Geographical distribution of ribosomal DNA variation in taro, Colocasia esculenta (L.) Schott, in eastern Asia

Restriction fragment length polymorphism (RFLP) at the ribosomal RNA gene loci (rDNA) was investigated in 227 accessions of taro, Colocasia esculenta (L.) Schott, from China, Japan, Taiwan, and Vietnam. Eighteen different restriction fragment patterns of rDNA were observed. The results were largely consistent with a previous classification based on isozyme data. Some rDNA patterns were distributed extensively in the temperate zone from inland China to Japan. On the other hand, some other patterns ranged in coastal and/or insular areas from the tropical zone to the temperate zone (Japan). These geographical distributions may suggest two different routes for the introduction of taro into Japan: one from China,and the other most likely from Southeast Asia, via Taiwan and the Ryukyu Islands (southern Japan). This revised version was published online in August 2006 with corrections to the Cover Date.     

Colocasia esculenta (L.) Schott,Colocasia antiquorum Schott,how many species? 1. A preliminary investigation

Summary The taxonomy of edible Colocasia (Cocoyam) is confusing. The existence of one species, C. esculenta var. antiquorum or C. esculenta and C. antiquorum as two separate species is controversial. Nine high yielding Nigerian cultivars of cocoyam made up of members of the two taxa were grown under the same environmental conditions. As a preliminary investigation, 17 characters were monitored and recorded to help in the classification of the cultivars. Results showed that cocoyams can be grouped into two separate species. The qualities possessed by TCe 23, Nwine and Ukpon cultivars which include pink tuber skin, long or club shaped cormels and non-irritation in the throat when boiled and eaten, clearly distinguished them from those of Tce 15, 19, 27, 36, Ede-ofe and Kochuom.     

The relationship between geographic distribution and ploidy level of taro,Colocasia esculenta

Summary The distribution of diploid and triploid domesticated and wild taro was investigated. It was found that going from south to north the frequency of diploid accession decreased, while that of triploids increased.     

Geographical differentiation of Asian taro, Colacasia esculenta (L.) Schott, detected by RAPD and isozyme analyses

Geographical differentiation and phylogenetic relationships of Asian taros, Colocasia esculenta (L.) Schott, and related species were analyzed by random amplified polymorphic DNA (RAPD) and isozymes of 13 enzyme systems with special interest in the accessions from the Yunnan area of China, which supposedly has served the secondary center of taro diversification and dispersal into the temperate Far East Asia. The RAPD analysis was found to be better suited for detecting genetic differences within taros and among its related species. However, both RAPD and isozyme analyses estimated quite similar genetic relationships within taros and between related species. Genetic differentiation was evident in the taro accessions of Nepal, Yunnan and other Asian areas; but, phylogenetic relationships between the differentiated taro groups were not clearly determined. When taro cultivation was introduced to a new area, only a small fraction of genetic variability in heterogeneous taro populations was transferred possibly causing random differentiation among locally adapted taro populations. Some of the Yunnan and Japanese accessions were found to be direct descendants of the common triploid population. Further analysis on taros from the eastern China and Korea is necessary to clarify the Yunnan's role in taro diversification and dispersal. The significant local differentiation in Asian taros was clearly demonstrated by RAPD and isozyme analyses in this study, and the results of this study will serve as a base to establish evolutionary and genetic relationships among Asian taros. This revised version was published online in August 2006 with corrections to the Cover Date.     

Molecular characterization of taro (Colocasia esculenta) using RAPD markers

Forty-four taro (Colocasia esculenta), two tanier (Xanthosoma species) and one Colocasia gigantea accessions were evaluated for genetic diversity using random amplified polymorphic DNA (RAPD) primers. Seventy-three of 112 primers amplified PCR DNA products used to fingerprint the accessions. Thirty-two primers were considered highly informative because they amplified more than 5 bands or amplified one or more polymorphic bands that distinguished between accessions. RAPDs showed high genetic diversity in taro accessions from Indonesia, were capable in distinguishing between Hawaiian accessions, and could separate triploid from diploid accessions. UPGMA cluster analysis of genetic similarity estimates (Jaccard's coefficient), separated the accessions into 3 main groups with C. esculenta divided into 5 subgroups. These primers will be useful for future genetic analysis and provide taro breeders with a genetic basis for selection of parents for crop improvement. Polymorphic markers identified in the DNA fingerprinting study will be useful to screen a segregating population which is being generated in our laboratory aimed at developing a taro genetic linkage map. This revised version was published online in July 2006 with corrections to the Cover Date.     

