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.     

Regulation of Leaf Senescence by Reproductive Sink Intensity in Cowpea (Vigna unguiculata L. Walp)

The relationship between seed number per pod and senescenceof the leaf in its axil was examined in a determinate cowpea(Vigna unguiculata L. Walp) variety C.779. The seed number perpod was reduced at all fruiting nodes by surgical excision ofpart of the 4-d-old pod. Leaf senescence as measured by lossof leaf area, chlorophyll content and soluble protein was sloweddown in leaves supporting the development of an artificiallyreduced number of seeds. Diminished nitrogen mobilization fromthe leaf could not account for the reduced rate of leaf senescence.The result suggests the involvement of a senescence signal fromthe developing seeds to the leaf in its axil. Development ofthe basal half of the excised pod in the cowpea provides a uniquesystem for manipulating seed number per pod. Senescence, monocarpic, chlorophyll, protein, Vigna unguiculata, cowpea     

Pythium seed decay and stem rot of cowpea (Vigna sinensis [Linn.] Savi) in southern Niǵria

Summary Pythium aphanidermatum (Edson) Fitzpatrick has been associated with seed decay and severe stem rot of cowpea in Nigeria. The symptoms produced on both seedlings and established cowpea plants are described. Fungus-induced losses of 0.94 per cent as seed decay and 11.10 per cent damage to adult cowpea plants have been recorded.     

Genetics of rough seed coat texture in cowpea

Seed coat texture is an important trait in determining the acceptability of cowpea varieties in different regions. A rough seed coat is preferred in western and central Africa, since it permits easy removal of the seed coat which is essential for indigenous food preparations. On the other hand, a smooth seed coat is preferred in eastern and southern Africa as well as in parts of South America where cowpea is consumed as boiled beans without removing the seed coats. This study was undertaken to elucidate the inheritance of seed coat texture so that cowpea breeders may adopt appropriate breeding strategy to develop cowpea varieties with preferred seed types for different regions. The F1 plants between smooth- and rough-seeded parents as well as between rough- and rough-seeded parents produced smooth seeds, indicating a complementary gene action and dominance for smooth seed coat. The F2 plants from the smooth x rough cross segregated into a 3 smooth:1 rough seed coat ratio, but the F2 plants from rough x rough crosses segregated into a 9 smooth:7 rough seed coat ratio. The F1 plants from backcross to the smooth parent were all smooth, while the F1 plants from backcross to rough parent segregated in a 1 smooth:1 rough seed coat ratio. However, both the backcross populations in rough x rough crosses segregated into 1 smooth:1 rough seed coat ratio. These results indicate that two pairs of independent recessive genes confer rough seed coat texture in cowpea and the presence of at least one dominant gene at each of the two loci results into smooth seed coat. The gene symbols rt1rt1 and rt2rt2 are being assigned for rough seed coat texture in cowpea.     

Dispersal and parasitizing abilities of Eupelmus vuilleti (Hymenoptera: Eupelmidae) within a column of cowpea seeds

Eupelmus vuilleti (Crawford) is an ectoparasitoid of the seed-eating beetle Bruchidius atrolineatus (Pic), which is an important pest of stored cowpea, Vigna unguiculata Walp, seeds in West Africa. Herein, we investigated the dispersal abilities of females within columns of seeds to assess the potential of E. vuilleti as a biological control agent of bruchids in cowpea granaries. The influence of host presence together with the 2 abiotic factors light and gravity on parasitoid movement and parasitization efficiency were analyzed. E. vuilleti females were able to travel through large seed masses and parasitize hosts located at the end of the seed column opposed to their introduction zone. Parasitoid movement was stimulated by light. E. vuilleti females exhibited a negative geotropism. Females introduced at the bottom of the seed column dispersed more and parasitized more hosts than females introduced at the top. Host presence had some influence on the dispersal of the parasitoids within the seed column at a host density of 10 infested seeds for 16,000-18,000 uninfested seeds. This depended on female introduction zone because gravity was the major factor influencing dispersal. The possible applications of these results for biological control of bruchids in cowpea granaries are discussed.     

