Identifying and selecting for genetic diversity in Papua New Guinea sweetpotato Ipomoea batatas (L.) Lam. germplasm collected as botanical seed

A total of 141 Ipomoea batatas (L.) Lam. accessionsderived from botanical seed originally collected from 26 sites in 4 Provinces inPapua New Guinea, a secondary center of genetic diversity for sweetpotato, weregenetically analyzed. Two hundred Amplified Fragment Length Polymorphism (AFLP)markers were identified and utilized in the analysis. Relatedness amongaccessions was estimated by analyzing the AFLP data using the Dice coefficientof similarity and UPGMA methods. The molecular analysis revealed relativelylimited genetic diversity within and between sites. Genotypes collected in agiven region often displayed molecular marker variability similar to thatobserved over the entire sampled area. However, a subset of 14 genotypes derivedfrom seed collected from New Ireland island differed from genotypes collected onNew Guinea island. Estimates of genetic diversity-based similarity valuescalculated from the AFLP data indicated a moderate level of diversity (0.767mean coefficient of similarity) across all plant materials analyzed. Threemethods of selection were evaluated for their efficacy in capturing themolecular marker diversity within the plant materials in the form of a subset.They were random, stratified-random (geographic based), and marker-assistedselection (MAS). MAS was the most efficient. A Maximally Diverse Subset (MDS) of12 genotypes capturing 92% of the molecular marker diversity was identified.     

Genetic diversity in sweetpotato [Ipomoea batatas (L.) Lam.] in relationship to geographic sources as assessed with RAPD markers

Available evidence shows that sweetpotato originated from either Central or South American lowlands with subsequent dispersal to North America, Europe, Africa, Asia and the pacific islands. A total of 71 polymorphic RAPD molecular markers were used to assess the genetic relationships amongst 74 sweetpotato varieties originating from a total of 23 sweetpotato producing countries within six geographical regions, namely, South America, Central America/Caribbean, United States of America (USA), East Africa, Asia and Oceania. An Analysis of Molecular Variance (AMOVA) indicated that 93.4% of the total variance was due to the differences between genotypes within regions. The difference between regions was significant (P < 0.001) but only contributed 6.6% to the variance. Genetic distance (PhiST) calculated with AMOVA and multidimensional scaling (MDS) revealed that the South American and the Central American/Caribbean genotypes formed two separate clusters. East African varieties, which have unique characteristics from other traditional varieties, were distinct from other traditional varieties from South America and Oceania. These results support the reported hypothesis of the origin and dispersal of the sweetpotato and indicate that the primary centre of diversity probably has two distinct genepools. It is proposed that the dispersal of the sweetpotato from its origin may have mainly involved varieties from Central America/Caribbean as opposed to varieties from South America. There is an indication that new genepools may be evolving in Africa and Asia due to hybridisation and adaptation to the local environments.     

Assessing genetic diversity of sweet potato (Ipomoea batatas (L.) Lam.) cultivars from tropical America using AFLP

The sweet potato genebank at the International Potato Center (CIP) maintains 5,526 cultivated I. batatas accessions from 57 countries. Knowledge of the genetic structure in this collection is essential for rational germplasm conservation and utilization. Sixty-nine sweet potato cultivars from 4 geographical regions (including 13 countries) of Latin America were randomly sampled and fingerprinted using AFLP markers. A total of 210 polymorphic and clearly scorable fragments were generated. A geographic pattern of diversity distribution was revealed by mean similarity, multidimensional scaling (MDS), and analysis of molecular variance (AMOVA). The highest genetic diversity was found in Central America, whereas the lowest was in Peru-Ecuador. The within-region variation was the major source of molecular variance. The between-regions variation, although it only explains 10.0% of the total diversity, is statistically significant. Cultivars from Peru-Ecuador, with the lowest level of within region diversity, made the most significant contribution to the between region differentiation. These results support the hypothesis that Central America is the primary center of diversity and most likely the center of origin of sweet potato. Peru-Ecuador should be considered as a secondary center of sweet potato diversity.     

