Distribution of two groups of melon landraces and inter-group hybridization enhanced genetic diversity in Vietnam

To understand the genetic diversity and differentiation of Vietnamese melon (Cucumis melo L.), we collected 64 landraces from the central and southern parts of the country and assessed molecular polymorphism using simple sequence repeat and random amplified polymorphic DNA markers. The Vietnamese melon was divided into seven cultivar groups, namely “Dua le”, “Dua vang”, “Dua bo”, “Dua gang-andromonoecious”, “Dua gang-monoecious”, “Dua thom”, “Montok”, and the weedy-type melon “Dua dai”. Among these, Dua le, Dua vang, Dua bo, and Dua gang-andromonoecious are cultivated on plains and they formed cluster II along with the reference accessions of Conomon and Makuwa. Based on genetic distance, Dua le and Dua vang were regarded as Makuwa and Dua bo and Dua gang-andromonoecious as Conomon. In contrast, Dua thom and Montok are cultivated in highlands, and they formed cluster III along with landraces from the southern and eastern foot of the Himalayas. Dua gang-monoecious which is commonly cultivated in the southern parts of Vietnam, exhibited the greatest genetic diversity, as explained by its possible origin through the hybridization between Dua gang-andromonoecious and Montok. Genetic differences in melon landraces between plains and highlands and hybridization between these two geographical groups have contributed to the enhancement of genetic diversity in Vietnamese melon.     

Genetic variation in root morphology and microsatellite DNA loci in upland rice (Oryza sativa L.) from Vietnam

Drought is a major constraint to the productivity of rice in upland ecosystems. The rice root system plays an important role in the regulation of water uptake and extraction from deep soil layers. The aim of this research was to study the variation in root morphology and the genetic diversity in upland rice accessions. Thirty-three upland rice accessions originated from Vietnam along with 13 selected upland rice lines from several other countries were used in this study. Variation in root morphology was observed in most of the investigated root traits such as maximum root length, total root dry weight, deep root to shoot ratio, and total root to shoot ratio. Most of the traits showed significant correlation and appeared interrelated. Genetic diversity among upland rice accessions was studied with microsatellite markers. Forty-one alleles were detected with 14 rice microsatellite primer pairs among all the rice accessions. Two dendrograms have been created based on 35 microsatellite alleles and 10 morphological traits data for 38 accessions and compared. These results provided useful information for the selection of suitable cross combinations for mapping quantitative trait loci (QTLs) related to drought resistance in upland rice.     

A melon genotype with superior competence for regeneration and transformation

Transformation efficiency of melon is low and is still regarded as a challenge. In this paper, the regeneration and transformation response of ‘BU‐21/3′, a newly characterized melon breeding line, is described. The line seems to be superior in this regard to previously evaluated genotypes. Agrobacterium‐mediated delivery of the GUS or GFP reporter genes into cotyledon explants was used to evaluate efficiency of transient and stable transformation. Good transient expression was observed, and stable transformation frequencies of 0.4‐1.5 transgenic shoots per explant were obtained. Transgenic plantlets were transferred to a contained greenhouse as early as 8‐10 weeks after transformation. Transgenic plants are fertile and exhibit a true‐to‐type phenotype. The ‘BU‐21/3’ line may become a useful tool for the facilitation of transgenic breeding in melon.     

