Insect and disease resistance from tropical maize for use in temperate zone hybrids

Biotic constraints (insects, diseases, parasitic weeds) and abiotic stresses (drought) are widespread and pose a constant threat to maize production worldwide. Tropical environments provide the greatest opportunity for evolution of insects and diseases because of the favourable year- round climatic conditions. Year-round breeding programs permit selection of stable general resistance against specific or combined challenges. The IITA Maize Program initiated a line-development project in 1979. The major objectives of this project were to develop vigorous, tropically adapted inbreds that confer general resistance or tolerance against specific African as well as common tropical production constraints. Important constraints in Africa are stem borer (Sesamia calamistis, Eldana saccharina and Busseola fusca), storage insects (Si-tophi/us spp.), foliar diseases (Maize Streak Virus, Puccinia palysora, Hel•mintho.parium maydu, Exserohilum turcicum, Curvularia palle.cens.downy mildew), stalk and ear rots (Fusarium moniliform, Botryodiplodiat Mobromae, Macrophomina phauolii, Striga hermonthica, and drought. Some of these problems occur in the U.S. Com Belt and in other parts of the world. The Maize Inbred Resistance (MIR) project of the University of Hawaii tested 120 tropically adapted inbred collections at 27 locations worldwide, including tropical. Sub-tropical and temperate regions. Sources for high levels of general resistance were found for most insects and diseases. The selected inbreds could be valuable sources of resistance for developing inbreds and hybrids adapted to the Com Belt. This paper presents current results regarding general resistance to the major production constraints of maize worldwide and introduces a pioneering approach for testing combining ability of tropical inbreds for temperate as well as tropical regions

Balanço do nitrogênio e fósforo em solo com cultivo orgânico de hortaliças após a incorporação de biomassa de guandu.

Os objetivos deste trabalho foram avaliar os efeitos de faixas de guandu (Cajanus cajan) e da incorporação da biomassa proveniente de sua poda na fertilidade do solo e na produtividade de três hortaliças sob cultivo orgânico. O delineamento usado foi de blocos casualizados completos em esquema de parcelas subsubdivididas com três repetições. As produtividades de beterraba, cenoura e feijão-de-vagem não foram afetadas pelos tratamentos. Nas parcelas onde não houve incorporação da biomassa de guandu, o balanço de nitrogênio no sistema foi negativo, ao passo que com a incorporação, esse balanço foi positivo. Embora tenha ocorrido balanço positivo para o fósforo nas parcelas sem a incorporação de biomassa de guandu, houve um aumento significativo na absorção desse elemento pelas hortaliças quando o material foi incorporado. O sistema de cultivo em aléias de guandu pode representar uma prática vantajosa para os produtores orgânicos, por contribuir na manutenção da fertilidade do solo

Systematics, self-incompatibility, breeding systems, and genetic improvement of leucaena species

Meeting: Leucaena Research in the Asian Pacific Region, 23-26 Nov. 1982, Singapore, SGIn IDL-762

Nitrogen fixing trees for fodder and browse in Africa

Meeting: International Workshop on Alley Farming in the Humid and Subhumid Tropics, 10-14 Mar. 1986, Ibadan, NGIn IDL-282

Combining ability of tropical maize germplasm in West Africa. III. Tropical maize inbreds

One hundred elite, open-pedigree tropical and subtropical inbreds of maize (Zea mays L.) that had been screened in 60 tropical trials were evaluated as inbreds and in testcrosses in Nigeria. The 24 superior inbreds among these were chosen to create two diallel sets for evaluation of grain yield and agronomic competence. Included were lines bred in Colombia, Florida, Hawaii, India, Kenya, Nigeria, South Carolina, Texas, and Thailand. The two diallels included 78 hybrids of 13 inbreds with yellow kernels and 55 hybrids of 11 inbreds with white kernels. The diallel of 13 yellow inbreds was evaluated in 11 replicated trials throughout Nigeria, and the white diallel was evaluated similarly in five environments. About 50% of the parental inbreds had dent kernels and 50% were flints. Most dent inbreds were related to Tuxpeño and Southern U. S. Dents and most flint lines were related to Caribbean germplasm. Grain yields of the 78 yellow hybrids were obtained from ten environments, whose averages ranged from 3.0 to 7.7 t/ha. The hybrids showed highly significant differences and interacted significantly with environments. General combining ability (GCA) values for the 13 elite parents, however, did not differ significantly. Every inbred served as parent of one or more outstanding hybrids. Similarly, the 55 white hybrids differed significantly in three measured environments, whose averages ranged from 2.9 to 4.5 t/ha. GCA values for the 11 elite white parents were significant (P = 0.05), and every inbred served as parent for one or more superior hybrids interactions of hybrids with environments were highly significant for the yellow diallel, but not for the white diallel, Yellow inhreds Fla2BT106 (Florida, dent) and Ki9 and Kil4 (Thailand, flint) had the highest GCA values and superior hybrids, while the four white inbreds with superior GCA values were all bred in Nigeria (TZi3, TZi8, TZi12 and TZi15) and all were flints or flinty dents, Some outstanding hybrids were flint x dent crosses, often representing the cross of Tuxpeño and Caribbean heterotic groups, but many were not. It could be argued that each of these inbreds and their close relatives represent a potential heterotic group, drawn as they were from such a wide range of tropical germplasm, and evaluated over such a wide range of environments, Breeding tropical maize inevitably focusses on resistances to diseases, insects and stresses. These data suggest that yield heterosis is no more significant as a constraint to the tropical hybrid breeder than is inbred and hybrid tolerance of biotic and abiotic stress

Resistance of tropical maize inbreds to major virus and viruslike diseases

Tropically-adapted maize inbreds of high combining ability were evaluated internationally for general resistance to seven virus and virus-like diseases, all insect-transmitted. Replicated trials under controlled viral epibiotics were conducted at five locations as part of the collaborative Maize Inbred Resistance project. The viruses and testing sites included CS (corn stunt mollicute complex) in Mexico, MBSDV (maize black-streaked dwarf virus) in Korea, MCDV (maize chlorotic dwarf machlovirus) in Ohio, MDMV (maize dwarf mosaic potyvirus strain A) in Hawaii and Ohio, SCMV-MB (sugarcane mosaic potyvirus MB) in Ohio, MMV (maize mosaic potyvirus) in Hawaii and MSV (maize streak geminivirus) in Nigeria. Over 100 open-pedigree inbreds, largely of tropical origin, were scored empirically to each virus and ranked on the basis of mean values for all entries. A relatively high proportion of the inbreds showed high or moderate resistance to MDMV-A (49%), MMV (42%) and SCMV-MB (33%), while fewer were resistant to CS (23%) and MSV (17%). Very few showed resistance to MBSDV and none to MCDV, both temperate viruses. Few inbreds showed combined resistance to more than two viruses. Only four instances of significant resistance correlations occurred, notably between the related potyviruses MDMV-A and SCMV-MB (r = 0.49). Resistance was derived primarily from regions where each virus was originally endemic