The effects of aflatoxin B1 and palmotoxins B0 and G0 on the germination and leaf colour of the cowpea (vigna sinensis)

Aflatoxin B₁, crude aflatoxins and palmotoxins B₀ and G₀ were tested for seed germination and chlorophyll formation using the cowpea. It was found that aflatoxin B and crude aflatoxins inhibited both chlorophyll formation and seed germination and palmotoxins inhibited these processes to a lesser extent. 3 — Indolylacetic acid reduced the inhibitory effects of the aflatoxins in seed germination and chlorophyll formation in the cowpea.     

A multi‐parent advanced generation inter‐cross (MAGIC) population for genetic analysis and improvement of cowpea (Vigna unguiculata L. Walp.)

Multi‐parent advanced generation inter‐cross (MAGIC) populations are an emerging type of resource for dissecting the genetic structure of traits and improving breeding populations. We developed a MAGIC population for cowpea (Vigna unguiculata L. Walp.) from eight founder parents. These founders were genetically diverse and carried many abiotic and biotic stress resistance, seed quality and agronomic traits relevant to cowpea improvement in the United States and sub‐Saharan Africa, where cowpea is vitally important in the human diet and local economies. The eight parents were inter‐crossed using structured matings to ensure that the population would have balanced representation from each parent, followed by single‐seed descent, resulting in 305 F₈ recombinant inbred lines each carrying a mosaic of genome blocks contributed by all founders. This was confirmed by single nucleotide polymorphism genotyping with the Illumina Cowpea Consortium Array. These lines were on average 99.74% homozygous but also diverse in agronomic traits across environments. Quantitative trait loci (QTLs) were identified for several parental traits. Loci with major effects on photoperiod sensitivity and seed size were also verified by biparental genetic mapping. The recombination events were concentrated in telomeric regions. Due to its broad genetic base, this cowpea MAGIC population promises breakthroughs in genetic gain, QTL and gene discovery, enhancement of breeding populations and, for some lines, direct releases as new varieties.     

Novel application of quantitative immunoassays for screening seed globulins of cowpea varieties

Using antibodies raised in rabbits, radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA) are standardized for cowpea (var. Pusa Barsati) seed globulins. The RIA, when used to screen three stages of seed development, reveals that maximum globulins are detected at 28 days after flowering. When three different varieties of cowpea are assayed for their globulin content by RIA and ELISA, it is observed that the Bold Grain cowpea has the highest amount of related globulin as compared to two other varieties, namely Pusa Phalgun and Asparagus Bean.NCL Communication No. 3821.     

Phenolics Impart Au3+-Stress Tolerance to Cowpea by Generating Nanoparticles

While evaluating impact of Au nanoparticles on seed germination and early seedling growth of cowpea, HAuCl₄ was used as control. Seedlings of cowpea raised in HAuCl₄, even at concentration as high as 1 mM, did not show any suppression in growth. Accordingly, Au³⁺, despite being a heavy metal, did not alter levels of stress markers (viz. proline and malondialdehyde) in cowpea. Interestingly, cowpea turned clear pale yellow HAuCl₄ solutions colloidal purple during the course of seed germination and seedling growth. These purple colloidal suspensions showed Au-nanoparticle specific surface plasmon resonance band in absorption spectra. Transmission electron microscopic and powder X-ray diffraction investigations confirmed presence of crystalline Au-nanoparticles in these purple suspensions. Each germinating seed of cowpea released ∼35 nmoles of GAE of phenolics and since phenolics promote generation of Au-nanoparticles, which are less/non toxic compared to Au³⁺, it was contemplated that potential of cowpea to withstand Au³⁺ is linked to phenolics. Of the different components of germinating seed of cowpea tested, seed coat possessed immense power to generate Au-nanoparticles, as it was the key source of phenolics. To establish role of phenolics in generation of Au-nanoparticles (i) seed coat and (ii) the incubation medium in which phenolics were released by germinating seeds, were tested for their efficacy to generate Au-nanoparticles. Interestingly, incubation of either of these components with Au³⁺ triggered increase in generation of Au-nanoparticles with concomitant decrease in phenolics. Accordingly, with increase in concentration of Au³⁺, a proportionate increase in generation of Au-nanoparticles and decrease in phenolics was recorded. In summary, our findings clearly established that cowpea possessed potential to withstand Au³⁺-stress as the phenolics released by seed coat of germinating seeds possess potential to reduce toxic Au³⁺ to form non/less toxic Au-nanoparticles. Our investigations also pave a novel, simple, green and economically viable protocol for generation of Au-nanoparticles.     

