吊罗山石碌含笑群落木本植物种间联结性研究

石碌含笑（Michelia shiluensis）是海南特有树种和国家Ⅱ级濒危保护植物,野外仅见分布于吊罗山、鹦哥岭、五指山等海南中南部山区。吊罗山是石碌含笑最集中的自然分布区,开展吊罗山石碌含笑群落木本植物种间联结性研究,有助于了解该树种在群落中的地位与作用,为制定合理的就地保护措施提供参考。本研究基于2×2列联表,综合运用χ²检验、Pearson相关系数检验和Spearman秩相关系数检验对吊罗山石碌含笑与群落内其他伴生种的种间关系进行了探讨分析。结果表明：石碌含笑种群与灌木层的正关联比乔木层多;石碌含笑与群落内绝大多数植物的种间联结不显著,种间关系表现出总体比较松散的趋势,种群间相互独立的趋势明显,乔木层和灌木层总体上与石碌含笑正关联物种多于负关联物种数,表明群落的发展朝着有益于石碌含笑种群发育的趋势。研究结果对制定合理的就地保护措施和恢复计划具有参考价值。     

海南中部山区植被演变阶段植物物种多样性与群落结构多样性变化规律

以海南中部山区的草地、灌丛、次生林和原始林为演替系列,研究植被演替过程中群落结构多样性与物种多样性的变化规律。结果表明,群落演替过程中植物科属种数、总体Shannon-Wiener指数和Margalef指数、乔灌木层的Shannon-Wiener指数和Margalef指数及垂直结构多样性指数都显著增大;群落结构多样性指数分别与群落植物科属种数、总体alpha物种多样性指数、灌木层和乔木层物种alpha多样性指数都显著正相关。通过恢复演替,植被复杂性和质量都呈增大趋势。     

热带海岸典型森林类型土壤有机碳储量和碳氮垂直分布特征

热带海岸森林是重要的碳库,很容易受到人类活动的干扰,包括森林砍伐和气候变化。因此,迫切需要探明森林土壤有机碳储量,为热带海岸森林的保护和恢复提供理论依据。以热带海岸4种典型森林类型为研究对象,研究土壤中有机碳和全氮垂直分布特征及其与其他土壤理化性状关系。结果表明:不同林型土壤有机碳和全氮在土壤剖面中的垂直变化规律一致,表层含量较高,随着剖面深度增加含量逐渐降低,且不同土壤层次间呈现显著性差异。不同森林类型土壤有机碳和全氮含量平均值分别为1.35~7.06、0.08~0.61 g/kg,其中椰子人工林的土壤有机碳和全氮含量平均值最高,分别为7.06、0.61 g/kg,其次是香蒲桃天然次生林(6.07、0.44 g/kg)。各森林类型土壤碳氮比平均值依次为大叶相思人工林﹥木麻黄人工林﹥香蒲桃天然次生林﹥椰子人工林。各森林类型0~100 cm土层土壤有机碳储量从大到小依次为椰子人工林、香蒲桃天然次生林、大叶相思人工林和木麻黄人工林。相关分析结果表明,各个森林类型土壤有机碳与土壤容重呈显著负相关,与全氮呈显著正相关。说明椰子人工林和香蒲桃天然次生林森林生态系统达到平衡稳定状态,其碳汇效益较木麻黄人工林和大叶相思人工林显著,对热带海岸森林生态系统健康的经营与维护具有重要意义。     

海南吊罗山不同海拔高度热带雨林种间联结性对比研究

在对吊罗山2块不同海拔高度的热带雨林样地乔木层树种的RA、RD、RF及IV分析的基础上,通过出现-不出现数据的方差比例、基于2×2联列表的种间联结分析和卡方（χ2）统计量检验,对其种间联结性进行研究,以揭示不同海拔高度热带雨林种间联结性之间的相互关系。结果表明： （1）在不同海拔高度热带雨林中,群落内所有树种间总体呈显著正联结; （2）对2块不同海拔高度热带雨林样地20种优势种190对种对进行 χ2检验, 发现种对间大都呈现无联结; （3）2个不同海拔高度热带雨林种间联结比例及强度变化表明,物种正负联结比例随着海拔高度的增加而增加,而无联结比例则随着海拔高度的增加而降低。     

