African Crop Science Journal African Crop Science Society ISSN: 1021-9730 EISSN: 2072-6589 Vol. 6, Num. 1, 1998, pp. 97-101

SHORT COMMUNICATION

A PARTIAL MALE STERILE MUTANT IN COWPEA

B.B. SINGH and H.K. ADU-DAPAAH^1

International institute of Tropical Agriculture (IITA), Kano Station, PMB 3112, Ibadan, Nigeria
^1 Crops Research Institute, P. O. Box 3785, Kumasi, Ghana

(Received 27 November, 1995; accepted 22 October, 1997)

Code Number:CS98010
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ABSTRACT

A partial sterile line of cowpea (Vigna unguiculata (L.) Walp.) resulting from spontaneous mutation was characterised. Plants were classified based on plant morphology, pollen viability and pod set. Partial sterile plants remained green past usual maturity and had thick leathery leaves with a few fleshy 1-3 seeded pods. Reciprocal crosses indicated partial female fertility. Pollen number per anther was variable and about 77% pollen from mutant plants were normally stained with acetocarmine compared with 98.3% for normal plants. The proportion of fertile to partial sterile plants in segregating populations indicated that the character is controlled by a single recessive gene which is being designated as "ps". The homozygous recessive plants bred true for partial sterility. The possible uses of this mutant are discussed. The line is being maintained as IT85D-3626.

Key Words: Mutation, partial sterility, segregation, Vigna unguiculata

RESUME

Une lignee partielle sterile de niebe (Vigna unquiculata (1) Walp). provenant d'une mutation spontanee a ete etudiee. Les plantes ont ete classes en tenant compte de la morphologie de la plante, de la viabilite du pollen et de la formation des gousses. Les plantes partiellement steriles etaient restees vertes apres la maturite habituelle et disposaient des feuilles coriaces et epaisses avec peu de gousses charnues a 1-3 graines. Les croisements reciproques indiquaient une fertilite femelle partielle. Le nombre de pollen par anthere etait variable et environ 77% de pollen provenant de plantes mutantes etaient normalement tachetes par l'acetocarmine par rapport aux 98,3% des plantes normales. La proportion des plantes fertiles par rapport aux plantes steriles dans la separation des populations a montre que le caractere est controle par un seul gene recessif appele "ps". Les plantes a genes recessifs homozygotes ont manifeste une vraie reproduction pour une sterilite partielle. Les eventuels usages de ce mutant sont discutes. La lignee est maintenue comme IT85D-3626.

Mots Cles: Mutation, sterilite partielle, segregation, Vigna unquiculata

INTRODUCTION

Male sterility, an inherited abnormality, has become an important tool in the breeding programmes of economic crops. Sterility in crop plants may either be complete or partial and stable or unstable (Patel and Singh, 1976; Stelly and Palmer, 1980a). Partial sterility denotes incomplete expression of male sterility because partial sterile plants produce and dehisce functional pollen in some environments (Stelly and Palmer, 1980b). Mutant alleles that confer partial sterility have been identified in cotton (Meyer, 1969), tomatoes (Rick and Boynton, 1967), petunia (Marrewijk, 1969), soybean (Caviness et al., 1970; Stelly and Palmer, 1980a), and broccoli (Dickson, 1970).

Partial sterility has potential application facilitating genetic recombination and in the production of commercial hybrid seeds (Rachie and Gardner, 1975). Partial sterile plants may be used as parents for pollination as well as propagated sexually as homozygotes (Stelly and Palmer, 1980b).

Several workers have reported male sterility in cowpea (Sen and Rhowal, 1962; Rachie et al., 1980), but there is no report of partial sterility in cowpea. The objective of this paper is to describe a partial male sterile mutant of cowpea.

MATERIALS AND METHODS

The materials for this study originated from spontaneous mutation in a backcross population of the cross, TVX 1850-01E x IT82E-603. One of the F3 families, IT84E-5-115 segregated into 11 normal and 5 partial sterile plants. Data on several characters were taken and individual plant progenies were evaluated for genetic segregation and other characteristics for 2 more generations at the International Institute of Tropical Agriculture (IITA), Ibadan. For each generation, progenies were grown in single rows, 4 m long, at a spacing of 75 cm x 20 cm.

