Genetic diversity among bambara groundnut accessions Essay
Bambara Indian potato accessions, native to African states, are evaluated for their familial diverseness to place of import forms for preservation and use bing familial resources.
Accessions obtained from the International Institute of Tropical Agriculture germplasm aggregation were analyzed based on 28 quantitative, 12 qualitative traits and DArT molecular markers ( diverseness arrays engineering ) . The seed pattern diverseness for a sum of one 1000, nine hundred and 73 accessions was besides considered. The highest diverseness indices and happening of form provinces in the Nigerian/Cameroon aggregations, relative to other parts confirmed earlier studies proposing Northern Nigeria and Northern as the harvest ‘s Centre of beginning. Some of the Cameroon/Nigeria accessions besides had unfastened growing wont and thicker shells characteristic of the wild type, bespeaking the cultivated type in this part is closer to the wild signifier. Population construction analysis based on the familial polymorphism by the DArT markers and phenetic tree based the forms, uncover similar tendencies indicating to Nigerian/Cameroon as Centre of beginning. Changing grades of sensitiveness to photoperiod was established in this germplasm, supplying chances for betterment of harvest seed output, since photoperiodic ordinance of its phenology must be good understood to capture the optimum daylenght in relation to the sowing season, blooming and fruit set. Better apprehension of the organisation of the familial diverseness from this survey will finally advance their direct public-service corporation in engendering for improved lines.
Bambara Indian potato [ Vigna subterranea ( L. ) Verdc. , syn. Voandzeia subterranea ( L. ) Thouars ] , a pulsation with subterraneous fruit-set, is cultivated by smallholders over much of semi-arid Africa ( Linnemann and Azam-Ali 1993 ) and found intercropped with cereals, root and tuber harvests. Although mean outputs ( 650 to 850 kgha-1 ) are less than other leguminous plants ( Stanton et al. 1966 ) , under predominating less favourable conditions, such as small rainfall and sterile dirt, it yields better ( National Research Council 1979 ) . In much of Africa, it is the 3rd most of import leguminous plant after Indian potato and black-eyed pea ( Sellschop 1962 ) .
As a preferable nutrient harvest of many local people, it is a good addendum to a cereal diet and nutritionally superior to other leguminous plants ( Azam-Ali et al. 2001 ) .Research workers interested in the beginning of bambara ( household: Leguminosae, subfamily: Papilionoideae ) all agreed that the harvest originated from the African continent. Suggestion by Jacques Felix ( 1946 ; 1950 ) pointed to Sudan as the Centre of beginning based diverse seed pattern diverseness at that place. Rassel ( 1960 ) supported this hypothesis by mention to old Arab paperss from the ocean trip of Ibn Batouta to Sudan dated 1380 ( Mac Guckin De Slane 1843 ) . De Candolle ( 1886 ) and Stuhlmann ( 1909 ) besides stated that Schweinfurth had found the harvest turning wild on the Bankss of Nile between Chartoum and Gondokoro in Sudan. However, a wild phase and Centre of beginning could non be confirmed in Sudan ( Harms 1912 ) .
Dalziel ( 1937 ) found bambara Indian potato in its echt wild province in the North Yola state of Nigeria and reported another determination by Ledermann near Garoua in northern Cameroon. Subsequently, Hepper ( 1963 ) undertook an expedition to West Africa and suggested the beginning between Yola and Garuoa, as antecedently supposed. He proposed a new terminology and treated the signifiers as assortments ( V. subterranean volt-ampere. subterranea and V.
subterrranea var. spontanea ) . Analysiss of the seed pattern diverseness within the big aggregation at IITA by Begemann ( 1988 ) showed that samples collected less than 200km from the putative Centre of beginning, between Yola and Garoua, systematically showed greater seed-pattern diverseness. Characterization surveies by Goli et Al. ( 1997 ) revealed the frequence of the seed form provinces for 1384 accessions from the IITA ( International Institute of Tropical Agriculture, Ibadan ) aggregation but survey on the geographical distribution was non considered.To engender qualities of opposition, adaptability, high output and better alimentary value into harvests, beginnings of familial fluctuation are needed. Old landraces are being displaced often by improved assortments taking to a familial simplification in traditional cropping systems ( Anchirinah et al. 2001 ) .
