. We screened F 2 and backcross populations for the presence of the dehydrin protein in seed using immunoblot analysis. Segregation of the dehydrin protein indicated a single dominant gene controls its expression. We screened four sets of cowpea accessions with diverse origins for the two traits that had been associated with chilling tolerance and the presence of hard seed that did not readily imbibe water. The hard seed trait also may enhance chilling tolerance since slower imbibition of water at low temperature can reduce chilling injury. We tested the hypothesis that the extent of these three chilling-tolerance traits may vary for germplasm populations of subtropical and tropical origins because tropical environments exhibit little chilling. The dehydrin protein was present in many landraces (59% out of 140) that evolved in subtropical zones around the Mediterranean sea where soils often are cool during emergence. However, the dehydrin protein also was present in most of the tropical accessions (88% out of 59), which suggests that it may have an additional adaptive role during seed maturation and/or germination since chilling tolerance would not be of significance in the tropics. Only three out of 61 US cultivars, which had been developed in subtropical zones where soils can be cool, contained the dehydrin protein. Only four out of 40 lines in a population of tropical origin that had been selected for chilling tolerance during vegetative and reproductive growth contained the dehydrin protein in their seed. Genotypes were identified that had similar slow electrolyte leakage from seeds at low temperature as the chilling tolerant line ‘UCR 1393-2-11’, but none of these accessions also contained the dehydrin protein as does ‘UCR 1393-2-11’. Frequency of hard seeds was high among Mediterranean landraces (48%) and US cultivars (21%) but low among tropical accessions (5%). We describe genotypes with traits associated with chilling tolerance during seedling emergence that could be useful in cowpea breeding.

Distribution of microsatellite alleles linked to Rht8 dwarfing gene in wheat

A wheat microsatellite locus, Xgwm 261, whose 192-bp allele closelylinked to the dwarfing gene Rht8, on chromosome 2D, was used toscreen 71 wheat cultivars from 13 countries to assess the variation at thislocus. Screening of this wheat collection showed that a 165-bp allele anda 174-bp allele were the most frequent. None of the New Zealand cultivarspossessed a 192-bp allele specific to Rht8, while only one cultivarfrom the US produced this important allele. The frequency of a 192-bpallele among these wheat cultivars was 5.63%. The highest allelefrequency was observed for a 174-bp fragment (52.11%) followed by a165-bp fragment (26.76%). The only durum wheat `Cham 1', did notshow any amplification due to the absence of D genome. Four new novelalleles, 180-bp, 198-bp, 200-bp and 204-bp present in the US and NewZealand wheat cultivars are reported.

Two simple sequence repeat markers to select for soybean cyst nematode resistance coditioned by the rhg1 locus

The soybean cyst nematode (SCN) (Heterodera glycines Inchinoe) is the most economically significant soybean pest. The principal strategy to reduce or eliminate damage from this pest is the use of resistant cultivars. Identifying resistant segregants in a breeding program is a difficult and expensive process which is complicated by the oligogenic nature of the resistance and genetic variability in the pathogen. Fortunately, resistance at one SCN-resistance locus, rhg1, is generally accepted as a necessity for the development of resistant genotypes using any source of resistance and when challenged by any SCN race. Thus, the development of SCN resistant cultivars would be expedited if an effective and rapid system were available to identify breeding lines carrying a resistance allele at the rhg1 locus. In this study we report two simple sequence repeat (SSR) or microsatellite loci that cosegregate and map 0.4 cM from rhg1. Allelic variation at the first of these loci, BARC-Satt309, distinguished most, if not all, SCN-susceptible genotypes from those carrying resistance at rhg1 derived from the important SCN-resistance sources ’Peking’, PI 437654, and PI 90763. BARC-Satt309 was also effective in distinguishing SCN resistance sources PI 88788 and PI 209332 from many, but not all, susceptible genotypes. BARC-Satt309 cannot be used in marker-assisted selection in populations developed from typical southern US cultivars crossed with the important resistance sources PI 88788 or PI 209332 because these genotypes all carry the identical allele at the BARC-Satt309 locus. A second SSR locus, BARC-Sat_168, was developed from a bacterial artificial chromosome (BAC) clone that was identified using the primers to BARC-Satt309. BARC-Sat_168 distinguished PI 88788 and PI 209332 from southern US cultivars such as ’Lee’, ’Bragg’ and ’Essex’. Both BARC-Satt309 and BARC-Sat_168 were used to assay lines from SCN-susceptible×SCN-resistant crosses and proved to be highly effective in identifying lines carrying rhg1 resistance from those carrying the allele for SCN susceptibility at the rhg1 locus.