热带海岸防护林土壤活性有机碳分布特征:人工林与天然次生林的比较

本研究旨在比较热带海岸天然次生林与人工林土壤活性有机碳的差异,从而提高沿海防护林土壤有机碳库的存储能力和维持土壤碳平衡提供理论依据。选取海南岛沿海防护林中典型的2种人工林和2种天然次生林作为研究对象,通过测定土壤活性有机碳及养分含量,对热带海岸天然次生林与人工林土壤有机碳的积累能力及土壤养分与有机碳相关性的差异进行分析。结果表明:(1)该研究区4种林分土壤总有机碳、轻组有机碳和易氧化有机碳均表现为琼崖海棠天然次生林香蒲桃天然次生林大叶相思人工林木麻黄人工林;(2)4种林分土壤轻组有机碳占总有机碳比例以天然次生林最高,而人工林则具有更低的轻组有机碳分配比例;反之,人工林的土壤易氧化有机碳占总有机碳比例显著高于天然次生林;(3)4种林分的土壤活性有机碳与土壤全氮、土壤容重相关性显著,此外,2种人工林林地土壤活性有机碳与土壤含水量、pH、碳氮比同样具有相关性。相关性分析结果表明,人工林土壤活性有机碳与土壤各因子的相关性较天然次生林更为密切。这说明热带海岸林地土壤碳含量总体较低,与人工林相比,天然次生林土壤有机碳具有较大稳定性。     

广西猫儿山高山湿地植物区系特征与群落演替进程

采用样方调查法对广西猫儿山高山湿地湿生草本植物到木本植物阶段的群落类型、物种多样性、演替度和径级结构进行分析，探究植物区系特征与群落演替进程与趋势。结果共记录到维管植物136种，隶属于62科103属，单属科、单种属所占比例大。物种组成的地理成分较为复杂，属的地理分布兼具热带、亚热带和北温带的过渡特征，包含中国特有分布的3个属及特有树种铁杉，多样性程度较高。铁杉湿地很少见，该区域的铁杉湿地却保持得非常原始，保护意义重大。植物种类数量一般会随着演替进程先增加后减少，在演替中后期出现最大值，植物种类丰富度高低并不能很准确地衡量群落的演替程度。根据重要值划分植物群系，比较各演替度，推测出该区域湿生草本植物到木本植物阶段的演替顺序为笄石菖草丛→条穗薹草草丛→尾叶悬钩子灌丛→中华槭灌丛→华西箭竹灌丛→针阔混交林铁杉群落→常绿阔叶林褐叶青冈+山桂花群落→常绿落叶混交林吴茱萸五加林群落，为自然条件下的正向演替。演替的最终结果会形成顶级群落。分析乔木群落优势种的径级结构，在乔木群落阶段演替进程中，各优势种群落发展趋势为铁杉群落波动较大，褐叶青冈和山桂花为稳定群落，以吴茱萸五加为主要落叶树种的种群发展有衰...     

平潭岛台湾相思群落优势种群生态位研究

台湾相思（Acacia confusa）是平潭海岛相思林的主要建群种,是海岛优良的造林阔叶树种,了解平潭岛台湾相思群落主要木本植物和草本植物种群的生态位特征有助于深入了解海岛群落物种共存与竞争机制。在对其内岛和附属岛屿进行群落调查的基础上,利用Levins和Shannon生态位宽度和Pianka生态位重叠指数分析平潭岛台湾相思群落各层片主要种群生态位。共调查到维管束植物144种隶属63科123属,以禾本科和菊科为主,与大陆植被存在显著差异;发现入侵风险植物14种,草本入侵现象较严重,其中1级恶性入侵的假臭草（Praxelis clematidea）、鬼针草（Bidens pilosa）和2级严重入侵的香丝草（Erigeron bonariensis）在群落中占据较大的生态位,可能对共生种群造成一定的生态干扰,应当引起足够重视;乔木层中的台湾相思和木麻黄（Casuarina equisetifolia）、灌木层中台湾相思幼树和雀梅藤（Sageretia thea）、草本层中芒（Miscanthus sinensis）和假臭草生态位宽度较大,生态位宽度小于0.5的物种数占总数的96.67%,重要值较大的物种生态位宽度也较大,但并非完全一致;优势种群生态位重叠表现为草本层（0.253）>灌木层（0.231）>乔木层（0.149）,均小于0.3,生态位重叠值普遍偏低,种群通过生态位分化来减弱种间竞争。海岛地区较强的环境过滤性导致种群产生不同程度的生境分化,同时,种群通过压缩生态位宽度,聚集在局部生境中,从而促进海岛群落物种共存,平潭岛台湾相思群落属于地带性顶级群落,种间关系稳定,种群更新缓慢。     

