Host specificity among five species in the cowpea cross-inoculation group

Summary In a cross-inoculation experiment using crushed nodules from cowpea (Vigna unguiculata), groundnut (Arachis hypogea), bambara groundnut (Voandzeia subterranea), lima bean (Phaseolus lunatus) and soybean (Glycine max.), it was found that soybean did not nodulate with Rhizobia from any of the other species whilst its Rhizobia nodulated with all species. Cowpea and lima bean, on the other hand, nodulated with Rhizobia from all species, but their Rhizobia nodulated only with each other. Groundnut and bambara groundnut nodulated with Rhizobia from all species except cowpea and lima bean, and their Rhizobia also nodulated with all species except soybean.     

Parasitism of cowpea by Striga gesnerioides: variation in virulence and discovery of a new source of host resistance

In glasshouse experiments in the United Kingdom, Striga gesnerioides-resistant cowpea varieties, Suvita-2 and 58–57, were assessed alongside a susceptible variety for their responses to seventeen samples of S. gesnerioides from four West African countries. The susceptible variety was attacked by all samples, while Suvita-2 was resistant to samples from Burkina Faso and Mali, and 58–57 was resistant only to samples from Burkina Faso.
At least three physiological groups of the parasite can be distinguished: samples from Burkina Faso attacking the smallest range of cowpea varieties; those from Mali being intermediate; those from Niger and Nigeria attacking all the cowpea varieties. A sample from Cameroon behaved slightly differently and may represent a fourth type.
A cowpea line from Botswana, B.301, selected for its field resistance to Alectra vogelii proved resistant to all Striga populations to which it was exposed, including those from Niger and Cameroon.     

Survival and life table parameters of soybean pod borer Maruca vitrata (Geyer) (Lepidoptera: Crambidae) on leguminous crop cultivars

The soybean pod borer, Maruca vitrata is one of the key insect pests of tropical legumes. It damages tender leaf axils, flower buds, flowers and pods by webbing and boring clusters of flowers and pods. In this study, we investigated the survival and life table parameters of M. vitrata on several leguminous crops; soybean (cvs. Daewon, Poongsannamool and Socheongja), azuki bean (cv. Hongeon), mung bean (cv. Sanpo), and cowpea (cv. Jangchae), compared to artificial diet to assess the antibiosis resistance to M. vitrata. The life‐variables of M. vitrata were significantly affected by the tested legume cultivars. None of the larvae fed cowpea cultivar Jangchae survived. The azuki bean cultivar Hongeon and mung bean cultivar Sanpo were found susceptible to M. vitrata, whereas cowpea cultivar Jangchae and soybean cultivar Daewon showed antibiosis resistance to M. vitrata. Further studies should examine the chemicals associated with leguminous crop cultivars and its mechanism to develop a control method against M. vitrata.     

Evolutionary conservatism of geographic variation in host preference in Callosobruchus maculatus

Abstract.  1. A study of host preference of four pairs of populations of the cowpea weevil Callosobruchus maculates was carried out. The pairs had different geographical origins.
2. One population of each pair had been maintained for about 110 generations on cowpea Vigna unguiculata , the other population had been maintained on mung bean V. radiata . Half of the tested females from each population were raised on cowpea and exposed to this host prior to the assay; the other half was raised on mung bean. This design permitted assessment of the relative contributions of geographical origin, recent host use in the laboratory, and individual experience, to variation in host preference.
3. Host preference was assayed by letting the females oviposit on an equal-weight mixture of cowpea and mung seeds; two experiments were performed six generations apart.
4. Both experiments revealed a strong effect of geographical origin: populations originating from Nigeria laid a much greater proportion (68–86%) of their eggs on cowpea than those originating from Uganda and Yemen (30–42%); those from Cameroon were intermediate (56–60%). These preferences were not affected consistently by about 110 generations of laboratory evolution on one or the other host, or by experience of individual females.
5. These results indicate considerable geographical variation in host preference, and suggest that host preference is behaviourally inflexible and evolutionarily conserved.     