Impact of resistant melon cultivars on Sphaerotheca fuliginea

Effects of the resistant cultivars of melon on the powdery mildew fungus, Sphaerotheca fuliginea, were investigated in a melon‐growing area of Japan. Powdery mildew fungi were isolated from four melon cultivars (‘HN21’, ‘Quincy’, ‘Earl's Knight Natsu 2’ and ‘Earl's Miyabi Natsu 2′) which are resistant to different races of S. fuliginea.‘HN21’is resistant to races 1 and N1,‘Quincy’ and ‘Earl's Knight Natsu 2’are resistant to races 1 and N2, and ‘Earl's Miyabi Natsu 2’is resistant to races 1, N1 and N2. All 155 strains isolated from ‘HN21’were identified as race N2. Seventy out of 81 strains isolated from ‘Quincy’ and ‘Earl's Knight Natsu 2’were identified as race N1, while other strains were identified as races 1, 2US, N2 and N3. Nineteen out of 29 strains isolated from ‘Earl's Miyabi Natsu 2’were identified as race N3, while other strains were identified as races 10, 2US, N1 and N4. These results suggest that, although the resistant cultivars are extremely effective for protecting the plants from their respective races, a race succession rapidly takes place, even in a small area, and other minor races become predominant.     

Effect of ethylene on Agrobacterium tumefaciens-mediated gene transfer to melon

The effect of ethylene on gene transfer mediated by an Agrobacterium tumefaciens harbouring a binary vector with the β‐glucuronidase (uid A) gene was investigated in melon, Cucumis melo L. Explants excised from melon cotyledons produced ethylene, the production of which was increased by the addition of 1‐aminocyclopropane‐1‐carboxylic acid (ACC, 20 or 200 μM), and inhibited by the addition of aminoethoxy‐vinylglycin (AVG, 10 μM). Agrobacterium inoculation of explants increased ethylene production, while application of AVG during inoculation reduced it. After 4 days of co‐cultivation with Agrobacterium, gene transfer in the explants was assayed by transient uid A expression. Application of ACC to the co‐cultivation medium reduced Agrobacterium‐mediated gene transfer to explants and that of AVG increased it. These results suggest that ethylene affects the A. tumefaciens‐mediated gene transfer to the explants excised from melon cotyledons, and the efficiency of Agrobacterium‐mediated gene transfer can be improved by inhibiting ethylene production from the explants.     

Sources of resistance to Watermelon Chlorotic Stunt Virus in melon

Watermelon Chlorotic Stunt Virus (WmCSV) is a bipartite geminivirus residing in the genus Begomovirus (family Geminiviridae) and is whitefly transmitted ( Bemisia tabaci ). WmCSV infects members of the Cucurbitaceae , and represents a considerable threat to melon and watermelon crops in Sudan, Yemen, and Iran. One hundred twenty-eight melon accessions, mostly collected from Sudan, were screened in the open-field in Sudan under severe whitefly inoculation pressure in order to identify sources of resistance to WmCSV. One WmCSV resistant line HSD 2445-005 selected from this first screening along with 22 new melon accessions were agro-inoculated with an infectious Sudanese clone of WmCSV. Ten accessions exhibited resistance to WmCSV infection upon agro-inoculation. Six of them were confirmed to have complete resistance to WmCSV through graft-inoculation as well as multiple field trials in Sudan. These lines include the Sudanese accession HSD 2445-005, the South African accession PI 282448, and three Indian accessions: 90625, PI 124112, and PI 414723. Resistant plants exhibited no disease symptoms, and virus DNA could not be detected by hybridization with a WmCSV-specific probe.     

Biochemical affinities between Cucumis hystrix Chakr. and two cultivated Cucumis species (C. sativus L. and C. melo L.) based on isozyme analysis

Isozymes of eight enzymes in Cucumis hystrix Chakr. and two cultivated Cucumis species (C. sativus L. and C. melo L.) were analysed electrophoretically to investigate the biosystematics of these three species. Cluster analysis using data from six enzymes indicated that considerable genetic distance existed between both C. hystrix and melon and between C. hystrix and cucumber. C. hystrix might be a key species for studying the evolution and taxonomy of genus Cucumis. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phenotypic expression of quantitative and qualitative components of partial resistance to powdery mildew (Sphaerotheca fuliginea race 1) in melon (Cucumis melo) germplasm

