西南弱光地区机插杂交籼稻“减穴稳苗”栽培的群体冠层质量特征

【目的】探明机插条件下减穴稳苗配置对杂交籼稻群体冠层质量的影响,为西南弱光稻区杂交籼稻机插栽培技术的推广应用提供理论支撑。【方法】2016—2017年采用两因素随机区组田间试验,因素1,2年均为不同田间配置,设常规配置（30 cm×12 cm）和减穴稳苗（30 cm×23 cm）;因素2,2016年为不同株型水稻品种（F优498,中后期株叶型松散;宜香优2115,中后期株叶型上紧下披）,2017年为不同基本苗（42×10⁴/hm²和63×10⁴/hm²）;研究了不同田间配置对机插杂交籼稻群体冠层结构、光合特性和微环境（冠层温度、湿度和透光率）的影响。【结果】（1）减穴稳苗齐穗期能维持与常规配置相当的单茎绿叶面积、粒叶比和上三叶比叶重,其中2017年倒二叶与倒三叶比叶重显著增大;齐穗期剑叶光合速率、气孔导度、蒸腾速率分别较常规配置显著提高23.84%、23.53%和13.79%。（2）较常规配置,减穴稳苗显著增大各时期冠层幅度,提高冠层透光率,降低收敛指数,群体通透性更好;减穴稳苗处理提高了2016年F优498孕穗期和齐穗期的一次分蘖角度,而宜香优2115的一次分蘖角度2年均表现为减穴稳苗小于常规配置。（3）相关分析表明,孕穗期冠层日均温、昼夜温差和昼夜湿差与齐穗期剑叶和倒二叶比叶重呈显著或极显著正相关,与齐穗期收敛指数呈显著负相关;此外,孕穗期冠层日均温和昼夜湿差还与齐穗期冠层幅度呈显著正相关;齐穗期冠层日均温和昼夜温差与分蘖盛期、拔节期及齐穗后20 d的一次分蘖角度呈显著或极显著负相关,日均相对湿度则相反。减穴稳苗有效地改善了植株冠层结构,从而显著提高孕穗期和齐穗期的冠层温度和昼夜温差,提高孕穗期、齐穗期和齐穗后20 d的昼夜湿差,并显著降低日均相对湿度。【结论】减穴稳苗田间配置优化了机插杂交稻的群体冠层结构和光分布,增大了群体内部昼夜温差和湿差,降低了相对湿度,提高了群体质量和光合速率,为高产稳产奠定了基础,是西南弱光稻区进一步推进机插秧发展的重要技术途径。     

Poorly crystalline iron and aluminium oxides contribute to the carbon saturation and sorption of dissolved organic carbon in the soil

Soil carbon (C) saturation implies an upper limit to a soil's capacity to store C depending on the contents of silt + clay and poorly crystalline Fe and Al oxides. We hypothesized that the poorly crystalline Fe and Al oxides in silt + clay fraction increased the C saturation and thus reduced the capacity of the soil to sorb additional C input. To test the hypothesis, we studied the sorption of dissolved organic carbon (DOC) on silt + clay fractions (<53 µm) of highly weathered oxic soils, collected from three different land uses (i.e., improved pasture, cropping and forest). Soils with high carbon saturation desorbed 38% more C than soils with low C saturation upon addition of DOC, whereas adsorption of DOC was only observed at higher concentration (>15 g kg^?1). While high Al oxide concentration significantly increased both the saturation and desorption of DOC, the high Fe oxide concentration significantly increased the desorption of DOC, supporting the proposition that both oxides have influence on the DOC sorption in soil. Our findings provide a new insight into the chemical control of stabilization and destabilization of DOC in soil.     

