Barriers to interspecific hybridization between Vigna unguiculata and Vigna vexillata

Abstract

Interspecific hybridization between Vigna unguiculata and V. vexillata always failed: no seed was obtained in both crossing directions. Two different barriers to crossability were found: a pre-zygotic barrier and a post-zygotic one. Many abnormalities were observed in pollen-tube development, which reduced the percentage of fertilization to 18-30%. Differences in the percentage of fertilization were detected between the two accessions of V. vexilIata involved in the interspecific crosses. The development of the interspecific embryo was analyzed and the embryo and endosperm nuclei always degenerated 5-8 days after pollination. The growth of the embryo stopped at a globular stage, which is too early for excision and in vitro culturing.

Resistance in Accessions of Cowpea to the Coreid Pod-Bug <I>Clavigralla tomentosicollis</I> (Hemiptera: Coreidae)

“…From our results, it could be anticipated that seed mechanisms may constitute the major resistance component in TVnu 151, whereas both pod and seed mechanisms would be involved in TVnu 72, the wild and resistant control of the V. vexillata species. Even though all attempts to obtain an interspeciÞc cross between V. unguiculata and V. vexillata have failed so far (Barone et al 1992, Fatokun 1991, the successful cross of cultivated cowpea with V. pubescence, a hairy wild relative, using tissue culture techniques to rescue the hybrid embryos (Fatokun and Singh 1987), holds promise in breeding cowpeas resistant to C. tomentosicollis, especially as evidence was provided of the heritability of resistance to seed damage and of growth inhibition of nymphs of the western plant bug in cowpea (Bosque-Perez et al 1987). Means Ϯ SE in each column followed by the same letter are not signiÞcantly different at the ␣ ϭ 0.05 level (ANOVA followed by SNK test).…”

“…Attempts to move this trait into agronomically acceptable cowpeas have failed because the incompatibility between accessions of these wild species and genotypes of the cultivated species prevented interspeciÞc crosses (Fatokun 1991, Barone et al 1992). More recently, research directed at other wild Vigna species has identiÞed some sources of resistance to C. tomentosicollis among accessions of a closer relative of the cultivated species, viz.…”

Vigna

“…unguiculata × V. vexillata Barone et al ( 1992 ) V. pubescens × V. unguiculata Fatokun and Singh ( 1987 ) V. umbellata , and V. angularis , while their reciprocal crossing was not successful. Nevertheless, by using sequential embryo rescue, the reciprocal hybrids between V. mungo and V. radiata could be successfully obtained (Gosal and Bajaj 1983a ;Verma and Singh 1986 ).…”

“…This is particularly important in those situations where the reason of incompatibility lies post-fertilization such as endosperm abortion. Barone et al ( 1992 ) observed that the embryos and endosperm in the cross between V. vexillata and V. unguiculata degenerated within 5-8 days after pollination. Using embryo rescue, successful crossing could be accomplished in V. mungo × V. umbellata (Biswas and Dana 1975 ;Chen et al 1983 ).…”

Pod Surface Characteristics in Wild and Cultivated Vigna Species and Resistance to the Coreid Bug Clavigralla tomentosicollis Stal. (Hemiptera: Coreidae)

“…Several biophysical factors contribute to this resistance, such as the pod trichomes which act as feeding deterrent against insects in several plants (Duffey, 1986;Oghiakhe et al, 1992;Yencho and Tingey, 1994), or the toughness of plant tissues reported to protect cowpea seeds from attacks by resisting the penetration of insects' mouth parts either through the pod wall or the seed coat (Owusu-Akyaw, 1987;Chiang and Jackai, 1988;Tayo, 1989). dekindtiana which, unlike accessions of V. vexillata, are cross-compatible with the cultivated genotypes (Fatokun and Singh, 1987;Barone et al, 1992). Therefore, the present study used three Vigna species, namely V. vexillata, V. unguiculata subsp.…”