Karyotypic and electrophoretic studies on taro and its origin

Summary Karyotypes and electrophoretic pattern of 15 strains of taro were studied. Strains collected from the northeast India hill state, Meghalaya were diploids and triploids whereas those from the plains of south India were diploids and of north India was a triploid. The diploids had 2n=28 and triploids showed 2n=42 chromosomes. The wild taro had the most asymmetrical karyotype. The protein content varied from 4.2 to 11.4 mg/g dry wt. The maximum protein content was found in a triploid strain 8 (11.4 mg/g dry wt) and minimum in the wild taro (4.2 mg/g dry wt). The number of protein bands was 7 in the wild taro (diploid) and 12 in one of the cultivated triploid strain. Meghalaya strains showed great variation with respect to leaf size and tuber shape and size. All the strains have diverged at morphological, karyotypic and genotypic levels. It is suggested that taro might have originated in the north-eastern India.     

First genetic maps and QTL studies of yield traits of taro (Colocasia esculenta (L.) Schott)

The paper presents the first taro (Colocasia esculenta L. Schott) genetic maps. Taro is an important vegetatively propagated root crop species in most subtropical areas. It is an allogamous and protogynous species with a basic chromosome number of x = 14. Two F₁ progenies of 123 and 100 individuals obtained from crosses between local cultivars from Vanuatu (VU101 × VU104 and VU373 × VU314) were chosen for this study. Both genetic maps contained 169 markers, mainly AFLPs and 8 SSRs, and were characterised by a high density of markers and a short map length. The maps had 14 and 18 linkage groups (LG) respectively and were not completely saturated. Twenty-four markers were identified across the two progenies and a good co-linearity was observed for the majority of these markers. A QTL detection study was conducted on both progenies with 91 and 89 individuals respectively. Several putative QTLs were identified for corm yield and corm dimensions (which were highly correlated traits) whereas no QTL was detected for dry matter content. This result was relatively unexpected since dry matter content was a more highly heritable trait than corm yield or corm dimensions. A major dominant gene, responsible for the yellow colour of the corm flesh, was also identified. Further mapping studies on taro should include a larger number of SSR markers, larger progenies should be created and other important traits related to yield and eating quality should be included in the QTL analyses.     

HPTLC screening of taro hybrids (Colocasia esculenta (L.) Schott) with high flavonoids and antioxidants contents

Taro (Colocasia esculenta) is the tropical root crop species featuring the greatest flavonoids diversity. Their quantification is important for breeding programmes focusing on biofortification. This study aims at developing an HPTLC protocol to compare the flavonoids fingerprints of more than 1800 hybrids belonging to 24 full‐sib families and to select genotypes with high levels of antioxidants. Twenty different chemical markers were identified based on bands R_f and colour. Flavonoids differ among individuals both quantitatively and qualitatively. Marker ‘A’ yielded the strongest antioxidant response to DPPH, equivalent to the one with quercetin pure standard. Overall, 377 high flavonoids content (HFC) hybrids were selected from 14 different families. The mean corm weight of HFC hybrids always appeared higher than the mean corm weight of the family they belong to. This method allows unambiguous selection of HFC hybrids. It also contributes to taro genetic improvement for nutritional value and access to new markets and to strengthen corm tolerance to pests and diseases. It could be applied to other tropical root crop species.     

Isozyme electrophoregrams of sixteen enzymes in five tissues of cassava (Manihot esculenta Crantz) varieties

Summary Methodology, based on starch and polyacrylamide gel electrophoresis, was developed for determining isozyme electrophoregrams (patterns) of 16 enzymes of cassava (Manihot esculenta Grantz) varieties as potential genotype markers. Extracts of five different tissues (root, stem, leaf, petiole and bud) were examined. In general, the nodal portions of the shoots gave isozyme patterns with the largest number of bands. Petiole extracts gave similar results but bud extracts gave poor patterns. The limited number of varieties that were examined could be distinguished by sequential classification on the basis of the isozyme patterns of acid phosphatase, esterase, glutamate oxaloacetase transaminase and phosphoglucoisomerase.Joint publication of the Centro Internacional de Agricultura Tropical and the Department of Plant Science (No. 716), University of Manitoba. Presented in part at the 2nd International Symposium on Biochemical Approaches to Identification of Cultivars and Evaluation of Their Properties, 5–9 May, 1985, Braunschweig, West Germany.     