单季稻田节肢动物群落演替规律

 运用种类丰富度、数量、申农指数等指标,对浙江省富阳市的稻田节肢动物群落的演替过程进行了描述、分析。可将整个演替过程划分为扩展期、波动期、衰减期三个时段,依据对水稻的不同作用性质将节肢动物群落分为天敌、害虫、中性昆虫三个亚群落。从以上三个指标的分析结果来看,三种亚群落的演替过程具有不同步性。相比而言,天敌亚群落具有最高的丰富度和多样性,其贡献率几乎达到50%;中性昆虫亚群落与害虫亚群落三个指标的每周累加值具有相似性,但数量消长呈负相关性。     

萌生杉木林经营前后杉木的空间分布格局及关联性

[目的]探索杉木萌生林的科学经营方法。[方法]以萌生杉木林为研究对象,采用双相关g(r)函数对经营前后杉木萌生林林分中杉木的空间格局及不同径级的关联性进行分析。[结果]萌生杉木林中的杉木种群经营前后在整体上和不同径级间,均表现为在3~10 m的尺度上为随机分布,在0~3 m的尺度上主要呈聚集分布或者均匀分布。经营前后杉木不同径级林木的空间关联表明,除径级Ⅱ和径级Ⅲ的杉木在0~1 m的尺度上表现为正相关,在1~2 m表现为弱的负相关外,其余各个径级间的空间关联均为相互独立。[结论]在对杉木萌生林的经营中应该参照当地天然林的分布格局和树种配置等特征,通过人工促进更新、栽植位置、密度控制、树种配置等森林经营措施,加速现有次生林的进展演替,逐步使林分朝着天然林经营的方式发展,最终实现林分的可持续经营。     

海南吊罗山热带低地雨林次生林乔木物种多样性研究

以吊罗山3块不同海拔热带低地雨林次生林为研究对象,分析了物种丰富度、物种组成、树高和径级分布以及不同起测胸径各样地生物多样性。结果表明,各样地群落有强的热带性,但同时具有热带-亚热带性质。样地乔木科属种组成丰富,单种科和单种属有较高的比例,不同海拔样地乔木树种都有较高的丰富度,中等海拔的样地最高。整个热带低地雨林次生林缺乏大乔木,群落整体低矮,胸径较小,目前未达顶级状态,植被处于旺盛的发展阶段。群落整体多样性较高,随起测胸径的增加,Shannon-wiener指数降低,中海拔样地由于有3个优势种,影响了其整体Shannon-wiener指数。Simpson指数随起测胸径增加而递减,但高海拔样地中≥2 cm起测胸径的Simpson指数由于富集种占比较高而较低。均匀度指数随起测胸径增加而增加,优势集中性指数显示出群落优势种的优势并不明显。与其它地区比较,吊罗山的热带低地雨林次生林乔木生物多样性较高。     

Pharmacokinetics of Marine-Derived Drugs

Marine organisms represent an excellent source of innovative compounds that have the potential for the development of new drugs. The pharmacokinetics of marine drugs has attracted increasing interest in recent decades due to its effective and potential contribution to the selection of rational dosage recommendations and the optimal use of the therapeutic arsenal. In general, pharmacokinetics studies how drugs change after administration via the processes of absorption, distribution, metabolism, and excretion (ADME). This review provides a summary of the pharmacokinetics studies of marine-derived active compounds, with a particular focus on their ADME. The pharmacokinetics of compounds derived from algae, crustaceans, sea cucumber, fungus, sea urchins, sponges, mollusks, tunicate, and bryozoan is discussed, and the pharmacokinetics data in human experiments are analyzed. In-depth characterization using pharmacokinetics is useful for obtaining information for understanding the molecular basis of pharmacological activity, for correct doses and treatment schemes selection, and for more effective drug application. Thus, an increase in pharmacokinetic research on marine-derived compounds is expected in the near future.     

