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Kui Lin, Zhi Huang, and Yong Xu

The effects of different light intensities and qualities on the biomass, physiological parameters, and biochemical contents of hydroponically grown lettuce (Lactuca sativa L.) were evaluated, with the aim of obtaining better quality and higher yield, as well as saving energy in lettuce cultivation. Three different light qualities, provided by red (R), green (G), and blue (B) light-emitting diodes (LEDs), were used to produce six different combinations of illumination: A1: R:G:B = 7:0:3 [photosynthetic photon flux density (PPFD) = 150 μmol·m−2·s−1]; A2: R:G:B = 6:2:2 (150 μmol·m−2·s−1); A3: R:G:B = 7:0:3 (120 μmol·m−2·s−1); B1: R:G:B = 3:0:7 (150 μmol·m−2·s−1); B2: R:G:B = 2:2:6 (150 μmol·m−2·s−1); and B3: R:G:B = 3:0:7 (120 μmol·m−2·s−1), and the fluorescent lamp (FL) at 150 μmol·m−2·s−1 was used as the control (CK). In most cases, treatment A2 resulted in higher biomass attributes, whereas higher physiological parameters were observed in treatment B2. However, a greater shoot dry weight (SDW) was observed in treatment A1. No significant difference was detected in chlorophyll [Chl (a + b)] and carotenoid (CAR) contents among the different treatments. Soluble sugar content was found the highest in treatment A1, although it was not significant compared with that observed in treatment A2. Soluble protein content was higher in treatments with a higher component of blue light. Vitamin C content was found the highest in treatment B3 and the lowest in treatment A1, whereas malondialdehyde (MDA) content was the highest in CK and the lowest in treatments B1 and B2. These results indicated that appropriate ratio of red to blue light can effectively promote the accumulation of biochemical compounds in lettuce and that replacement of a certain portion of red light, blue light, or both with green light was more effective in promoting plant growth and quality.

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Yong Xu, Fan Wu, and Rong-Cai Ma

MADS box genes regulate most of the development processes in plants. Studying peach MADS box genes will provide insights into its flower and fruit development. Five MADS box cDNAs with complete coding regions were cloned in this study. PpMADS2 cDNA is 1116-bp long. RT-PCR analysis indicated that PpMADS2 is expressed in leaf, flower, fruit, and nutlet. PpMAD4 cDNA is 824-bp long, which is the homologue of Agamous. RT-PCR analysis indicated that PpMADS4 is expressed in the two inner parts of flower, fruit, and nutlet; and was absent in leaf and the two outer parts of the flower. This expression pattern is similar to that of Agamous gene in A. thaliana. PpMADS4 could promote the flowering process in A. thaliana tested by genetic transformation. PpMADS5 cDNA is 873-bp long, which is the homologue of SEP3. RT-PCR analysis indicated that PpMADS5 is expressed in the three inner parts of flower, fruit, and nutlet; and was absent in leaf and sepal, similar to the expression pattern of SEP3 gene in Arabidopsis. PpMAD6 cDNA is 1037-bp long, which is the homologue of FUL. RT-PCR analysis indicated that PpMADS6 is expressed in leaf, sepal, petal, carpel, and fruit; and was absent in stamen and nutlet. PpMAD7 cDNA is 1147-bp long, which is the homologue of SEP1. RT-PCR analysis indicated that PpMADS7 is expressed in the four parts of flower and fruit, and was absent in leaf, stamen, and nutlet. Furthermore, two SSRs were identified in the 5' UTR in the two MADS box genes, PpMADS2 and PpMADS7, respectively. The SSR in PpMAD2 was more polymorphic than that in PpMADS7 in the 39 Prunus accessions collected.

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Aoxue Wang, Fanjuan Meng, Xiangyang Xu, Yong Wang, and Jingfu Li

Leaf mold, caused by the fungus Cladosporium fulvum, is a serious disease of tomato. In the current study, the main physiological races of C. fulvum collected from three northeastern provinces of China were identified using a set of identification hosts. The results showed that the prevalent pathogenic physiological races were 1.2.3, 1.3, 3, 1.2.3.4, and 1.2.4. F1, F2, and BC1 tomato plants were obtained by crossing C. fulvum-resistant cultivar 03748 carrying the Cf-6 gene and susceptible cultivar 03036. Three 10-mer oligonucleotide random amplified polymorphic DNA (RAPD) primers and two simple sequence repeat (SSR) primers were selected for the further molecular marking analysis after 210 RAPD primers and 50 SSR primers were screened using the bulked segregate analysis method. The polymorphic DNA bands were amplified among parents, 10 F1 plants, 184 F2 plants including 145 resistant plants and 39 sensitive plants using three RAPD primers and two SSR primers so that three RAPD molecular markers and two SSR molecular markers linked to the Cf-6 loci were identified. Three RAPD markers were linked to the Cf-6 resistant locus separated with 8.7 cM, 20.3 cM, and 33.4 cM. Also, one RAPD codominant marker S374619/559 was found. The locations of the two SSR markers were 12.6 cM and 9.7 cM away from the Cf-6 locus. After cloning and sequencing two specific DNA fragments closely connected to the Cf-6 resistant and susceptible alleles respectively, in the RAPD codominant marker S374619/559 and one codominant sequence characterized amplified region marker S674619/559 was converted from RAPD marker S374619/559. In the RAPD marker S374619/559, the length difference of two specific fragments, 619-bp fragment and 559-bp fragment, is the result of one insertion (60 bp) in the 619-bp fragment. These markers will facilitate the selection of resistant tomato germplasm containing the Cf-6 gene and cloning of Cf-6 to breed new C. fulvum resistant tomato cultivars.