Determination of Lignin and Tannin Contents of Cowpea Seed Coats

Tannins in the seed coats of cowpea cultivars interfere withthe determination of lignin by the acetyl bromide method butthe tannins can be removed by extraction with acetone:water(70:30) allowing a direct determination on the residue. Furthermore,the difference between the absorbance values determined by theacetyl bromide method before and after the removal of tanninscan be used as a measure of tannin content in cowpea seed coats.Copyright1995, 1999 Academic Press Cowpea, Vigna unguiculata, lignin, tannin, acetyl bromide     

Construction of a SSR-based genetic map and identification of QTL for domestication traits using recombinant inbred lines from a cross between wild and cultivated cowpea (<Emphasis Type="Italic">V. unguiculata</Emphasis> (L.) Walp.)

Cowpea (Vigna unguiculata (L.) Walp.) is a grain legume commonly grown and consumed in many parts of the tropics and subtropics. A genetic linkage map was constructed using simple sequence repeat (SSR) markers and a recombinant inbred (RI) population of159 individuals derived from a cross between the breeding line 524B, a California Blackeye, and 219-01, a perennial wild cowpea from Kenya. Out of 912 primer combinations predicted to amplify SSRs in cowpea, 639 reliably produced amplification products in PCR assays and 202 (31.6%) were polymorphic between the two parents. These polymorphic SSRs were used to construct a genetic map consisting of 11 linkage groups (LGs) spanning 677 cM, with an average distance between markers of 3 cM. Agronomic traits related to domestication (seed weight, pod shattering) were analyzed together with the genotypic data. Six quantitative trait loci (QTL) for seed size were revealed with the phenotypic variation ranging from 8.9 to 19.1%. Four QTL for pod shattering were identified with the phenotypic variation ranging from 6.4 to 17.2%. The QTL for seed size and pod shattering mainly cluster in two areas of LGs 1 and 10, facilitating the use of marker-assisted selection to eliminate undesirable wild phenotypes in breeding activities involving introgression of traits from wild germplasm. The generation of an SSR-based molecular map and additional trait-linked markers also contributes to the expanding tool kit available to cowpea breeders, especially in Africa.     

Studies on host-plant selection by the cowpea seed moth, Cydia ptychora

The Cowpea seed moth, Cydia ptychora, was able to complete its full life-cycle on a wide range of tropical grain legumes. In glasshouse tests, the adult moth showed oviposition p references between grain legume species but not between cowpea varieties, although there were differences in larval damage to the seeds of the latter. On cowpea, most eggs were laid on 8–10-day-old pods and also in particular micro-habitats; such behaviour was seemingly influenced by the mode of pod carriage. The moth undergoes no known diapause during the dry season in southern Nigeria and cowpea plants in a suitable condition are infested throughout the year. Wild leguminous hosts were not identified during the present study.     

豇豆优异种质综合评价

摘要 以60份具有早熟、矮秆、多荚、大粒、抗逆、抗病虫、高蛋白性状的优异种质为材料,在河北、河南与安徽进行多点农艺性状综合评价,评选出48份优异种质,其中34个品种达到一级优异种质标准.这些优异种质已结合鉴定繁种入国家中期库,以备科研与生产利用.     

