Fruit set and plant regeneration in cassava following interspecific pollination with castor bean

Abstract

The increasing demand for cassava ( Manihot esculenta Crantz) for food and non-food uses in the tropics necessitates that its breeding for increased root productivity be made faster. The characteristic long breeding cycle and heterozygous nature of this crop, pose a major obstacle to its rapid genetic improvement. This study aimed at inter-pollinating cassava with castor bean ( Ricinus communis ), with a purpose of inducing and regenerating cassava doubled haploids (DHs). A total of 3,349 flowers from twelve elite cassava varieties were inter-pollinated with caster bean. A total of 803 fruits were harvested for early embryo rescue and/or ovule culture. Of these, three were dissected to obtain seven unique embryos, while 800 were dissected to obtain 1312 young ovules, all of which were cultured in vitro. Overall, 82 (6.25%) of the cultured ovules formed callus that originated from the embryosac region, which is haploid. Four out of seven rescued embryos (57.1%) regenerated into plantlets. Ploidy analyses of 24 samples using flow cytometry revealed that 23 of the analysed samples were diploid. However, one callus sample was anueploid. Only one sample had an exceptionally high level of homozygosity ( 84.2%). These findings lay a foundation for future research aimed at induction of haploids in cassava.La demande croissante de manioc (\ua0 Manihot esculenta \ua0Crantz\ua0) \ue0 usage alimentaire et non alimentaire dans les tropiques\ua0n\ue9cessite que sa reproduction pour une productivit\ue9 accrue des racines soit faite plus rapidement.\ua0Le long cycle de reproduction et le caract\ue8re h\ue9t\ue9rozygote de cette plante constituent un obstacle majeur dans la rapidit\ue9 de son am\ue9lioration g\ue9n\ue9tique.\ua0Cette \ue9tude visait \ue0 inter-polliniser le manioc avec le haricot (\ua0 Ricinus communis \ua0), dans le but d\u2019induire et de r\ue9g\ue9n\ue9rer le manioc d\u2019haplo\uefdes doubl\ue9 (HD).\ua0Un total de 3 349 fleurs de douze \ue9lites vari\ue9t\ue9s de manioc ont \ue9t\ue9 inter-pollinis\ue9es avec le haricot.\ua0Un total de 803 fruits ont \ue9t\ue9 r\ue9colt\ue9s pour les embryons pr\ue9matur\ue9s qui etaient sauves et\ua0/ ou la\ua0culture d\u2019ovules\ua0.\ua0Parmi ceux-ci,\ua0trois ont \ue9t\ue9 diss\ue9qu\ue9s pour obtenir sept embryons uniques\ua0,\ua0tandis que 800 ont \ue9t\ue9 diss\ue9qu\ue9s pour obtenir 1312 jeunes ovules, qui ont tous \ue9t\ue9 cultiv\ue9s\ua0in vitro\ua0.\ua0Un total de 82 (6,25%) des ovules en culture ont form\ue9 des cals provenant de la\ua0r\ue9gion\ua0embryonnaire\ua0, qui est haplo\uefde. Quatre parmi sept embryons sauv\ue9s (57,1%) se sont r\ue9g\ue9n\ue9r\ue9s en plantules.\ua0Les analyses de plo\uefdie de 24 \ue9chantillons par cytom\ue9trie en flux ont r\ue9v\ue9l\ue9 que 23 des \ue9chantillons analys\ue9s \ue9taient diplo\uefdes.Cependant, un \ue9chantillon de cals \ue9tait anueplo\uefde.\ua0Un seul \ue9chantillon pr\ue9sentait un niveau d\u2019homozygotie exceptionnellement \ue9lev\ue9\ua0(84,2\ua0%).\ua0Ces r\ue9sultats sont les bases des recherches dans le futur sur la cause des haplo\uefdes dans le manioc