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University of Gezira (2012)

Variability and Host Specificity of Striga hermonthica (Del.) Benth, Populations in the Sudan

Belal, Awadallah Belal Dafaallah

Titre : Variability and Host Specificity of Striga hermonthica (Del.) Benth, Populations in the Sudan

Auteur : Belal, Awadallah Belal Dafaallah

Université de soutenance : University of Gezira

Grade : Doctor of Philosophy Crop Protection (Weed Science) 2012

Striga spp., Orobanchaceae, are obligate root parasites on important cereals and leguminous crops in Sub-Saharan Africa. Existence of physiological strains, ecological variants and races of the parasite together with variability in size of the seed bank offer serious obstacles for development of simple and effective control measures. Field surveys, laboratory and greenhouse experiments were conducted during seasons 2008/2009 and 2009/2010 to investigate variability and host specificity of Striga hermonthica (Del.) Benth. Field surveys were conducted during the rainy season in endemic areas in Eastern, Central and Western Sudan to investigate i) variability within S. hermonthica populations with respect to morphological characters, ii) possible reductions in growth and yield attributes of host and iii) relationship between the parasite and soil characteristics. Five locations were selected at random in each region. The laboratory and greenhouse experiments, designed to study host specificity and physiological variability, were undertaken at the Faculty of Agricultural Sciences, University of Gezira. S. hermonthica seeds used in these studies were collected from under sorghum in Eastern and Central Sudan, and millet in Western Sudan. Sorghum (cv. Abu-70) and millet (cv. Ashana) were used as test plants. In the laboratory studies, effects of GR 24, root exudates and root extracts of Abu-70 and Ashana on germination and early developmental stages were investigated. The green house experiments were setup to evaluate differential virulence of S. hermonthica populations on the aforementioned cereal cultivars. Treatments were laid in a randomized complete block design (RCBD) with three replications. Growth and harvest attributes on the parasite and crops were determined. Data were transformed, when necessary and subjected to statistical analysis as appropriate. The results of the surveys revealed that, S. hermonthica was pre-dominant on sorghum in Eastern and Central Sudan. While, in Western Sudan the parasite was reported on both sorghums and millet. S. hermonthica populations collected from Eastern Sudan showed the highest incidence, growth and harvest attributes followed, in descending order, by populations collected from western and central Sudan. S. hermonthica populations, invariably, showed considerable variations in flower characters. Striga infestation, on the average, reduced growth of sorghum and millet by 53.3 and 64.3%, and yield by 79.7 and 91.7%, respectively. The parasite effected significant differences in growth reduction and yield losses within cultivars, among locations and within locations. Striga population density, height, number of leaves, number of internodes and shoot dry weight were negatively (r = – 0.99 to – 0.7) correlated with pH, nitrogen, available phosphorous and exchangeable potassium in soils. However, they were positively (r = 0.89- 0.97) correlated with total carbon. The laboratory experiments revealed that, root exudates and extracts of all plants induced seed germination and haustorium initiation in S. hermonthica. The highest attachment and penetration attained by each of the were on their respective hosts. The greenhouse experiments showed that emergent S. hermonthica, capsules per plant, shoot dry weight and underground Striga plantlets were highest on the respective host. It is noteworthy that some of the Striga, sorghum populations, displayed limited emergence on millet and produced seeds. S. hermonthica populations significantly reduced growth and yield of sorghum and millet. However, the magnitude of the damage attained, by each population was highest on the respective host. These findings suggest the existence of both inter-and intra-crop specialization. Moreover, the results confirmed the existence of two strains of S. hermonthica, one specific to sorghum and the other to millet. These findings showed clearly the complexity of obtaining sorghum and millet cultivars with high and durable resistance across locations.


Page publiée le 27 mars 2019, mise à jour le 12 mai 2021