At flowering, plants were classified as partially sterile based on anther and pollen appearance as well as anther dehiscence. The classification of phenotypes for inheritance studies were made at maturity when the plants were easily identifiable due to reduced pod set and retention of foliage and chlorophyll on the partial sterile plants. The ratio of partial sterile to fertile plants in the segregating rows of each family was determined at maturity. Ten plants from both groups were randomly tagged and the number of pods/plants, seeds/pod, pod length and plant height were recorded.

To asses female fertility of the mutant, 200 flowers from 20 randomly selected plants were emasculated and crossed with pollen from fertile plants. The mutants were manually self-pollinated to test their fertility.

Flower buds were collected just before anthesis from 10 randomly selected mutant and normal plants into separate vials containing 1:3 glacial acetic-ethanol fixative. Anthers were discerned from flowers and stained with 1% acetocarmine for observation under a microscope. Stained pollen grains of normal size were considered viable, while those that were either abnormally small or large and stained only partially, or not at all, were counted non-viable.

RESULTS AND DISCUSSION

Partial sterile plants. The differences between normal and mutant plants became evident at the time of flowering and were more pronounced at maturity. The mutant plants were slightly shorter in height than normal plants (Table 1) and had poor anther dehiscence. The mutants looked green at maturity and retained their foliage when normal plants were senescing (Fig. 1.) Similar observations were made by Adu-Dapaah (1989) in cowpea. Furthermore, these mutants continued flowering beyond the usual period of flowering. The retention of foliage and chlorophyll permitted easy classification of phenotypes at maturity. The mutant used in the present study was considered partially male sterile because it was able to set pods upon selfing. Similarly, Stelly and Palmer (1980b) reported that partially sterile soybean lines were able to set pods upon selfing.

Podding characteristics. Mutant plants from segregating progenies had some pods with one to three seeds/pod (Fig. 1) with irregular gaps in the pods. In most cases, a proliferation of poorly developed and seedless pods were observed following anthesis. Fertile plants had more pods/ plant, more seeds/pod and longer pods than the mutant plant (Fig. 1; Table 1). Plant height was similar to normal if pod length was not taken into account. The podding characteristics observed in this study are similar to those reported in soybean by Caviness et al. (1970) and Stelly and Palmer (1980a).

Partial male sterile plants used as female parents in crosses with fertile plants gave about 16% pod set with 1 or 2 seeds per pod and irregular gaps indicating partial female sterility. Controlled self pollination gave about 42% pod set indicating male fertility but all these pods were filled with only 1-3 seeds per pod and had irregular gaps indicating partial female sterility (Martin and Crawford, 1951).

Pollen characteristics. The pollen grains from partial male sterile plants appeared normal in size but the mean percentage of stained pollen grains was 77.0 compared to 98.3% for normal plants. Apparently, the pollen viability in mutant plants was less than the normal ones. This observation is in consonance with work done by Caviness (1970) in soybean.

Inheritance. The original progeny row, IT84E-5-115 had 11 normal and 5 partial male sterile plants which fitted well to a 3:1 ratio (X2 = .33, P= .50-.70). Progeny tests in the following season further confirmed monogenic inheritance. Of the 11 normal plant progenies, 8 segregated and 3 bred true for normal which fitted well to an expected 2:1 ratio (X2 = .18, P= .50-.70). Of the 5 progenies derived from partial male sterile plants only 3 had sufficient seeds and all these bred true for sterility. Each of the 8 individual segregating progenies fitted well to a 3 normal: 1 partial sterile ratio and were homogenous. When pooled over all the progenies, there were 84 normal and 31 partial sterile plants which also fitted well to 3:1 ratio (X2=.23, P=.50-70).

