Robert I. Hamilton

Weed Biomass Production Response to Plant Spacing and Corn (Zea mays) Hybrids Differing in Canopy Architecture1

Field experiments were conducted in 1996, 1997, and 1998 at Ste. Anne de Bellevue, Quebec, Canada, and in 1996 at Ottawa, Ontario, Canada, to quantify the impact of corn hybrids, differing in canopy architecture and plant spacing (plant population density and row spacing), on biomass production by transplanted and naturally occurring weeds. The treatments consisted of a factorial combination of corn type (leafy reduced stature [LRS], late-maturing big leaf [LMBL], a conventional Pioneer 3979 [P3979], and, as a control, a corn-free condition [weed monoculture]), two weed levels (low density [transplanted weeds: common lambsquarters and redroot pigweed] and high density [weedy: plots with naturally occurring weeds]), two corn population densities (normal and high), and row spacings (38 and 76 cm). At all site-years under both weed levels, the decrease in biomass production by both transplanted and naturally occurring weeds was greater due to the narrow row spacing than due to the high plant population density. The combination of narrower rows and higher population densities increased corn canopy light interception by 3 to 5%. Biomass produced by both transplanted and naturally occurring weeds was five to eight times less under the corn canopy than in the weed monoculture treatment. Generally, weed biomass production was reduced more by early-maturing hybrids (LRS and P3979) than by LMBL. Thus, hybrid selection and plant spacing could be used as important components of integrated pest management (weed control) for sustainable agriculture. Nomenclature: Common lambsquarters, Chenopodium album L. #3 CHEAL; corn, Zea mays L.; redroot pigweed, Amaranthus retroflexus L. # AMARE. Additional index words: Competitivness, early maturity, weed management. Abbreviations: LAI, leaf area index; Lfy, leafy; LMBL, late-maturing big leaf; LRS, Leafy reduced stature; P3979, Pioneer 3979; rd1, reduced stature.

Leaf profile of maize resistance factors to European corn borer,Ostrinia nubilalis.

The feeding preference of European corn borer larvae for immature whorl tissue of maize was examined by conducting leaf bioassays and quantifying resistance factors along the length of mid-whorl leaves from the maize synthetic BS9(C4) developed by recurrent selection for resistance. Potential resistance factors that were quantified included percent foliar nitrogen, gravimetric determination of soluble metabolites and fiber, soluble phenolics and hydroxamic acids, cell-wall-bound phenolics, leaf toughness, and UV absorbance of the epidermal cell wall determined by microspectrophotometry. Larvae consumed immature tissue at a higher rate than more mature tissue outside of the whorl, despite higher levels of DIMBOA in immature tissue. Consumption rate was highly negatively correlated with epidermal cell wall absorbance and leaf toughness. Fiber content and phenolic fortification of cell walls are proposed as the major resistance components that influence European corn borer feeding preference within the resistant synthetic BS9(C4).

Leafy reduced-stature maize for short-season environments: morphological aspects of inbred lines

Development of maize (Zea mays L.) types that produce leaf area rapidly and finish vegetative development quickly would increase production of maize in mid- to short-season areas. The Leafy (Lfy1) and reduced-stature (rd1) traits each make contributions to this end. However, these two traits have not previously been combined. Our objective was to evaluate the morphological aspects of non-leafy normal-stature (NLNS), leafy reduced-stature (LRS), non-leafy reduced-stature (NLRS), and leafy normal-stature (LNS) maize inbreds. Two traits, Lfy1 and rd1, were incorporated into a series of inbreds, resulting in a range of canopy architectures. Twelve variables were recorded for each of 30 inbreds over three years. The 12 variables were: seed emergence, above-ear leaf number, below-ear leaf number, dead leaf number at tasselling, live leaf number at tasselling, total leaf number, above-ear leaf area, ear leaf length, ear leaf width, ear height, internode length, and plant height. Inbreds containing the Lfy1 trait had more above-ear leaf area, above-ear leaf number, dead leaf number at tasselling, total leaf number and number of live leaves at tasselling than non-leafy inbred lines. Below-ear leaf number was not different among LRS, LNS, and NLNS inbred lines. LRS and NLRS inbred lines were also not different for below-ear leaf number. Plant height, ear height, and ear leaf length and width were higher in normal-stature than reduced-stature plants. The proportion of the seeds which emerged was higher for LRS inbreds than the other trait groups.

Leafy reduced-stature maize for short-season environments: Yield and yield components of inbred lines

Development of maize (Zea mays L.) types that produce leaf area and mature quickly would increase production of maize in mid- to short-season areas. The leafy (Lfy1) and reduced-stature (rd1) traits both make contributions to this end. However, these two traits have not previously been combined. Our objective was to evaluate the yield and yield components of non-leafy normal-stature (NLNS), leafy reduced-stature (LRS), non-leafy reduced-stature (NLRS), and leafy normal-stature (LNS) maize inbred lines. The two genes, ‘Lfy1’ and ‘rd1’, were incorporated into a series of inbred lines resulting in a range of canopy architectures. Ten variables were recorded for each of 30 inbred lines over three years. The 10 variables were: corn heat unit requirement from planting to tasselling, corn heat unit requirement from planting to silking, days between tasselling and silking, grain moisture content, husk dry weight, cob dry weight, ear length, maximum ear circumference, grain yield and ratio of grain yield to moisture content. Reduced-stature inbred lines reached anthesis more quickly than normal-stature inbred lines. Grain moisture content was less in reduced-stature inbred lines than normal stature trait groups. Leafy-reduced stature plants had the highest ratio of grain to moisture content and the lowest grain moisture content at harvest. Inbred lines containing the rd1 trait matured more rapidly than other trait groups. The LRS trait group yielded more than the other groups, and showed great potential for use in mid- to short-season environments.

