In vitro embryo rescue and plant regeneration following self-pollination with irradiated pollen in cassava (Manihot esculenta Crantz)

Cassava is a highly heterozygous species; hence, current methods used in classical cassava breedingcannot match the urgent need to high yielding varieties. Recently, progress was made through androgenesis and gynogenesis as pathways for raising doubled cassava haploid lines to overcome problems associated with cassava’s inherent reproductive biology, but these efforts were limited (nocandidate cassava plantlets were regenerated). For the first time, this study shows that pollen irradiation coupled with self-pollination and embryo rescue regenerated 62 candidate cassava plantlets. Plants of an elite cassava variety, Nase14, served as a mother plant and as the pollen donor for the irradiation. Irradiation dosages of 50 to 250 Gray studied across five pollination events and 300 or 500 Gray in one pollination event caused a reduction in pollen germination up to 67.0%. By 15 days after pollination (DAP) with irradiated pollen, up to 89.7% of the pollinated flowers had aborted. By embryo rescue time (42 DAP), significant differences were observed in number of fruits, seeds and embryos generated, with the non-irradiated pollen treatments having significantly higher numbers. Sixteen (16) heterozygous SSR markers in the parent and ploidy analysis showed that none of the regenerated plants was haploid or homozygous. However, the plantlets resulting from pollination with non-irradiated pollen had 56.2% homozygous loci, while progeny derived from irradiated treatments had frequencies of homozygous loci between 28.1 and 55.0%. This is the first time to use irradiated pollen in cassava as a pathway to generate candidate plantlets as an initial step in double haploid production.Key words: Cassava, doubled haploids, embryo rescue, plant regeneration, pollen germination, pollenirradiation

Responding to the soybean rust epidemic in sub-Saharan Africa: A review

Soybean rust (Phakopsora pachyrhizi Sydow), a major threat to soybean production, is a new pathogen on the African continent, where it is increasingly threatening soybean production. The fungus is highly variable, and this complicates most disease management strategies. Most research on soybean rust, its epidemiology and management has been in the Orient, and only limited work has been done in Africa. However, experiences in the Orient will be important for soybean rust researchers in Africa, who are currently combating the epidemic. This approach will be necessary to design and implement rust management strategies in the African countries already affected, and those as yet unaffected. Because there is little information on distribution, epidemiology, and management of soybean rust from Africa, this paper provides an overview on 1) soybean rust epidemiology, disease assessments and management, as experienced in the endemic areas, 2) the distribution of soybean rust in Africa, 3) on-going research activities in the African countries most affected, and 4) discusses priority research activities. This review is intended to stimulate future research activities, leading to a better understanding of the pathogen, its biology and ecology, and management. Key Words: Control, epidemiology, Phakopsora pachyrhizi, yield losses RÉSUMÉ La rouille du soja (Phakopsora pachyrhizi Sydow), une menace majeure de production du soja, est un nouveau pathogène sur le continent Africain, où il est entrain de menacer de manière croissante la production du soja. Le champignon est hautement variable, et ceci complique la plupart des stratégies de gestion de la maladie. La plupart des recherches sur la rouille du soja, son épidémiologie et sa gestion ont été faite en orient, et seulement du travail limité a été fait en Afrique. Cependant, les expériences en orient seront importantes pour les recherches de la rouille en Afrique, qui combattent couramment l'épidémie. Cette approche sera nécessaire pour concevoir et implémenter les stratégies de gestion de la rouille dans les pays Africains déjà affectés, et ceux pas encore atteints. Parce que il y a peu d'information sur la distribution de la rouille du soja, l'épidémiologie et la gestion de la rouille venant de l'Afrique, cet article fourni une vue générale sur 1) la rouille du soja, l'épidémiologie, l'évaluation et la gestion de la maladie,telle que expérimentée dans les aires endémiques, 2) la distribution de la rouille du soja en Afrique, 3) les activités de recherche courantes dans les pays Africains les plus affectés, et 4) discute la priorité des activités de recherche. Cette évaluation est proposée pour stimuler les activités futures de recherche, menant à une meilleure compréhension de pathogène, sa biologie et son écologie, et sa gestion. Mots Clés: Contrôle, épidémiologie, Phakospsora pachyrhizi, les pertes de rendement African Crop Science Journal Vol.11(4) 2003: 301-31