Effect of farm management on topsoil organic carbon and aggregate stability in water: A case study from Southwest England,UK

There are few reliable data sets to inspire confidence in policymakers that soil organic carbon (SOC) can be measured on farms. We worked with farmers in the Tamar Valley region of southwest England to select sampling sites under similar conditions (soil type, aspect and slope) and management types. Topsoils (2–15 cm) were sampled in autumn 2015, and percentage soil organic matter (%SOM) was determined by loss on ignition and used to calculate %SOC. We also used the stability of macroaggregates in cold water (WSA) (‘soil slaking’) as a measure of ‘soil health’ and investigated its relationship with SOC in the clay‐rich soils. %SOM was significantly different between management types in the order woodland (11.1%) = permanent pasture (9.5%) > ley‐arable rotation (7.7%) = arable (7.3%). This related directly to SOC stocks that were larger in fields under permanent pasture and woodland compared with those under arable or ley‐arable rotation whether corrected for clay content (F = 8.500, p < .0001) or not (F = 8.516, p < .0001). WSA scores were strongly correlated with SOC content whether corrected for clay content (SOC_adj R² = .571, p < .0001) or not (SOC_unadj R² = 0.490, p = .002). Time since tillage controlled SOC stocks and WSA scores, accounting for 75.5% and 51.3% of the total variation, respectively. We conclude that (1) SOC can be reliably measured in farmed soils using accepted protocols and related to land management and (2) WSA scores can be rapidly measured in clay soils and related to SOC stocks and soil management.     

Banishing barberry: The history of Berberis vulgaris prevalence and wheat stem rust incidence across Britain

Wheat stem rust, caused by the fungus Puccinia graminis f. sp. tritici (Pgt), is a notoriously damaging disease of wheat and barley. Pgt requires two hosts to complete its lifecycle; undergoing asexual reproduction on cereal crops and completing sexual reproduction on Berberis spp. The latter stage of its lifecycle is of particular importance in temperate regions such as western Europe, where asexual urediniospores are unable to survive cold winter weather. In the past, the crucial role of Berberis in the lifecycle of stem rust led to intensive eradication campaigns, initially carried out by farmers in the face of hostile scientific opinion. In the United Kingdom, common barberry (Berberis vulgaris) is today a relatively rare plant. Stem rust is, however, currently experiencing a resurgence; at the same time, there has been a general increase in the prevalence of barberry and an upsurge in its planting which, in the United Kingdom, is associated with attempts to encourage the endangered barberry carpet moth (Pareulype berberata). This article situates current developments within a broader chronological framework, examining changing attitudes towards barberry and rust in England in the past and the history of the plant's use and cultivation. It assesses how widespread B. vulgaris really was in the environment historically, and thus the scale of its eradication. We suggest that Berberis was never widely established as an archaeophyte in the United Kingdom. Current attempts to re-establish it are based on a misunderstanding of the plant's historical status and could potentially pose a serious threat to food security.     

SnToxA,SnTox1, and SnTox3 originated in Parastagonospora nodorum in the Fertile Crescent

The centre of origin of the globally distributed wheat pathogen Parastagonospora nodorum has remained uncertain because only a small number of isolates from the Fertile Crescent were included in earlier population genetic and phylogeographic studies. We isolated and genetically analysed 193 P. nodorum strains from three naturally infected wheat fields distributed across Iran using 11 neutral microsatellite loci. Compared to previous studies that included populations from North America, Europe, Africa, Australia, and China, the populations from Iran had the highest genetic diversity globally and also exhibited greater population structure over smaller spatial scales, patterns typically associated with the centre of origin of a species. Genes encoding the necrotrophic effectors SnToxA, SnTox1, and SnTox3 were found at a high frequency in the Iranian population. By sequencing 96 randomly chosen Iranian strains, we detected new alleles for all three effector genes. Analysis of allele diversity showed that all three effector genes had higher diversity in Iran than in any population included in previous studies, with Iran acting as a hub for the effector diversity that was found in other global populations. Taken together, these findings support the hypothesis that P. nodorum originated either within or nearby the Fertile Crescent with a genome that already encoded all three necrotrophic effectors during its emergence as a pathogen on wheat. Our findings also suggest that P. nodorum was the original source of the ToxA genes discovered in the wheat pathogens Phaeosphaeria avenaria f. sp. tritici 1, Pyrenophora tritici-repentis, and Bipolaris sorokiniana.     