Involvement of Volatile Substances in Systemic Resistance of Barley Against Erysiphe graminis f. sp. hordei Induced by Pruning of Leaves

Horsegram yellow mosaic disease was shown to be caused by a geminivirus; horsegram yellow mosaic virus (HYMV). The virus could not be transmitted by mechanical sap inoculation. Leaf dip and purified virus preparations showed geminate virus particles, measuring 15-18 * 30 nm. An antiserum for HYMV was produced and in enzyme-linked immunosorbent assay (ELISA) and immunosorbent electron microscopy (ISEM) tests HYMV was detected in leaf extracts of fieldinfected bambara groundnut, french bean, groundnut, limabean, mungbean, pigeonpea and soybean showing yellow mosaic symptoms. Bemisia tabaci fed on purified HYMV through a parafilm membrane transmitted the virus to all the hosts listed above but not to Ageratum conyzoides, okra, cassava, cowpea, Croton bonplandianus, Lab-lab purpureus, Malvastrum coromandalianum and tomato. No reaction was obtained in ELISA and ISEM tests between HYMV antibodies and extracts of plants diseased by whitefly-transmitted agents in India such as A. conyzoides yellow mosaic, okra yellow vein mosaic, C. bonplandianus, yellow vein mosaic, M. coromandalianum yellow vein mosaic, tomato leaf curl and cassava mosaic. HYMV was also not found to be related serologically to bean golden mosaic, virus.     

Predictable modification of body size and competitive ability following a host shift by a seed beetle

Interfertile populations of the seed beetle Callosobruchus maculatus differ genetically in several behavioral, morphological, and life-history traits, including traits that affect the intensity of larval competition within seeds. Previous studies have suggested that this variation depends on differences in host size. I performed a selection experiment in which replicate beetle lines were either maintained on a small, ancestral host (mung bean) or switched to a larger, novel host (cowpea). After 40 generations, I estimated survival, development time, and adult mass on each host, both in the presence and absence of larval competition. The shift to cowpea substantially reduced body size; irrespective of rearing host, adults from the cowpea lines were more than 10% lighter than those from the mung bean lines. Switching to cowpea also improved survival and reduced development time on this host, but without decreasing performance on the ancestral host. The most striking effect of the shift to a larger host was a reduction in larval competitiveness. When two even-aged larvae co-existed within a seed, the probability that both survived to adult emergence was > or = 65% if larvae were from the cowpea lines but < or = 12% if they were from the mung bean lines. The adverse effects of competition on development time and adult mass were also less severe in the cowpea lines than in the mung bean lines. By rapidly evolving smaller size and reduced competitiveness, the cowpea lines converged toward populations chronically associated with cowpea. These results suggest that evolutionary trajectories can be predictable, and that host-specific selection can play a major role in the diversification of insect life histories. Because host shifts by small, endophagous insects are comparable to the colonization of new habitats, adaptive responses may often include traits (such as larval competitiveness) that are not directly related to host use.     

Molecular taxonomic relationships in the genus Vigna based on RFLP analysis

Summary The taxonomy of the genus Vigna has been primarily based on morphological attributes. We have used 27 genomic clones from soybean, common bean, mungbean and cowpea to examine restriction fragment length polymorphism (RFLP) among 44 accessions of different species belonging to four subgenera of the genus Vigna. One accession each of common bean (Phaseolus vulgaris) and soybean (Glycine max) was included in the study. Total DNA from the various genotypes was digested with one restriction enzyme (Eco RV). Results of a numerical taxonomic analysis showed a high level of genetic variation within the genus with a remarkably higher amount of variation associated with Vigna sp. from Africa relative to those from Asia. The distinctness of the Asiatic grams in subgenus Ceratotropis, cowpea in section Catiang, bambara groundnut (V. subterranean) and members of the subgenus Plectotropis was elucidated by this study. Members of the subgenus Plectotropis were closer in genome homology to those of subgenus Vigna section Catiang than to those of subgenus Ceratotropis. The relative positions of some genotypes to one another on the dendrogram and minimum spanning tree were discussed in regard to hybridisations aimed generating well-saturated genomic maps and interspecies transfer of desirable genes.     

How labile are the egg‐laying preferences of seed beetles?