Polymorphic simple sequence repeat markers in chloroplast genomes of Solanaceous plants

PCR-based markers were developed from mononucleotide simple-sequence repeats in the chloroplast genome of Nicotiana tabacum and applied to the analysis of genetic diversity. These markers were found to detect high levels of polymorphism at three taxonomic levels in Solanaceous plants. Of 36 chloroplast loci examined, 26 show some degree of polymorphism among potato accessions. Among a set of 30 tetraploid potato cultivars it is apparent that a single chloroplast haplotype is prevalent, presumably a result of the widespread use as a female parent of the imported US cultivar Rough Purple Chili in the latter half of the 19th century. Nonetheless, there is considerable chloroplast diversity in the cultivated potato, and it is clear that a large proportion of this variability has arisen through the use of wild or primitive cultivated species of potato in introgression programmes. This variability should be used in future breeding programmes. An examination of single accessions from 24 potato species, as well as representatives from tobacco and other members of the Solanaceae, reveals high levels of inter-specific chloroplast DNA variation. These data, and the ease of use and potential for multiplexing of these markers, suggest that cpSSRs will be of great utility in population genetics, germplasm management, evolutionary and phylogenetic studies as well as in, the analysis of material from introgression and somatic-fusion experiments. Interestingly, the polymorphism arising from one of the more-polymorphic chloroplast loci examined, does not originate solely from the SSR, and is due to variation in the copy number of two tandemly arrayed sequence elements.

Genetic variation detected by DNA fingerprinting with a rice minisatellite probe in Oryza sativa L.

A rice minisatellite probe detecting DNA fingerprints was used to assess genetic variation in cultivated rice (Oryza sativa L.). Fifty-seven cultivars of rice, including 40 closely related cultivars released in the US, were studied. Rice DNA fingerprinting revealed high levels of polymorphism among distantly related cultivars. The variability of fingerprinting pattern was reduced in the closely related cultivars. A genetic similarity index (S) was computed based on shared fragments between each pair of cultivars, and genetic distance (D) was used to construct the dendrograms depicting genetic relationships among rice cultivars. Cluster analysis of genetic distance tended to group rice cultivars into different units corresponding with their varietal types and breeding pedigrees. However, by comparison with the coefficients of parentage, the criterion of relatedness based on DNA fingerprints appeared to overestimate the genetic relationships between some of the closely related US cultivars. Although this may reduce the power of fingerprints for genetic analysis, we were able to demonstrate that DNA fingerprinting with minisatellite sequences is simpler and more sensitive than most other types of marker systems in detecting genetic variation in rice.

DNA SEQUENCE POLYMORPHISM BASED GENETIC DIVERSITY STUDIES IN SWEETPOTATO GERMPLASM

Highly polymorphic DNA markers were identified in sweetpotato (Ipomoea batatas) using PCR amplification and arbitrary primers. More than 100 accessions representing US cultivars and their progenitors, and germplasm lines from around the world were analyzed. Sweetpotato germplasm exhibited high genetic variability and individual-specific profiles were obtained for all accessions. US cultivars formed a tight cluster in the principal coordinate analysis suggesting a narrow genetic base. The genetic relationship data of US cultivars and their progenitors based on DNA polymorphisms was in agreement with their known pedigree. The putative paternal parents of certain cultivars selected through open pollination were identified based on shared polymorphisms. The PCR-based markers are valuable in the characterization of sweetpotato germplasm and in ensuring a broad genetic base for future cultivars.

ENVIRONMENTAL EFFECTS ON YIELD AND INSECT DAMAGE OF STORAGE ROOTS AND FOLIAGE OF SWEET POTATO IN PERU

Yield and insect damage of 50 potato cultivars, representative of genetic variation found in CIP germplasm collection, were evaluated over two years in a wide range of environmental conditions throughout Peru, from 4°S to 17°S, including coastal desert, cool highland and humid jungle, at altitudes from 180m to 3280m. Storage root and foliage yields were related to maximum and minimum temperature, photoperiod, precipitation, soils, and insect damage. Genotypic yield varied considerably from one location to another. Jonathan (Peruvian cultivar) produced well in Cañete (coastal desert) but not in the jungle or highlands. Jewel (US cultivar) produced well in Yurimaguas (jungle) but not in coastal deserts. Pesticides were not used but several cultivars had little or no insect damage, others were badly damaged. Some cultivars produced a reasonable yield over a wider range than did others. Results suggest that a cultivar can be strongly adapted to a particular set of environmental conditions. Data provide valuable information for growers-breeders.