La pourriture fongique des tubercules de pomme de terre en atmosphère contrôlée

Résumé Fusarium culmorum et, dans une moindre mesure,F. avenaceum, F. sambucinum, Colletotrichum coccodes etCylindrocarpon sp. ont été isolés de tubercules entreposés en atmosphère contr?lée (AC) et atteints de pourriture grave. Des expériences d'inoculation de tubercules avec 10 espèces ou variétés fongiques et conservation en AC à 8 et 10°C ont montré que: 1) les champignons non pathogènes en atmosphère normale (ex.:Cylindrocarpon sp.) le devenaient en AC, 2) ceux qui étaient faiblement pathogènes en atmosphère normale étaient nettement plus virulents en AC (ex.:F. culmorum), 3) les espèces ou variétés virulentes en conditions d'air normales (Fusarium sulphureum etPhoma exigua var.foveata) ne provoquaient pas de pourriture plus grave en AC et leur activité pouvait même être légérement freinée.

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Summary The extensive rotting of tubers which occurred during storage trials in controlled atmospheres has led to a mycological and pathological study of the rots. The most frequently isolated species wasFusarium culmorum althoughF. avenaceum, F. Sambucinum, Coletotrichum coccodes and aCylindrocarpon sp. were also present. Tubers of cvs Bintje and Ulla were inoculated with 19 isolates of 10 fungal species or varieties associated with rotting of stored tubers (Table 1). The tubers were incubated at 8 or 10°C in normal or controlled (2% O₂:1% CO₂, 2% O₂:6% CO₂, 2% O₂:12% CO₂, 6% O₂:6% CO₂) atmospheres and the extent of rotting was determined a month later (Tables 2 and 3 and Fig. 2). Species which were weakly virulent in a normal atmosphere (variousFusarium spp. andPhoma exigua var.exigua) were clearly more aggressive in the controlled atmosphere and this was especially evident in the case ofF. culmorum. Species ot pathogenic in a normal atmosphere under experimental conditions (Colletotrichum coccodes, Cylindrocarpon sp.,Phoma eupyrena) caused rotting in the controlled atmosphere. The two species which were virulent in a normal atmosphere (F. sulphureum andP. exigua var.foveata) were also virulent in the controlled atmosphere and in some cases the extent of rotting was even less. As a general rule, rotting caused by weakly virulent fungi was greater in both cultivars in the controlled than in a normal atmosphere.

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Zusammenfassung Eine starke F?ulnis von in Kontrotrollierter Atmosph?re gelagerten Kartoffelknollen veranlasste eine mykologische und pathologische Untersuchung. Der am h?ufigsten isolierte Pilz warFusarium culmorum. F. avenaceum, F. sambucinum, Colletotrichum coccodes undCylindrocarpon sp. wurden ebenfalls bestimmt. Neunzehn St?mme von 10 Pilzsorten oder-Arten welche bei Lagerf?ulnis vorkommen (Tab. 1) wurden auf Knollen der Sorten Bintje und Ulla inokuliert. Die Lagerung wurde bei 8 oder 10°C under Normalbedingungen oder kontrollierter Atmosph?re durchgeführt (2% O₂:1% CO₂, 2% O₂:6% CO₂, 2% O₂:12% CO₂, 6% O₂:6% CO₂). Der F?ulnisgrad (Abb. 1) wurde nach einem Monat bonitiert. Die Ergebnisse sind in den Tabellen 2 und 3 dargestellt und in der Abb. 2 illustriert. Unter in Normalbedingungen nur schwach virulente Arten (verschiedeneFusarien undPhoma exigua var. exigua) waren deutlich aktiver in kontrollierter Atmosph?re. Dies was besonders der Fall fürF. culmorum. Pilze, die im Versuch unter Normalbedingungen nicht pathogen waren (Colletotrichum coccodes, Cylindrocarpon sp., Phoma eupyrena), haben unter kontrollierter Atmosph?re Sch?den verursacht. Hingegen werden die beiden unter Normalbedingungen sehr pathogenen Arten (F. sulphureum undP., exigua var.foveata), durch kontrollierte Atmosph?re wenig beeinflusst. Es wurde sogar in einigen F?llen eine gewisse Verringerung des F?ulnisbefalls beobachtet. Ganz allgemein haben die getesteten kontrollierten Bedingungen die Entwicklung der Pilzf?ulnis an beiden Kartoffelsorten gef?rdert, speziell durch Pilzarten, welche unter Normal-bedingungen wenig Sch?den verursachen.