Analysis of genetic diversity in a sweet potato (Ipomoea batatas L.) germplasm collection from Tanzania as revealed by AFLP

Sweet potato (Ipomoea batatas L.) is the fifth most important crop in the developing countries after rice, wheat, maize and cassava. The amplified fragment length polymorphism (AFLP) method was used to study the genetic diversity and relationships of sweet potato accessions in the germplasm collection of Sokoine University of Agriculture, Morogoro and Sugarcane Research Institute, Kibaha, Tanzania. AFLP analysis of 97 sweet potato accessions using ten primer combinations gave a total of 202 clear polymorphic bands. Each one of the 97 sweet potato accessions could be distinguished based on these primer combinations. Estimates of genetic similarities were obtained by the Dice coefficient, and a final dendrogram was constructed with the un-weight pair-group method using arithmetic average. AFLP-based genetic similarity varied from 0.388 to 0.941, with a mean of 0.709. Cluster analysis using genetic similarity divided the accessions into two main groups suggesting that there are genetic relationships among the accessions. Principal Coordinate analysis confirmed the pattern of the cluster analysis. Analysis of molecular variance revealed greater variation within regions (96.19%) than among regions (3.81%). The results from the AFLP analysis revealed a relatively low genetic diversity among the germplasm accessions and the genetic distances between regions were low. A maximally diverse subset of 13 accessions capturing 97% of the molecular markers diversity was identified. We were able to detect duplicates accessions in the germplasm collection using the highly polymorphic markers obtained by AFLP, which were found to be an efficient tool to characterize the genetic diversity and relationships of sweet potato accessions in the germplasm collection in Tanzania.     

Genetic diversity and systematic relationships in sweetpotato (Ipomoea batatas (L.) Lam.) and related species as revealed by RAPD analysis

Summary Fifteen 10mer primers, in combination with the Stoffel fragment, were used to detect random amplified polymorphic DNA (RAPDs) among 26 accessions of sweetpotato (I. batatas (L.) Lam.) from Oceania, Peru, the Philippines, and the United States and between 8 Ipomoea species from section Batatas. Phenetic and principal coordinate analysis of the 56 polymorphisms detected within the hexaploid I. batatas clearly delineated the South Pacific and the Peruvian sweetpotato lines. The two U.S. cultivars clustered with the Oceanic materials. Cladistic and phenetic analysis of 8 Ipomoea species supports previously published phylogenies based on morphological and RFLP data. Among the species examined, I. tabascana, I. trifida and the tetraploid forms of I. batatas from Mexico and Ecuador, including I. batatas var. apiculata, are the taxa most closely related to the cultivated hexaploid I. batatas. These findings support the utility of RAPD markers for evaluating genetic diversity in sweetpotato and for establishing taxonomic and evolutionary relationships in Ipomoea.     

Differences in mycorrhizal infection and P uptake of sweet potato cultivars (Ipomoea batatas L.) during their early growth in three soils

Summary Mycorrhizal infection in the roots of 10 sweet potato cultivars was assessed 7 weeks after planting in three soils collected from Ibadan, Fashola and Onne in southern Nigeria, three soils which contained 21.0, 7.8 and 54.8 mg P kg^–1, respectively. Mycorrhizal infection averaged 17% in the soil from Ibadan, 24% in the soil from Fashola and 7% in the acid soil from Onne. The plants grown in the Fashola soil contained the same percentage of P as plants grown in the Onne soil. Although the percentage of P in sweet potato was lowest in the Ibadan soil, shoot dry weights were 35% higher in this soil than in the other two soils. There was no correlation between the level of mycorrhizal infection and plant dry weight in the partially sterilized soil from Ibadan. Sweet potato inoculated in this soil with infected roots of Leucaena leucocephala showed a higher level of mycorrhizal infection than uninoculated plants. Dry-matter production was, however, the same for all treatments. The sweet potato cultivars differed in their level of mycorrhizal infection and in their response to applied P. Cultivars TIS 2498 and TIS 70357 consistently showed the lowest percentage of infection; and TIb 4, TIS 8441 and TIS 8524 showed infection levels above 20% in the Fashola and Ibadan soils. When the low-yielding cultivar, TIb 4, and an improved clone, TIS 9265, were grown in the presence of 50 and 100 mg single superphosphate per kg soil, TIb 4 produced more dry matter in the presence of P fertilizer than it did without the fertilizer. Growth and mycorrhizal infection of TIS 9265 were not affected by the fertilizer.     

