This study investigated the induction and loss of dormancy in oilseed rape (Brassica napus). Twenty genotypes were preliminary screened; from these, two genotypes, RGS003 and Hayola 308, which possess high potential for dormancy induction (HSD) and medium potential to induce secondary dormancy (MSD), were selected. The stratification of seeds at alternating temperatures of 5–30°C (in dark) significantly relieved secondary dormancy, but dormancy was not fully released. The ψb(50) values were −1.05 and −1.06 MPa for the MSD and the HSD before dormancy induction. After inducing dormancy, the ψb(50) values for the MSD and the HSD were increased to −0.59 and −0.01 on day 0 stratification at 20°C. The hydrothermal time (θHT) value was low for one-day stratification for HSD in comparison with other stratification treatments. Water stress can induce dormancy (if the seeds have the genetic potential for secondary dormancy) and warm stratification (in dark) can only reduce the intensity of dormancy. The seeds with a high potential of dormancy induction can overcome dormancy at alternating temperatures and in the presence of light. It can, therefore, be concluded that a portion of seeds can enter the cycle of dormancy ↔ non-dormancy. The secondary dormant seeds of B. napus cannot become non-dormant in darkness, but the level of dormancy may change from maximum (after water stress) to minimum (after warm stratification). It seems that the dormancy imposed by the conditions of deep burial (darkness in combination with water stress and more constant temperatures) might be more important to seed persistence than secondary dormancy induction and release. The dormancy cycle is an important pre-requisite in order to sense the depth of burial and the best time for seed germination.
Field experiments were conducted to investigate the influence of cowpea (Vigna unguiculata) density (0, 15 or 30 plants/m 2 ) and sowing date (15 days prior to maize sowing or simultaneously with maize), and of maize (Zea mays) planting density (7.5 or 9 plants/m 2 ) on weed biomass and maize crop yield. Results showed that increasing the maize density from 7.5 to 9 plants/m 2 reduced the weed biomass by 21.5%. Furthermore, cowpea acted as a living mulch, reducing weed biomass by up to 45.5% and 39.6% when intercropped with maize at a density of 7.5 and 9 plants/m 2 , respectively. Under weed-free conditions, an increase in maize density from 7.5 to 9 plants/m 2 resulted in maize grain yield increasing from 8.92 to 9.40 t/ha; however, the addition of cowpea only increased the maize grain yield by about 4.2%, on average, under these conditions. By contrast, under weed-infested conditions, there was a large decrease in maize grain yield (up to 32%), but intercropping with cowpea reduced this to only a 16% decrease. Under weed-free conditions, there was no effect of sowing date on maize grain yield; however, under weed-infested conditions, yield was greater on the second sowing date. Thus, it is concluded that the planting of maize at a density of 9 plants/m 2 and simultaneously intercropping with cowpea at a density of 30 plants/m 2 could be an appropriate control measure for weed suppression.
Ghabel R., Rajabipour A., Ghasemi-Varnamkhasti M., Oveisi M., 2010. Modeling the mass of Iranian export onion (Allium cepa L.) varieties using some physical characteristics. Res. Agr. Eng., 56: 33-40.Mass modeling can be used for development of post-harvest equipment related to onion (Allium cepa L.) processing such as grading, packing and food production processes. There are instances in which it is desirable to determine relationships among crop physical characteristics. In this study, the mass of Iranian export onion varieties (Azarshahr and Sefide Qom) was predicted by using different physical characteristics applying linear models with three different classifications: (1) -single or multiple variable regressions of onion dimensional characteristics, (2) -single or multiple variable regressions of onion projected areas, (3) -estimating onion mass based on measured (actual) volume and volumes of assumed shapes (prolate spheroid and ellipsoid). The results showed that mass modeling of onion based on length and three projected areas are the most appropriate models in the first and second classification, respectively. In third classification, the highest determination coefficient was obtained for mass modeling based on the actual volume as R 2 = 0.99 whereas corresponding values were 0.96 for both assumed onion shapes (prolate spheroid and ellipsoid), respectively. In economical and agronomical point of view, suitable grading system of onion mass was obtained based on length as nonlinear relation M = 0.035a 2 -1.64a + 36.137, R 2 = 0.96.
Continuous use of herbicides has triggered a phenomenon called herbicide resistance. Nowadays, herbicide resistance is a worldwide problem that threatens sustainable agriculture. A study of over a decade on herbicides in Iran has revealed that herbicide resistance has been occurring since 2004 in some weed species. Almost all the results of these studies have been published in national scientific journals and in conference proceedings on the subject. In the current review, studies on herbicide resistance in Iran were included to provide a perspective of developing weed resistance to herbicides for international scientists. More than 70% of arable land in Iran is given over to cultivation of wheat, barley, and rice; wheat alone covers nearly 52%. Within the past 40 years, 108 herbicides from different groups of modes of action have been registered in Iran, of which 28 are for the selective control of weeds in wheat and barley. Major resistance to ACCase-inhibiting herbicides has been shown in some weed species, such as winter wild oat, wild oat, littleseed canarygrass, hood canarygrass, and rigid ryegrass. With respect to the broad area of wheat crop production and continuous use of herbicides with the sole mechanism of action of ACCase inhibition, the provinces of West Azerbaijan, Tehran, Khorasan, Isfahan, Markazi, and Semnan are at risk of resistance development. In addition, because of continuous long-term use of tribenuron-methyl, resistance in broadleaf species is also being developed. Evidence has recently shown resistance of turnipweed and wild mustard populations to this herbicide. Stable monitoring of fields in doubtful areas and providing good education and training for technicians and farmers to practice integrated methods would help to prevent or delay the development of resistance to herbicides.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.