African Crop Science Journal African Crop Science Society ISSN: 1021-9730 EISSN: 2072-6589 Vol. 4, Num. 2, 1996, pp. 139-144

C. O. Ilori, A.O. Togun and I. Fawole

Department of Agricultural Biology, University of Ibadan, Ibadan, Nigeria.

(Received 27 June, 1994; accepted 2 May, 1995)

Code Number: CS96050
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ABSTRACT

Variation in growth and development characteristics among three cultivated and one weedy cowpea (Vigna unguiculata L. Walp) lines and their reciprocal hybrids were studied. Most of the characters varied significantly among the parental lines. Reciprocal differences were observed in the length as well as the width of cotyledonary leaves in most of the F1 hybrids, particularly all those involving the weedy line as a parent. The greatest amount of variability among the parental lines and the hybrids was in 100-seed weight. The 100 seed-weight was positively correlated with length of cotyledonary leaves, number of days to first flower, width of cotyledonary leaves and pod length. The 100-seed weight was highly significantly negatively correlated with number of pods/plant, number of peduncles/plant, number of seeds/pod and number of ovules/pod. It would seem that selection for large cotyledonary leaves could be a means of selecting for higher seed yield in cowpea.

Key Words: Genetic variation, reciprocal hybrids, Vigna unguiculata

RESUME Les caracteristiques de croissances et de developpement de trois cultivars et une lignee herbacee de niebe (Vigna unguiculata L. Walp) et de leurs hybrides reciproques etaient etudiees. Pour la plupart des caracteristiques, il y a une variabilite significative chez les lignees parentales. Des differences reciproques sont observees pour la longeur et la largeur des feuilles cotyledonaires dans la plupart des hybrides F1, surtout pour les hybrides avec la lignee herbacee comme parent. La plus grande variabilite chez les lignees parentales et les hybrides etait notee dans le poids de 100 grains. Une correlation positive etait observee entre le poids de 100 grains et la longueur de feuilles cotyledonaires, le nombre de jours jusqula premire floraison, la largueur de feuilles cotyledonaires et la longeur de gousses. La correlation entre le poids de 100 grains et le nombre de gousses par plante, le nombre de pedoncules par plante, le nombre de grains par gousse et le nombre dles par gousse etait negative. Il semble qu selection pour des feuilles cotyledonaires larges est un moyen de selection pour un rendement eleve chez le ni_b_.

Mots Cles: Variabilite genetique, hybrides reciproques, Vigna unquiculata

INTRODUCTION

Variation exists among cowpea (Vigna unguiculata L. Walp) lines with respect to leaf size; long leaf is dominant to short leaf (Kolhe, 1970). The greatest amount of variability exists in seed size which is the most important contributing character to genetic diversity in cowpea (Mehndiratta and Singh, 1971). Seed size is inherited quantitatively and gene action is mainly additive (Fawole; 1973, Drabo et al., 1984). Large seeded varieties are known to produce seedlings with greater initial leaf area than smaller seeded varieties (Lush and Wien, 1980), while 100-seed weight is positively correlated with yield (Kheradnam and Niknejad, 1974).

The wild and weedy forms of crop species are reported to be sources of desirable traits not found in cultivated forms (Leppik, 1970; Stalker, 1980). These traits could be transferred from the wild to the cultivated form through hybridization. This study assessed the growth and development characteristics in reciprocal crosses between weedy and cultivated cowpea lines.

