Identification and pathogenic characterization of endophytic <Emphasis Type="Italic">Fusarium</Emphasis> species from cowpea seeds

Isolates of Fusarium were obtained and identified from seeds of cowpea, Vigna unguiculata (L.) Walp., by means of blotter tests and slide cultures. Species were differentiated according to the morphology of the macroconidia, microconidia and their arrangement in chains or false heads, the size and type of conidiophore, and the presence or absence of chlamydospores. The species were identified as F. semitectum, F. equiseti, F. oxysporum, F. solani, F. anthophilum, F. sporotrichioides, F. moniliforme, and Fusarium sp. Among the species, F. semitectum was the most frequently detected. None of these species were pathogenic when inoculated in susceptible cowpea cultivar (BR 17- Gurgueia). But, an isolate of F. oxysporum f. sp. tracheiphilum used as a standard of comparison for pathogenicity (control) induced symptoms of yellowing, vascular wilting, and death of a susceptible cowpea cultivar under the same environmental conditions.     

Parasitism of grain legumes by Alectra species (Scrophulariaceae)

In glasshouse pot experiments in the United Kingdom, the host preference of nine seed samples of Alectra vogelii from Eastern, Western and Southern Africa and of two samples of A. picta from Cameroon and Ethiopia, to cultivars of cowpea, groundnut, bambara and mung bean, was assessed. A susceptible cowpea cultivar, Blackeye, and four cultivars of groundnut were attacked by all samples of both parasitic species regardless of whether the host of origin was cowpea, groundnut or bambara. Five “strains” of A. vogelii were distinguished using two criteria: their ability to parasitise bambara and/or mung bean and their ability to parasitise cowpea B301 and bambara TVU 870. The latter proved in an associated experiment to be resistant to collections of the parasite from some locations. Strain 1, including populations from Mali, Nigeria and Cameroon, attacked all groundnuts, cowpea cultivar Blackeye, but not cowpea line B301, mung bean or bambara. Strain 2, from Botswana, differed in attacking B301 and mung bean. Three other strains were identified which attacked susceptible lines of all four legume species. Strain 3 from Kenya failed to attack either cowpea B301 or bambara TVU 870, strain 4 from Malawi attacked cowpea B301, but not bambara TVU 870, while strain 5 from Northern Transvaal, South Africa, attacked bambara TVU 870, but not cowpea B301. Cowpea B359 was resistant to A. vogelii samples from all locations and also to A. picta, which has a similar host preference to strain 1 populations of A. vogelii from West Africa. Two out of 13 groundnut lines tested showed low susceptibility to A. vogelii from Cameroon suggesting there is scope for selecting resistance in this crop also.     

Modelling the effect of varying soil water on root growth dynamics of annual crops

We present a simple framework for modelling root growth and distribution with depth under varying soil water conditions. The framework considers the lateral growth of roots (proliferation) and the vertical extension of roots (root front velocity). The root front velocity is assumed to be constant when the roots descend into an initially wet soil profile. The lateral growth of roots is governed by two factors: (1) the current root mass or root length density at a given depth, and (2) soil water availability at that depth.Under non-limiting soil water conditions, the increase in root mass at any depth is governed by a logistic equation so that the root length density (R _v) cannot exceed the maximum value. The maximumR _v, is assumed to be the same for all depths. Additional dry matter partitioned to roots is initially distributed according to the current root mass at each depth. As the root mass approaches the maximum value, less dry matter is partitioned to that depth.When soil water is limiting, a water deficit factor is introduced to further modify the distribution of root dry matter. It is assumed that the plant is an energy minimiser so that more root mass is partitioned to the wetter regions of the soil where least energy will be expended for root growth. Hence, the model allows for enhanced root growth in areas where soil water is more easily available.Simulation results show that a variety of root distribution patterns can be reproduced due to varying soil water conditions. It has been demonstrated that broad patterns of root distribution reported in the literature can also be simulated by the model.     

The resistance of cowpea seeds to bruchid beetles is not related to levels of cysteine proteinase inhibitors

A cDNA encoding a cysteine proteinase inhibitor was isolated from a cDNA library prepared from developing seeds of an insect-resistant line of cowpea. The sequence of the encoded protein was homologous with those of other plant cysteine endoproteinase inhibitors, and with Type 2 cystatins from animals. Southern blot analyses indicated that small gene families were present in both resistant and susceptible lines of cowpea, while northern blot analyses showed similar levels of expression. It is concluded that the levels of expression of the inhibitor do not account for the differences in insect resistance of the two lines.     