Abstract.  1. Previous studies have produced conflicting results with respect to the genetic lability of host preference in the seed beetle Callosobruchus maculatus .
2. In this study, replicate lines of an Asian population were kept on an ancestral host (mung bean) or switched to a novel host (cowpea). After 40+ generations, lines were assayed for host preference (in choice tests) and host acceptance (under no-choice conditions), and were compared to African lines chronically associated with cowpea.
3. Host preference diverged in the expected direction. When presented a mixture of cowpeas and mung beans, females from the cowpea lines laid a greater fraction of their eggs on cowpea than did females from the mung bean lines. Preference for cowpea was nearly as strong in the cowpea lines as it was in the cowpea-adapted African lines.
4. In contrast, the experimental host shift did not affect long-term host acceptance. African females laid more eggs if given cowpeas than if given mung beans, but realised fecundities in the cowpea and mung bean lines were similar on the two hosts. Females from all lines laid more eggs if they were reared on cowpea than on mung bean, but rearing host had no effect on either relative host acceptance or host preference.
5. Comparisons with earlier studies suggest that the lability of host preference varies among beetle populations, which precludes generalisation at the species level. Because lines were maintained under no-choice conditions, modification of host preference probably occurred via a lower acceptance threshold for the novel host, without a concomitant change in the long-term acceptance of the ancestral host.     

Assessing host range,symbiotic effectiveness,and photosynthetic rates induced by native soybean rhizobia isolated from Mozambican and South African soils

Host range and cross-infectivity studies are important for identifying rhizobial strains with potential for use as inoculants. In this study, 10 native soybean rhizobia isolated from Mozambican and South African soils were evaluated for host range, symbiotic effectiveness and ability to induce high rates of photosynthesis leading to enhanced plant growth in cowpea (Vigna unguiculata L. Walp.), Bambara groundnut (Vigna subterranean L. Verdc.), Kersting’s groundnut (Macrotyloma geocarpum Harm) and soybean (Glycine max L. Merr). The test isolates had different growth rates and colony sizes. Molecular analysis based on enterobacterial repetitive intergenic consensus (ERIC)-PCR revealed high genetic diversity among the test isolates. The results further showed that isolate TUTLBC2B failed to elicit nodulation in all test plants, just as TUTNSN2A and TUTDAIAP3B were also unable to nodulate cowpea, Kersting’s bean and Bambara groundnut. Although the remaining strains formed ineffective nodules on cowpea and Kersting’s bean, they induced effective nodules on Bambara groundnut and the two soybean genotypes. Bacterial stimulation of nodule numbers, nodule dry weights and photosynthetic rates was generally greater with isolates TUTRSRH3A, TUTM19373A, TUTMCJ7B, TUTRLR3B and TUTRJN5A. As a result, these isolates elicited significantly increased accumulation of biomass in shoots and whole plants of Bambara groundnut and the two soybean genotypes. Whole-plant symbiotic nitrogen (N) of soybean and Bambara groundnut was highest for the commercial strains CB756 and WB74, as well as for TUTRLR3B, TUTMCJ7B and TUTRSRH3A, suggesting that the three native rhizobial isolates have potential for use as inoculants.     

Bacterial Antagonist as Seed Treatment to Control Leaf Blight Disease of Bambara Groundnut (Vigna subterranea)

Summay Soil samples were taken from 48 fields in the southern part of Thailand in which either bambara groundnut (Vigna subterranea) or groundnut (Arachis hypogeae) had been planted. Bacillus spp. were isolated using soil dilution plates and heat treatment to screen for endospore-producing bacteria. Among 342 Bacillus spp. isolates tested, 168 isolates were not antagonistic to Bradyrhizobium sp. strain NC-92 using dual culture technique. Further testing found 16 isolates of Bacillus spp. had the ability to inhibit mycelial growth of Rhizoctonia solani, a causal agent of leaf blight of bambara groundnut. Among these isolates, Bacillus spp. isolate TRV 9-5-2 had the greatest activity in anti-microbial tests against R. solani. This isolate was later identified as B. firmus. A powder formulation of B. firmus was developed by mixing bacterial endospores, talcum, sodium carboxymethylcellulose (SCMC) and polyvinylpyrolidone (PVP). The formulations contained bacterial levels ranging from 10⁸ to 10¹⁰ c.f.u./g and the viability of bacteria in all formulations remained high after 1 year storage at room temperature (26–32 °C). All formulations showed satisfactory effectiveness in vitro in suppressing mycelial growth of R. solani using dual culture technique. The application of formulations as seed treatment showed that these formulations did not cause abnormality of seedling shape and had no effect on the germination of bambara groundnut seeds.     

