Inheritance of shortday induced dwarfing in photosensitive cowpeas

Abstract

Cowpea [ Vigna unguiculata (L.) Walp.] is an important source of food and fodder in the dry savanna of West Africa. Traditional cowpea varieties are photosensitive (PS), growing profusely when planted in long days and they flower when days become shorter. However, we have observed that all PS cowpea varieties exhibit dwarf characteristics when planted during short-days. This study was undertaken to confirm this observation and to elucidate the inheritance of shortday induced dwarfing in PS cowpea. Two PS and two Photoinsensitive (PI) cowpea varieties were evaluated at IITA Kano Station, Nigeria (12003'N latitude and 8032'E longitude) at 4 planting dates. As expected, PS varieties flowered earlier when planted during short days (<12.5 h., February and October plantings) and later during long days (>13 h., May and July plantings). However, they became extremely dwarf during short days due to lack of internode elongation resulting in a rosette appearance. The mean plant heights of PS varieties were 20.5 cm, 142 cm, 89.0 cm and 15.0 cm, when planted in February, May, July and October, respectively. The corresponding plant heights of the PI varieties were 39.0 cm, 31.5 cm, 26.0 cm and 24.5 cm. The parental, F1, F2 and backcross populations derived from a PI variety IT87D-941-1 and a PS variety, Kanannado were evaluated in short day conditions and selected F3 progenies tested in long-day conditions. The genetic segregation revealed that short-day-induced dwarfing of PS is controlled by a single recessive gene pair which is designated as 'psps (photosensitive). The complete correspondence between dwarfing under short-day conditions and PS for flowering, indicates that both phenomena are manifestation of the same PS gene pair.

RESUME

Le niebe [Vigna unguiculata (L.) Walp.] est une importante source de nutriture et de fourage dans la savanne seche de l' Afrique de l'Ouest. Les varietes traditionnelles de vigna sont photosensibles, poussant exuberamment quand elles sont plantees en jours longs et elles flourissent quand les jours reccounissent. Cependant, nous avons observe que toutes les varietes de niebe manifesterent des caracteristiques de nanisme quand elles sont plantees en jours courts. Cette etude fut entreprise pour confirmer cette observation et pour elucider l'heritabilite du nanisme induit par les jour courts. Chez les varietes de vigna photosensibles. Deux varietes photosensibles et deux insensibles a la photoperiod furent evaluees a la Station Kano, IITA, Nigeria a 4 dates de semis comme attendu la varietes photosensibles fleurirent plus tot quand elles furent plantees en jours courts (<12,5 h, semis de fevrier et d'Octobre) et plus tard en jours longs (> 13 h semis de Mai et Juillet). Cependant, elles devinrent extremement naines durant les jours courts a cause d'une abscence d'elongation des entrenceuds, resultant a un aspect de rossette. Les hauteurs moyennes des plantes des varietes photosensibles furent 20,5 cm, 142,0 cm, 89,0 cm et 150,0 cm, quand elles sont semees en Fevrier, Mai, Juillet et Octobre respectivement. Les hauteurs de plant correspondantes des varietes non photosensibles furent 39,0 cm 31,5 cm, 26.0 cm et 24.5 cm. Les parents, F1, F2 et les populations issues de backcross de la variete non photosensibles IT87D-941-1 et la variete photosensible Kanannado furent evalues en conditions de jours courts et les descendants F3 selectionnes testes en conditions de jours longs. Le segregation genetique revela que le nanisme induit par les jours courts des varietes photosensibles est controle par une seule paire de genes recessives qui est designee ''psps''(photosensible). La correspondence complete entre nanisme en conditions de jours courts et le photosensibilites pour fleurir indique que les deux phenomenes sont la manifestation de la meme paire de genes de photosensibilite.


(African Crop Science Journal 2001 9(2): 369-376)