A study was conducted to investigate the expression of four components of partial resistance to Sphaerotheca fuliginea race 1 in selected melon (Cucumis melo L.) lines viz. infection frequency, latent period, spore production, and disease-severity score. Those components were evaluated at two developmental stages of the host: the cotyledon stage and the stage of the first two true leaves. Detached plant parts (disks of cotyledons and true leaves) were inoculated using a vacuum-operated settling tower. All four components showed significant variation among genotypes, and correlations between components at both developmental stages were large and significant. The line ‘CNPH 83–095’ (without any major resistance gene to powdery mildew) presented the highest level of partial resistance in both vegetative stages for almost all components evaluated. The lines ‘W-6’ (Pm1Pm1, Pm2Pm2), ‘Cinco’ (Pm1Pm1, Pm2Pm2), and CNPH ‘84–147’ (Pm1Pm1), even though carrying the major gene Pm1 for complete resistance to race 1 of the fungus, showed slight but significant differences for quantitative components of partial resistance at the cotyledonal stage. Different levels of partial resistance may be expressed, even in lines with a major race-specific resistance gene to powdery mildew, in specific developmental stages of the melon plants.     

Race identification in powdery mildew (Sphaerotheca fuliginea) on melon (Cucumis melo) in Japan

Powdery mildew fungi isolated from single lesions on leaves of susceptible melon genotypes during semi-forcing and late-raising cultivation in Japan were tested. All 80 of the isolated strains were identified as Sphaerotheca fuliginea. The dominant fungus races found during semiforcing cultivation were race 5 in March (100%) and race 1 in May (100%), and race 1 (80%) during late-raising cultivation. Although the frequencies were quite low (13% in late August, but no isolation earlier in the season), two new races of S. fuliginea, which could not be identified by the differential genotypes, appeared during late-raising cultivation. These results suggest that the resistance gene to races 1 and 5 of S. fuliginea should be introduced into the breeding materials in Japan.     

雷州山羊和隆林山羊遗传多样性的微卫星分析

为了调查中国热带、亚热带主要山羊品种的遗传资源现状,应用14对微卫星引物,检测了隆林山羊和雷州山羊不同分布地区的群体遗传多样性水平。隆林山羊（柳州）、隆林山羊（百棚）、雷州山羊（徐闻）、雷州山羊（海南）各群体平均多态信息含量（PIC）分别为0.645、0.600、0.483、0.518;平均杂合度（H）分别为0.281、0.421、0.121、0.157;平均等位基因数（k）分别为5.17、4.93、4.64、4.5,3组数据综合说明两个山羊品种遗传多样性相对匮乏,群体遗传变异较低;NJ法聚类显示,隆林山羊两个群体聚为一类,再与雷州山羊（徐闻）聚在一起,最后为雷州山羊（海南）,这与两个品种的来源及地理分布基本一致。此研究结果为中国热带、亚热带山羊品种资源开发利用提供了基础资料和科学数据。     

Inheritance of resistance to races 1, 2 and 5 of powdery mildew in the melon TGR-1551

The inheritance of resistance to races 1, 2 and 5 of Podosphaera xanthii in the melon TGR-1551 was studied in a cross with the susceptible cultivar 'Bola de oro'. Under artificial inoculation conditions, four phenotypic classes were defined according to the level of fungal sporulation. The segregation ratios for resistance/susceptibility observed in the different populations and the results of the progeny test indicated that resistance to races 1, 2 and 5 of P. xanthii in TGR-1551 was governed by two independent genes, one dominant and one recessive, which means that the genetic control is a dominant–recessive epistasis. This is the first time that a recessive gene that confers resistance to more than one race of powdery mildew has been identified in melon. TGR-1551 could be considered a good genetic source for the development of powdery mildew resistant breeding lines.     

