Nodulation status of native woody legumes and phenotypic characteristics of associated rhizobia in soils of southern Ethiopia

The nodulation of provenances of Acacia seyal, Acacia tortilis and Faidherbia albida, and other indigenous multipurpose tree species were tested in 14 different soil samples collected from diverse agro-ecological zones in southern Ethiopia. Associated rhizobia were isolated from these and from excavated nodules of field standing mature trees, and phenotypically characterized. Indigenous rhizobia capable of eliciting nodules on at least one or more of the woody legume species tested were present in most of the soils. Tree species were markedly different in nodulation in the different site soils. Sesbania sesban and Acacia abyssinica showed higher nodulation ability across the different sites indicating widespread occurrence of compatible rhizobia in the soils. The nodulation patterns of the different provenances of Acacia spp. suggested the existence of intraspecific provenance variations in rhizobial affinity which can be exploited to improve N fixation through tree selection. Altogether, 241 isolates were recovered from the root nodules of trap host species and from excavated nodules. Isolates were differentiated by growth rate and colony morphology and there were very fast-, fast-, slow-, and very slow-growing rhizobia. The bulk of them (68.5%) were fast-growing acid-producing rhizobia while 25.3% were slow-growing alkali-producing types. Fast-growing alkali-producing (2.9%) and slow-growing acid-producing strains (3.3%) were isolated from trap host species and excavated nodules, respectively. All isolates fell into four colony types: watery translucent, white translucent, dull glistering and milky (curdled) type. The diversity of indigenous rhizobia in growth rate and colony morphology suggested that the collection probably includes several rhizobial genera.     

Renodulation and characterization of Rhizobium isolates from cicer milkvetch (Astragalus cicer L.)

In 1993 and 1994, 12 bacterial isolates were isolated from root nodules of cicer milkvetch (Astragalus cicer). In the tests for nodulation of A. cicer by these bacterial isolates, five were found to form hypertrophic structures, while only two formed true nodules. These true nodules were formed in a sterilized soil system. This system might be able to act as a DNA donor to provide residual DNA to other microbes in the soil. The rhizobial isolates were thought to have lost genetic material crucial to nodulation during the isolation process. This hypothesis was supported by an experiment in which isolate B2 was able to nodulate A. cicer in vermiculite culture after being mixed with heat-killed rhizobia, Rhizobium leguminosarum bv. trifolii and R. loti. The nodulation would not occur in vermiculite culture system without the heat-killed rhizobia. Based on the biochemical data, the B2 and 9462L, which formed true nodules with A. cicer, were closely related. The rhizobia type cultures that nodulate A. cicer include Bradyrhizobium japonicum, Rhizobium leguminosarum bv. trifolii, R. leguminosarum bv. viceae, and R. loti. All of these rhizobia were from different cross-inoculation groups. The B2 and 9462L isolates could only nodulate Medicago sativa, Phaseolus vulgaris, and Melilotus officinalis, but not these species within the genus from which they were isolated: Astragalus. The traditional cross-inoculation group concept obviously does not fit well in the classification of rhizobia associated with Astragalus. The rhizobia isolated from A. cicer can be quite different, and the rhizobia able to renodulate A. cicer also quite diverse. Received: 27 June 1996     

Infection potential of farm soils as mycorrhizal inocula for Leucaena leucocephala

