A field study was conducted to determine the combined effects of row spacing, plant density, and herbicides on weed management and dry bean (Phaseolus vulgaris) yield. In weed-free dry bean, a reduction in row spacing from 69 to 23 cm increased yield by 19% and an increase in density from 20 to 50 plants/m2 increased yield by 17%. In the presence of weeds, narrow rows and high plant densities increased dry bean yield, but without herbicides, yields remained low. However, when combined with herbicides, narrow-row and high-density production practices resulted in better weed control and higher dry bean yield than that attained in a wide-row and low-density production system. Herbicide combinations, often at reduced rates, controlled weeds as well or better than the full rate of any individual herbicide. Ethalfluralin applied preplant incorporated followed by reduced rates of imazethapyr or bentazon postemergence (POST) consistently controlled weeds. Imazamox exhibited the potential to provide a total POST weed control option in dry bean production. Information gained in this study will be used to develop improved weed management programs appropriate for either wide- or narrow-row dry bean production systems.
An understanding of the genetics of the long daylength response of soybean [Glycine max (L.) Merrill] would facilitate the development of cultivars adapted to the long days of the northernmost growing areas of North America and Europe. The objective of this study was to determine the genetic control of soybean response to extension of the natural daylength to 20h using incandescent lamps. Three pairs of near‐isogenic lines (NIL) plus a long daylength insensitive check were grown outdoors and rated visually for response to incandescent long day (ILD). The same entries were further grown indoors and rated for response to extension of the natural daylength to 20h using cool white fluorescent lamps (FLD). Based on these results, entries were classified for alleles at the E3 and E4 maturity loci. Check OX619 and ILD‐insensitive NILs X2398, X2403, and X2396 were classified genotypically as e3e3 e4e4. The respective recurrent parents were all ILD‐sensitive and were classified: Evans‐e3 and Harosoy‐e3 as e3e3 E4E4 and ‘Maple Arrow’ as E3E3 e4e4. Analyses of F2 and F2:3 populations from five crosses revealed that only the e3e3 e4e4 genotype is ILD‐insensitive. Consequently, a model of two (E3 and E4), each with two alleles, each with dominance, plus epistasis of E3 on e4> is proposed to explain the ILD‐insensitivity. It was concluded that E3 is the major locus conferring long daylength insensitivity in soybean, but both E3 and E4 have to be considered when breeding for insensitivity to long daylength using ILD.
Delays in reproductive development of soybean [Glycine max (L.) Merr.l segregants grown under the long daylengths of higher latitudes have impaired the use of elite germplasm from lower latitudes when developing cultivars for short‐season areas. The responses of soybean to long daylength are under the control of at least two loci, but only E3 has been shown to affect the phenology of plants grown in the field. The objectives of this study were to measure the effect of E4 on the phenology of Maturity Group (MG) 00‐I soybeans grown in the field and under incandescent long daylength (ILD) created by extending the natural daylength to 20 h using incandescent lamps, and to identify the growth stage at which selection for ILD‐insensitivity is appropriate. Most ILD‐insensitive plants were able to mature before frost under ILD and selection conducted at or close to R5 under ILD permits identification of ILD‐insensitive genotypes. Growth stage measurements recorded on three different F2 populations (homozygous for e3) grown in the field indicated dominance of E4 over e4. Alleles of E4 influenced the duration of pre‐and post‐flowering periods on ‘Evans’ and ‘Harosoy’ backgrounds, whereas it only affected post‐flowering period in ‘Maple Amber’ background. The E4 locus had a stronger delaying effect in later maturing backgrounds, indicating a potential nonadditive interaction between E4 and other unknown maturity loci. It was concluded that selecting e3e3 e4e4 segregants in a population arising from a late by early maturity cross should help to limit the number of backcrosses to early elite lines required to recover acceptable maturity. This may allow more genes from the late parent to be retained by the early segregants, thereby broadening the gene poll available in a given maturity group.
Dry bean (Phaseolus vutgarts\tolerance to imazethapyr' Can' J' Plant Sci' 76: gl5-g1g. A field study was conducted during 3 y. io'aet.rrine tne fiowttr and yield response of Pinto' Pink, Red, and Great Northem dry beans to various doses of imazelhupyt. f-"".tttnpyr wasipplied posiemetgence a1 O.' ]S'.fO' 75' 100' 150' and 200 il;:i; .rrirr .i"5 "r a.y bean. Results
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