Together with publicity of modern assortments, factors such as a displacement to monoculture, human colonies busying the home grounds of harvest relations, land glade and the extinction of tribal civilizations account for the familial eroding. Consequently, the preservation of familial diverseness is important to engendering plans.The survey aims to advance preservation of the familial resources and finally their direct public-service corporation to engendering for improved lines through a better apprehension of the organisation of the familial diverseness and variableness. Based on molecular marker analysis and phenotypic forms, Nigeria and Cameroon was validated as the Centre of beginning every bit good as demoing the highest phenotypic diverseness.
Material and methods
Plant stuffOne 1000, one hundred and 73 accessions of bambara Indian potato were obtained from the genebank aggregation at IITA.
All 1173 accessions were sown on the 15th of April 2002 in Ibadan and scored for the figure of yearss from seeding to the first blossoming ( DFF ) and 50 % blossoming ( D50 ) . From this test, 539 accessions were scored for DFF, while merely 461 of these accessions were scored for D50. For comparing, informations for the same set of accessions was obtained from a test at Ikenne, planted on the 3rd of December 1986. A subset consisting 124 accessions were selected for farther survey based on their beginning of beginning, latitude and longitude, growing wont and twenty-four hours to adulthood so as to entree their diverseness, while a subset of the 124 accessions consisting 40 accessions were genotyped utilizing a Diversity Arrays Technology ( DArT ) . The seed pattern diverseness was evaluated on all the accessions ( 1973 ) bing in the germplasm aggregation ( Table 1 ) .Experimental site and conditionsThe experimental site at IITA, Ibadan, is located within the passage zone between the humid and sub-humid tropical climes surrounding to its South, and a dry Savannah zone bordering to its North.
It lies within latitude 70 30?N and longitude 30 54?E on an lift of about 160m. The bimodal rainfall distribution extremums in June and September and separated by a period of lower precipitation in August, while December through to February constitutes the major prohibitionist season ( Moormann et al. 1974 ) . The mean one-year rainfall exceeds 1250mm and the annual average temperature is 26.60C ( IITA 1984 ) , with a minimal temperature scope between 210C and 230C, while the upper limit is between 280C and 340C. Radiation is about 5285 MJ/m2/year, while average comparative humidness is in the scope of 64-83 % . The dirts at IITA are classified as ferrous luvisols harmonizing to the FAO categorization ( Moormann et al.
1974 ) . The longest daylength at the latitude 7 & A ; deg ; 30’N is estimated at 12 hours 30minutes and the shortest daylength at 11hours 30minutes. The daylength is longest on the 21st or 22nd twenty-four hours of June and the shortest daylength on the 21st or 22nd twenty-four hours of December.At seeding in April and at the initial phase of turning of the immature workss, the field in Ibadan was irrigated with overhead sprinklers while the harvest sown in December 1986 in Ikenne was wholly dependent on overhead sprinkler irrigation till the harvests were harvested.
Based on extrapolation from the findings of Doku and Karikari ( 1971a ) , the extremum of the blossoming of the harvest planted in April coincides with the longest daylength in June while the extremum of blossoming of the harvests planted in December should be at the terminal of January when the daylength was about the shortest during the twelvemonth.Phenotypic DataThe methods of hiting for 40 of the traits were based on forms for bambara Indian potato published by IPGRI et Al. ( 2000 ) ( a alteration of the original IBPGR, IITA and GTZ publication, IBPGR et Al. 1987 ) , while 7 extra forms ( bloom coloring material, banner/flag petal length, flying length, spread between the streamer and flying tips, ratio of streamer to flying lengths, peduncle length, and pedicel length ) were included. A sum of 28 quantitative and 19 qualitative traits were used in this survey.Deoxyribonucleic acid extraction and DArt Marker analysis& A ; lt ; DNA extraction, DArT analysis, DArT markers and hiting & A ; gt ;Statistical analysisThe plan STRUCTURE version 2.3.3 ( Pritchard et al.
2000 ) was used to prove the hypotheses of K = 1 to K = 6 i.e. 1 to 6 populations utilizing an alloy theoretical account, a burn-in stage of 1 ten 104 and a sampling stage of 5 ten 104 replicates. The optimum division of the population in to subpopulations was determined when the chance of K was really little for K less than the appropriate value ( efficaciously nothing ) and so more-or-less tableland for larger K ( Pritchard et al. 2009 ) .
The construction analysis was performed at K = 4, a burn-in stage of 1 ten 105 and a sampling stage of 5 ten 105 replicates.The agencies comparing among the 124 selected accessions was performed for quantitative traits, while frequences of qualitative form provinces were specified for each part. The Shannon-Weaver ‘s diverseness Index ( , where pi is the proportion of accessions for a peculiar form province ) ( Shannon and Weaver 1963 ) was calculated to compare diverseness among parts. The diverseness index takes into history the proportion of each province, every bit good as the copiousness of accessions. The quantitative traits were correlated against each other, while the chief constituent analysis was performed to supply information on the comparative importance of forms for germplasm word picture. The information was analysed utilizing the SAS Version 8.