Maize landraces of the St. Lawrence-Great Lakes region of North America

Thirty-five white maize (Zea mays L.) landraces were obtained by the Indian Agricultural Program of Ontario (IAPO) from native farmers in Ontario and New York State between 1986 and 1989. These landraces probably belong to the racial complex Northern Flints and Flours. The 35 landraces, one experimental population and one control hybrid were evaluated in field experiments at two sites in 1993 and 1994. Data were collected on 24 traits in order to characterize and classify the IAPO landraces. Most quantitative traits examined exhibited considerable variation among the IAPO landraces. Variation was also observed within many of the landraces for ear and cob colour, and for endosperm texture. Most ears had eight rows of kernels, but there was some variation for this among and within landraces. Based on seven traits from the two sites in 1994, the IAPO population was grouped into 10 clusters by centroid clustering analysis.

Evidence for spatial niche partitioning in predaceous aphidophaga: Use of plant colour as a cue

A field experiment involving aphid-free control and nutrient-stressed plants of 5 maize (Zea mays L.) genotypes was conducted to determine if predaceous aphidophaga use plant cues, such as colour, to select plants on which to forage. Nutrient stress resulted in plants lighter in colour (Yellow) than control plants in all the maize genotypes. Coccinellids were significantly more abundant on yellow plants than on greener control plants whereas chrysopids were significantly more numerous on controls in 3 out of 5 maize genotypes. These two groups of predators may use plant colour to partition habitat spatially and exploit their aphid prey while minimizing intraguild interactions.RésuméUne expérience de terrain avec des plants de maïs (Zea mays L.) de 5 génotypes différents et non infestés par des pucerons a été menée afin de déterminer si les prédateurs aphidiphages utilisaient un critère particulier pour choisir un plant. Plus précisément, l’intérêt était de savoir si les prédateurs étaient capables de discriminer entre des plants nutritionnellement stressés et des plants normalement fertilisés, étant donné que des carences nutritionnelles conduisent à des plants en apparence plus pâles (jaune). Des différences significatives ont effectivement été trouvées dans les choix qu’ont faits les prédateurs. Les coccinelles étaient plus abondantes sur les plants stressés que sur les plants non stressés alors que les chrysopes étaient plus nombreux sur les plants non stressés d’au moins 3 des 5 génotypes utilisés. Il est suggéré que les deux groupes de prédateurs se servent de la couleur des plants afin d’exploiter différentiellement dans l’espace les colonies de pucerons présentes dans un habitat donné. De cette façon, ces deux groupes de prédateurs minimisent les effets négatifs des interactions intraguildes.

Improved diagnosis of cowpea aphid-borne mosaic virus in Africa: significance for cowpea seed-indexing, breeding programs and potyvirus taxonomy

SummaryLarge-scale surveys in Africa for blackeye cowpea mosaic (BlCMV) and cowpea aphid-borne mosaic (CABMV) showed that several CABMV isolates from Southern Africa were either not or poorly recognized by monoclonal antibodies prepared to isolates collected in West Africa. Selection of three new monoclonal antibodies prepared against the Maputo (Mozambique) isolate of CABMV, and their incorporation into a revised panel of monoclonal antibodies, resulted in the assignment of four of these new CABMV isolates to existing serotypes (II, IV, and V) and three others to a new serotype (VI). The South African isolate of passiflora mosaic virus was shown to be related to CABMV isolates in serotype IV. It is proposed that CABMV isolates be assembled into a distinct species in the legume-infecting, aphid-transmissible potyviruses.

Taxonomy of Mexican landraces of maize, Zea mays, based on their resistance to European corn borer, Ostrinia nubilalis.

SummaryThe resistance to the European corn borer, Ostrinia nubilalis (Hubner), of thirty-seven indigenous landraces of Mexican maize was examined. The relationship of resistance and existing taxonomy of maize according to Wellhausen et al., (1952), was subjected to numerical analyses. Variables examined were: seedling DIM-BOA content, the extent of leaf feeding damage by early instar larvae both in the field and in the laboratory, the extent of plant breakage and stalk tunneling by late instar larvae, plant height, and the extent of fungal damage by Gibberella zeae and Ustilago maydis. Significant differences in resistance among the major taxonomic groupings were reflected in the existing taxonomy of maize (Wellhausen et al., 1952). The most resistant landrace grouping was Wellhausen et al.s Prehistoric Mestizos. Eighty-five percent of a series of modern inbred lines, pools, and Argentine landraces were found to have affinities with one of the more susceptible groupings, the Ancient Indigenous Races, based upon analysis of the resistance data.