The genetic, morphological and physiological evaluation of African cowpea genotypes

[摘要] English: Cowpea (Vigna unguiculata) is a staple food crop of significant economicimportance worldwide. Cowpea is valued for the high vitamin and mineral contentpresent in young leaves, pods and seed. The crop is unique in that it providesfood, cash and fodder. However, cowpea production is limited by numerous biotic(insects, microbial and fungal diseases, and other pests) and abiotic (hightemperature, drought) factors. Because of its widespread use, numerousinitiatives have been undertaken to improve various agronomic and nutritionaltraits of cowpea. Analysis of genetic relationships among and within crop speciesis a prerequisite for any genetic improvement and central to successful breedingprogrammes. This can be achieved through characterisation of germ plasm eitherusing morphological, biochemical or DNA markers. Fifteen qualitativemorphological traits and 12 quantitative morphological traits were used in thisstudy to group 20 cowpea accessions from three different African regions intoclusters according to their genetic distance, in order to quantify the extent ofphenotypic and genetic diversity among these accessions and identify desirablegroups that could be utilised in breeding programmes.The results showed a relatively high level of dissimilarity among the accessionsfor most of the morphological traits analyzed, especially for accessions fromdifferent countries. This indicates better possibilities for genetic improvement ofthe crop through selection and cross breeding. However, a very high level ofsimilarity was revealed between many accessions from the same region for mostof the characters studied. Makueni, Gacaga, M.66, Kamurugu 1, Bafoussam 1,MTA22, AS-94 and Okhalweni were the group of accessions different from theother accessions for most of the traits studied and can therefore be used forcowpea improvement programmes through cross breeding.Drought is a serious environmental stress affecting cowpea production throughoutthe world. Twenty cowpea accessions were characterised for drought toleranceusing three different screening methods (pot screening method, cell membranestability and stomatal behaviour).For the pot screening method, seeds were planted in pots in the glasshouse atthe University of the Free State. After germination plants were kept well watered,until they had completed the early development stage, after which 500 ml of waterwas given per day per pot up to the flowering stage when the watering wasterminated. After 21 days, each plant was scored using the International Board forPlant Genetic Resources (IBPGR) descriptors for cowpea. The results showed awide range of drought tolerance among the studied accessions and this suggeststhe possibility of breeding cowpea drought tolerant cultivars. Bafoussam 1 andBafoussam 2 were found to be highly drought tolerant and could be valuablematerials for drought tolerance improvement in cowpea.Drought tolerance potential of the accessions was also characterised based ontheir ability to close their stomata, and the number of stomata per unit leaf areaunder water deficit conditions. The results showed that cowpea (Vignaunguiculata) in Kenya, South Africa and Cameraan were rich in drought tolerantaccessions. The general trend showed that accessions from the humid areas ofKenya and Cameraan had a relative high stomata density and also had thelowest ability to regulate the degree of their stomatal opening under droughtstress. Meanwhile accessions from the arid and semi-arid areas of South Africa,Cameroon, and Kenya did show a relatively good ability to regulate the degree oftheir stomatal opening under the imposed drought stress and had a relatively lowstomatal density. Materials with good drought tolerance included Bafoussam 4,MT22, AS-94, Balen, Hluhluwa, Mpenbeni, Bafoussam 5 and K.80. However,Bafoussam 4 was the only accession found to have both a low stomatal densityand a good ability to regulate the degree of its stomatal opening under theimposed drought stress. Therefore it was not possible to confirm any correlationbetween the ability to regulate the degree of stomatal opening and stomataldensity among the accessions studied.The results of the cell membrane stability test also showed that there wassignificant variation among the accessions for electrolyte leakage. Kamurugu 2,Ken-Kunde, Kasuku, and K.80 had the highest percentage level of injury andwere found to be the most susceptible to drought stress, when the accessionswere exposed to simulated osmotic stress. Bafoussam 2, Okhalweni, andBafoussam 4 had the lowest percentage level of injury and were found to be theleast susceptible to drought stress.The results of the three techniques seemed to be promising in discriminating theaccessions tested for their drought tolerance ability as presented in Appendix.However, extensive field screening is required to confirm the results obtained inthis study

[发布机构] University of the Free State