Agricultural development and maize diversity in Mexico

Mexico is within the center of origin of Zea mays and has among the highest levels of maize genetic diversity in the world. This diversity is traced to factors at the regional and farm levels. Loss of crop genetic diversity has been related to economic and agricultural development, although opposed views of this exist for the Mexican case. Agricultural development appears to be affecting virtually all types of farms in Mexico. A case study in Chiapas suggests that the adoption of some improved varieties has enhanced genetic diversity in maize, but one improved type competes with landraces in the most favorable land. The adoption of this improved type is associated with greater access to capital and with lower risk.The research for this project was carried out with the support of the UC/MEXUS program of the University of California and CONACYT. We wish to acknowledge the advice and assistance provided by Esteban Betanzos of the Chiapas office of the Instituto Nacional de Investigaciones Forestales y Agropecuarios, Efraim Hernandez of the Colegio de Postgraduados at Chapingo, Robert Tripp of the Centro Internacional de Mejoramiento de Maiz y Trigo, and to Manuel Parra of the Centro de Investigaciones Ecologicas del Sureste in San Cristobal de las Casas. The authors wish to thank J. Edward Taylor, Andraes Buerkert, Aaron Zazueta, and Daniel Mountjoy for their useful comments on an earlier draft.     

干扰方式对香蕉园入侵杂草群落种间关联的影响

【目的】探讨干扰方式对香蕉园入侵杂草群落种间关联的影响。【方法】在样方调查的基础上,运用方差比率法(V_R)、χ²检验、联结系数A_c、Ochiai指数I_O、Spearman秩相关分析法研究人工挖除、药剂除草、机械割除3种干扰方式下香蕉园入侵杂草的种间关联特征。【结果】白花鬼针草、阔叶丰花草、鹅肠菜为香蕉农田入侵杂草的主要建群种,入侵杂草群落总体方差比率V_R均大于1,3种杂草管理方式群落种间总体呈显著正联结趋势。χ²检验显示,人工挖除方式有3个种对显著联结,1个种对(香附子-两耳草)极显著联结;药剂除草方式有3个种对显著联结;机械割除方式有6个种对显著联结,3个种对(鹅肠菜-败酱叶菊芹、阔叶丰花草-败酱叶菊芹、阔叶丰花草-无刺含羞草)极显著联结。联结系数A_c、联结程度I_O分析得到的结果与χ²检验基本一致,达到显著和极显著联结的种对较少,大部分入侵杂草种间联结性较弱。Spearman相关性分析显示,人工挖除、药剂除草、机械割除3种干扰方式的入侵杂草显著相关的种对比例均较低,分别为18.2%、14.3%、13.6%。【结论】3种干扰方式的香蕉园入侵杂草种间关系均较松散,机械割除方式的杂草群落更趋于稳定。阔叶丰花草在不同干扰方式下与种间都有显著的关联性,对杂草群落稳定共存发挥重要作用,在香蕉园杂草生物防治中具有利用潜力。     

The alien flowering plants of Mexico

A list of 618 species of alien flowering plants recorded for Mexico is presented; they are distributed in 355 genera and 87 families. The families with the largest number of species are Poaceae (171), Fabaceae sensu lato (57), Asteraceae (56), and Brassicaceae (45). The representation of most families with alien species in Mexico agrees with the average distribution frequencies estimated by Pysek (1998 ) for 26 floras throughout the World. Exceptions are an under‐representation of Asteraceae and an over‐representation of Poaceae. Most alien species (78.9%) in Mexico have their origin in the Old World; South America ranks second with 9.6%. As defined by Richardson et al. (2000 ), 19.8% of the alien species could be considered casual aliens and 80.2% of them naturalized. The proportion of alien species relative to the 22,968 native flowering plant species recorded for Mexico is 2.7%.     

云南马先蒿属植物的生物地理及物种多样性

马先蒿属（Pedicularis)是被子植物中最大的属之一,在云南植物区系中占有重要地位。按照钟补求系统,该属植物在云南有151种分属于13个群72个系。马先蒿属在云南的地理分布体现了下列特点：（1）种类十分丰富,占整个属总种数的25％,占中国的42．6％。（2）包括了该属全部花冠类型,即无齿、有齿的原始类型各为24种、短管具喙的中间过渡类型87种,较进化的长管类型16种。（3）马先蒿属植物分布在云南的11个地理分布区域中,但该属植物在康藏高原区最为丰富,有108个种在本区有分布,占云南种数的71．5％;横断山植物区和东喜马拉雅植物区是本属的现代分布中心和多样性中心。（4）特有现象十分明显,其中8个系、52个种为云南特有,横断山和东喜马拉雅的特有种量为丰富,也是本属的特有中心。（5）民先蒿植物与邻近的四川（西南部）和西藏（东南部）在区系上联系密切,与缅甸和不丹有一定的联系。     

