Patterns Of Striga Resistance In Sorghum And Millets With Special Emphasis On Africa

Although host plant rcsistance in sorghum was denlonstrated as carly as 1920 both in Africa and India, its exploitation it1 breeding broad-spectrum stablc resistant cultivars started only recently. In pearl millet, however, the cxistcncc of host plant resistance is not yet clearly demonstrated. Striga-resistant sorghum varieties are in general agronomically poor. Multi-locational evaluation in Africa revealed that Framida ahd N 1 3 are the most stable rcsistant varieties. These two varieties were resistant to both S. asiatica and S-. herm-onthica. Some of the varieties like Najjadh, 12610C and IS 9830 revealed a narrow spectrum of rcsistance when tcsted across different seed samples of S. hcrmonthica. Ccnetic analysis of field rcsistancc in sorghum revealed that it is controlled predominantly by additive genc action and thus straight selection is effective. A pedigree approach to transfer resistance into elite agronomic backgrounds was successful. Several sclcctions with promising levels 01 resist~nce, stablc grain yiclds and good grain quality wcre identified and arc now in 'on farm' tests. In millet, a few less susceptible lincs have been identified. Intercrossing them and following the pedigree system of selection resulted in increased levels of rcsistancc and grain yields, The need for integrated Striga rnanagemcnt, ~ncluding resistant cultivars and complementary agronomic control practices, is cmphasised

Physiological Specialization Of Striga Hermonthica And Crop Specificity

Six samples of Strlga hermcnthica (Del.) Benth. from sorghum and eight from millet (Pennisetum anlerlcanuls (L.) K. Schum) were tested against two susceptible cultivars each cf sorghum and millet in 1981 and 1982 pot exparlments to present evldence for crc'p specificity. The Striga seed samples were collected from latitudes renging from 10°42'N to 13O29'N ariS ~~IiY€pSie Sti2ta ~~arro&rr ~&7k;!..:,: di~tribdtior,o f Stri~a-h -e rrcz?k!ce<. The results indicate that sorghun cultivars were able t,o germinate and support Striga from both sorghum and nlllet hosts whereas millets could orily support Striga from millet. However, ~n certain regions both the crops were attacked by both types of Striga. Extreme host specificity was not exhibited by the Striga samples Included in the present investigation. They represent intermediate forms which were able to attack sorghum more than 11,~:1esti nce sorghum is more exter~slvelyg rown in the region under study. In areas where millet Strlpa :aqjles were collected they attackfd mlilet but also retained the capsc:ty to attack sorghums. It is sugyrst~r: tt,;>t speclallzatlon is the outcorte of the Intensity with which a particular i'ost crop is grown at the exclusion of the other thus creating a r3L;roduct ~veis olation between so:gii~l...s qd ~IllIet Strlg? strains

Striga (Witchweeds) in Sorghum and Millet: Knowledge and Future Research Needs

Striga spp (witchweeds), are notorious root hemiparasites on cereal and legume crops grown in the semi-arid tropical and subtropical regions of Africa, the southern Arabian Peninsula, India, and parts of the eastern USA. These weed-parasites cause between 5 to 90% losses in yield; total croploss data have been reported. Immunity in hosts has not been found. Past research activities and control methods for Striga are reviewed, with emphasis on the socioeconomic significance of the species. Striga research involving biosystematics, physiological biochemistry, cultural and chemical control methods, and host resistance are considered. We tried to itemize research needs of priority and look into the future of Striga research and control In light of existing information, some control strategies which particularly suit subsistence and emerging farmers' farming systems with some minor adjustments are proposed. The authors believe that a good crop husbandry is the key to solving the Striga proble

Proceedings of the Second International Workshop on Striga

More than 1800 phanerogamic parasites have been recorded throughout the world. Among the most important are the parasitic figworts or Scrophulariaceae, which are economically damaging root parasites. The genus Striga, with more than 50 species, belongs to this family; however, only a few are completely parasitic and damaging to their hosts. Undoubtedly, the major species are S. hermonthica-a widespread and important pest of cereals in Af r ica-and S, asiatica, an important pest both in Asia and in eastern and southern Africa. Although precise estimates of crop loss are difficult to make and data are incomplete, it is well known that severe losses, amounting in many seasons to total crop failure, are caused by these parasitic weeds. However, there is still a general lack of awareness of the magnitude and importance of the problem. These Proceedings bring together the results of discussions held at Ouagadougou, Upper Volta, in October 1981, where the latest research findings and proposals for further research were presented. They highlight the important advances made in knowledge of the pest species, methods of control, and techniques for breeding for resistance to these noxious weeds. It is hoped that this publication will prompt increased effort to be focused on methods of combat ing Striga and reducing the serious losses it causes to cereal production, and on strengthening links between scientists working in numerous programs to produce solutions to outstanding research roblems