MATERIALS AND METHODS

The cowpea lines used in this study are three mutants (Ife BPC, Ibadan heptafoliolate and Ibadan BPC) from cultivated varieties and one weedy variety (WC Ibadan-10). Two experiments were carried out using the randomised complete block design. The first was carried out in the crop garden of the Department of Agricultural Biology,University of Ibadan, Nigeria. Seeds for the experiment were from the germplasm maintained in the Agricultural Biology Department. The seeds of the four parental lines were sown on 20 September 1988, on the flat at a spacing of 60 cm between plots and 30 cm within each plot. The experiment had 4 replicates, each containing 4m plot rows with the parental lines. The stem length, number of branches plant^- 1, number of pods plant^-1 and number of peduncles plant^-1, were measured on the best eight plants plot^-1. The number of seeds pod^-1, number of ovules pod^-1 and pod length were obtained from the mean of 24 best pods from each plot. The second experiment was carried out on the roof top garden of Agricultural Biology Department to determine the growth and development characteristics of the parental lines and all twelve possible crosses between them. The twelve crosses and the four parental lines were the treatments and were randomly allocated. There were six replicates each containing sixteen 25 cm plastic pots filled with crop garden soil. Each pot served as a plot. The seeds were sown on 9 December 1988 at the rate of 2 seeds per pot, but thinned on establishment (2 weeks after sowing) to one per pot. The length and width of cotyledonary leaves were measured (from the average of the two for each plant) after the leaves were fully expanded. Pod length, number of seeds pod^-1 and number of ovules per pod were obtained from the mean of 6 best pods plant^-1.

Analysis of variance was carried out for each trait and Duncanultiple range test (DMRT) was used for mean separation. Correlation coefficients were calculated for 100-seed weight and selected characters.

RESULTS

The parental lines differed signifficantly from each other in most of the traits studied (Table 1). However, pod length, number of seeds pod^-1 and 100-seed weight were not significantly different between Ife BPC and Ibadan BPC. The number of ovules per pod was not significantly different between heptafoliolate and WC Ibadan-10. The weedy line did not also differ from heptafoliolate and Ibadan BPC in the number of peduncles per plant, and from Ife BPC in main stem length. Coefficient of variation was low for number of ovules pod^-1 and pod length, but very high for stem length and 100-seed weight (Table 1).

Table 1

Length and width of cotyledonary leaves, number of leaves and branches/plant. The parental lines differed significantly from each other in the length and width of cotyledonary leaves, but the values for length and width of cotyledonary leaves in the hybrids were similar to those of the female parents particularly in all hybrids involving WC Ibadan-10. The number of leaves plant^-1 also differed significantly among parental lines except between WC-Ibadan-10 and Ibadan BPC. However, there was no significant difference between the weedy line and all hybrids involving it as parent in the number of branches plant^-1 whose values were more or less similar to that of the weedy line (Table 2).

Table 2

Number of days to first flower. The parental lines differed significantly from each other and from their reciprocal crosses in the number of days from planting (DFP) to first flower except between heptafoliolate and heptafoliolate X WC Ibadan-10 and both reciprocal crosses between heptafoliolate and Ibadan BPC. The F1 hybrids of crosses involving WC Ibadan-10 had lower values for days from planting to first flower (DFPFF) than their parental lines. Significant differences were recorded between the cultivated lines and the reciprocal crosses between them and the weedy lines except between heptafoliolate and both reciprocal crosses between it and the weedy lines. All the cultivated lines differed significantly from the hybrids involving them and the weedy lines in number of pods plant^-1 except Ife BPC X WC Ibadan-10 (Table 2).

Pod length and number of ovules per pod. There were significant differences between the weedy line and all hybrids involving it and the cultivated parents in pod length. Only heptafoliolate did not differ significantly from the reciprocal crosses involving it and the weedy parents. There were also significant differences in pod length between the cultivated lines and all their hybrids except heptafoliolate X Ife BPC which was not significantly different from heptafoliolate as well as Ife BPC X Ibadan BPC which did not significantly differ from Ife BPC. Only the hybrids between the weedy line and all cultivated lines differed significantly from the cultivated lines. Also the number of ovules per pod differed significantly between the weedy lines and all the hybrids involving it while the hybrids between the weedy lines and the cultivated lines also differed significantly from the cultivated lines. The coefficient of variation was lowest for number of ovules per pod when compared to other traits studied (Table 2).

Hundred seed weight. There were significant differences between the weedy lines and all hybrids involving it with respect to 100-seed weight; also the hybrids between weedy and cultivated lines differed significantly from the cultivated parent. All the hybrids between the cultivated lines except Ife BPC X Ibadan BPC differed significantly from their parents in 100-seed weight. The value for 100-seed weight of the hybrid between the weedy line and the cultivated lines tended towards the value for the weedy line. The coefficient of variation was highest for 100-seed weight when compared to other traits (Table 2).