A greenhouse experiment was conducted to assess the arbuscular mycorrhizal (AM) fungi inoculum potential for Leucaena leucocephala in a range of nutrient-depleted farm soils in western Kenya. Leucaena was grown in 12 uninoculated farm soils with pH 5.0–6.7, with or without rock P and farmyard manure. Root infection, nodulation, and shoot and root weight were determined 25, 46, and 69 days after planting. Spore concentrations in the farm soils at the start of the experiment ranged from 44 to 126 live spores per 100 g dry soil with 6–10 species per soil, principally Scutellospora spp. and Acaulospora spp. Nodulation was absent or poor in all soils, indicating the need for rhizobial inoculation of species belonging to the leucaena crossinoculation group in this agrosystem. Rock-P alone increased final shoot dry weight by a factor of 1.4, manure alone by 1.8, and rock-P plus manure by 1.9, compared with no ameliorant. Root infection with AM fungi was detected in all soils 25 days after planting and increased linearly in the different farm soils to values of 33–65% 69 days after planting. Soil pH and root infection 25 days after planting accounted for much of the variation in final shoot weight among soils with no amelioront (87%). As early root infection increased from 20 to 40% at soil pH 5.0, the predicted final shoot dry weight was doubled, and the response to ameliorants was reduced by two-thirds. The growth responses to increased infection became smaller as pH increased from 5.0 to 6.5.     

Hormone-like effect and enhanced nitrate uptake induced by depolycondensed humic fractions obtained from Allolobophora rosea and A. caliginosa faeces

Summary Treatment with acetic acid at pH 2.5 brings about depolycondensation of humic substances and allows isolation of two fractions with apparent molecular weights greater (HSp) and less (HEf) than 3500. A hormone-like effect and nitrate uptake enhancement are exhibited only by the HEf fraction. There is evidence that HSp acts as a support for HEf and regulates its activity on plant metabolism.     

Rhizobia nodulating African Acacia spp. and Sesbania sesban trees in southern Ethiopian soils are metabolically and genomically diverse

The diversity of 110 rhizobial strains isolated from Acacia abyssinica, A. seyal, A. tortilis, Faidherbia albida, Sesbania sesban, Phaseolus vulgaris, and Vigna unguiculata grown in soils across diverse agro-ecological zones in southern Ethiopia was assessed using the Biolog™ system and amplified fragment length polymorphism (AFLP) fingerprinting technique. By cluster analysis of the metabolic and genomic fingerprints, the test strains were grouped into 13 Biolog and 11 AFLP clusters. Twenty-two strains in the Biolog method and 15 strains in the AFLP analysis were linked to eight and four reference species, respectively, out of the 28 included in the study. Most of the test strains (more than 80% of 110) were not related to any of the reference species by both methods. Forty-six test strains (42% of 110) were grouped into seven corresponding Biolog and AFLP clusters, suggesting that these groups represented the same strains, or in some cases clonal descendants of the same organisms. In contrast to the strains from S. sesban, isolates from Acacia spp. were represented in several Biolog and AFLP clusters indicating the promiscuous nature of the latter and widespread occurrence of compatible rhizobia in most of the soil sampling locations. The results showed that indigenous rhizobia nodulating native woody species in Ethiopian soils constituted metabolically and genomically diverse groups that are not linked to reference species.     

The importance of wild potato species resistant to the potato cyst nematode,Globodera pallida,pathotypes P4A and P5A,in potato breeding. I. Resistance studies

Summary Seven wild diploid potato species, Series Tuberosa, representing 1023 clones were screened for resistance to the potato cyst nematode, Globodera pallida. Over 25% of the clones were resistant to pathotype P₄A and almost 30% were resistant to pathotype P₅A. The resistance in hybrid progenies of these and other resistant species with cultivated potatoes was evaluated, and over 2200 seedlings were screened. High frequencies of resistance (>50%) to P₄A were found in progenies with Solanum leptophyes, S. vernei, S. gourlayi and S. capsicibaccatum, whereas resistance to P₅A was found in these species as well as S. sparsipilum. The importance of nematode resistant wild species for potato breeding is discussed.     