     

Marine Pharmacology in 2016–2017: Marine Compounds with Antibacterial,Antidiabetic, Antifungal,Anti-Inflammatory,Antiprotozoal, Antituberculosis and Antiviral Activities; Affecting the Immune and Nervous Systems,and Other Miscellaneous Mechanisms of Action

The review of the 2016–2017 marine pharmacology literature was prepared in a manner similar as the 10 prior reviews of this series. Preclinical marine pharmacology research during 2016–2017 assessed 313 marine compounds with novel pharmacology reported by a growing number of investigators from 54 countries. The peer-reviewed literature reported antibacterial, antifungal, antiprotozoal, antituberculosis, and antiviral activities for 123 marine natural products, 111 marine compounds with antidiabetic and anti-inflammatory activities as well as affecting the immune and nervous system, while in contrast 79 marine compounds displayed miscellaneous mechanisms of action which upon further investigation may contribute to several pharmacological classes. Therefore, in 2016–2017, the preclinical marine natural product pharmacology pipeline generated both novel pharmacology as well as potentially new lead compounds for the growing clinical marine pharmaceutical pipeline, and thus sustained with its contributions the global research for novel and effective therapeutic strategies for multiple disease categories.     

Effects of Micronutrient Deficiencies on Human Health: Its Status in South Asia

SUMMARY

Vitamin A, iodine, and iron deficiencies affect large numbers of people worldwide. A deficiency of one or more of these micronutrients adversely affects the physical and mental abilities of humans. South Asia contains a high percentage of these individuals, not just because of its large population, but also the prevalence of deficiency is higher there than in many other parts of the world. The reasons for the high rates of deficiency in South Asia are many, but they include inadequate availability of micronutrient-rich foods, sub-optimal dietary habits, and high rates of infection. Across the region, national plans vary from (a) increasing availability of appropriate foods, (b) introducing new dietary behaviors, (c) improving health status, and (d) directly addressing deficiency through intervention programs. The extent to which each of the countries is making progress toward the goals of these plans can help in understanding the priorities for future efforts to address micronutrient malnutrition. This article discusses the adverse effects of micronutrient deficiencies in humans with special reference to South Asia.     

Irrigation but not N fertilization enhances seedhead density in plains rough fescue ( F estuca hallii)

Plains rough fescue ( F estuca hallii) is an important forage grass species in western Canada. Seed for use in pastures and ecological restoration is in high demand but supply is limited because F. hallii is an erratic seed producer. Seed producers require an understanding of the factors that influence flowering and seed set in this species. The aim of this study was to assess the effect of irrigation and nitrogen fertilization on the flowering and growth of F. hallii in a native rough fescue prairie in Alberta, Canada. Irrigation had a strong positive effect on seedhead density, whereas fertilization had limited effects on growth and reproduction of F. hallii. These results demonstrate that under field conditions, available moisture is likely to be a key factor driving flowering and seed production in F. hallii.     

Management of Soil Micronutrient Deficiencies in the Rice-Wheat Cropping System

Summary

Within the last three decades, the rice-wheat cropping system has triggered, and with time, aggravated soil micronutrient deficiencies in the Indo-Gangetic Plains (IGP). This has largely been due to the shift from an earlier rice and wheat monoculture with low yielding, long duration indigenous varieties, to an intensive rice-wheat rotation cropping system with short duration modern high yielding varieties on the same piece of land. The problems related to micronutrient deficiency in the IGP are more due to the size of its available pools in the soil rather than its total contents and are greatly influenced by crop management, or rather its mismanagement. Deficiency of zinc is widespread in the IGP, but with the extensive use of zinc sulfate, zinc deficiency has reduced in some areas of the region. Meanwhile, the deficiency of Fe, Mn and B has increased in the IGP. Deficiency of Cu and Mo is location specific and can limit rice and wheat yields. The adoption and spread of the rice-wheat system in permeable coarse textured soils, particularly in the western IGP, not only caused iron deficiency in rice but also resulted in the emergence of manganese deficiency in wheat. In highly calcareous and acidic soils, boron is the next limiting micronutrient in crop production after zinc. Bumper rice and wheat harvests in the past decade, the declining use of organic manures in the region and except for the widespread use of zinc sulfate, a general lack of awareness amongst farmers on micronutrient deficiency problems has contributed to micronutrients limiting rice and wheat yields in the IGP. Approaches to alleviating micronutrient deficiencies include matching the crop removals of the micronutrients with its replenishments through their respective external carriers, supplementation through organic sources and mobilization/utilization through cultivation of micronutrient efficient crop cultivars. Identification of efficient micronutrient carriers and finding the optimum rate, mode and time of its application is important in ameliorating the micronutrient deficiencies. This article reviews the extent of micronutrient deficiency and discusses various management options available to reduce micronutrient deficiency induced crop yield reduction for rice and wheat in the Indo-Gangetic Plains.     

