Tracking agronomic diversity in land races of cowpea [ Vigna unguiculata ( L . ) Walpers ] collected from Pakistan

Seventy one accessions of Vigna unguiculata (L.) Walpers belonging to 31 districts of three provinces across Pakistan were characterized. High variation was recorded in plant height, branches per plant, pods per plant, grain yield, biomass and harvest index. It has been derived from current studies that migration of germplasm or seeds were observed across various areas that might be due to frequent exchange of grains, between different markets and transportation without any provincial laws implementations. High phenotypic diversity indicates the potential land races collected from farmer’s field might be utilized for crop improvement programs viz., 27028, 27029, 27038, 27040, 27042, 27047, 27083 and 27097. Phenotypic diversity analyzed within each district indicated the possibility of migration of landraces at one hand and on the other hand variation appears attributable to different districts without influence that how frequently area was explored. Intra and inter-specific variances deviated from central tendency depicted on the map of Pakistan shall be proved beneficial for future germplasm collectors to devise strategy for collecting genes of interest. New expeditions may be conducted in the main cowpea growing areas with focusing geographically and ecologically distinct areas, rather than fields closer to motorable roads.

Despite its importance, the production of cowpea ranges from half to one tonne per hectare that is very low as compared to its potential [7].It is cultivated on marginal soils in Pakistan, especially in NWFP and Northern Punjab on an area of 16.9 thousand hectares with an annual production of 7.8 thousand metric tonnes [8].To cater biodiversity impact for socioeconomic values is based on indigenous genetic resources whereas information about geobotanicals is pre-requisite for collecting highest diversity and to devise a fruitful strategy for future collections [9][10][11].Intra and inter specific variation played significant role in the improvement of agrobotanical traits.Rate of loss of biodiversity have been studied throughout the world and efforts have been made to preserve the existing biodiversity by means of gene banks, ex-situ conservation at farmer's field, world herbaria and botanical museums by breeders and biologists.During last three decades eighty cowpea accessions have been collected and stored for short duration (5-10 years) at 5 o C, medium term (15-20 years) at 0 o C and long term (more than 50 years) at -20 o C.These are suggested to be used for evaluation, characterization and planning future strategies for further collections.The cowpea is a neglected crop having potential to become more useful as its genetic diversity is preserved under CBD (Convention on Biological Diversity), whereas major crops like wheat, rice, chickpea and maize have been genetically eroded due to evolution of new cultivars.The aim of the current study was to uncover intra-accession variability occur in collections of 31 districts of three provinces with respect to agronomic traits.It will enable for developing future strategy to preserve high variation with respect to the needs of the growing population.

Materials and methods
Seventy one (71) landraces, collected predominantly from farmers' fields in 31 districts of three provinces were characterized for agronomic traits to choose high yielding landraces and to make future germplasm collection strategy.During 2013, 71 land races were planted in an augmented design with three replications in the mid of October.Ten single plants from all the accessions were sampled at random, tagged, harvested and threshed individually.Progenies of these individual plants were sown under field conditions during October 2014 and harvested in March 2015.Bed length was maintained at 4 meter, whereas two rows of each accession were planted with 1 meter intra and inter row distance.Plant to plant spacing was kept as 15 cm.After 10 rows, a local check was repeated.Pesticides were sprayed to protect the crop from pests especially white fly (Bemisia tabaci Genn.), a vector for Mungbean Yellow Mosaic Virus (MYMV).Data was recorded following IPGRI descriptors for Vigna unguiculata (IBPGR 1983).Agronomic traits including plant height (cm), branches/plant (number), pods/plant (number), grain yield (g) and biomass yield (g) were recorded.Harvest index was calculated as grain yield over biomass in percentage.Data recorded were then subjected to statistical analysis by means of variance to find intra and inter-specific variation along with average agronomic performance for individual accessions with deviation from central tendency using the methods provided by Steel and Torrie [12].Further, variance was derived from summery of statistics and then presented as percent of mean for all characters.Aggregated variances were then calculated for each set of accession, as collections were made from 31 districts.Standard deviation from aggregated variance were taken as an indicator for genetic biodiversity which are represented as in percentage plant samples differed i.e., from none to 100 percent and consequently depicted on the map along with total number of accessions.

