Effect of mentor pollen on pistil-pollen incongruities among species of Cucumis L.

Summary The merits of mentor pollen in certain interspecific hybridizations in the genus Cucumis L. were evaluated. African wild cucumber species Cucumis metuliferus Naud. and C. africanus L. and Asian species C. sativus var. hardwickii Alef and var. sikkimensis Hook, were reciprocally crossed. Pollen tube growth was arrested halfway down the style in all combinations except in C. sativus × C. africanus. Mentor pollen irradiated with 100 and 200 krad grew through the style and into the ovules in all species. Fruitset was obtained in all cases when mentor pollen was used either alone or in mixtures. Fruits set after self pollination with mentor pollen yielded only seeds without embryos.In several crosses, aided by mentor pollen, a number of relatively large seeds (with enlarged embryosac) were obtained. A sample of these embryosacs contained a globular structure like an embryo. Embryosacs with embryo-like structures were explanted on several different media but no development was obtained.     

Resistance in Cucumis sativus L. to Tetranychus urticae Koch. 7. The inheritance of resistance and bitterness and the relation between these characters

Summary The inheritance of resistance to the twospotted spider mite and of bitterness in cucumber has been studied in three sets of P₁, P₂, F₁, F₂, B₁₁ and B₁₂ of crosses between three bitter, resistant lines and one non-bitter, susceptible line. Resistance to the twospotted spider mite as measured by acceptance and oviposition appeared to be determined by several to many genes, which are inherited mainly in an additive fashion. Bitterness is basically governed by the gene Bi, which, contrary to earlier reports, is inherited in an intermediary way, while the expression of Bi is influenced by additively inherited intensifier genes. Whereas Bi and the bitterness intensifier genes are not related to the resistance factors acceptance and oviposition, they are related to resistance or tolerance as measured by the damage index. This relation is explained by linkage rather than by identity of the genes concerned. Changes in the test methods and breeding consequences are discussed.     

优质、脆肉、耐贮型厚皮甜瓜品种好运52的选育

好运52是由广西农业科学院园艺研究所育成的优质、脆肉型、耐贮运杂交一代早中熟厚皮甜瓜新品种,适于我国南部和东部多雨地区保护地栽培及西北干旱地区露地栽培。果实发育期40～45d;中椭圆形,单果重2.0～2.5kg;果皮金黄,网纹中等,近脐部光皮,皮韧,耐贮存;果肉橙红色,中心可溶性固形物含量16%左右,质地实脆,口感清甜,品质上佳。2005年1月通过广西壮族自治区农作物品种审定委员会审定。     

Iron and zinc absorption characteristics and copper inhibitions in cucurbitaceae

Iron and Zn absorption, interactions, and Cu inhibitions were characterized in cucumber (Cucumis sativus L.), watermelon (Citrullus lanatus Thunb.), and pumpkin (Cucurbita moschata Poir.) by kinetic parameters V_max and K_m. Influx and V_max values for Fe and Zn absorption decreased in each species as plant age increased. For the Michaelis constant, K_m, Fe values in cucumber and watermelon and Zn values in watermelon and pumpkin were relatively unchanged with increased plant age. K_m values for Zn absorption in cucumber and Fe absorption in pumpkin decreased as plant age increased. Among species, watermelon appeared to have a particularly effective uptake mechanism for Zn at low solution concentrations. Non‐competitive inhibition of Zn absorption by Fe (20, 50 uM) was indicated in each species. Iron uptake in pumpkin was inhibited non‐competitively by Zn (5, 10 uM), however no significant effects of Zn on Fe absorption were evident in either watermelon or cucumber. Copper (0.5, 1, 5 uM) inhibited uptake of Fe non‐competitively and Zn competitively in each species.     

优质厚皮甜瓜新品种‘明珠1号’

 ‘明珠1号’属早中熟甜瓜品种, 果实发育期35～40 d。植株生长势中等, 综合抗性好, 容易坐果, 丰产性好, 果实圆形、白色、光皮, 单果质量1.5 kg左右, 耐贮运。果肉白色, 厚4 cm左右, 腔小, 肉质松软, 清香, 含糖量16%以上, 口感风味佳。     

Monitoring physiological races of<Emphasis Type="Italic">Podosphaera xanthii</Emphasis> (syn.<Emphasis Type="Italic">Sphaerotheca fuliginea</Emphasis>), the causal agent of powdery mildew in cucurbits: Factors affecting race identification and the importance for research and commerce

Identification of the physiological races ofPodosphaera xanthii (syn.Sphaerotheca fuliginea), the causal agent of powdery mildew in cucurbits, is based upon the differing responses of various melon cultigens to the pathogen. Eight races of the pathogen have been identified to date in the USA, Africa, Europe and around the Mediterranean Sea, and four new races were reported from greenhouse melons in the major growing area of Japan. Plant responses to powdery mildew may be affected by environmental factors such as light intensity, temperature and humidity, as well as by age and nutritional status of the plants. The same factors affect the accuracy and reliability of race identification. In an attempt to overcome those obstacles, the genetic diversity ofP. xanthii was studied using molecular markers. Unfortunately, no correlation was found between DNA polymorphism and the race of the pathogen as identified by biological tests. The usefulness of race identification as a guide for the grower in selecting appropriate cultivars is limited because changes or shifts in the pathogen population are common. Such changes may be found among growing seasons, geographic regions and hosts, and also within a single greenhouse during a single season. On the other hand, race identification is important for basic research and is especially important for the commercial seed industry, which requires accuracy in declaring the type and level of resistance to powdery mildew in its products. http://www.phytoparasitica.org posting March 2, 2004. Contribution from the Agricultural Research Organization. No. 501/04.     