Characterization of isozyme variation in walnut(Juglans regia L.)

Summary Four leaf enzymes malate dehydrogenase (MDH), 6-phosphogluconate dehydrogenase (6PGD), peroxidase (PX) and aspartate aminotransferase (AAT) of 17 walnut cultivars and two pollen enzymes malate dehydrogenase (MDH) and 6-phosphogluconate dehydrogenase (6PGD) of 15 walnut cultivars were analysed using horizontal starch gel electrophoresis. Walnut cultivars of different origin exhibited different numbers of electrophoretic bands and also different relative mobility. Different activity levels and phenotypic groups were detected in studied enzyme systems. Pollen enzymes revealed higher variability than enzymes extracted from the leaves. 15 walnut cultivars were classified into 10 malate dehydrogenase phenotypic groups and 14 6-phosphogluconate dehydrogenase phenotypic groups based on pollen analyses. 17 cultivars were classified into 9 peroxidase phenotypic groups and 7 6-phosphogluconate dehydrogenase phenotypic groups based on analyses of leaves. All of the 15 walnut cultivars could be identified and distinguished with electrophoretic analyses of MDH and 6PGD from the pollen while only 10 cultivars were distinguishable with analyses of 6PGD and PRX from the leaves. No variability useful for cultivar identification was observed in MDH and AAT from the leaves.     

Pollen storage in cocoyam (Xanthosoma sagittifolium (L.) Schott)

Summary The effect of different storage conditions on cocoyam pollen viability was investigated. Two levels of temperature (0° and 5°C) and four levels of relative humidity (0, 10, 20 and 30 percent) represented the storage environments.Viable cocoyam pollen could be obtained after 28 days in storage. The best storage condition was 5°C and 30% relative humidity.     

Isozyme polymorphism in three gene pools of cultivated chicory (Cichorium intybus L.)

Summary Polymorphism of ten enzymes, acid phosphatase (APH), isocitrate dehydrogenase (IDH), leucine aminopeptidase (LAP), phosphorylase (PP), superoxide dismutase (SOD), malic enzyme (ME), glutamate oxaloacetate transaminase 1 and 2 (GOT-1, GOT-2) and phosphoglucomutase 1 and 2 (PGM-1 and PGM-2), was investigated in three gene pools of cultivated chicory, including six cultivated wild chccory, eight industrial chicory and eight Brussels chicory varieties. LAP, APH, PP and PGM-2 showed high phenotypic polymorphism whilst GOT-1 and ME had poor polymorphism. For three enzyme coding loci Lap, Pgm-1 and Got-2, allele frequencies were determined. Isozyme composition in the three chicory gene pools was significantly different, showing, respectively, high, intermediate and poor average amount of phenotypic polymorphism in cultivated wild chicory, industrial chicory and Brussels chicory. Isozyme variation within and between varieties of the three gene pools is discussed in relation to breeding practices.     

Assessment of genetic variation among asparagus (Asparagus officinalis L.) populations and cultivars: agromorphological and isozymic data

Summary The morphological variation and the isozymic polymorphism in 19 asparagus accessions currently used in cultivation and breeding are described. Moreover 2 wild populations from Turkey were added in the isozymic study. Characters of ramification height permit to separate accessions usually cultivated for white asparagus and accessions usually cultivated for green asparagus. Starch and polyacrylamide gel electrophoresis was realized to assay 7 enzyme systems. 29 polymorphic bands were taken into account in the study. Four accessions show specific bands for glutamate oxaloacetate transaminase, shikimate dehydrogenase and alcohol dehydrogenase. In particular, the two populations from Turkey and one population traditionally cultivated in local area of Spain are well differentiated from the remaining accessions. Accessions from the United States representing different selections are relatively well separated from each other.     