Genetic relationships and diversity among Brazilian cultivars and landraces of common beans (Phaseolus vulgaris L.) revealed by AFLP markers

The genetic variation and relationships among 31 accessions of Phaseolus vulgaris L., and two representatives of Vigna unguiculata L., were evaluated by AFLP analysis. A total of 263 DNA fragments across all materials were scored using nine primer combinations, averaging 32 per primer. More than 95% of the amplification products showed polymorphism, indicating high variation at the DNA level among these accessions. Pair-wise genetic similarity (Jaccard's coefficient) ranged from 0.553 to 0.840, with a mean of 0.765. Twenty-three accessions (70%) clustered into three groups. A majority of the commercial cultivars (91%) clustered within a single group, whereas the landraces were distributed along all the variation. An apparent correlation with phaseolin types was detected. Results of this study suggest that Brazilian landraces truly represent the overall genetic variability of Phaseolus vulgaris, confirming the multiple origins of these materials, and their potential as a source of variation for breeding programs.     

RAPD variation in sweetpotato (Ipomoea batatas (L.) Lam) cultivars from South America and Papua New Guinea

The island of New Guinea is considered a secondary center on diversity for sweetpotato, because of its range of isolated ecological niches and large number of cultivars found within a small area. Information of genetic diversity in Papua New Guinea (PNG) sweetpotato is essential for rationalizing the global sweetpotato germplasm collection. Using random amplified polymorphic DNA (RAPD), we compared the genetic variation and genetic diversity in 18 PNG cultivars versus 18 cultivars from South America. The analysis of molecular variance revealed large genetic diversity in both groups of cultivars. The within-group (among individuals) variation accounted for 90.6% of the total molecular variance. However, the difference between PNG and South American groups is statistically significant, although it explained only 9.4% of the total molecular variance. The PNG cultivars are also less divergent than their South American ancestors as the mean genetic distance in PNG group is significantly smaller than that of South American group. The lower level of genetic diversity in PNG cultivars was also reflected by multidimensional scaling. This study shows that PNG cultivars, after many years of isolated evolution in an unique agro-ecological environment are substantially divergent from their ancestors in South America. The genetic diversity level in PNG cultivars is significantly lower than that in South American cultivars. It thus provides a baseline for continuing studies of genetic diversity in different sweetpotato gene pools.     

AFLP assessment of diversity in sweetpotato from Latin America and the Pacific region: Its implications on the dispersal of the crop

Although originally domesticated in tropical America, the sweetpotato [Ipomoea batatas (L.) Lam.] has a long history of cultivation in the Pacific region. While the post-Columbus dispersal of sweetpotato to Asia and the Pacific is well documented, the hypothesis that there was a prehistoric transfer of sweetpotato by Peruvian or Polynesian voyagers from Peru to Oceania has long been a controversial issue. The objective of this study was to assess the genetic diversity and interrelationships of sweetpotato landraces from the Pacific region and Latin America, and test the hypothesis of human transfer of this crop to the Pacific Island in prehistoric times. Seventy-five sweetpotato landraces from Peru, Ecuador, Mexico, the Philippines, Papua New Guinea (PNG) and 5 Oceania countries were analyzed using amplified fragment length polymorphism (AFLP). Multidimensional scaling (MDS) and analysis of molecular variance (AMOVA) revealed a large genetic variation in the Oceania gene pool, far greater than that in Peru-Ecuador. The Mexican cultivars were grouped together with those of Oceania. In contrast, there is little association between the Peru-Ecuador germplasm and that of Oceania. These results suggest that Peru-Ecuador may not be the source of the Oceania sweetpotato germplasm. Natural dispersal from Mesoamerica is an alternative explanation, to the Kumara hypothesis, for the origin of the Oceania sweetpotato.     

Assessment of genetic diversity, and phylogenetic relationships based on ribosomal DNA repeat unit length variation and Internal Transcribed Spacer (ITS) sequences in chickpea (Cicer arietinum) cultivars and its wild species

Repeat unit length variation and internal transcribed spacer (ITS) sequences of nuclear ribosomal DNA were used to assess genetic diversity, and phylogenetic relationships in chickpea (C. arietinum) cultivars, and its related wild species. Total genomic DNAs of 76 accessions of 10 Cicer species, belonging to three sections of the genus, were restricted with seven enzymes and the restriction fragments were hybridized to heterologous ribosomal clones of wheat pTa71 and Vicia faba probes Ver 6-5 and Ver18-6. A single repeat unit length class of 11.4 kb or 10.5 kb was recognized across Cicer accessions with pTa71. The intraspecific variation was negligible in those species where more than one accession was studied, except the four C. judaicum accessions, which were different from the rest. EcoRI and DraI digests gave two and one-two fragments, respectively. All the accessions produced three and three-five bands with BamHI and SacI, respectively. Both the accessions of C. yamashitae differed in their rDNA repeat unit length as well as restriction site variation. Maximum likelihood tree with rDNA RFLP recognized five clades which were more or less congruent with the previous data. Length of ITS-1 region was more variable (235–239 bp) than the ITS-2 region (212–213 bp). Cladistic analysis of ITS data revealed two major clades, clade I consisting of C. arietinum, C. reticulatum and C. echinospermum, and clade II comprised of C. judaicum, C. chorassanicum, C. bijugum and C. cuneatum. C. microphyllum grouped with the above four species. C. pinnatifidum was present as a separate branch. C. yamashitae emerged as the most distinct species.     

