Keyword

Cytogenetic, intra-varietal, exotic, asymmetrical, phylogenetic

Introduction

With more than half of 2015, the MDGs target year already spent, one agenda that is consistently featuring in the many post target year summits is appraisal of the degree of achievement of the set goals and charting the way forward. For the first goal of reducing hunger and malnutrition by half this year, much still needs to be done to meet the target.. Crop improvement, the processes involved in creating crop varieties with higher yields and better qualities, is strategic to reaching the target. Crop improvement is a continous process as every crop can be made to do better than it is currently doing given the right input and expertise

For Capsicum, one of the most important vegetable-cumspice crops valued for their taste, aroma and pungency, the future is bright. The advances made in the improvement of the crop as witnessed in advanced agricultural economies give credence to the proposition that the indigenous varieties of Africa can do better[5,10,13]. With sustained effort at improvement of our indigenous varieties would usher in an era when African countries would go for their fair share of the multimillion United States dollars which this crop is worth in the global commodity market For purposeful improvement of this crop, as any other crop, breeders would require information on their cytological and chromosomal status as well as other aspects of their karyological profiles. Generating these and other relevant data is the main aim of this investigation.

Material and methods

Ripe fruits of Capsicum annuum var. paprika were obtained from four rural locations spread around Owerri. These locations were Uratta in Owerri north local government, Obinze and Irette (in Owerri west), Akabo in Ikeduru local government area. These fruits were certified at the Herbarium Laboratory of the Department of Plant Science and Biotechnology, Imo State University Owerri. Seeds were extracted from the ripe fruits and air-dried. The seeds were later processed for cytological investigations and germinated in the laboratory. Germinating young root tips were pretreated in 0.05% colchicine for five hours and fixed in acetic alcohol for 24 hours. After washing the roots were stored in 70% ethanol

Roots were later hydrolysed, stained and squashed. Cytological data including chromosome counts, total chromatin length (TCL), length of longarm (L), length of shortarm (S), centromeric position etc were obtained from good metaphase plates

PLATE 1: (A) Fruit morphology C annuum var. paprika. (B) Karyotype of the crop (C) Ideogram of the crop

Table 1

Karyotype data of C. Annuum var. Paprika

Variety aHl. bL.arm cS. arm Total d d e r f Loc. g 2N
Paprika I 3.16 3.15 6.31 0.01 1.01 M 24
II 3.13 3.13 6.26 1 M
III 3.11 3.11 6.22 1 M
IV 3.05 3.05 6.10 1 M
V 3.01 3.00 6.01 0.01 1.01 M
VI 2.90 2.90 5.80 1.00 M
VII 2.82 2.81 5.63 0.01 1.01 M
VIII 2.65 2.65 5.30 1 M
IX 2.51 2.50 5.11 0.01 1.01 M
X 3.01 1.51 4.52 1.50 1.99 SM
XI 2.88 1.45 4.33 1.43 1.98 SM
XII 3.43 0.53 3.96 2.90 6.47 ST
Total 35.66 29.79 65.45

KEY

a = Homologue, b = Long, c = Short, d = difference (L-S), e = ratio (L/S), f = Location of Centromere, g = diploid number, M = Metacentric, SM = Submetacentric, ST = Subtelocentric

Table 2

Summary of karyological parameter indices of Capsicum annuum var. Paprika

PARAMETER VALUE
2n 24
N 12
TCL 65.45
Č 5.45
TF% 45.45
A1 0.1550
A2 0.1008
Total asymmetry 0.2558
CV 10.08
Chromosome formula 0M + 9m + 2sm + 1st

KEY

TCL = Total Chromatin Length, Č = Mean chromosome length, TF% = Total Form Percent, A1 = Intrachromosomal asymmetry index, A2 = Interchromosomal asymmetry index, CV = Coefficient of variation, 2n = Diploid number, N = Haploid number.

Discussion

The chromosome number of this plant was found to be 2n = 24 (Plate 1A). This observation is in agreement with reported chromosome counts in the genus Capsicum [11,2,6,8,14,4,9,12]. It is significant to note that despite the variations in vegetative and fruit morphology, there is some measure of genetic stability in this plant. This stability may have accounted for the regularityobserved in mitosis, as indicated by the fact that no mitotic abnormalities were observed in all the cells examined. These facts lend credence to the suggestion that a balanced genetic system is in operation in Capsicum annuum var. paprika and so differences in vegetative and floral morphology do not have deep rooted genetic basis

The degree of genetic variability of the karyotype, measured by the coefficient of variation in chromosome sizes was 10.08%. This value, though moderate, indicates the presence of sufficient variability in chromosome characteristics, a phenomenon which may explain the existence of wide structural variations in fruit morphology of the Capsicums. This moderate CV value may also support the proposition that there is room for improvement in this crop using crop improvement regimes such as selection and intra specific hybridization, two methods which usually rely on the existence of variabilities. In a morphogenetic variability study conducted in Anarcadium [1] the wide variability present in the Karyotype of the crop was utilized as an opportunity for the exploitation of useful genes for improvement of the crop. Based on the report, a recurrent selection breeding strategy was developed that involved the hybridization of identifiable promising genotypes of parents

The preponderance of metacentric chromosomes in the karyotype (75%), as well as, the moderate to large sizes of the chromosomes (Č = 5.45µm), are both clear indications that in phylogenetic sense, this taxon can be said to be primitive. Additional evidence to support this proposition is obtained from the high TF% value of 45.45, which denotes symmetrical karyotype. Reports from studies on the Crepis, Error! Reference source not found. showed that in plants, symmetrical karyotypes are primitive compared to their asymmetrical counterparts. Also, after comparison of the highly asymmetrical species of Capsicum with less asymmetrical species, the postulation that the asymmetrical ones were derived from the less asymmetrical was made [7]

Conclusion

The karyological characterization of Capsicum annuum var. paprika, as undertaken in this study, has revealed a balanced genetic background which controls a prolific array of vegetative, floral and fruit morphological forms, which make this crop the breeders delight. With a chromosome status of 2n = 24, a total chromatin length (TCL) of 65.45µm and a coefficient of variation (CV) valueof 10.08%, this plant is naturally endowed with sufficient genetic variability in its karyotype that predisposes it to respond positively to crop improvement methods such as selection and intra-varietal hybridization