0 ( 2000 ) . The Hierarchical bunch of 40 accessions was based on the UPGMA ( Unweighted pair-grouped method with arithmetic averaging ) method utilizing the NTSYS-pc package bundle version 2.02j.
Between the daylength continuances from the two seasons, differences ( DIFF ) computed from the yearss to first blossoming ( DFF ) was used to divide the accessions into categories. T-test process was used to compare the mean of the differences in the mated observations from the two tests ( equal sample sizes and had a normal distribution ) . The group comparison t-statistic was computed based on the premise that the discrepancies are unequal ( Cochran and Cox 1950 ; Satterthwaite 1946 ) . The assurance bounds were besides computed harmonizing to Cochran and Cox ( 1950 ) estimate ; an equal tailed and uniformly most powerful indifferent assurance intervals.
The assurance bound for the standard divergence established how much going off from the mean could be permitted within experimental mistake beyond which indicated a response to alter in daylength continuance. An analysis of discrepancy was performed on values ( DIFF ) generated from the braces of DFF and D50 between the two tests and between the two blossoming parametric quantities. The informations sets were analyzed with SAS Version 8.0 ( 2000 ) .
Familial diverseness, phenetics and population StructureBased on a subset of 40 accessions and 544 DArT markers, 4 subpopulations were delineated with each of the subpopulations incorporating accessions from West Africa ( Fig. 1 ) .
However, the East/South African accessions were restricted to subpopulation III, constellating with accessions from Cameroon. This indicates common allelomorphs between a subset of the Cameroon and the East/South African accessions and that the East/South African accessions were likely derived from around this part in Cameroon. Merely one accession from Madagascar was a consequence of hybridisation between the subpopulation III and I ( lone accessions from Cameroon ) , with about equal part from both subpopulations.Even though the phenetic tree does non needfully reflect evolution or evolutionary relationship, the tendency observed in the population construction analysis above was besides mirrored in the phenetic tree ( Fig. 2 ) , which is based on the overall similarity between accessions utilizing the phenotypic forms. Based on the phenetic tree, all the East/South African accessions clustered together with accessions from Nigeria and Cameroon.Quantitative traits of bambara Indian potato accessionsRelatively, the Cameroon/Nigeria and West African parts ( Republic of Benin, Burkina Faso, Cote d’Ivoire, Ghana, Gambia and Mali ) had higher diverseness indices for the quantitative traits ( Table 2 ) , with the norm of the diverseness indices in Cameroon/Nigerian part transcending that of any other parts.
The East African ( Kenya and Tanzania ) accessions were the least diverse i.e. low diverseness indices for most of the forms and lowest norm of the diverseness indices.Blooming in Cameroon/Nigeria, West and East African accessions were earlier than North/Central ( Sudan and Central Republic of Africa ) and South African ( Madagascar, Zambia and Zimbabwe ) accessions during the mid-April planting.
Flowers of North/Central and South African accessions were smaller. South and East African accessions comprise of bigger workss reflected in larger works spread, works tallness, terminal cusp length and petiole length, while Cameroon/Nigeria, North/Central and West Africa accessions had smaller workss. The East and South African accessions were characterized by low 100-seed weight, cod length and cod breadth. Average output values of seeds for Cameroon/Nigerian, West and North/Central African accessions at 457.22 kgha-1, 333.
52 kgha-1 and 245.27 kgha-1 exceeded that of South and East African accessions at 75.31 kgha-1 and 27.86 kgha-1 severally ( Supplementary Table 1 ) .Three constituents generated from the chief constituent analysis explained 39.29 % of the entire fluctuation contributed by all quantitative traits ( Table 3 ) . The streamer length, spread between streamer and flying tips, ratio of streamer and flying lengths, peduncle length, petiole length, works diameter, works tallness, 100-seed weight, output, seeds per cod, yearss to first blossoming and twenty-four hours to adulthood all had a high burden in the first constituent which accounted for 18.
06 % of the entire fluctuation. The 2nd constituent accounts10.75 % of the entire fluctuation, while the 3rd constituent accounted for 10.48 % of the entire fluctuation. The traits with systematically high burdens on more than one of the chief constituent will be really appropriate for the word picture bambara Indian potato germplasm since they are better at defining accessions.