Genetic variation of seedling traits responded to brassinosteroid and gibberellin inhibitors in maize (Zea mays) doubled haploid lines

The purpose of this study was to examine the genotypic variation in maize doubled haploid (DH) lines response to brassinosteroid and gibberellin inhibitors. Plant responses to hormone inhibitors were determined in growth chamber experiments using germination paper for three different seedling treatments: application of propiconazole (Pcz), uniconazole (Ucz) or water (control). Mesocotyl length (ML) was more sensitive to hormone inhibitors, especially to the Ucz treatment, than other seedling traits. ML was significantly correlated with other traits in the Ucz treatment. All the seedling traits showed moderate-to-high broad sense heritability values, ranging from 0.39 to 0.82. The Euclidian genetic distances of inbred line pairs ranged from 1.27 to 19.94, indicating there was a high level of variability across the maize DH lines used in this study. DH lines with extreme MLs were identified, which can provide valuable breeding resources for improving abiotic stress tolerance, and for further genetic studies.     

Molecular identification of blast resistance genes in rice landraces from northeastern India

Rice blast disease caused by the fungus Magnaporthe oryzae is one of the most devastating diseases causing huge losses worldwide. In the present study, major blast resistance genes were investigated in landraces originating from northeastern India. Based on phenotypic evaluation, 288 landraces were classified into three distinct groups: resistant (75), moderately resistant (127) and susceptible (86). The genetic frequencies of the 18 major blast resistance genes were between 6.2% and 27.4%, with only two genotypes possessing a maximum of nine blast resistance genes. The cluster and population structure analysis grouped the landraces into two groups. Through principal coordinate analysis, the scatter plots partitioned the resistant and moderately resistant landraces into different groups. Analysis of molecular variance showed maximum (96%) diversity within populations and least (4%) diversity between populations. Association analysis identified six markers, CRG4_2, RM72, tk59-2, pi21_79-3, RM1233 and RM6648, that are significantly associated with blast disease and explained a phenotypic variance of 1.1–6.5%. The associated genes could be used in marker-assisted rice breeding programmes for gene pyramiding to develop rice varietal resistance against blast disease. The present study represents a valuable blast resistance genetic resource that could be used for identification of new R genes, donors for blast resistance, and genomic studies.     

Assessing the efficacy and impact of management of an invasive species in a protected area: Poa annua on sub‐Antarctic Macquarie Island

Plant eradication is difficult, particularly in remote, protected areas. The Southern Ocean Islands are very isolated and highly protected, but the flora contains many alien plants. Small restricted populations have been eradicated, but eradication of established species has proven difficult. A better understanding of the efficacy of control methods at sub‐Antarctic temperatures and their off‐target impacts may increase eradication success. With interest in controlling non‐native Poa annua in the region, we aimed to determine if physical and chemical methods can control P. annua (the sub‐Antarctic biotype) in sub‐Antarctic conditions and examined their impact on native plants. We quantified the effectiveness of physical control methods on P. annua in situ on sub‐Antarctic Macquarie Island through field‐based experiments and assessed their selectivity on P. annua compared with native grasses. We also quantified the effectiveness of several herbicides on P. annua at sub‐Antarctic temperatures and assessed their selectivity on native grasses. Of the four physical disturbance methods tested, none effectively reduced P. annua cover as one‐off treatments. Of the herbicide treatments, glyphosate and trifloxysulfuron sodium were effective and were less damaging to native grass species, indicating potential selectivity. Physical control was of limited effectiveness, but did not affect native species richness. An integrated weed management programme utilising the strategic use of selective herbicides with follow‐up chemical and physical intervention may balance control and biodiversity outcomes. This research highlights the importance of site‐specific testing of control methods and understanding off‐target impacts of control when managing alien plant species in protected areas.     

Commuting distances to local non‐farm workplaces and out‐migration: The case of Northeast Thailand

The relationship between commuting distances and where people work has been studied for urban contexts in both developed countries and developing countries. However, few studies have examined the situation in rural areas, and none look at commuting distances to non‐farm workplaces in rural areas of developing countries. This paper investigates how commuting distance, and thus accessibility, to local non‐farm work influences non‐farm employment and out‐migration from rural villages in Northeast Thailand. The main issues examined are: (i) the distance that rural residents travel to work in local non‐farm jobs; and (ii) the influence that local non‐farm employment has on the number of outmigrants from rural villages. The study finds: (i) distance between villages and non‐farm work sites impact the number of villagers who are employed in regular wage work; (ii) beyond 20 km villagers are less likely to travel to non‐farm employment using their own means of transportation; and (iii) employment in regular wage work decreases outmigration. The findings from this study contribute to the debates over the drivers of rural out‐migration, rural livelihood changes, and agrarian changes that are taking place in Southeast Asia.