Results and discussion
Average data in 71 accessions collected from 31 districts of Pakistan along with standard error and deviation from means for all the six traits viz., plant height/plant, branches/plant, pods/plant, grain yield/plant, biomass/plant and harvest index/plant is presented in Table 1.It is obvious from the results that almost all the characters exhibited a wide inter-accession range which reflecting an idea to choose accessions for high genetic potential.Although variation within accessions was statistically insignificant for most of the accessions but higher magnitude for variation that is reflected in deviation from central point indicated the presence of land races or heterogeneous mixture of homozygous lines (Table 2).Five accessions, 27009, 27029, 27038, 27083 and 27097 gave high yield along with high intraaccession variation that could be evaluated to isolate superior plant progenies within these accessions.Further it could help in identifying plants to be used in hybridization for cowpea improvement.For strengthening gene pool one way is to collect material from geographically diverse origins from proposed centers of diversity in case of individual samples.Authentic samples from the complete geographical range of the crop species can help maintaining conservation of co-adapted genes [13][14][15].Cowpea is an important summer pulse crop and widely cultivated under rainfed areas.Current collection was made from different areas of the country with more emphasis have been provided to those areas which were closer and approachable to motorable roads, that is also indicated in intra accession variance.One of the reasons might be strategy to provide first priority to those areas which are easily approachable and more prominent to genetic erosion and have adaptability to accept advanced breeding material near major towns and cities.Alternatively to gather maximum diversity, it is important to plan and explore those areas which are not explored earlier, preferably like interior territories, remote areas, cross border and mountainous areas.On the basis of correlation results, pods were observed as the best basic criteria for selection in almost all the collection districts except material from Gujrat, Jhang, Mansehra, Muzzafargarh and Pakpatan (Table 2).This might be due to less presentation of area for diversity or uniformity of germplasm collected from these areas.The accessions collected from the districts of Chakwal, Dir, Faisalabad, Jehlum, Lahore, Loralai, Muzzafargarh, Okara, Sheikhupura and Swat were observed low for variance that indicated less representation of these areas although high number of accessions were collected from some of these districts (Figure 1).It could be explained as those maximum accessions might be pure lines with common ancestors.Another threat is exchange of material is frequent within and between various districts which violates seed quarantine laws.   of Sindh but no representation is available in the gene bank that is needed to explore this area prior to genetic erosion due to introduction of superior cultivars of cowpea or other alternative crops.This material is expected to provide some good lines tolerant to drought.Additionally it is suggested from current findings that areas with rich biodiversity of cowpea should be explored systematically and efforts should also be concentrated on geographically and ecologically distinct areas as possible, rather approachable sites only.Remote areas and provinces which have more genetic resources to focus required number of expeditions and collection missions with the involvement of local community who are the ultimate stake holders as also been advocated for tetraploid wheat [24,25].Further building of genetic stocks required expeditions of those areas where genetic erosion is expected like in cowpea along with the locations from where existing genetic diversity has not yet gathered is recommended to explore for genepool establishment and starting successful breeding program [26].Current work could help in devising future strategy for cowpea germplasm collections across the country.

Conclusion
Cowpea is a protein rich food crop which is recommended for not only marginal lands but for areas with low irrigation.There is need to conserve and preserve cowpea genetic resources on comprehensive basis before they might be lost due to various environmental factors.Small scale crop specific genetic resources conservation station is also suggested to be establish in the remote areas to save unique genes of interest.
Introduction Cowpea (Vigna unguiculata (L.) Walp) is an underutilized crop of tropical Africa, Asia, Central and South America [1, 2].The crop is well adapted to diverse environmental conditions and can be easily grown in poor soils and semi arid regions [3].It is rich in protein contents ranging from 22.5 to 25.6 %.Number of vitamins and minerals are present in cowpea that makes it vital for human and animal dietary needs [4-6].