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Haiying Zhang, Shaogui Guo, Guoyi Gong, Yi Ren, Angela R. Davis, and Yong Xu

Powdery mildew of cucurbits, incited by Podosphaera xanthii (Castagne) Braun & Shishkoff (syn. Sphaerotheca fuliginea auct. p.p.), is an economically important foliar disease. which is now common in watermelon [Citrullus lanatus (Thunb.) Mastum. & Nakai]. This disease occurs in all watermelon-growing areas and can reduce yields by up to 30%. Finding and breeding for resistance to this disease is important to reduce dependence on fungicides and to use in combination with fungicides to limit the spread of fungicide-resistant P. xanthii. This is the first English report that race 2WF of P. xanthii can infect watermelon. It is the prevalent race of watermelon powdery mildew in Beijing.

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Yong Yang, Xueyong Liu, Yuanli Jiang, Zuoxiang Xiang, Qingguo Xu, Na Zhao, and Bichao Shu

Salt-affected soils may retard plant growth and cause metabolic alterations. The objective of this study was to investigate the effect of salinity in deep soil on root growth and metabolic changes of tall fescue (Festuca arundinacea). Tall fescue seeds (cv. Houndog V) were planted in polyvinylchloride (PVC) tubes (9 cm diameter × 45 cm long) for 2 months with three treatments of growth substances: (1) control, filled with peat-sand mixtures for full tubes (40 cm height, sand:organic fertilizers = 7:3, w/w); (2) T20, 20 cm saline soil covered with 20 cm organic fertilizers and sand; (3) T30, 30 cm saline soil covered with 10 cm organic fertilizers and sand. Turf quality and vertical shoot growth rate (VSGR) significantly decreased in T30, but not for T20, when compared with the control. Salinity in deep soil obviously inhibited the root growth as indicated by the lower root length, root projected area, root diameter, root fresh, and dry weight, but increased the level of amino acids (Asp, Glu, Ser, Gly, etc.) and soluble sugars (glucose, fructose, sucrose). Root activity in top layer (0–10 cm) of saline soil increased while decreased in deeper layer (20–40 cm) when compared with the control. The increase of root activity and free amino acids in roots from upper layer and the accumulation of soluble sugars in roots from deeper soil layer under salinity conditions were the adaptive responses and regulative mechanisms that for supporting the above-ground plant growth in tall fescue when exposed to deep soil salinity conditions. These results also suggested that a 20 cm of improved mixture of organic fertilizers with sand on the top of saline soil could be sufficient to supply basic space for the normal growth of turfgrass with regular spray irrigation.

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Haiying Zhang, Guoyi Gong, Shaogui Guo, Yi Ren, Yong Xu, and Kai-Shu Ling

Because of the growing threat of global warming, drought stress could severely affect the normal growth and development of crop plants. To alleviate such an adverse effect, there is a need to screen watermelon germplasm collections to identify genetic sources for potential drought tolerance. In the present study, 820 accessions of USDA's Citrullus PIs and 246 watermelon breeding lines were evaluated for their drought tolerance at the seedling stage under extreme water stress conditions in a greenhouse. Significant variations in drought tolerance were observed in the Citrullus germplasm collections. Using fast clustering analysis, the tested watermelon materials could be assigned into four groups, including tolerant, intermediate tolerant, moderately sensitive, and sensitive, respectively. The most drought-tolerant Citrullus germplasm, including 13 Citrullus lanatus var. lanatus and 12 C. lanatus var. citroides accessions, were originated from Africa. These genetic materials could be used for rootstock breeding or for developing drought-tolerant watermelon cultivars.

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Renbing Zhang, Yong Xu, Ke Yi, Haiying Zhang, Ligong Liu, Guoyi Gong, and Amnon Levi

A genetic linkage map was constructed for watermelon using 117 recombinant inbred lines (RILs) (F2S7) descended from a cross between the high quality inbred line 97103 [Citrullus lanatus var. lanatus (Thunb.) Matsum. & Nakai] and the Fusarium wilt (races 0, 1, and 2) resistant U.S. Plant Introduction (PI) 296341 (C. lanatus var. citroides). The linkage map contains 87 randomly amplified polymorphic DNA (RAPD) markers, 13 inter simple sequence repeat (ISSR) markers, and four sequenced characterized amplified region (SCAR) markers. The map consists of 15 linkage groups. Among them are a large linkage group of 31 markers covering a mapping distance of 277.5 cM, six groups each with 4 to 12 markers covering a mapping distance of 51.7 to 172.2 cM, and eight small groups each with 2-5 markers covering a mapping distance of 7.9 to 46.4 cM. The map covers a total distance of 1027.5 cM with an average distance of 11.7 cM between two markers. The map is useful for the further development of quantitative trait loci (QTLs) affecting fruit qualities and for identification of genes conferring resistance to Fusarium wilt (races 0, 1 and 2). The present map can be used for further construction of a reference linkage map for watermelon based on an immortalized mapping population with progenies homozygous for most gene loci.