Mung bean (<Emphasis Type="Italic">Vigna radiata</Emphasis>) cultivars mediated oviposition preference and development of <Emphasis Type="Italic">Callosobruchus chinensis</Emphasis> (Coleoptera: Chrysomelidae: Bruchinae)

The Azuki bean weevil, Callosobruchus chinensis (L.), is a destructive pest of stored mung bean [Vigna radiata (L.) Wilczek] as well as other leguminous seeds. The development of resistant seeds to manage this pest is of current great interest to plant breeders. In this study, we investigated the oviposition preference and development of C. chinensis on two susceptible mung bean cultivars (Seonhwa and Gyeongseon) and one previously reported resistant cultivar (Jangan), compared to the susceptible cowpea (Vigna unguiculata L.), cultivar (Yeonbun) using both multiple-choice and no-choice tests. In addition, the development of C. chinensis was also examined at four constant temperatures (20, 25, 30, and 35 °C). Both tests found cowpea to be the most suitable seed for oviposition. Total developmental time from oviposition to adult emergence ranged from 27.01 to 38.2 days, being shortest on cowpea and longest on the mung bean, cv. Jangan. However, no successful development of C. chinensis larvae on mung bean, cv. Jangan, occurred at any temperature. The highest rate of adult emergence and the longest adult longevity both occurred on cowpea and certain mung bean cultivars (Seonhwa and Gyeongseon), with the dramatic exception of cv. Jangan. These results suggest that the higher preference and performance of C. chinensis on cowpea (3.3 egg/seed) and least on mung bean, cv. Jangan (0.4 egg/seed). This information may facilitate the exploration of resistant genetic materials and chemicals associated with seeds for successful breeding. Further studies should examine the chemicals associated with mung bean cultivars and its resistant mechanism to develop a control method against bruchines.     

Rapid Evolution of Lifespan in a Novel Environment: Sex-Specific Responses and Underlying Genetic Architecture

Animal lifespans can vary substantially among closely related species and even among conspecific populations, but it is often difficult to identify environmental and genetic factors producing such variation. We used experimental evolution to examine how transfer to a novel environment affects adult lifespan and rates of senescence in a seed-feeding beetle. Three replicate lines of Callosobruchus maculatus (F.) were switched to a new host plant (cowpea), and each evolved shorter adult lifespans compared to a line maintained on the ancestral host (mung bean). However, the evolution of lifespan differed between the sexes; female lifespan was reduced by ~11% in all cowpea replicates, whereas male lifespan decreased by an average of only 5.6% and the magnitude of the reduction varied among replicates. Reduced lifespan in lines switched to cowpea mirrored the shorter lifespan observed in a separate population chronically associated with cowpea. We then performed crosses between the mung bean and cowpea lines to estimate the genetic architecture underlying the rapid evolution of a shorter lifespan on cowpea. Dominance (overdominance) contributed substantially to the difference between the cowpea and mung bean lines for female lifespan but not for male lifespan. However, details of the genetic architecture varied among the three replicate crosses, so that the convergent evolution of shorter female lifespan in the different cowpea lines did not arise from identical allelic substitutions. Our study demonstrates that insect lifespan can be predictably modified by a switch to a novel host plant, that both the magnitude of this response and its underlying genetic architecture can be sex-specific, and that convergent evolution of a complex trait such as lifespan can arise from different genetic mechanisms.     

Phylogeny of bradyrhizobia from Chinese cowpea miscellany inferred from 16S rRNA, atpD, glnII, and 16S-23S intergenic spacer sequences

The cowpea (Vigna unguiculata L.), peanut (Arachis hypogaea L.), and mung bean (Vigna radiata L.) belong to a group of plants known as the "cowpea miscellany" plants, which are widely cultivated throughout the tropic and subtropical zones of Africa and Asia. However, the phylogeny of the rhizobial strains that nodulate these plants is poorly understood. Previous studies have isolated a diversity of rhizobial strains from cowpea miscellany hosts and have suggested that, phylogenetically, they are from different species. In this work, the phylogeny of 42 slow-growing rhizobial strains, isolated from root nodules of cowpea, peanut, and mung bean from different geographical regions of China, was investigated using sequences from the 16S rRNA, atpD and glnII genes, and the 16S-23S rRNA intergenic spacer. The indigenous rhizobial strains from the cowpea miscellany could all be placed in the genus Bradyrhizobium , and Bradyrhizobium liaoningense and Bradyrhizobium yuanmingense were the main species. Phylogenies derived from housekeeping genes were consistent with phylogenies generated from the ribosomal gene. Mung bean rhizobia clustered only into B. liaoningense and B. yuanmingense and were phylogenetically less diverse than cowpea and peanut rhizobia. Geographical origin was significantly reflected in the phylogeny of mung bean rhizobia. Most cowpea rhizobia were more closely related to the 3 major groups B. liaoningense, B. yuanmingense, and Bradyrhizobium elkanii than to the minor groups Bradyrhizobium japonicum or Bradyrhizobium canariense . However, most peanut rhizobia were more closely related to the 2 major groups B. liaoningense and B. yuanmingense than to the minor group B. elkanii.     