Qualitative traits of bambara Indian potato accessionsFor the qualitative traits, the greatest diverseness was besides found in the Cameroon/Nigerian, West African and North/Central African parts ( Table 4 ) . Again diverseness in the East Africa part is shown to be least with the lowest diverseness index. On the overall, the Cameroon/Nigeria, West and South Africa parts were observed to hold more happenings of the form provinces than the North/Central and East Africa parts.Seed pattern diverseness in bambara Indian potato accessionsCollections from the single states have the unit of ammunition and egg-shaped seed form except for South Africa and most states in the East Africa ( Burundi, Ethiopia and Kenya ) . Most West African states ( excepting Republic of Benin and Togo ) , South African states ( Madagascar, Swaziland, Zambia and Zimbabwe ) and Central Republic of Africa had high proportions of both province.
West African accessions had more fluctuation in their seed episperm form ( particularly Burkina Faso, Cameroon, Ghana, Nigeria and Togo ) except in Cote d’Ivoire where the frequence was low ( Supplementary Table 2 ) . The seed episperm pattern fluctuations in Central Republic of Africa and some South African states were besides high. The highest fluctuations of form provinces ( Fig. 3 and 4 ) were observed in Nigeria aggregations followed by Ghana, Cameroon, Burkina Faso, Central democracy of Africa and Zimbabwe. Collections from the Cameroon/Nigeria showed the greatest diverseness index in all seed characters except for the land colour of the episperm ( Supplementary Table 3 ) .
Blooming response to fluctuation in photoperiodComparison of informations from the two tests utilizing the t-test process indicated that informations from the two seasons were significantly different ( p ? 0.0001 ) . The lower and upper assurance bounds for DFF are 2.24 and 2.44 severally, while those of the D50 are 4.00 and 4.
35 severally ( Auxiliary Tables 4 ) . Hence, any DIFF value ( i.e. difference between DFF or D50 values between the two seasons ) outside these assurance bounds were attributed to the response due to the fluctuations in daylength instead than experimental mistake ( Auxiliary Tables 5 and 6 ) .After hiting 539 accessions for DFF, 127 accessions were sensitive to alter in daylength continuance, while 412 accessions were insensitive. Of the 461 accessions scored with D50, 134 accessions were sensitive, while 327 accessions were insensitive. Sing the 461 accessions common to both DFF and D50 tonss, 337 accessions had a similar response to fluctuation in daylength, while 124 accessions were inconsistent in their response ( i.e.
42 sensitive accessions scored for DFF turned out to be insensitive when scored for D50, while 83 sensitive accessions scored for D50 turned out to be insensitive when scored for DFF ) and were frequently observed to hold a low sensitiveness ( low DIFF ) to alter in daylength.None of the daylength continuances recorded prevented blossoming ( qualitative long-day or short-day response ) , instead, a quantitative long twenty-four hours and short twenty-four hours was observed. Delayed response to blooming due to the short daylength was observed in every bit much as 100 accessions ( quantitative long twenty-four hours ) ; nevertheless, they flowered early under the long daylength continuance. Quantitative short daylength accessions were found to outnumber the quantitative long twenty-four hours accessions ( Auxiliary Tables 7 and 8 ) . Changing grades of sensitiveness to daylength continuances were established among the quantitative long twenty-four hours and short twenty-four hours accessions, while accessions with a greater grade of sensitiveness to daylength continuances were observed to hold been collected farther off from the equator.The beginning of fluctuation was observed among the state of beginning and between the DFF and D50 for quantitative long twenty-four hours and short twenty-four hours accessions.
For the quantitative short twenty-four hours accessions, no important difference existed between the DFF and D50 except for the DIFF values of 4, 7 and 9 yearss. Merely the 3 yearss difference was significantly different for the quantitative long twenty-four hours accessions. Among the states of beginning, the 12 and 5 yearss differences were significantly different for the quantitative short and long twenty-four hours accessions severally.
We report on the proof of the Centre of beginning for bambara Indian potato utilizing molecular markers. This is peculiarly interesting, sing that bambara Indian potato ‘s generic name was changed from Voandzeia into Vigna, the same genus as Cowpea ( Verdcourt 1980 ) , since no morphological character of importance separated Voandzeia from Vigna. Although controversial, it is suggested that black-eyed pea, cultigroup Unguiculata, had been introduced from West Africa to East Africa and Asia ( Ng and Marechal 1985 ) .