Growth and acquisition of Na,K and Ca in some elite sweetpotato [Ipomoea batatas (Lam.) L.] genotypes under salinity stress

Soil salinity is a concern in the wake of climate change challenges due to rising sea levels and coastal salinity in Papua New Guinea. A greenhouse experiment was conducted in Split Plot design, with five elite sweet potato genotypes (main-plot factors) and three levels of sodium chlroide (NaCl) concentrations (sub-plot factors) replicated six times. The vine cuttings of genotype RAB 45 showed very low mortality percentage (33%) at 600 mM NaCl concentration. At salinity level of 200 mM NaCl, aerial dry biomass of the genotypes was inversely but significantly (r = –0.40; p < 0.05) related to the accumulation of sodium (Na⁺) in the tissues. The Na⁺ accumulation in the tissues was antagonistic to the potassium (K⁺) and calcium (Ca²⁺) ions. Among the sweetpotato genotypes, Na⁺/K⁺ ratio decreased in the following order: RAB 45> KAV 11 > Northern Star > DOY 2 > L 46, which was more or less corroborated with the trend in the aerial dry matter.     

Genetic relationships among cultivated and wild <Emphasis Type="Italic">Vigna angularis</Emphasis> (Willd.) Ohwi et Ohashi and relatives from Korea based on AFLP markers

Genetic variation and relationships among members of the azuki bean complex (Vigna angularis) including wild (V. angularis var. nipponensis), weedy, and cultivated types (V. angularis var. angularis), V. nakashimae, and rice bean (V. umbellata) from Korea were examined using the Amplified fragment length polymorphism (AFLP) method. AFLP analysis of 50 accessions revealed 333 (72.1%) polymorphic fragments out of 462 fragments amplified using seven primer combinations. The number of polymorphic fragments within each species was 70 in the azuki bean complex and 41 in V. nakashimae, but there was no polymorphism in rice bean. The number of shared fragments among species ranges from 142 between the azuki bean complex and V. nakashimae to 166 between the azuki bean complex and rice bean. Within the azuki bean complex, the range of shared bands was from 231 between cultivated and weedy types to 238 between cultivated and wild types. A dendrogram generated from Jaccard’s similarity matrix was divided into three groups, which correspond to V. nakashimae, azuki bean complex, and rice bean. The relationship between azuki bean and rice bean is closer than between azuki bean and V. nakashimae. Phenetic distances averaged 0.502 between the azuki bean complex and V. nakashimae and 0.467 between the azuki bean complex and rice bean. Within the azuki bean complex, the weedy type was more closely related to wild than cultivated types. But UPGMA dendrogram of the azuki bean complex reveals that each type is not clearly isolated. These results will help to understand genetic diversity and evolutionary dynamics of Vigna in Korea.     

Phylogenetic relationships within <Emphasis Type="Italic">Citrus</Emphasis> and its related genera as inferred from AFLP markers

We investigated the phylogenetic relationships among Citrus and its relatives, including 29 genotypes belonging to Citrus, Poncirus, Fortunella, Microcitrus, Eremocitrus, Atalantia and Severinia using AFLP analysis. Cluster analysis was conducted using neighbour joining (NJ) method. The results demonstrated that Poncirus, Microcitrus and Eremocitrus are distant from Citrus. A strong affiliation exists between C. halimii and Fortunella and the results did not support C. halimii as the fourth basic species. Further evidence was provided that P. polyandra should not be the hybrid between trifoliate orange and Citrus genotypes and it deserves species status. Neither the separation of subgenus Papeda and Citrus nor the separation of subgenus Archicitrus and Metacitrus were clearly resolved in the dendrogram. C. ichangesis is a distinct species very different from other Citrus genotypes, and the results showed it is improper to classify it into subgenus Metacitrus. C. reticulata, C. maxima and C. medica were separated into three distinct clusters. Therefore if only cultivated Citrus species are considered, the three basic species concept is acceptable. However, it is not applicable for whole genus Citrus.     