Narrow rows reduce biomass and seed production of weeds and increase maize yield

Smallholder farmers in southern African countries rely primarily on cultural control and hoe weeding to combat weeds, but often times, they are unable to keep up with the weeding requirements of the crop because of its laboriousness, causing them to incur major yield losses. Optimisation of crop planting pattern could help to increase yield and suppress weeds and to reduce the critical period of weed control and the weeding requirements to attain maximum yield. Experiments were carried out in Zimbabwe during two growing seasons to assess the effect of maize density and spatial arrangement on crop yield, growth and seed production of weeds and to determine the critical period for weeding. Planting maize at 60 cm row distance achieved higher yields and better weed suppression than planting at 75 or 90 cm row distance. Increasing crop densities beyond the customary three to four plants m⁻² gave modest reductions in weed biomass but also diminished crop yields, probably because of increased competition for water and nutrient resources. Maize planted in narrow rows (60 cm) intercepted more radiation and suffered less yield reduction from delaying hoe weeding than those planted in wider rows (75 or 90 cm), and the duration of the weed-free period required to attain maximum grain yield was 3 weeks shorter in the narrow spacing than that in the 75- and 90-cm row spacings. Weeding was more effective in curtailing weed seed production in the narrow row spatial arrangements than in the wide row planting. The results of these studies show that narrow row spacings may reduce weeding requirements and increase yields.     

Soil fertility management effects on maize productivity and grain zinc content in smallholder farming systems of Zimbabwe

Biochar is produced as a by-product of the low temperature pyrolysis of biomass during bioenergy extraction and its incorporation into soil is of global interest as a potential carbon sequestration tool. Biochar influences soil nitrogen transformations and its capacity to take up ammonia is well recognized. Anthropogenic emissions of ammonia need to be mitigated due to negative environmental impacts and economic losses. Here we use an isotope of nitrogen to show that ammonia-N adsorbed by biochar is stable in ambient air, but readily bioavailable when placed in the soil. When biochars, containing adsorbed ¹⁵N labelled ammonia, were incorporated into soil the ¹⁵N recovery by roots averaged 6.8% but ranged from 26.1% to 10.9% in leaf tissue due to differing biochar properties with plant ¹⁵N recovery greater when acidic biochars were used to capture ammonia. Recovery of ¹⁵N as total soil nitrogen (organic+inorganic) ranged from 45% to 29% of ¹⁵N applied. We provide a proof of concept for a synergistic mitigation option where anthropogenic ammonia emissions could be captured using biochar, and made bioavailable in soils, thus leading to nitrogen capture by crops, while simultaneously sequestering carbon in soils.     

Keepers of maize in Chiapas,Mexico

This study concerns the knowledge and selection of biological diversity of maize (Zea mays) within its center of domestication in Mesoamerica. Maize farmers in central Chiapas of Southern México keep local varieties (landraces) belonging to six races and four race mixtures. Fifteen local varieties are recognized. In spite of widespread adoption of a modern, high yielding variety, maize farmers continue to select local varieties for specific soils and because of agronomic and use criteria. Farmers maintain maize varieties primarily through seed selection. Spatial and temporal separation do not seem sufficient to maintain varieties. The management of improved varieties can lead from a uniform population to a heterogeneous one as hybridization with local maize populations occurs.     

Genomic analyses provide insights into the polyploidization-driven herbicide adaptation in Leptochloa weeds

Polyploidy confers a selective advantage under stress conditions; however, whether polyploidization mediates enhanced herbicide adaptation remains largely unknown. Tetraploid Leptochloa chinensis is a notorious weed in the rice ecosystem, causing severe yield loss in rice. In China, L. chinensis has only one sister species, the diploid L. panicea, whose damage is rarely reported. To gain insights into the effects of polyploidization on herbicide adaptation, we first assembled a high-quality genome of L. panicea and identified genome structure variations with L. chinensis. Moreover, we identified herbicide-resistance genes specifically expanded in L. chinensis, which may confer a greater herbicide adaptability in L. chinensis. Analysis of gene retention and loss showed that five herbicide target-site genes and several herbicide nontarget-site resistance gene families were retained during polyploidization. Notably, we identified three pairs of polyploidization-retained genes including LcABCC8, LcCYP76C1 and LcCYP76C4 that may enhance herbicide resistance. More importantly, we found that both copies of LcCYP76C4 were under herbicide selection during the spread of L. chinensis in China. Furthermore, we identified another gene potentially involved in herbicide resistance, LcCYP709B2, which is also retained during polyploidization and under selection. This study provides insights into the genomic basis of the enhanced herbicide adaptability of Leptochloa weeds during polyploidization and provides guidance for the precise and efficient control of polyploidy weeds.     