Variation in responses to susceptible and resistant cowpeas among West African populations of Callosobruchus maculatus (Coleoptera: Bruchidae)

The cowpea seed beetle, sometimes also known as the cowpea weevil, Callosobruchus maculatus (F.), is a major pest of stored cowpeas (Vigna unguiculata Walpers) in West Africa. Control methods have included development of 'resistant' varieties as an environmentally benign alternative to insecticides, but there is concern over their effectiveness because of population variation among the insects and the possibility of adaptation overcoming seed resistance. Populations of C. maculatus from Nigeria, Ghana, Benin, and Niger, were used to examine variation in response to resistant and susceptible cowpea varieties at two geographical scales. Among seven Nigerian populations, there were significant differences in development times, the pattern of adult emergence, adult weights, and female fecundity when reared under identical conditions. Development in the resistant variety was retarded, produced higher mortality and lower adult weights. Significant interactions between variety and population were evident in terms of their effects on adult weight and development time; development times in the resistant variety were longer and emergences occurred over a longer period in some populations than in others. Population responses to resistant seeds were therefore unpredictable, but there was no evidence to suggest adaptation to overcome seed resistance within three generations. On a larger geographical scale, variation in performance was much greater and therefore, even less predictable. Mortality in resistant seeds was also higher among populations collected from outside Nigeria and may be explained by significant adaptation among Nigerian populations to previous release of resistant varieties. The findings are discussed in relation to understanding the extent of intraspecific variation in C. maculatus and its implications for future pest management.     

Evidence for Orthologous Seed Weight Genes in Cowpea and Mung Bean Based on RFLP Mapping

A well saturated genomic map is a necessity for a breeding program based on marker assisted selection. To this end, we are developing genomic maps for cowpea (Vigna unguiculata 2N = 22) and mung bean (Vigna radiata 2N = 22) based on restriction fragment length polymorphism (RFLP) markers. Using these maps, we have located major quantitative trait loci (QTLs) for seed weight in both species. Two unlinked genomic regions in cowpea contained QTLs accounting for 52.7% of the variation for seed weight. In mung bean there were four unlinked genomic regions accounting for 49.7% of the variation for seed weight. In both cowpea and mung bean the genomic region with the greatest effect on seed weight spanned the same RFLP markers in the same linkage order. This suggests that the QTLs in this genomic region have remained conserved through evolution. This inference is supported by the observation that a significant interaction (i.e., epistasis) was detected between the QTL(s) in the conserved region and an unlinked RFLP marker locus in both species.     

Striga seed-germination activity of root exudates and compounds present in stems of Striga host and nonhost (trap crop) plants is reduced due to root colonization by arbuscular mycorrhizal fungi

Root colonization by arbuscular mycorrhizal (AM) fungi reduces stimulation of seed germination of the plant parasite Striga (Orobanchaceae). This reduction can affect not only host plants for Striga, resulting in a lower parasite incidence, but also false hosts or trap crops, which induce suicidal Striga seed germination, thereby diminishing their effectiveness. In order to better understand these AM-induced effects, we tested the influence of root colonization by different AM fungi on the seed-germination activity of root exudates of the Striga hermonthica nonhost plants cowpea and cotton on S. hermonthica. We also tested the effect of AM fungi on the seed-germination activity of the Striga gesnerioides host plant cowpea on S. gesnerioides. Moreover, we studied whether mycorrhization affects the transport of seed-germination activity to above-ground plant parts. Mycorrhization not only resulted in a lower seed germination of S. gesnerioides in the presence of root exudates of the S. gesnerioides host cowpea but also seed germination of S. hermonthica was also lower in the presence of root exudates of the S. hermonthica nonhosts cowpea and cotton. Downregulation of the Striga seed-germination activity occurs not only in root exudates upon root colonization by different AM fungi but also in the compounds produced by stems. The lowered seed-germination activity does not appear to depend on the presence of seed germination inhibitors in the root exudates of mycorrhizal plants. The implication for Striga control in the field is discussed.     