Biosynthesis of the 2-arylbenzofuran phytoalexin vignafuran in Vigna unguiculata

Feeding experiments using l-phenylalanine-[U-¹⁴C], dl-phenylalanine-[1-¹⁴C] and -[2-¹⁴C] together with degradative studies have been used to investigate the biosynthesis of the 2-arylbenzofuran phytoalexin vignafuran in UV-treated seedlings of cowpea (Vigna unguiculata). During the biosynthetic process, C-3 of phenylalanine appears to be lost, and the resulting labelling pattern is consistent with vignafuran being derived from an isoflavonoid precursor, but the phenylalanine-derived aromatic ring becomes the 2-aryl substituent and not part of the benzofuran system. A previously proposed pathway to 2-arylbenzofurans by loss of C-6 from a coumestan is thus excluded. Alternative routes are suggested.     

Structure and function of the elongation sink in the stems of higher plants.*

Abstract. Application of an acid aerosol generated from an aqueous HC1 or HNO₃ solution (pH 1-2) to the hypocotyl segment of Vigna sesquipedalis, excised from the elongation zone and abraded with alumina gel, induced rapid elongation growth comparable with that induced by aerosol generated from neutral 1 mol m^?3 1AA aqueous solution. The activity of the first electrogenic ion pump, whose activity is known to be stimulated by IAA aerosol in advance of the increase in growth rate, was little affected by acids. The latent period of the growth response to acids was only 1 min shorter than that to IAA (mean value: 12min), or than the period from the stimulation of the electrogenic ion pump activity by IAA to the beginning of growth acceleration (mean value: 4 min). The growth rate, together with the activities of the first and the second ion pump, was reduced by anoxia in the presence of acid. The acid N₂-sol was ineffective to stimulate the elongation under anoxia. The acid aerosol was ineffective to stimulate the elongation of a non-abraded segment with intact cuticle layer on its surface.     

Age dependence of cowpea protoplasts for uptake of spermidine and infectibility by alfalfa mosaic virus

Cowpea protoplasts were prepared from plants of different ages and examined for their ability to take up polyamines and for their infectibility by alfalfa mosaic virus. A lag period of 20 h was necessary before the onset of rapid polyamine uptake; the occurrence of this rapid uptake depended on the age of the leaves used for protoplast preparation. The percentage of infection of cowpea protoplasts by alfalfa mosaic virus, and the amount of virus produced also depended on the age of the plants used for protoplast preparation. In contrast, the uptake of amino acids was rapid in all cowpea protoplasts tested.     

The Histopathological Reactions of Vigna sinensis to Separate and Concomitant Parasitism by Meloidogyne javanica and Rotylenchulus reniformis

Cellular alterations in cowpea roots and nodules induced by single and concomitant Meloidogyne javanica and Rotylenchulus reniformis were investigated. M. javanica induced giant cells inside the vascular bundles of roots and nodules, and syncytia in cortical tissue of the nodules. In contrast, R. reniformis stimulated hypertrophy of pericycle and endodermal cells of the roots and nodules. Syncytia induced in the roots involved a sheet of pericycle cells and an endodermal cell. Cortical ceils of nodules also responded to R. reniformis infection, initiating wall gaps that led to syncytial formation. Coincidence of giant cells or syncytla of both nematodes was observed either in one vascular bundle or in separate ones. The histopathology of roots and nitrogen nodules infected by the two species remained unique even when they were feeding in close proximity. R. reniformis induced characteristic syncytia and M. javanica induced giant cells.     

The nature of the increase in ribonuclease activity in germinating seeds of cowpea treated with gibberellic acid or cyclic-amp

There was a two- to three-fold stimulation of RNAase activity by the application of GA₃ and cAMP to cowpea seedlings. The increase in activity was inhibited by the administration of actinomycin D, cycloheximide, cordycepin, 5-fluorouracil and amino acid analogues. Purification of labelled RNAase revealed that GA₃ and cAMP enhanced the RNAase activity predominantly by its fresh synthesis.     

Effects of aluminium on tap-root elongation of soybean (Glycine max), cowpea (Vigna unguiculata) and green gram (Vigna radiata) grown in the presence of organic acids

The role of fulvic, malic, and oxalic acids in alleviating the toxic effects of aluminium (Al) on tap-root elongation of soybean cv. Fitzroy, cowpea cv. Vita 4, and green gram cv. Berken was studied. Treatments consisted of a factorial combination of four Al concentrations (0, 12.5, 25 and 50 µM as Al(NO₃)₃·9H₂O) and two concentrations either of malic or oxalic acid (0, 50 µM) or fulvic acid (0, 65 mg L^-1 of organic carbon). The free monomeric Al in solution was determined using a pyrocatechol violet procedure which distinguishes between monomeric and organically complexed Al. Fulvic acid completely alleviated the toxic effect of Al at all concentrations on soybean and cowpea and at concentrations <25 µM on green gram. The non-toxic Al-fulvate complex remained in solution. Both malic and oxalic acid, at the concentrations tested, failed to alleviate Al toxicity on any species; a much higher proportion of the added Al remained in monomeric form in the presence of these acids.