Morphological and molecular characterization of <Emphasis Type="Italic">Oidium</Emphasis> subgenus <Emphasis Type="Italic">Reticuloidium</Emphasis> (powdery mildew) newly occurred on cucumber in Japan

In 2002, a powdery mildew with catenate conidia lacking fibrosin bodies was found on cucumber in a greenhouse in Kanagawa Prefecture, Japan. Morphological observation revealed that the fungus belongs to Oidium subgenus Reticuloidium, anamorph of the genus Golovinomyces. Molecular phylogenetic analyses of the nucleotide sequences of the rDNA ITS regions and D1/D2 domains of the 28S rDNA indicated that the fungus belongs to the clade of G. orontii with other Golovinomyces fungi from a wide range of host plants, suggesting that the fungus was newly transported from abroad. Because there has been no prior report of cucumber powdery mildew caused by Reticuloidium, further research on the physiology, epidemiology, control and resistant cucumber varieties is required.     

Molecular polymorphisms between populations of Pseudoperonospora cubensis from Greece and the Czech Republic and the phytopathological and phylogenetic implications

Molecular genetic polymorphisms within Pseudoperonospora cubensis isolates of different geographic origins were investigated to establish their phylogenetic relationships and to assess genetic variability between two distant pathogen populations. Thirty isolates originating from Greece (Crete; 15), the Czech Republic (13), the Netherlands (one) and France (one) were analysed by AFLP fingerprinting and ITS 5·8S rDNA sequence analysis. All isolates were obtained from cucumber ( Cucumis sativus ) plants showing typical downy mildew symptoms. Four AFLP primer combinations produced a total of 288 high-quality bands of which 45% were polymorphic, allowing isolates to be grouped into two separate clusters: one including the Central European (Czech Republic) and Western European (the Netherlands and France) and the other the Cretan isolates. Within each AFLP cluster there was some variation, which could be accounted for by geographic origin or pathogenicity. The two populations (Cretan vs. Central and Western European) exhibited a high degree of genetic isolation. There was no clear AFLP grouping of isolates on the basis of pathotypes. No variability was detected in the ITS1 region; however, ITS2 sequences grouped P. cubensis isolates in two subclusters: one with all investigated European and the other with Asian isolates. The two subclusters formed a larger P. cubensis cluster which was differentiated from the cluster of the neighbouring species Pseudoperonospora humuli . Within P. cubensis , AFLP fingerprints could resolve genetically isolated populations, even on small or medium geographic scales, while ITS2 sequence showed differences on a global scale, being only suitable for phylogenetic analyses.     

Occurrence of Corynespora cassiicola isolates resistant to boscalid on cucumber in Ibaraki Prefecture, Japan

A total of 651 isolates of cucumber corynespora leaf spot fungus ( Corynespora cassiicola ) collected from cucumber in Japan, either with (438 isolates) or without (213 isolates) a prior history of boscalid use, were tested for their sensitivity to boscalid by using a mycelial growth inhibition method on YBA agar medium. Additionally, seven isolates of C. cassiicola obtained from tomato, soybean, eggplant (aubergine) and cowpea in different locations in Japan were tested before boscalid registration. Minimum inhibitory concentration (MIC) and 50% effective concentration (EC₅₀) values for 220 isolates from crops without a prior history of boscalid use ranged from 0·5 to 7·5 μg mL⁻¹ and from 0·04 to 0·59 μg mL⁻¹, respectively. Two hundred and fourteen out of 438 isolates collected from ten cucumber greenhouses in Ibaraki Prefecture, Japan, which received boscalid spray applications showed boscalid resistance, with MIC values higher than 30 μg mL⁻¹. Moreover, resistant isolates were divided into two groups: a moderately resistant (MR) group consisting of 189 isolates with EC₅₀ values ranging from 1·1 to 6·3 μg mL⁻¹, and a very highly resistant (VHR) group consisting of 25 isolates with EC₅₀ values higher than 24·8 μg mL⁻¹. MR isolates were detected from all ten greenhouses, but VHR isolates were detected from only three. As a result of fungus inoculation tests which used potted cucumber plants, control failures of boscalid were observed against resistant isolates. Efficacy of boscalid was remarkably low against VHR isolates in particular. This is the first known report on boscalid resistance in Japan.