Synergistic effects of vesicular-arbuscular mycorrhizal fungi and diazotrophic bacteria on nutrition and growth of sweet potato (Ipomoea batatas)

Summary Sweet potatoes were micropropagated and then transplanted from axnic conditions to fumigated soil in pots in the greenhouse. Spores of Glomus clarum were obtained from Brachiaria decumbens or from sweet potatoes grown in soil infected with this fungus and with an enrichment culture of Acetobacter diazotrophicus. Three experiments were carried out to measure the beneficial effects of vesicular-arbuscular mycorrhizal (VAM) fungi-diazotroph interactions on growth, nutrition, and infection of sweet potato by A. diazotrophicus and other diazotrophs obtained from sweet potato roots. In two of these experiments the soils had been mixed with ¹⁵N-containing organic matter. The greatest effects of mycorrhizal inoculation were observed with co-inoculation of A. diazotrophicus and/or mixed cultures of diazotrophs containing A. diazotrophicus and Klebsiella sp. The tuber production was dependent on mycorrhization, and total N and P accumulation were increased when diazotrophs and G. clarum were applied together with VAM fungal spores. A. diazotrophicus infected aerial plant parts only when inoculated together with VAM fungi or when present within G. clarum spores. More pronounced effects on root colonization and intraradical sporulation of G. clarum were observed when A. diazotrophicus was co-inoculated. In non-fumigated soil, dual inoculation effects, however, were of lower magnitude. ¹⁵N analysis of the aerial parts and roots and tubers at the early growth stage (70 days) showed no statistical differences between treatments except for the VAM+Klebsiella sp. treatment. This indicates that the effects of A. diazotrophicus and other diazotrophs on sweet potato growth were caused by enhanced mycorrhization and, consequently, a more efficient assimilation of nutrients from the soil than by N₂ fixation. The possible interactions between these effects are discussed.     

Assessment of genetic relationships among Pyrus species and cultivars using AFLP and RAPD markers

Twenty-five Pyrus communis L. cultivars including eight traditional Portuguese pears, and four commercial Pyrus pyrifolia (Burm.) Nak. (Japanese pear or `nashi') cultivars were analysed by RAPD and AFLP techniques focusing on their molecular discrimination and the assessment of their genetic relatedness. Twenty-five primers generated 324 RAPD markers, among which 271 (84%) were polymorphic. The AFLP technique, using seven primer combinations, revealed a similar level of molecular polymorphisms (87%), representing 418 polymorphic bands among a total of 478 scored in autoradiographs. The high reproducibility of RAPD and AFLP techniques was confirmed comparing DNA samples from different extractions and different digestions of DNA from the same plant. Three genetic similarity matrices and respective dendrograms were elaborated on using RAPD, AFLP or joint RAPD and AFLP data. Both molecular marker techniques proved their reliability to assess genetic relationships among pear cultivars. P. pyrifolia cultivars exhibit a closer genetic relatedness, clustering apart from P. communis cultivars. Within P. communis, `William's', as well as `Doyenne du Comice', cluster close to their hybrids. Most of the Portuguese cultivars tend to cluster together, indicating to constitute a relatively independent genetic pool, which can be of interest in pear breeding programs.     

Evaluation of genetic diversity and relationships within an on-farm collection of Perilla frutescens (L.) Britt. using microsatellite markers

The present study demonstrates utilization of 11 microsatellite markers to explore genetic diversity held in Perilla frutescens (L.) Britt. landrace accessions growing on farms in different parts of Korea and Japan and to assess their genetic relationships. All microsatellite loci were polymorphic and produced a total of 96 alleles ranging from 4 to 20, with an average of 8.7 alleles per locus. Of the 96 alleles found, a total of 15 unique landrace-specific alleles were observed at 9 different loci. The locus GBPFM203 provided the highest number of alleles (20), of which five were unique and each specific to a particular landrace accession. The occurrence of unique, accession-specific alleles presented molecular evidence for the generation of new alleles within on-farm collection of Perilla. The mean values of observed (H _O) and expected heterozygosity (H _E) were 0.39 and 0.68, respectively, indicating a considerable amount of polymorphism within this collection. A genetic distance-based phylogeny grouped the two Perilla varieties, var. frutescens and var. crispa (Thunb.) Decne into two distinct groups. Accessions belonging to var. frutescens could also be divided into two subgroups at a close genetic distance (GD = 0.432). The overall clustering pattern did not strictly follow the grouping of accessions according to their geographic origins. These observations are indicative of extensive germplasm exchange among farms from different geographical regions. The genetic similarity observed among the Perilla landraces may be useful for future Perilla crop variety identification, conservation, and improvement programs.     