杭州外来杂草的种类组成与生境特点

通过野外调查和大量文献资料的整理和分析,确定杭州有外来杂草75种,隶属于30科55属。通过对杭州外来杂草的种类组成、原产地、入侵途径和生境特点进行分析,结果表明：杭州的外来杂草主要为菊科、苋科、大戟科、豆科和旋花科,占总数55%;来源于美洲的外来杂草对杭州容易入侵并造成较大危害;荒地等地表裸露较大的生境外来杂草容易入侵定居。并对如何加强管理和控制外来物种提出几点建议。     

Diversity and trophic structure of insects associated with grains of three maize landraces in San Agustín Loxicha,Oaxaca, Mexico

Diversity and trophic structure of grain insect communities were examined in Olotillo, Nal‐Tel and Comiteco maize landraces cultivated within a milpa agroecosystem by Zapotec ethnic groups in Mexico. Higher insect diversity was expected in Olotillo, whose cultivation comprises a wide variety of agroecosystems, and low insect abundance in Nal‐Tel with small grains and thick testa. Forty Olotillo cobs were collected at low, medium and high elevations, and 40 each of Nal‐Tel at low elevation and Comiteco at high elevation. Cobs were monitored for 30 days under controlled laboratory conditions until all insects emerged. Thickness of testa of 400 grains from each landrace was measured. Community composition and trophic structure were described and standard diversity indices were estimated. A total of 9,708 insects, corresponding to five orders, 24 families and 36 species, were recorded, with six species not previously reported in this region. Insect guilds were composed of 70% phytophages, 22% parasitoids and 8% predators. Species richness was S = 27, 16 and 8 in Olotillo, Comiteco and Nal‐Tel, respectively. Nal‐Tel and Olotillo had the highest diversity index values (H′ = 1.32 and 1.2, respectively) and no significant differences; Comiteco had the lowest value (H′ = 0.65) and differed significantly from the other landraces. Comiteco and Olotillo, which have large grains and thin testa, showed higher insect abundance than Nal‐Tel, which has small grains and thick testa and showed lower abundance. Results support our hypotheses and highlight the role of traditional crop management in insect agrobiodiversity maintenance and conservation.     

外来杂草在我国的危害性及其管理对策

外来杂草已对我国的农作物生产、果园、草坪、环境和生物多样性等赞成了严重危害。外来杂草之所以能在传入地产生危害,与它们所具有的特性和当地缺乏环境阻力密切相关。对外来杂草的管理应从防止外来杂草传入和对现有的外来杂草初稿除两方面采取措施。防止传入的措施包括：（1）加强植物检疫;（2）建立外来植物引种驯化的风险性评价制度;（3）鼓励利用本土植物。对现有外来杂草的防除,则应采取综合性的防除措施：（1）防治生态破坏;（2）开展外来杂草的生物控制;（3）利用经济植物进行生境替代控制;（4）开展对外来杂草的利用。     

昆虫CYP6家族多样性与进化

了解昆虫CYP6家族的多样性与进化 ,对认识昆虫细胞色素P45 0参与抗药性发生、发展的分子生物学机制具有重要的意义。作者就昆虫CYP6家族多样性的各种表现形式及其形成原因、自然进化史、内部进化关系及进化的分子机制作一综述     

Interference of horse purslane (Trianthema portulacastrum L.) and other weeds affect yield of autumn planted maize (Zea mays L.)

To assess comparative losses of Trianthema portulacastrum (HP) relative to other weeds, the experiment was set during consecutive summer seasons 2018 and 2019 at the Research Farm MNS-University of Agriculture, Multan, Pakistan. Experiment consisted three replications which were laid out under randomized complete block design. Experiment consisted of ten treatments viz: weeds free (whole season), HP free till 20 Days after emergence (DAE), HP free till 40 DAE, HP free till 60 DAE, all weeds free 20 DAE, all weeds free 40 DAE, all weeds free 60 DAE, weedy check (all weeds), weedy check except HP and weedy check containing only HP. During 2018 in all weeds weedy check, maximum HP relative density (33.33%) was observed while in 2019, plot where weeds were controlled from growing till 20 DAE showed (80%) relative density at 30 DAE. HP maximum frequency (66.67%, 77.78%) and relative frequency (66%, 100%) was recorded at 45 DAE in plots where HP was kept controlled till 20 DAE and all weeds kept controlled till 20 DAE, respectively. Maximum number of grains per cob (738, 700.68), 1000 grain weight (306.66, 271.51 g) and grain yield (6150, 8015 kg hec^-1) were recorded in plots which were kept all weed free till 60 DAE. As the competition period of weeds increased over 40 DAE, it substantially reduced yield of maize. Keeping the plots HP free till 40 DAE in the maize fields with HP as the major dominating weed, likely increase in maize grain yield is up to 30% compared to the fields where HP left un attended throughout the growing season. However, if maize field is infested with a mix of weeds with more than one dominating weeds including HP, compared to weedy situation the whole season, 30% higher grain yield can be obtained if all weeds are kept controlled till 40 DAE. Hence it can be concluded that whether the farmers face heavy HP infestation only or the mix of weeds as dominating weeds, in either case farmer should control weeds within first 40 days in maize field for better grain yield.     