Alarming increase in the incidence of Cucumber mosaic virus in cowpea (Vigna unguiculata (L.) Walp.) in northern Nigeria

Cowpea plays a key nutritional role in the diet of the Nigerian people. Viral diseases are a major limitation to cowpea production worldwide, and thus, constant viral surveillance is crucial for monitoring and management purposes. In this study, cowpea leaf samples from fields in three northern Nigeria states, Kano, Kaduna and Niger, were tested to determine the status of six common viruses previously reported in these cowpea-producing states following the release of virus-resistant varieties. Cowpea aphid-borne mosaic virus (CABMV), Blackeye cowpea mosaic virus (BICMV), Cowpea mottle virus, Southern bean mosaic virus and Cucumber mosaic virus (CMV) were detected. Cowpea yellow mosaic virus, which was previously reported in all three states, was not detected in any of the samples tested, while CMV that was previously regarded as unimportant to cowpea production in Nigeria had the highest incidence in all three states, and the overall highest incidence of 58.8%, while CABMV had the lowest incidence (7.5%). CMV was also present in seven of the ten mixed infection combinations detected. Dual infection of CMV and BICMV, which often results in cowpea stunt, the most devastating cowpea disease in the USA, was the most frequently detected mixed infection (28.1%) and was detected in all three states. This observed elevation in CMV infection in cowpea must be closely monitored and swiftly managed to avert possible devastating crop yield losses.     

The role of maize-legumes-cassava intercropping in the management of maize ear borers with special reference to Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae)

The effects of intercropping maize with cowpea, lima bean, soybean, three leguminous cover crops (Tephrosia vogelii Hook F., Canavalia ensiformis L., Sesbania rostrata Bremek. & Oberm.) and cassava on the infestation of Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae) and other lepidopteran ear borers were studied. Field experiments were conducted in four locations in Benin using a 4x2 pattern of maize-legumes or maize-cassava planting. Intercropping reduced the number of eggs (by >25%) and larvae (by 17.9–53%) of M. nigrivenella compared with the monocrop. Maize-C. ensiformis and maize-T. vogelii proved to be the most effective combinations for reducing M. nigrivenella populations in the different locations. Grain loss and ear damage, which were significantly correlated with the number of insects in the ear, were significantly affected by the intercrops, with losses abated by 47–84% in the four sites. No parasitized larvae were found in any of the locations.     

Immunochemical identification of mung bean actin like protein and its cellular involvement during germination

Actin like protein, extracted and purified fromVigna radiata (mung bean) seedling, has been found to give positive enzyme-linked immunosorbent assay with mouse monoclonal antiactin antibody. In vivo studies show that cytochalasin B at sublethal dose inhibits the chromosomal movement at metaphase stage during germination. Fromin vitro studies it is found that the actin like protein isolated from mung bean seedling has a cytochalasin B binding property with a Kd value 1.2 × 10⁻⁵ M. From these two specific observations it appears probable that the biological function of mung bean actin like protein is to take part in cell division process directly or indirectly during the time of seedling development.     

Scab disease of cowpea (Vigna unguiculata) caused by Sphaceloma a species of the fungus

Scab disease of cowpea (Vigna unguiculuta) was shown to be caused by Sphaceloma sp. It affects all above ground parts of the plant. The first symptom of the disease, appearing within 3 to 6 days of inoculation, is puckering of the lamina. Spots on mature leaves are white with or without brown margins. Typical scab lesions on petiole, stem, peduncle and pod are white turning dark brown when chlamydospores are formed and are oblong-elongate except for pod lesions that are ovoid. The most destructive phase is scab of the flowering axis which causes flower and, or, pod abortion or completely prevents flower formation. Inoculation of asparagus pea (V. sesquipedalis) with a cowpea isolate of Sphaceloma sp. produced symptoms similar to those on cowpea. Inoculated hyacinth bean (Lablab niger) produced atypical mild lesions. The following legumes were not affected when artificially inoculated with the fungus: black gram (Phaseolus mungo), green gram (P, aureus), French bean (P. vulgaris), Lima bean (P. lunatus), groundnut (Arachis hypogaea), and soyabean (Glycine max). The characteristics of the fungus on potato dextrose agar are described.     