Marine Drugs Regulating Apoptosis Induced by Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL)

Marine biomass diversity is a tremendous source of potential anticancer compounds. Several natural marine products have been described to restore tumor cell sensitivity to TNF-related apoptosis inducing ligand (TRAIL)-induced cell death. TRAIL is involved during tumor immune surveillance. Its selectivity for cancer cells has attracted much attention in oncology. This review aims at discussing the main mechanisms by which TRAIL signaling is regulated and presenting how marine bioactive compounds have been found, so far, to overcome TRAIL resistance in tumor cells.     

Biochemical and morphological characterization of potato clones differing in their resistance to late blight

Summary Morphological and biochemical parameters that could be involved in resistance to late blight were studied in non-infected and in infected potato hybrids resulting from a cross betweenSolanum phureja, resistant toPhytophthora infestans, and a susceptibleSolanum tuberosum. Some morphological differences between resistant and susceptible hybrids, indicating a positive correlation between stem diameter and phloem thickness in the stem and resistance toP. infestans, were observed. The lignin content in the leaves of the resistant hybrid rose upon infection byP. infestans. In the leaves of the susceptible hybrid, a diminution of the lignin content could be observed upon infection byP. infestans. In the same context, peroxidasic activity raised upon infection byP. infestans in both resistant and susceptible hybrids. Further characterization of the hybrid clones based on the polymorphism of peroxidases was attempted using isoelectric focusing.     

Applied Biotechnology to Combat Late Blight in Potato Caused by <Emphasis Type="Italic">Phytophthora Infestans</Emphasis>

Potato is an important crop, grown worldwide. It suffers from many pests and diseases among which late blight, caused by the oomycete Phytophthora infestans, is the worst. The disease is still causing major damage in many potato production areas and control is only possible by applying fungicides frequently. The knowledge on the molecular biology and genetics of the interaction between the plant and the oomycete is developing rapidly. These are relevant fields of study, currently dominated by the discovery of many resistance genes and numerous effector proteins and the analysis of their specific mode of action. These studies may yield essential information needed for the development of durable resistance. The long-term and worldwide effort to breed for resistance so far has had little effect. A novel breeding approach may change this. It is based on cisgenic modification (CM) consisting of marker-free pyramiding of several resistance genes and their spatial and temporal deployment yielding dynamic varieties that contain potato genes only. It is envisioned that this CM approach with potato’s own genes will not only prove societally acceptable but may also result in simplifications in the legislation on use of the CM approach. Various parties in the potato research arena intend to cooperate in this novel approach in a number of developing countries where potato substantially contributes to food security. The use of resources such as land, water and energy improves when the effect of late blight is markedly reduced.     

Resistance to <Emphasis Type="Italic">Potato virus Y</Emphasis> in a Multitrait Potato Breeding Scheme without Direct Selection in Each Generation

In an experimental breeding scheme to improve late blight (Phytophthora infestans) and white potato cyst nematode (Globodera pallida) resistance of tetraploid potato over three generations of crossing and selection, 15 clones survived the final selection, and these were derived from 15 great-grandparents. There was no direct selection for resistance to Potato virus Y (PVY), but 14 out of the 15 great-grandparents were resistant to PVY and three had extreme resistance. Thirteen of the 15 descendants had PVY resistance and one extreme resistance. This was within the range expected for a random (unselected) sample from the genotypes of the great-grandparents. Hence, we found no evidence for any positive or negative association between PVY resistance and the attributes selected. The conclusion is that laborious selection is not required in every generation when many parents have PVY resistance, including some with more than one copy of a PVY resistance gene or resistance at more than one locus. However, in the future, determining the major virus resistance genes present in potential parents in each generation using diagnostic molecular markers would prevent susceptible × susceptible crosses being made and maximise the number of resistant × resistant ones.