Since backcross populations were not available, the inheritance was further confirmed by testing the progenies of 24 randomly selected normal plants and 10 partially sterile plants from segregating rows. Patel and Singh (1976) used a similar procedure to study the inheritance of male sterility in soybean. All the 10 progenies from partial sterile plants bred true for sterility. Of the 24 normal progenies, 17 segregated and 7 bred true for normal plants. This fitted well to 2:1 ratio (X2 = .18, P=.50-.70). The data on normal and partial sterile segregates in each of the 17 progenies are presented in Table 2. Segregation in each of these progenies showed a close fit to 3 normal : 1 partial sterile and all the families were homogeneous. Pooled over all 17 progenies, there were 519 normal and 153 partial sterile plants which also fitted well to a 3:1 ratio. These data reconfirmed the earlier observation that this partial sterility is controlled by a single recessive gene for which the gene symbol Ôps' is being assigned. Stelly and Palmer (1980a) working on soybean reported that partial male sterility was controlled by single recessive gene. The data further indicated that the homozygous recessive plants (ps ps) give rise to uniformly partial sterile plants and thus, this trait can be maintained in homozygous condition.

This trait may be quite useful in a breeding programme and may permit the use of recurrent selection methods (Rachie and Gardner, 1975). Planned outcrossing experiments have not been conducted using homozygous plants carrying this trait but field observations indicated significant outcrossing which may lead to greater heterogeneity and heterozygosity in breeding populations. Further work is in progress to study outcrossing and fertility of this line.

When plants have such a limitation as partial sterility, some environments could shift it towards more sterility which could be manipulated in a recurrent selection programme (Martin and Crawford, 1951). In a crop like cowpea, it could also be used to produce hybrid cowpea seeds. Further studies need be conducted to elucidate the effect of environment on partial sterility.

REFERENCES

Adu-Dapaah, H.K. 1989. Studies on Phenotypic Stability and Male Sterility in Cowpea (Vigna unguiculata (L.) Walp. Ph.D Thesis, University of Ibadan, 265 pp.

Caviness, C.E., Walter, H.J. and Johnson, D.L. 1970. A partially male-sterile strain of soybean. Crop Science 10:107-108.

Dickson, M.H. 1970. A temperature sensitive male-sterile gene in broccoli, Brassica oleracea L. var italica. Journal American Society of Horticultural Science 95:13-14.

Ladeinde, T.A.O., Watt, E. and Onajole, A.A.O. 1980. Segregation pattern of three different sources of male-sterile genes in (Vigna. unguiculata (L) Walp). Journal of Heredity 71:431-432.

Marrewijk, G.A.M. Van. 1969. Cytoplasmic male sterility in Petunia. I. Restoration of fertility with special reference to the influence of environment. Euphytica 18:1-20.

Martin, J.A. and Crawford, J.H. 1951. Several types of sterility in Capsicum frutescence. Journal of American Society of Horticultural Science 57:335-338.

Meyer, V.G. 1969. Some effects of genes, cytoplasm and environment on male sterility in cotton (Gossypium). Crop Science 9:242.

Patel, A.B. and Singh, B.B. 1976. Male sterility in soybeans. Indian Journal of Genetics and plant Breeding 36:238-243.

Rachie, K.O. and Gardner, C.O. 1975. Increasing efficiency in breeding partially out-crossing grain legumes. In: Proceedings International Workshop on Grain Legumes, pp. 285-300. ICRISAT, Hyderabad, India.

Rachie, K.O., Rawal, K., Frankswiak , J.D. and Akinpule, N.A. 1975. Two sub-crossing mechanisms in cowpea (Vigna unguiculata (L) Walp.). Euphytica 24:159-163.

Rick, C.M. and Boynton, J.E. 1967. A temperature-sensitive male sterile mutant of tomato. American Journal of Botany 54: 601-611.

Sen, N.K. and Bhowal, J.G. 1962. A male-sterile mutant in cowpea. Journal of Heredity 53:44-46.

Stelly, D.M. and Palmer, R.G. 1980a. A partially male-sterile mutant line of soybean, Glycine max (L.) Merri: inheritance. Euphytica 29:295-303.

Stelly, D.M. and Palmer, R.G. 1980b. A partially male-sterile mutant line of soybean, Glycine max (L.) Merri: characterisation of phenotype variation. Euphytica 29:539-546.

Copyright 1998, African Crop Science Society

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