Integrated agroforestry systems improve soil carbon storage,water productivity,and economic returns in the marginal land of the semi-arid region

Environmental crises, land degradation, and frequent crop failure threaten the livelihoods of millions of the populace in the semi-arid agroecosystems. Therefore, different combinations of annual crops with perennial fruit trees were assessed to restore the soil carbon, and enhance farm productivity and profitability in a semi-arid climate. The study hypothesized that the integration of perennial fruit trees with seasonal crops may enhance farm productivity, economic returns, and environmental sustainability. Integration of phalsa (Grewia asiatica) with mung bean (Vigna radiata) - potato (Solanum tuberosum) system recorded the highest system productivity (25.9 Mg/ha) followed by phalsa with cowpea (Vigna unguiculata) -mustard (Brassica juncea) systems (21.2 Mg/ha). However, Karonda (Carissa sp.) with mung bean - potato system recorded maximum net return (3529.1 US$/ha), and water use efficiency (33.0 kg/ha-mm). Concerning the benefit-cost (B:C) ratio, among the agroforestry systems, the karonda + cowpea - mustard system registered a maximum BC ratio (3.85). However, SOC density remained higher (9.10 Mg/ha) under the phalsa + cowpea - mustard and Moringa + mung bean - potato system (9.16 Mg/ha) over other systems. Similarly, phalsa + mung bean - potato system had the highest C sustainability index (27.6), carbon sequestration potential (0.6–0.67 Mg/ha/year), and water use efficiency (33.0 kg/ha-mm). Hence, the study suggested that the integration of short-duration leguminous and oilseeds with fruit trees offer a myriad of benefits and an efficient system for restoring the soil C without compromising the food and livelihood security of the rural populace in semiarid regions.     

Effects of water deficit on N2(C2H2) fixation in cowpea and groundnut

The effect of water deficit on nodulation, N₂ fixation, photosynthesis, and total soluble sugars and leghemoglobin in nodules was investigated in cowpea and groundnut. Nitrogenase activity completely ceased in cowpea with a decrease in leaf water potential ( _leaf) from –0.4 MPa to –0.9 MPa, while in groundnut it continued down to –1.7 MPa. With increasing water stress, the acetylene reduction activity (ARA) declined very sharply in cowpea, but ARA gradually decreased in groundnut. Even with mild water stress ( _leaf of 0.2 MPa), nodule fresh weight declined 50% in cowpea partly due to a severe nodule shedding whereas nodule fresh weight declined in groundnut only when _leaf decreased by 1.0 MPa. No nodule shedding was noticed even at a higher stress level in groundnut. Photosynthesis and stomatal conductance were also more stable in groundnut than in cowpea under water stress. There was a sharp increase in total soluble sugars and leghemoglobin in the nodules of groundut with water stress, but no definite trend could be found in cowpea.     

STUDIES ON THE GERMINATION OF SEEDS OF THE ROOT PARASITES,ALECTRA VOGELII AND STRIGA GESNERIOIDES. I. ANATOMICAL CHANGES IN THE EMBRYOS

Anatomical changes in the radicle and shoot meristems of embryos of germinating seeds of the obligate root parasites, Alectra vogelii and Striga gesnerioides were studied. When germination of seeds was stimulated by cowpea (Vigna unguiculata) root exudate, growth occurred mainly in the radicular pole of embryos and minimally in the plumular pole, resulting in seedlings with elongated radicles. Maximum radicle elongations of about 3 mm in A. vogelii and 2 mm in S. gesnerioides were recorded during a period of 8 and 11 days, respectively. Analysis of the radicular tip during the course of seed germination revealed that the activity of the meristematic tissue progressively decreased until it completely disappeared. When germinated seeds were cultured on nutrient agar media, the radicle meristem of A. vogelii continued to grow producing a normal root with a root cap. On the other hand, the radicles of cultured S. gesnerioides seeds elongated only slightly before meristematic activity ceased. During continued growth of seedlings of both species on agar media, lateral roots whose tips had typical angiosperm root topography, were initiated from the radicle.