Seed protein diversity in Solanum melongena L. and its wild and weedy relatives

Seed protein profiles by SDS-PAGE were studied in 72 accessions ofSolanum melongena L. and its related taxa in subgenusLeptostemonum (Dunal) Bitter. Comparisons based onJaccard's similarity and UPGMA clustering revealed interrelationships broadly inconformity with the conventional taxonomic treatments. Thus,S. viarum Dunal (sectionAcanthophora Dunal), S.torvum Swartz (section Torva Nees) andS. sisymbriifolium Lam. (sectionCryptocarpum Dunal) were located on separate branches ofthe dendrogram while all taxa of section Melongena Dunal,except S. macrocarpon Dunal, wereclustered closer together. S.melongena, incanum and insanum,all members of the eggplant complex, were revealed to bear very high similaritywith each other. Most of their accessions had identical band patterns supportingthe contention that these represent an interbreeding complex with limitedgenetic differentiation.     

Phylogenetic relationships of Cajanus cajan (L.) Millsp. (pigeonpea) and its wild relatives based on seed protein profiles

Total seed storage protein of 9 accessions of cultivated C. cajan and 10 wild Cajanus species was reported and compared by sodium dodecyl sulphate polyacrylamide gel electrophoresis. A considerable variation was detected among the protein profiles of different accessions of C. cajan while those of wild species were very specific and distinctly different from each other. Relative similarities between various taxa were estimated by Jaccard's similarity index and cluster analysis was performed to produce a UPGMA dendrogram. The clustering of 10 wild species and C. cajan more or less agrees with their sectional classification and available data based on morphological characteristics, crossability, genome pairing in hybrids and nuclear RFLPs. The species closest to C. cajan is C. cajanifolia although the accessions of C. cajan also share some bands present in the profiles of C. scarabaeoides, C. goensis, C. lineatus, C. acutifolius and C. volubilis. This points towards polyphyletic origin of the cultigen which has been discussed in this paper.     

Genetic diversity of Syrian pistachio (<Emphasis Type="Italic">Pistacia vera</Emphasis> L.) varieties evaluated by AFLP markers

Pistachio (Pistacia vera L.) is a strategic nut tree species in the Middle East which holds comparative advantage over other fruit trees in view of its hardiness, income generation opportunities and benefits for the ecosystem. Yet pistachio cultivation depends on a very narrow genetic base, in spite of the existence of many varieties still marginally exploited. Syria is an important center of diversity for pistachio. A country wide ecogeographic survey in this country was carried out to determine the extent of pistachio genetic diversity and its use. As a whole, 114 accessions were collected from 37 farms to assess diversity at morphological and molecular level. Molecular evaluation was carried out using Amplified Fragment Length Polymorphism (AFLP) technique and performed using seven primer pair combinations. Results from the studies allowed the identification of 25 pistachio female varieties in Syria, some of which unique and described for the first time. Three groups of pistachio diversity were identified by cluster analysis which provides useful information about the distribution of genetic diversity in Syria for enhanced use and sustainable conservation.     

Interactions of Glomus clarum with Acetobacter diazotrophicus in infection of sweet potato (Ipomoea batatas), sugarcane (Saccharum spp.), and sweet sorghum (Sorghum vulgare)

Summary Spores of the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus clarum obtained from sweet potatoes grown in soil inoculated with this fungus and with an enrichment culture of Acetobacter diazotrophicus contained A. diazotrophicus and several other bacteria, including a diazotrophic Klebsiella sp. Inoculation of micropropagated sweet potatoes with G. clarum and A. diazotrophicus enhanced spore formation in soil compared to VAM inoculation alone. Plants inoculated with VAM spores containing the bacteria showed additional increases in the number of spores formed within roots. A. diazotrophicus infected aerial plant parts only when inoculated together with VAM or when present within VAM spores. Micropropagated sugarcane seedlings inoculated with the same VAM spores containing the diazotrophs also contained much higher numbers of A. diazotrophicus in aerial parts than seedlings inoculated in vitro with the bacteria alone. When grown in non-sterile soil, the sugarcane seedlings again showed the greatest infection of aerial parts after inoculation with VAM spores containing the diazotrophs. This treatment also increased VAM colonization and the numbers of spores formed within roots. Similar effects were observed in sweet sorghum except that the aerial plant parts were not infected by A. diazotrophicus.