The effect of seven intra row spacing (10, 20, 30, 40, 50, 60, 70 cm) on the incidence and severity of downy mildew of pearl millet and yield components of a local pearl millet variety (Zango) were studied under field conditions in 2002 and 2003 at Samaru, Nigeria. Intra row spacing did not have significant effect on the incidence and severity of the disease but significantly increased plant height, panicle length and weight, 1000-grain weight and grain yield.

Aphid landing rates were monitored with horizontal mosaic green pan traps in monocultures of soybean, Glycine max (L.) Merrill, and in additive mixtures of soybean with dwarf or tall isolines of sorghum, Sorghum bicolor (L.) Moench. Rhopalosiphum maidis (Fitch) colonized sorghum whorls and was the major species caught in pan traps. Weekly aphicide spot applications to sorghum whorls, starting at 36 d after planting, did not suppress R. maidis colonies significantly until after the third application. ...

Rhopalosiphum maidis (Fitch) dominated the aerial aphid plankton in bean (Phaseolus vulgaris L.) monocultures and mixed cultures of bean with corn (Zea mays L.) in Illinois. It was also the most common species landing on bean plants in this study during the summer of 1987. More flight activity was recorded in the monocultures than in the mixtures. More R. maidis flew at the top of the bean canopy than at the level of the corn canopy. Densely planted corn rows suppressed flight activity more than ...

As population structure can result in spurious associations, it has constrained the use of association studies in human and plant genetics. Association mapping, however, holds great promise if true signals of functional association can be separated from the vast number of false signals generated by population structure1,2. We have developed a unified mixed-model approach to account for multiple levels of relatedness simultaneously as detected by random genetic markers. We applied this new approach ...

A method is presented for designing the outer‐end sprinkler of a center‐pivot irrigation system to prevent surface runoff. The smallest wetted diameter, for which soil infiltration capacity equalled or exceeded nozzle application rate, was determined by equating a nozzle application rate relationship and a Green and Ampt infiltration rate relationship. The computed wetted diameter was used in developing relationships to select nozzle type, orifice diameter, and operating pressure. Sensitivity ...

From 1985 to 1989 five large scale surveys were made to document the spread of the cassava mealybug (CM) Phenacoccus manihoti Matile‐Ferrero (Hom., Pseudococcidae) and the releases and successful establishment of its exotic parasitoid Epidinocarsis lopezi (De Santis) (Hym., Encyrtidae) through most cassava‐growing areas of Malawi. In a multiple regression analysis involving 29 meteorological, agronomic and plant variables from 476 fields, the duration of E. lopezi's presence was the major factor ...

Non-pathogenic endophytic Fusarium oxysporum inoculated into banana (Musa spp.) tissue culture plants can provide protection against banana weevils (Cosmopolites sordidus) and nematodes (Radopholus similis). The degree of control probably depends, in part, upon the level of endophyte establishment following inoculation. In this study, we compared three methods of inoculating endophytic fungi into eight week-old tissue culture plants: (1) Dipping the roots and rhizomes in a spore suspension, (2) ...

Host resistance is an important component for the management of late blight [Phytophthora infestans] on potato, in the highland tropics, where effective fungicide use is limited because of the cost of application. Potato cultivars with major resistance genes to late blight (population A) and minor or quantitative resistance genes to the disease (population B) were evaluated in field studies at two locations in Kenya during 2000, 2001, and 2002 cropping seasons. Disease severity, area under disease ...

Ten Cassava (Manihot esculenta, Crantz) genotypes were assessed for phenotypic fresh tuber yield stability for 2 years in nine locations in three West African countries (Nigeria, Ghana and Benin). From a combined analysis of variance for fresh yield, all main effects were significant. First order interaction genotype x year was not significant, while genotype and location interaction was significant. By Finlay and Wilkinson'sb-values tability statistic 82/00058 was considered highly yielding with ...

Selection of an appropriate sampling strategy is an important prerequisite to establish core collections of appropriate size in order to adequately represent the genetic spectrum and maximally capture the genetic diversity in available crop collections. We developed a simulation approach to identify an optimal sampling strategy and core-collection size, using isozyme data from a CIP germplasm collection on an Andean tetraploid potato. Five sampling strategies, constant (C), proportional (P), ...