Natural hybridization between Solanum acaule Bitt. and S. megistacrolobum Bitt. in the province of jujuy,Argentina

Summary Evidence is provided that hybridization of the tetraploid (2n=4x=48), self-fertile tuber-bearing species Solanum acaule Bitt. with the diploid (2n=2x=24), self-incompatible, tuber-bearing S. megistacrolobum Bitt. takes place in several localities of the province of Jujuy in the high, cold plateaux of the Argentine Puna. The triploid hybrids (2n=3x=36) closely resemble S. acaule in growth habit, leaf morphology and floral structures and for this reason they can be easily overlooked for that species in the field. Experimental data show that S. acaule can be crossed with S. megistacrolobum though the crossability is rather low and variable according to the particular cross considered. The artificial hybrid obtained compares well with the natural hybrid in morphology and chromosome number. The hybrids, though almost completely male sterile, are successful colonizers of disturbed areas around farmers' dwellings, cattle enclosures and other areas where the soil is rich in organic matter.There is some evidence that the Tilcara material of S. acaule subsp. aemulans and the hybrids of S. acaule x S. megistacrolobum have some characters in common, which can be interpreted as having a similar origin.It is postulated that S. acaule subsp. aemulans, in Jujuy at any rate, is not a primitive form of S. acaule as thought by Hawkes and Hjerting, but rather a fertile hybrid derivative of S. acaule x S. megistacrolobum through the functioning of 2n gametes.We also provide evidence that S. bruecheri Correll should not be considered a hybrid of S. acaulle x S. megistacrolobum but a synonym for S. gourlayi Hawkes. The new name, S. x indunii Okada et Clausen, is proposed to designate this hybrid.     

Comparative study of the discriminating capacity and effectiveness of AFLP, STMS and EST markers in assessing genetic relationships among evergreen azaleas

The application of amplified fragment length polymorphism (AFLP), sequence tagged microsatellite site (STMS) and expressed sequence tag (EST) markers to study the genetic relationships in an evergreen azalea gene pool was investigated. STMS and EST markers revealed a higher genetic distance detection capacity than AFLPs, which, nevertheless, were the most efficient marker system due to their highest polymorphism detection capacity. Similarity matrices showed weak, yet significant, correlations when Mantel's test was applied. To assess the usefulness of the overall information provided by these marker data for establishing phylogenetic relationships and horticultural classification, cluster analysis was performed. The joint AFLP, STMS and EST data were demonstrated to be remarkably effective for group discrimination and phylogenetic studies. The use of these polymerase chain reaction marker systems is discussed in terms of the choice of appropriate marker techniques for different aspects of evergreen azalea germplasm evaluation.     

Coffee biotechnology and its application in genetic transformation

The most important advances obtained on in vitro coffee regeneration systems and in coffee genetic transformation, drawing perspectives and scopes to further studies in these fields are presented and discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic relationships among cultivated bananas and plantains from Asia and the Pacific

Summary Isozyme variation was studied to determine genetic relationships among 563 accessions of Musa, including diploid (AA and BB), triploid (AAA, AAB, and ABB), and a few tetraploid (ABBB) clones from Asia and the Pacific. Several open-pollinated seedling progenies of wild, diploid M. acuminata and M. balbisiana were also studied. Cryogenic preservation of leaf tissue in liquid nitrogen allowed sampling of a wide array of germplasm from Papua New Guinea and several Pacific Islands without transporting propagules which are subjected to quarantine regulations. Electrophoretic variation was recorded in three enzyme systems, MDH, PGI and PGM. In total, 52 distinct electromorphs were identified among 192 different isozyme phenotypes (zymotypes). Multivariate analyses of the data clearly differentiated the major genome groups and revealed patterns of association within groups. The isozyme data suggest that the genes contributed by the M. acuminata genome to the triploid Pacific plantain AAB subgroup are similar to those of the acuminata/banksii complex of Papua New Guinea. It is likely that the Pacific plantain subgroup, including the Hawaiian Maoli, Pp'ulu and Iholena cultivars, originated in Papua New Guinea/Melanesia, rather than in Asia or the Malay Archipelago.Journal Series no. 3783 of the Hawaii Institute of Tropical Agriculture and Human Resources.