Generation means analysis of plant architectural traits and fruit yield in melon

Unique architectural phenotypes have the potential for increasing yield in commercial melon (Cucumis melo L.). Therefore, a generation means analysis was conducted to investigate the inheritance of architectural traits (days to anthesis, primary branch number, fruit number and weight, and average weight per fruit). Progeny (F₁, F₂, BC₁P₁ and BC₁P₂) from a cross between US Department of Agriculture (USDA) line, USDA 846‐1 (P₁) and ‘TopMark’ (P₂) were evaluated at Arlington (AR) and Hancock (HCK), Wisconsin in 2001. Significant (P ≤ 0.05) environment effects and genotype × environment interactions (G × E) analyses necessitated analysis by location. Significant differences (P ≤ 0.05) among parents and generations were observed for all traits, and the two parental lines differed significantly for primary branch number, fruit number and average weight per fruit. Additive gene effects were most important in governing primary branch number and fruit number per plant, while dominance and epistatic genetic effects mainly controlled days to anthesis, fruit weight per plant and average weight per fruit. Narrow‐sense heritabilities were 0.62 (AR) for days to anthesis, 0.71 (AR) and 0.76 (HCK) for primary branch number, 0.68 (AR) and 0.70 (HCK) for fruit weight per plant, 0.33 (AR) and 0.45 (HCK) for fruit weight per plant, and 0.06 (AR) and 0.79 (HCK) for average weight per fruit. Estimations of the least number of effective factors for primary branch number were relatively consistent at both AR (approx. 4) and HCK (approx. 2). Results suggest that introgression of yield‐related genes from highly branched melon types (e.g. USDA 846‐1) into US Western Shipping germplasm may aid in the development of high‐yielding cultivars with concentrated fruit set suitable for machine and/or hand‐harvesting operations.     

Genomic variation and genetic relationships in Ipomoea spp.

Random amplified polymorphic DNA (RAPD) markers were used to develop genetic fingerprints and analyse genetic relationships among 29 Ipomoea accessions from different geographical locations around the world, including unique wild species, and reproducible profiles were obtained for all accessions using random decamer primers. The primers generated 46 polymorphic markers, one primer alone having 10 products, enabling the discrimination of all 29 accessions. A high level of genetic variability in sweet potato collections was suggested by the degree of polymorphism. Half of the Japanese land races were closely related while accessions from Papua New Guinea and The Philippines were distinct and exhibited the greatest genetic diversity. The wild species Ipomoea gracilis and Ipomoea tiliacea formed a group distinct from the cultivated sweet potato. The wild tetraploid accession K233 and the species Ipomoea trifida were progressively more related genetically to the cultivated sweet potato and are the probable progenitors of Ipomoea batatas, and may be suitable as germplasm for genetic enhancement. RAPDs proved to be useful for sweet potato systematics and should be valuable for germplasm management, gene tagging and efficient choice of parents in breeding programmes.     

利用微卫星和线粒体DNA标记研究山羊群体间的遗传关系

本研究利用微卫星和线粒体DNA分析山羊的遗传多样性及系统进化关系,用25个微卫星位点分析了安哥拉山羊、山东莱芜黑山羊、罕山白绒山羊、太行山羊及乌珠穆沁绒山羊这5个山羊品种的遗传多样性,共祖遗传距离的UPGMA聚类表明遗传距离和地理距离是一致的,如内蒙的罕山白绒山羊和乌珠穆沁绒山羊聚到一起。利用线粒体DNA分析安哥拉山羊、山东莱芜黑山羊、鲁北白山羊、太行山羊及乌珠穆沁绒山羊,揭示这5个山羊品种分成A和C 2个支系,并进行了群体结构和群体扩张分析。通过比较2种分子标记的分析结果,发现利用微卫星来研究群体的遗传多样性及品种间的关系具有较高的准确性,而线粒体在研究群体系统进化具有一定的优势,在分析品种间关系方面可能不是理想标记。     

