research
projects
locations UK – scientific experiments Kenya, Tanzania, Uganda – field experiments date March 2008 – March 2012 project team Joseph Mulema Daniel Karanja Lucy Karanja Duncan Chacha
breeding black rot resistant brassicas
Cabbage (Brassica oleracea ssp. capitata) and kales (B. oleracea ssp. acephala) are key crops for smallholder farmers in East Africa both for home consumption and to generate income.
so what’s the problem? Black rot caused by the bacterium Xanthomonas campestris pv. campestris (Xcc) is the most serious threat to brassica production here. Losses in excess of 90% have been reported in susceptible varieties. The disease is seedborne meaning that cultural control methods are less effective. Therefore, deployment of resistant varieties is the most effective management strategy. Use of this strategy however, is complicated by the high variability of the pathogen.
what is this project doing? This multidisciplinary project combines expertise in genetics, breeding, genomics and pathology to generate new information on quantitative resistance (way of determining the ranges of resistance) to black rot. The major objectives include determining the race structure of the East African strain of black rot. Also, as cabbages and kales are highly susceptible to black rot and Brassica rapa (Chinese cabbage) isn’t, our studies will concentrate on charactering factors essential for resistance and look at the potential of this resistance to protect against a range of black rot isolates. We also aim to fine-map the original identified genomic regions that control this resistance to identify closely linked molecular markers for use in plant breeding. Finally, we will identify black rot resistant varieties for cabbage and kale breeding programmes in East Africa. All this information will help breeders in the region to develop and deploy potentially resistant brassicas.
KNOWLEDGE FOR LIFE
results so far A survey of the status of black rot was conducted on smallholder farms in East Africa, from which a total of 250 isolates of the bacterium (141, 79 and 30 isolates from Kenya, Tanzania and Uganda respectively) were isolated and categorized. Race (variety) 1 was observed in Kenya and Tanzania while race 4 was observed in the three countries. Genomic fingerprinting with repetitive-PCR (a type of polymerase chain reaction that targets the repetitive sequences in bacterial genomes) revealed clusters that did not depict significant correlations between isolates and geographical location, isolates and host adaptation or isolates and race. It did however demonstrate existence of genetic differences within the East African black rot strains indicating that it is not just a cloned population. The next activity is to assess field resistance of the third-generation brassicas bred during the project, together with cabbage and kale varieties commonly grown in East Africa, and pre-breeding cabbage and kale lines for resistance to black rot. This will involve replicated field trials throughout two seasons in Kenya. And, on-going work involves fine mapping of the identified genomic regions.
www.cabi.org/blackrot partners Harper-Adams University College University of Warwick Kenya Agricultural Research Institute (KARI) Food and Environment Research Agency (FERA) in the UK The World Vegetable Centre - Regional Centre for Africa (AVRDC-RCA) sponsors Biotechnology and Biological Sciences Research Council (BBSRC) Department for International Development (DfID)
contact CABI, ICRAF Complex, United Nations Avenue, Gigiri, PO Box 633-00621, Nairobi, Kenya T: +254 20 72 24450 F: +254 20 71 22150 E: africa@cabi.org www.cabi.org/africa
ID-BLACKROT-06-12
Joseph Mulema, Project Manager