Meiotic chromosome behaviour and sexual sterility in two Nigerian species of Aloe Linn

Abstract

The behaviour of meiotic chromosomes and the subsequent behaviour of the meiotic products were investigated in two Nigerian species of Aloe, namely Aloe keayi and Aloe macrocarpa var major with a
view to uncovering the cause of their inability to reproduce sexually. The two plant materials used in this study were already under cultivation in the Aloe Research Garden situated in the Crop Type
Museum of the Department of Crop, Soil and Pest Management, Federal University of Technology, Akure, Nigeria. All the various meiotic stages from leptotene to pollen development were studied. Number of chromosomes per complement in the two taxa is 2n = 14. The 14 chromosomes were resolved into seven bivalents all of which show incomplete pairing thereby lowering the frequency of chiasma formation. Chromosome aberration involving deletion of a segment from one of the longest chromosomes was detected in A. macrocarpa var major. Though the percentage of pollen stainability is high in both taxa, the percentage of pollen germinability, both in vitro and in vivo, is very low in A. keayi
when compared with what obtains in A. macrocarpa var major. The morphology and behaviour of chromosomes in the two taxa, the failure of the flowers to form fruits in A. keayi and the failure of the
fruits to attain maturity in A. macrocarpa var major are all evidences that sexual sterility in the two taxa is attributed to genetic instability and deficiency in the genotype of the spores as a result of their hybrid
origin.