Genetic diversity among pearl millet maintainers using microsatellite markers

Genetic diversity among 70 maintainers and two pollinators of sub-Saharan and Indian origin was studied for simple sequence repeat (SSR) loci using 34 primer pairs. A total of 213 alleles were detected with an average of 6.26 alleles per locus. Polymorphic information content (PIC) ranged from 0.05 to 0.96 with a mean of 0.58 for the SSR loci. Mean PIC across the linkage groups and number of alleles in dinucleotide motifs varied significantly. The lowest PIC (0.239) for linkage group 6 indicated comparatively conserved nature of this linkage group. Genetic similarity estimates ranged from 0.05 to 0.73 with an average value of 0.29. This indicated sufficient diversity among the maintainer and pollinator lines. The 72 lines fell in five clusters, and the clustering pattern corroborated with their pedigree and characteristic traits. Pollinator ICMR 356 was more diverse from the maintainer lines analysed, and can be a potential parent for pearl millet hybrid development.     

‘河套’蜜瓜果实内源激素含量变化以及ABA对果实成熟的影响

以‘河套’蜜瓜果实为试材,通过内源检测和外源温育方法,研究果实发育期间内源激素的动态变化以及脱落酸对果实成熟的影响。结果显示：果实发育前期生长素和玉米素含量较高;进入缓慢生长期后赤霉素含量逐渐升高;脱落酸含量则在果实成熟期间一直维持较高水平。进一步研究脱落酸对果实成熟期间糖分转化的影响,结果显示,脱落酸温育处理后果实圆片蔗糖合成酶活性大幅提高,转化酶活性被显著抑制,相应地果实圆片蔗糖含量增加,葡萄糖含量下降。综合分析认为,生长素、玉米素和赤霉素与果实发育前期细胞分裂、膨大有关;脱落酸对启动果实成熟发挥重要作用,通过调节蔗糖代谢相关酶活性来调节果实蔗糖积累,并促进果实向成熟品质转化是其作用机制之一。     

甜瓜柄蔓夹角主基因+多基因遗传分析

柄蔓夹角是甜瓜株型重要性状之一,通过对甜瓜柄蔓夹角的遗传特性进行研究,以期为甜瓜株型改良育种提供理论基础。本研究以柄蔓夹角小的紧凑型甜瓜材料B103和柄蔓夹角大的疏散型甜瓜材料B297为亲本,构建四世代群体(P1、P2、F1和F2),应用植物数量性状主基因+多基因混合遗传模型多世代联合分析方法,对甜瓜柄蔓夹角进行遗传分析。两年的研究结果显示,甜瓜柄蔓夹角性状表现为数量性状,不同年份柄蔓夹角的最适遗传模型均为E-1模型,即柄蔓夹角由两对加性-显性-上位性主基因+加性-显性多基因控制。2015年秋,F2分离世代主基因遗传率是72.28%,多基因遗传率是0;2016年春,F2分离世代主基因遗传率为52.06%,多基因遗传率为0。结果表明甜瓜柄蔓夹角的遗传符合两对加性-显性-上位性主基因+加性-显性多基因遗传模型(E-1),这一性状由主基因控制,同时受环境影响。     

Two complementary recessive genes conferring resistance to Cucurbit Aphid Borne Yellows Luteovirus in an Indian melon line (cucumis melo L.)

The genetic control of resistance to cucurbit aphid-borne yellows luteovirus (CABYV) in Cucumis melo L. was studied in three progenies obtained from the cross between a resistant Indian line, PI 124112, and a susceptible cultivar of Charentais type, Védrantais. An F2 progeny and recombinant inbred lines were screened respectively in 1993 and 1995 under natural infection conditions in open field at Montfavet, France whereas the back cross (PI 124112 × F1) was inoculated by viruliferous Myzus persicae in controlled conditions. ELISA was used for assessing degree of virus multiplication in the plants resistance. In the three trials performed, segregation analysis were consistent with the hypothesis that the resistance to CABYV in PI 124112 is conferred by two independent complementary recessive genes, for which the symbols cab-1 and cab-2T are proposed. This revised version was published online in July 2006 with corrections to the Cover Date.