Showing papers on "Plant disease resistance published in 1972"

Directed Mass Selection for Developing Multiple Pest Resistance and Conserving Germplasm in Alfalfa

Abstract: Recurrent phenotypic selection, a form of mass selection, proved effective for developing resistance in two populations of alfalfa (Medicago sativa L.) to the following (i) diseases: rust, common leafspot, bacterial wilt, and anthracnose, caused by Uromyces striatus Schroet. var. medicaginis (Pass.) Arth., Pseudopeziza medicaginis (Lib.) Sacc., Corynebacterium insidiosum (McCull.) H. L. Jens., and Colletotrichum trifolii Bain and Essary, respectively; and (ii) insect pests: spotted alfalfa aphid [Therioaphis maculata (Buckton)] and potato leafhopper [Empoasca fabae (Harris)]. general vigor of the populations also increased in generations of selection conducted in the field. The success of mass selection in alfalfa prompted us to suggest ways in which this breeding method could be used to conserve genetic diversity still available in alfalfa, develop combined resistance to disease and insect pests, and reduce dependence on pesticides. We propose an integrated program of worldwide collection, recombination, and mild selection to conserve and improve alfalfa germplasm resources. The key feature of the program is the development of seven gene pools by mass selection, representing seven geographic regions and a wide range of environments, to provide improved source material for breeding regionally adapted, multiple pest-resistant varieties. Resistant varieties developed by recurrent mass selection can be expected to be less vulnerable to attack by mutant forms of the pathogen or insect than varieties developed by breeding procedures which give more attention to genetic uniformity.

Research on vascular wilt disease of the oil palm.

Abstract: La fusariose du palmier à huile fut signalée pour la première fois par "\VARDLAW en 1946 (a) au Zaïre. La même année un Fusarium oxysporum a été isolé des palmiers malades [WARDLAw, 1946 b]. Plus tard FRASELLE (1951) a pu reproduire la maladie en inoculant ce Fusarium oxysporum à des plantules de palmiers. La maladie a été reconnue au Nigeria [WARDLAW, 1948], en Côte-d'Ivoire [BACHY et al., 1957], au Congo Brazzaville et au Dahomey. Les dégâts qu'elle cause sont importants. GuLDENTOPS (1962) signale au Zaïre des plantations de dix ans où la moyenne des palmiers disparus ou en voie de disparition atteint 25 p. 100. Sur la Plantation Expérimentale R. Michaux de l'i. R. H. O. à Dabou, le pourcentage moyen annuel de palmiers fusariés s'élève à 1 p. 100. L'effet de la lignée est extrêmement important et, si certains croisements présentent déjà 40 p. 100 d'arbres fusariés à 8 ans, d'autres sont beaucoup plus résistants et n'en renferment que 3 à 4 p. 100 au même âge. Dans une parcelle de 6,25 ha contenant 20 p. 100 de palmiers morts ou atteints de fusariose, on a pu évaluer que les pertes représentent 12 p. 100 de la production moyenne cumulée pendant les quatre premières années. Tout cela en fait sans aucun doute la maladie cryptogamique la plus importante du palmier à huile en Afrique. En Côte-d'Ivoire, on peut estimer qu'elle occasionne chaque année la disparition d'environ 10 000 palmiers dans la seule savane de Dabou. Son apparition récente dans les plantations des zones forestières périphériques de la savane ou dans la plantation de l'i. R. H. O. à La Mé prouve en particulier que la maladie peut exister en zone forestière et qu'elle est une menace pour les quelque 60 000 ha de palmiers à huile de la SO. DE. PALM. déjà plantés. Dans le cas d'une maladie vasculaire, la recherche de matériel végétal résistant est le seul moyen efficace de lutte. Des observations déjà anciennes sur le terrain et des contaminations de jeunes plants par F. oxysporum avaient montré que des différences de sensibilité existaient. Ces résultats ont été exploités et en s'inspirant d'une méthode utilisée par PRENDERGAST (1963), des tests ont été mis au point et effectués à grande échelle dans le but de produire des lignées résistantes. 1. 1 NTRODUCTIO N

Introduction: disease resistance in plants

Abstract: This paper discusses in general terms the mechanisms proposed to explain the resistance of higher plants to infection and colonization by bacteria and fungi, especially the type of resistance associated with rapid killing of host cells and very limited growth of the pathogen; that is, with the hypersensitive reaction of the plant to infection (h.r.). The main points considered are: the significance of the h.r. for obligate and other types of parasites; the nature of the h.r. and the means by which it is invoked; the absence of the h.r. in compatible host-parasite combinations; the h.r. and the production of phytoalexins, and the role of the latter in resistance; the part played by cell-wall degrading enzymes in the earliest stages of infection; the relation between the h.r. in interactions between races of a pathogen and different forms of a host species, on the one hand, and the resistance of all plants to almost all pathogens, on the other. Also discussed is the less specific but important type of resistance in which the pathogen continues to grow in resistant plants more slowly than in susceptible plants.

Quantitative genetics of sugarcane : IV. Genetics of Fiji disease resistance.

Abstract: 1. Fiji disease is an important virus disease of sugarcane in many countri es. In Fiji, its vector is the leafhopper Perkinsiella vitiensis. 2. The usual measure of resistance under insectary test conditions is the number of days required after exposure to viruliferous hoppers for half the test plants of a clone to show the diagnostic symptoms (SD50). Previous studies have shown this measure is related to resistance under field conditions and is convenient to record. 3. A quantitative genetic analysis has been made of resistance to Fiji disease in a hybrid sugarcane population. 4. The SD50 measure of resistance showed a heritability and repeatability of about 0.4. These results indicated that Fiji disease resistance can be improved by breeding and selection. 5. No unfavourable correlations were detected between resistance and other commercial attributes. 6. In a mixed stand, sugarcane clones differ for the number of leafhoppers found on them. However no necessary relationship was detected between this character and resistance to Fiji disease.