Brita Dahl Jensen

Field evaluation for resistance to the black rot pathogen Xanthomonas campestris pv. campestris in cabbage (Brassica oleracea)

Black rot, caused by Xanthomonas campestris pv. campestris, (Xcc), is one of the most serious diseases of crucifers world-wide. Forty-nine genotypes were evaluated for resistance under field conditions in Tanzania after artificial inoculation with Xcc race 1. Open pollinated white cabbage cultivars were generally susceptible, while Portuguese and pointed cabbages exhibited partial resistance. Some F1 white cabbage cultivars were highly susceptible, whereas others exhibited a high level of partial resistance. The most promising of the hybrid cultivars were T-689 F1, Gianty F1, No. 9690 F1, N 66 F1, and SWR-02 F1. Breeding line Badger I-16 exhibited the highest level of resistance of all genotypes. The genotypes accounted for 72.9–75.5% of the variation of the disease severity when assessed on the leaves, and 71.4% of the variation when assessed as internal black rot in heads at harvest. High correlations (equal to or above 0.7) were found between disease severities assessed on leaves three times during the growing season and also with the amount of internal black rot in heads. Leaf loss also was correlated with disease severity. The high genetic determination of the trait and the high correlations between disease assessments indicate that selection for resistance to black rot will be efficient when field screenings are carried out. Evaluation of genotypes for disease severity on leaves during the growing season combined with evaluations of head resistance in the most promising genotypes may be a simple method to select resistant cultivars.

On-farm yield potential of local seed watermelon landraces under heat- and drought-prone conditions in Mali

On-farm yield experiments were carried out in the Tombouctou region of Mali in 2009/10 under heat- and drought-prone desert conditions with three local landraces of seed-type watermelons. The landraces, named Fombou, Kaneye and Musa Musa by the farmers, exhibited distinct characteristics for fruit morphology, but in particular for seed traits. On average, the three landraces produced a fruit yield of 11·6 t/ha and an estimated seed yield of 364 kg/ha, with no significant differences among landraces. Kaneye showed the highest stability of fruit number/ha in different field environments, suggesting this landrace is the best among the three for a poor growing environment, whereas Fombou and especially Musa Musa responded positively to more favourable environments. Seed weight revealed a different trend, with Fombou as the most responsive to favourable conditions, while Kaneye and Musa Musa were less responsive. The yields obtained suggest that these local landraces of watermelon are valuable plant genetic resources for securing food supply in arid, heat- and drought-prone areas.

Traditional uses and cultivation of indigenous watermelons (Citrullus lanatus) in Mali

Traditional knowledge associated with uses and cultivation of indigenous watermelon landraces was surveyed in five regions of Mali. Production of local types of watermelon plays an important role for many households. Farmers in charge of the production were mostly men, while women were in charge of seed extraction and processing. In total, ten types of landraces were differentiated, of which seven were seed types. The frequency of the types differed in the five regions, reflecting different agroecological conditions and traditions. Red, sweet flesh types used for dessert dominated in the more humid areas of West and Central Mali and were used as a cash crop. White flesh types, mainly grown for their seeds, were more important towards the desert region in the North. Here, a wild type was also used for human consumption. The seed was processed into sauces, snacks, and porridge, contributing fat and protein to the diet. Seed for sowing was sourced on-farm. In West and Central Mali, watermelons were intercropped with cereals. In the North, watermelon was cultivated as a sole crop in the sandy soils. Some of the landraces possess high heat and drought tolerance, a trait of interest to enhance food security in arid and desert areas.