中国鹅膏菌属(担子菌)的物种多样性

鹅膏菌属（Ａｍａｎｉｔａ）是一个近世界性广布的大属,全球已被描述而又被承认的有近５００种。在文献中,我国此属已记载约２００种。然而,许多种都是原初描述于欧洲或北美的种类。近来的研究表明,东亚的鹅膏菌独特且有其自身的分布范围。东亚的有些种虽与产于欧洲或北美的某些种相似,但仔细的野外观察,详尽的形态解剖学和分子进化生物学研究结果表明,东亚的鹅膏菌是独立的分类群。在欧洲,人们有采集著名食菌恺撒鹅膏菌的习     

Weeds as crops: The value of maize field weeds in the valley of Toluca, Mexico

Maize field weeds or agrestals are widely used in central Mexico as potherbs (quelites) and forage. This work presents quantitative data on these uses from the village of San Bartolo del Llano, Municipio de Ixtlahuaca, Valley of Toluca, an area with a relatively intensive, semicommercial agriculture. We interviewed 24 families of the village and 10 vendors at the market of Ixtlahuaca regularly during one rainy season (1995) on type and quantity of weed use. Also, the weed vegetation was surveyed and we interviewed 49 farmers on their farming practices and on costs. All of the 74 weed species found in maize fields were useful as forage, potherb, medicinal, or ornamental. Within the village, 11 species were eaten; an average family consumed 4.5 kg of wild potherbs per month during the rainy season. In Ixtlahuaca, 2150 kg of 10 species were sold, worth 3054 pesos (US $611). For quantity and gross economic value, forage was much more important. On the average, 1 ha of maize field produced a harvest of 1.5 t of green forage, worth about 25% of the gross value of the maize harvest, and 55% of its net value. The combination of maize with forage weeds for stabled animals constitutes an interesting integrated farming system. The weeds increase the useful biomass of the field, improve nutrition of the farmers, do not reduce the yield of the main crop, as the fields are kept weed free during the critical period, and provide erosion control, shade, and green manure.     

Measuring the ecological preference for growth of 150 of the most influential weeds in weed community structure associated with agronomic and horticultural crops

The phytosociological researches which intent for studying the performance of weeds and the structure of weed assemblages associated with different crops derives their importance mainly from the adverse effect of weeds on crop productivity. Consequently, it is worth questioning about the ecological preferences of the weed growth in response to three main drivers for weed community structure associated with agronomic, and horticultural crops: crop diversification, crop seasonality, and soil type. A study area was selected comprising farmland of Nile Delta and its adjoining east and west territories, Egypt. A total of 555 species were recorded in 30 agroecosystems monitored and depending on species frequency/abundance values, 150 species were designated as the most influential weeds in weed community structure associated with agronomic and horticultural crops. The ecological preference of species for crop seasonality was evident through the results of Agglomerative hierarchical clustering. Three weed assemblage groups (WAG) identified: WAG A associated with winter agronomic crops, WAG B associated with summer agronomic crops, and WAG C associated with perennial agronomic crops and horticultural crops (orchards). Their diversity evaluated at different levels. The growth preference of the 150 species which were assigned as most influential weeds was gauged in response to the three environmental variables. 61 species were faithful to WAG A, 45 to WAG B, and 44 to WAG C. Concerning crop diversification, 34-species were significantly affected and scored coefficient of variation ≥ 100%. As for soil type, indicator species analysis revealed that 66-species show growth preference in fine grained soil while 84-species prefer coarse grained soil. In the three vegetation units (WAG A – C), 12 within-group associations (alliances) were specified of less-common (differential) species. The record of these alliances match to a specific environmental condition (ecological niche) and in them 29 strong indicators are identified. Redundancy analysis was used to extract and summarize the variation in species records in the response matrix (species vs. sites) that can be explained by the three different types of growth preference (explanatory variables), and the partial linear effect of them was evaluated by variation partitioning.