Comparison of reciprocal crosses. There were significant differences between all reciprocal crosses except between heptafoliolate X Ibadan BPC and its reciprocal for width of cotyledonary leaves and number of DFPFF. Reciprocal differences were not observed between all crosses in the number of peduncles plant^-1 and number of ovules pod^-1, except for crosses between heptafoliolate and WC Ibadan-10 (Table 2).

Correlation between seed size and other traits. There was significant positive correlation between 100-seed weight and length of cotyledonary leaves. There were highly significant positive correlations between 100-seed weight and both width of cotyledonary leaves and length of pods, while highly significant negative correlation existed between 100-seed weight and number of peduncles plant^-1, number of seeds pod^-1, as well as number of ovules pod^-1 (Table 3).

Table 3

Large variation in growth and development characters exists among the four cowpea lines used in this study. There were significant differences in the length and width of cotyledonary leaves in the reciprocal F1 progeny, particularly those crosses between the cultivated and weedy lines, suggesting that the lines used as female parents have a direct effect on the length and width of cotyledonary leaves. Reciprocal differences were also observed in all crosses involving the weedy line as parent with respect to number of days to first flower. The hybrids in which the weedy line was made the female parent had small initial leaf area even when large seeded lines were made the pollen parents; this may be attributed to the small seed size of the weedy line. Lush and Wien (1980) reported that large seeded varieties produced seedling with greater initial leaf area than smaller seeded varieties in cowpea, while in pigeon pea (Cajanus cajan L.) large seeds have been shown to give rise to larger seedling than smaller seeds (Narayanan et al., 1981).

The parental lines and the hybrids did not vary much in the number of branches plant^-1, pod length, number of seeds pod^-1 and number of ovules pod^-1. The least amount of variation was noticed in the number of ovules pod^-1. There were no reciprocal differences in all the crosses for number of ovules pod^-1 and number of peduncles plant^-1. Any of the parental lines can therefore be made the female parent for these traits. For the other traits where reciprocal differences were observed in some crosses, the appropriate female parent can be chosen depending on the traits of interest. This suggests that the occurrence of reciprocal differences in crosses between weedy and cultivated cowpea lines has implication for the choice of female parents in crosses.

The greatest amount of variation was observed for 100-seed weight. This is in line with the assertion of Mehndiratta and Singh (1971) that 100-seed weight was the greatest contributing factor to genetic diversity in cowpea. Significant positive correlation exists between 100-seed weight and length of cotyledonary leaves, width of cotyledonary leaves, as well as length of pods. Since 100-seed weight is positively correlated with yield (Kheradnan and Niknejad, 1974), it is concluded that selection for large cotyledonary leaves may be a means of selecting for higher seed yield in cowpea.

REFERENCES

Drabo, I., Redden, R., Smithson, J.B. and Aggrawal, V.D. 1984. Inheritance of seed size in cowpea (Vigna unguiculata (L.) Walp). Euphytica 33:929-934.

Fawole, I. 1973. Inheritance of Seed Weight in Cowpeas. M.Phil. Thesis, University of Ife, Nigeria. 67 pp. Kheradnam, M. and Niknejad, M. 1974. Heritability estimates and correlations of agronomic characters in cowpea (Vigna sinensis L.) Journal of Agricultural Science, Cambridge 82:207-208.

Kolhe, A.K. 1970. Genetic studies in Vigna sp. Poona Agricultural College Magazine 59:126-137.

Leppik, E.E. 1970. Gene centres of plants as sources of disease resistance. Annual Review of Phytopathology 8:323-344.

Lush, W.M. and Wien, H.C. 1980. The importance of seed size in early growth of wild and domesticated cowpea. Journal of Agricultural Science, Cambridge 94:177-182.

Mehndiratta, P.D. and Singh, K.B. 1971. Genetic diversity in respect of grain yield and its components in cowpea germplasm from the Punjab. Indian Journal of Genetics and Plant Breeding 31:388-392.

Narayanan, A., Saxena, N.P. and Sheldrake, A.R. 1981. Varietal differences in seed size and seedling growth of pigeon pea and chick pea. Indian Journal of Agricultural Science 51:389-393.

Stalker, H.T. 1980. Utilization of wild species for crop improvement. Advances in Agronomy 33:111-147.

Copyright 1996 The African Crop Science Society

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