Intra species variation in Atylosia scarabaeoides (L.) Benth., a wild relative of pigeonpea (Cajanus cajan (L.) Millsp.)

Summary Atylosia scarabaeoides (L.) Benth., a wild relative of pigeonpea, possesses several useful genes which can be utilized for pigeonpea improvement. In the present study, 33 accessions of A. scarabaeoides were evaluated at ICRISAT Center during the 1987 rainy season for variation in some useful traits to identify parents for inter-generic hybridization. A large variation was observed for leaf components, seed size, pod length, seeds/pod, days to flowering, seed protein, sulphur amino acids, resistance to cyst nematode, phytophthora blight, sterility mosaic, fusarium wilt, pod borer, pod fly, and pod wasp. Only four accessions were found to have more than 28% protein content. Methionine and cystine contents were marginally higher than in pigeonpea but the variation was not large enough to utilize them in the breeding program. In A. scarabaeoides. accessions resistant to fusarium wilt, phytophthora blight, sterility mosaic, and cyst nematode were detected. Compared to pigeonpea, the A. scarabaeoides accessions were less susceptible to lepidopteran borer and were immune to pod fly damage. Accessions ICPW 89 and ICPW 111 in short- (100–120 days), and ICPW 94 and ICPW 118 in medium-duration (140–180 days) were identified as potential parents for use in inter-generic hybridization.ICRISAT Journal Article No. 967     

Isozyme variation in a number of populations of Theobroma cacao L. obtained through various sampling regimes

Summary Isozyme polymorphism in four enzyme systems was used to estimate the genetic diversity in nine populations of Theobroma cacao L. The distribution of allelic variation observed in this study was inconsistent with the currently held view that the Upper Amazon region of Peru is the centre of cacao genetic diversity. All the populations analysed from this area of Peru were genetically similar, and contained a low level of isozyme polymorphism. It is argued that this is a result of genuine low diversity in the region rather than a sampling artifact. If a centre of diversity of wild cacao truly exists, this work indicates that it lies further north in Ecuador and Colombia.Although they are morphologically highly variable, Trinitario cacao populations derived from cultivation are currently accorded low priority for conservation. This phenotypic variation was observed to be reflected in high levels of isozyme polymorphism. It is suggested that the present strategy for the conservation of cacao germplasm, which accords priority to the Upper Amazon region of Peru while neglecting the Carribbean should be reconsidered.     

Geographical patterns of morphological variation in sorghum (Sorghum bicolor (L.) Moench) germplasm from Ethiopia and Eritrea: Quantitative characters

A total of 415 sorghum (Sorghum bicolor (L.) Moench) accessions representing different regions of Ethiopia, Eritrea and a group of introduced lines were evaluated for 15 quantitative characters to determine the extent and geographical pattern of morphological variation. The extent of variation was highly pronounced for agronomically important characters for sorghum. These characters included plant height, days for 50% flowering, peduncle exsertion, panicle length and width, number and length of primary branches per panicle and thousand seed weight. Significant regional variation was also observed for most of the characters. The results implied that environmental factors such as altitude, rainfall, temperature and growing period are important in regional variation. Mean for plant height and for days for 50% flowering showed clinal variation along the gradients of rainfall pattern and growing period in Ethiopia. Moreover, there were significant positive correlation coefficients between most of the characters. This included the correlation between agronomic characters of primary interest in sorghum breeding such as plant height and days for 50% flowering and also between various characters and the altitude of the collection sites. The implications of the results in plant breeding, germplasm collection and conservation as well as the probable sources of the wide range of variation are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heredity of seventeen isozyme loci in cassava (Manihot esculenta Crantz)

Summary Starch gel electrophoresis was used to assess isozyme polymorphism in two Manihot species. Crude extracts were obtained from leaves and pollen. Ten enzymes were examined for their polymorphism in a germplasm collection of 365 cultivated plus 109 wild accessions, mainly from Africa. The inheritance of these enzymes was examined using 13 intra and interspecific progenies. Seventeen polymorphic loci were found for the ten enzyme systems, with 59 alleles. All the markers showed disomic heredity and three linkage groups were identified.