Adaptation to a novel host modifies host discrimination by the seed beetle Callosobruchus maculatus

Females of the seed beetle Callosobruchus maculatus avoid adding eggs to seeds that already bear eggs. Geographical variation in this behaviour has been thought to depend on differences in host size. In populations that attack small-seeded legumes, only one or two larvae can develop within a seed, and females are especially adept at detecting and rejecting occupied (egg-laden) seeds. We performed a mass-selection experiment in which replicate lines of a population associated with a small host (mung bean, Vigna radiata) were either maintained on this host or were transferred to a larger host (cowpea, Vigna unguiculata) that can support several larvae per seed. After more than 40 generations, we estimated the strength of host discrimination by presenting females a choice of egg-free and egg-laden seeds, and by quantifying how uniformly females spread their eggs among egg-free seeds. Compared to females maintained on mung bean, females from cowpea lines were more likely to accept occupied seeds in choice tests. They also distributed their eggs less uniformly, especially when cowpea served as the test host. Cowpea lines thus evolved to resemble populations that have long been associated with the larger host. A separate study showed that weaker host discrimination in the cowpea lines was accompanied by a decline in larval competitiveness, which may have further relaxed selection for avoidance of occupied hosts. Our results demonstrate that switching to a novel resource can produce rapid and predictable changes in a fitness-related insect behaviour. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour     

Evolution of larval competitiveness and associated life‐history traits in response to host shifts in a seed beetle

Resource competition is frequently strong among parasites that feed within small discrete resource patches, such as seeds or fruits. The properties of a host can influence the behavioural, morphological and life‐history traits of associated parasites, including traits that mediate competition within the host. For seed parasites, host size may be an especially important determinant of competitive ability. Using the seed beetle, Callosobruchus maculatus, we performed replicated, reciprocal host shifts to examine the role of seed size in determining larval competitiveness and associated traits. Populations ancestrally associated with either a small host (mung bean) or a large one (cowpea) were switched to each other's host for 36 generations. Compared to control lines (those remaining on the ancestral host), lines switched from the small host to the large host evolved greater tolerance of co‐occurring larvae within seeds (indicated by an increase in the frequency of small seeds yielding two adults), smaller egg size and higher fecundity. Each change occurred in the direction predicted by the traits of populations already adapted to cowpea. However, we did not observe the expected decline in adult mass following the shift to the larger host. Moreover, lines switched from the large host (cowpea) to the small host (mung bean) did not evolve the predicted increase in larval competitiveness or egg size, but did exhibit the predicted increase in body mass. Our results thus provide mixed support for the hypothesis that host size determines the evolution of competition‐related traits of seed beetles. Evolutionary responses to the two host shifts were consistent among replicate lines, but the evolution of larval competition was asymmetric, with larval competitiveness evolving as predicted in one direction of host shift, but not the reverse. Nevertheless, our results indicate that switching hosts is sufficient to produce repeatable and rapid changes in the competition strategy and fitness‐related traits of insect populations.     

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.     

The Influence of Genotype, Temperature and Moisture on Seed Longevity in Chickpea, Cowpea and Soya bean

Seed of three chickpea (Cicer arietinum L.), three cowpea [Vignaunguiculata (L.) Walp.] and four soya bean [Glycine max (L.)Merr.] cultivars were hermetically stored for up to 2 yearsin various constant environments which included temperaturesfrom —20 to 70 °C and moisture contents (fresh weightbasis) from 5 to 25 per cent. In all cases the survival curvescould be described by negative cumulative normal distributions.The longevity of the various seed lots differed but the valueof the standard deviation (the reciprocal of which gives theslope of the survival curve when percentage germination is transformedto probit) was the same for all cultivars within a species whenstored under similar conditions. Within each species the relativeeffects of moisture and temperature on longevity did not differsignificantly between cultivars. In all three species therewas a negative logarithmic relationship between seed moisturecontent and longevity, but the relative effect of moisture contentdiffered between the species: differences in the longevity ofsoya bean seed as a function of moisture content were less thanfor either cowpea or chickpea. The relative effect of temperatureon seed longevity did not differ between the three species,and the seed of all three species showed increasing temperaturecoefficients for the change in rate of loss of viability withincrease in temperature. The complete pattern of loss in viabilityin all three species can be described by a single equation whichwas developed for barley and has also been shown to apply toonion seed. The constants applicable to the three grain legumeshave been calculated so that it is now possible to predict percentageviability of any seed lot of these species after any storageperiod under a very wide range of storage conditions. Cicer arietinum L., chickpea, Glycine max (L.) Merr., soya bean, Vigna unguiculata (L.) Walp., cowpea, seed longevity, seed storage, moisture content, temperature