A time-course study of early establishment stages of parasitic angiosperm Striga asiatica on susceptible sorghum roots

A time-course study of the early establishment stages of Striga asiatica was carried out on a susceptible sorghum hybrid, CSH 1, using polyethylene bags and whole-root clearing and staining techniques. Preconditioned Striga seeds were applied to different aged segments of primary root but the results did not differ for these different aged segments. Most of the Striga seeds (63%) germinated within 24 h of inoculation on the host roots. The attachment of Striga radicles to host root was rapid and it occurred between 36 and 48 h after inoculation. Only 9% of the germinated Striga seeds attached to the host root but 65% of these attachments successfully penetrated through the epidermis and entered the host cortex within 72 h. Penetration through the cortical cells was difficult; only 17% of attachments were able to reach the endodermis. Penetration took from 12 to 43 h after the first appearance of haustorial cells in the cortex; a total of 84 to 120 h after inoculation on the host root. Penetration through the endodermis and establishment on the host stele was relatively easier, as most of the haustoria reaching the endodermis were able to establish on the host stele. But this is a slow process taking a minimum of 24 h, and a maximum of 60 h after first contact of haustorial cells with the endodermis. The minimum time taken from inoculation of ungerminated Striga seed on the host root to establishment is about 108 h. The results are discussed in relation to published reports on other parasitic species such as Agalinis purpure

Inheritance of Striga seed-germination stimulant in sorghum

Inheritance of Striga seed-germination stimulant from S. asiatica seed collected at ICRISAT Centre was investigated in sorghum using 3 low-stimulant-producing (resistant) cultivars (555, Framida and SNR6496) and 6 high-stimulant-producing (susceptible) cultivars (Swarna, NJ2006, IS508, 168, 148 and M35-1). From a study of the parents, F1, F2 and backcross F2 seedling progenies of 9 crosses between resistant and susceptible parents, it was concluded that low stimulant production is under the control of a single recessive allele. It was not determined whether this allele was the same in the 3 resistant parent

Selection of sorghum (Sorghum bicolor (L.) Moench) varieties resistant to the parasitic weed Striga hermonthica (Del.) Benth

Pot and field experiments were performed in Burkina Faso in 1987 and 1988 to evaluate the resistance of selected ‘low-stimulant’ sorghum (Sorghum bicolor (L.) Moench) varieties to the parasitic weed (Striga hermonthica (Del.) Benth. In a pot experiment, the variety IS-7777 supported the lowest number and had the latest emergence of Striga, compared with the other varieties tested. The varieties IS-14825, IS-6961, IS-7739, IS-14928 and IS-14975 also had signifi cantly lower numbers of emerged Striga per pot than the resistant control Framida. The resist ance of IS-7777 was confirmed in field experi ments, as was that of IS-7739, IS-6961 and IS-14928. However, the yield potential of these poorly adapted varieties was low in Striga-infested fields. The varieties IS-14975, IS–14825 and Seguetana Niarabougou exhibited a low susceptibility associated with a grain yield equivalent to that of the other varieties in farm fields infested by Striga. As Seguetana is already grown by Sahelian farmers, its use could be recommended in the absence of resistant varieties adapted to Sahelian agroclimatic conditions. The exceptionally high level of restance exhibited by IS-7777 could be exploited in studies on the genetics and mechanisms of resistance of the host plant to the parasite, as well as in sorghum improvement programme

Ti:sapphire-pumped deep-infrared femtosecond optical parametric oscillator based on CdSiP2

We report on a femtosecond optical parametric oscillator (OPO) for the deep-infrared (deep-IR) based on the Kerr-lens-mode-locked Ti:sapphire laser as the pump source. By deploying a novel cascaded intracavity arrangement, comprising a femtosecond OPO based on the nonlinear crystal, CdSiP2CdSiP2, synchronously pumped internal to a MgO:PPLN femtosecond OPO, we have generated broadly tunable radiation across 5958–8117 nm using rapid static cavity delay tuning, with a maximum power of 64 μW at 6791 nm, limited by the absorption in mirror substrates as well as polarization-dependent intracavity losses. The deep-IR idler power exhibits excellent passive stability of better than 1.1% rms over 2 h, with a spectral bandwidth as large as ∼650  nm∼650  nm at ∼6800  nm∼6800  nm. The demonstrated concept is generic and can be similarly deployed in other operating time scales and wavelength regions, also using different laser pump sources and nonlinear materials.Peer ReviewedPostprint (author's final draft