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Haiying Zhang, Jianguang Fan, Shaogui Guo, Yi Ren, Guoyi Gong, Jie Zhang, Yiqun Weng, Angela Davis, and Yong Xu

Watermelon belongs to the genus Citrullus. There have been continuing interests in breeding of watermelon for economic benefits, but information on the scope and utilization of genetic variations in Citrullus is still limited. The present study was conducted in 2012–13, to evaluate the genetic diversity and population structure of the 1197 line watermelon collection maintained by the Beijing Vegetable Research Center (BVRC), which belongs to seven Citrullus species including Citrullus naudinianus, Citrullus colocynthis, Citrullus rehmii, Citrullus ecirrhosus, Citrullus amarus, Citrullus mucosospermus, and Cirullus lanatus subsp. vulgaris. Twenty-three highly informative microsatellite markers evenly distributed in the watermelon genome were used to assess genetic diversity in this collection. The markers detected on an average of 6.05 alleles per locus with the average value of polymorphism information content (PIC) at 0.49. A high level of gene diversity [Nei’s gene diversity index (Nei) = 0.56] and a low observed heterozygosity (H o = 0.10) were revealed within the collection. Structure analysis grouped the 1197 accessions into two main populations (Pop I and Pop II) and an admixture group. Pop I contained 450 accessions from C. lanatus subsp. vulgaris (446) and C. mucosospermus (4). Pop II comprised 465 accessions, 379 of which belonged to C. lanatus subsp. vulgaris and 86 to C. naudinianus (3), C. ecirrhosus (2), C. rehmii (2), C. colocynthis (11), C. amarus (58), and C. mucosospermus (10). The remaining 282 accessions were classified as an admixture group. The two main populations were further subdivided into four subgroups. The groupings were consistent with the estimation of F statistics (F st) and Nei’s genetic distances in collections. We confirmed the distinct genetic backgrounds between American and East Asian ecotypes. Subsequently, we defined a core set consisting of 130 accessions including 47 from Pop I, 68 from Pop II, and 15 from the Admixture group. This core set was able to capture all 133 alleles detected by 23 simple sequence repeats (SSRs) in 1197 accessions. These results will facilitate efficient use of genetic variations in Citrullus in watermelon breeding and help optimization of accessions in genomewide association studies.

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Ke-peng Che, Chun-yang Liang, Yue-guang Wang, De-min Jin, Bin Wang, Yong Xu, Guo-bing Kang, and Hai-ying Zhang

Amplified fragment length polymorphism (AFLP) analyses were used to assess genetic diversity among 30 genotypes of watermelon [Citrullus lanatus (Thunb.) Mansf.] representing a broad genetic base, including breeding lines and commercial germplasm. Eight AFLP primer combinations selected from 64 primer combinations were polymophic. The polymorphism was 13.0% to 31.9% within the 28 cultivars examined, and 45.3% to 64.2% among all the genotypes. Each genotype could be successfully distinguished based on AFLP scoring. Cluster grouping of accessions based on the AFLP analysis was consistent with that from classification by pedigrees and ecotypes.

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Li-Xiao Yao, Yong-Rui He, Hai-Fang Fan, Lan-Zhen Xu, Tian-Gang Lei, Xiu-Ping Zou, Ai-Hong Peng, Qiang Li, and Shan-Chun Chen

Ferric chelate reductase (FRO) is a critical enzyme for iron absorption in strategy I plants, reducing Fe3+ to Fe2+. To identify FRO family genes in the local Citrus junos cultivar Ziyang Xiangcheng and to reveal their expression model, the citrus (Citrus sp.) genome was searched for homologies of the published sequence CjFRO1. Five FROs were found, including CjFRO1; these were named CjFRO2, CjFRO3, CjFRO4, and CjFRO5, respectively, and cloned via reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) PCR. The deduced amino acid sequences of five CjFROs contained flavin adenine dinucleotide (FAD)-binding motifs, nicotinamide adenine dinucleotide (NAD)-binding motifs, and 6–10 transmembrane domains, with isoelectric points between 6.73 and 9.46, and molecular weights between 67.2 and 79.9 kD. CjFRO1 and CjFRO2 were predominantly found in the aboveground parts of C. junos, with CjFRO1 highly expressed in leaves, and CjFRO2 largely expressed in stems and leaves. CjFRO3 was less expressed in roots, stems, and leaves. CjFRO4 and CjFRO5 were predominately found in roots. Under iron-deficient conditions, CjFRO4 was significantly and specifically increased in the roots of C. junos, whereas CjFRO1 was upregulated in the roots and leaves.