Similarly, Hepper suggested that bambara Indian potato was introduced to East Africa from West Africa ( Hepper 1963 ) .Based on Vavilov ‘s theory ( Vavilov 1926 ) , the Centres of beginning are considered the country of greatest diverseness. Diversity survey based on the phenotypic traits considered support the hypothesis of Hepper ( 1963 ) , which suggested the country between Yola ( Northern Nigerian ) and Garuoa ( Cameroon ) as Centre of beginning for bambara Indian potato. The distribution of accessions from the population construction analysis, phenetic tree and the diverseness indices of the quantitative and qualitative traits reveal the greatest diverseness in the Cameroon/Nigeria aggregation. For diverseness in seed forms of 1973 accessions, the Cameroon/Nigeria part was once more evidently the most diverse.Doku and Karikari ( 1971b ) studied the development of bambara Indian potato as a species and concluded that the cultivated 1s originated from the wild signifier ( Vigna subterranean volt-ampere.
spontanea ) and evolved through series of gradual alterations i.e. exchanging from unfastened to bunch growing wont, from outbreeding to inbreeding, and a decrease in shell thickness. From the informations gathered from this survey, some Cameroon/Nigerian accessions are characteristic of the wild type since it ‘s the lone part that consist of thicker shells and unfastened growing wont accessions. The Centre of beginning in the part has been verified by Dalziel ‘s ( 1937 ) aggregations that contain many wild relations, hence, the beginning of dominant cistrons.With bambara Indian potato ‘s low mean outputs, runing from 650 to 850 kgha-1 ( Stanton et al.
, 1966 ) , TVSu 23, 25, 32, 86, 231, 360, and 405 showed potencies for high outputs ( i.e. 1362.
33 kgha-1, 1019.48 kgha-1, 972.16 kgha-1, 1025.74 kgha-1, 1189.50 kgha-1, 2473.38 kgha-1, 1983.
10 kgha-1 severally ) . Their seed sizes were comparatively big with bunchy or semi bunchy growing wonts, while susceptibleness to Cercospora was comparatively low. Information to heighten and cut down cost in germplasm word picture was provided by the comparative importance of traits that have consistent high burdens in the chief constituents ( Days to first blossoming, 50 % blossoming and adulthood ; streamer, flying and peduncle lengths ; ratio of streamer to flying lengths ; works diameter, works tallness and output ) .We besides report on the consequence of photoperiod on growing and development of bambara Indian potato considerable the relationship to effects on seed output as shown in photoperiod sensitive field harvests such as Soybean ( Kantolic and Slafer 2007 ) . Apparently, photo-regulation of development provides the works with flexible mechanism to accommodate to fortunes that create seasonal fluctuations in the length of the turning period. Though preliminary observations about the photoperiod insensitiveness of bambara Indian potato accessions have been reported, other surveies show a hold in blossoming and a strong consequence on fruit set ( Linnemann 1991 ; 1993 ) .
The oncoming of blossoming, procedure of blossoming, oncoming of podding and advancement in cod growing have been good studied and shown to be impeded, with a stronger consequence on podding than on blossoming ( Nishitani 1988 ; Linnemann 1993 ) .Our preliminary observations on the insensitiveness of most bambara Indian potato accessions to daylength in this survey hold with findings by Linnemann ( 1991 ) and Nishitani ( 1988 ) . In contrast to old surveies, response to daylength fluctuation from the larger sample size in this survey implies that insensitiveness is a dominant trait within the population, with less than 30 % of the accessions been quantitatively sensitive to long and short daylengths. This is similar in wheat genotypes, where insensitiveness is dominant, while assorted grades of sensitiveness to short daylength were observed in some Chinese wheat genotypes ( McIntosh et al.
1995 ) . Apart from the quantitative short twenty-four hours behaviours found and supported by earlier consequences, a different photoperiodic behavior of quantitative long twenty-four hours was besides revealed ( i.e. delayed response to blooming due to short daylength ) . Likewise, broad scopes of fluctuations have besides been observed in the flowering response of rice to photoperiods ( Vergara and Chang 1985 ) . The long twenty-four hours and short daylength accessions that are more sensitive to alter in daylength are likely adapted to the short and long daylength continuances that occur farther off from the equator. The familial and environmental control of flowering clip is a cardinal determiner of the version of harvests to the environment. The ability to foretell the clip of blooming and harvest for optimum output is important to fiting harvest germplasm to the resources available for harvest growing within a given cropping system and to avoiding nerve-racking environments.
Since most of bambara Indian potato accessions are daylength insensitive, most of the accessions can be adapted to different ecotypes with fluctuations in daylength at anytime of the twelvemonth.